Neuromuscular function during drop jumps in young and elderly males

The Hoffman reflex (H-reflex), indicating alpha-motoneuron pool activity, has been shown to be task - and in resting conditions - age dependent. How aging affects H-reflex activity during explosive movements is not clear at present. The purpose of this study was to examine the effects of aging on H-reflexes during drop jumps, and its possible role in drop jump performance. Ten young (26.8 ± 2.7 years) and twenty elderly (64.2 ± 2.7 years) subjects participated in the study. Maximal drop jump performance and soleus H-reflex response (H/M jump) 20 ms after ground contact were measured in a sledge ergometer. Maximal H-reflex, maximal M-wave, Hmax/Mmax-ratio and H-reflex excitability curves wer…

Conditioning hops increase triceps surae muscle force and Achilles tendon strain energy in the stretch-shortening cycle

Postactivation potentiation can improve athletic performance, but the underlying mechanisms are poorly understood. This study investigated the effect of conditioning hops on triceps surae muscle force and tendon strain and its contribution to potentiated stretch-shortening cycle (SSC) performance. Thirty-two subjects participated in two experiments. In both experiments, subjects performed three drop jumps (DJs) after prior conditioning with 10 maximal hops, three unconditioned DJs served as control. Ground reaction forces, kinematics, and triceps surae electromyographic activity were recorded. Ultrasound imaging was used to determine fascicle lengths (FASC) of the gastrocnemius (GM) and sol…

Running in highly cushioned shoes increases leg stiffness and amplifies impact loading

AbstractRunning shoe cushioning has become a standard method for managing impact loading and consequent injuries due to running. However, despite decades of shoe technology developments and the fact that shoes have become increasingly cushioned, aimed to ease the impact on runners’ legs, running injuries have not decreased. To better understand the shoe cushioning paradox, we examined impact loading and the spring-like mechanics of running in a conventional control running shoe and a highly cushioned maximalist shoe at two training speeds, 10 and 14.5 km/h. We found that highly cushioned maximalist shoes alter spring-like running mechanics and amplify rather than attenuate impact loading. T…

Changes in muscle activity with increasing running speed.

Electromyographic (EMG) activity of the leg muscles and the ground reaction forces were recorded in 17 elite male middle-distance runners, who performed isometric maximal voluntary contractions (MVC) as well as running at different speeds. Electromyograms were recorded from the gluteus maximus, vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior. The results indicated that the averaged EMG (aEMG) activities of all the muscles studied increased (P < 0.05) with increasing running speed, especially in the pre-contact and braking phases. At higher speeds, the aEMG activities of the gastrocnemius, vastus lateralis, biceps femoris and gluteus maximus exceeded 100% MVC in these s…

Forefoot strikers exhibit lower running-induced knee loading than rearfoot strikers.

AB Purpose: Knee pain and Achilles tendinopathies are the most common complaints among runners. The differences in the running mechanics may play an important role in the pathogenesis of lower limb overuse injuries. However, the effect of a runner's foot strike pattern on the ankle and especially on the knee loading is poorly understood. The purpose of this study was to examine whether runners using a forefoot strike pattern exhibit a different lower limb loading profile than runners who use rearfoot strike pattern. Methods: Nineteen female athletes with a natural forefoot strike (FFS) pattern and pair-matched women with rearfoot strike (RFS) pattern (n = 19) underwent 3-D running analysis …

Triceps surae fascicle stretch is poorly correlated with short latency stretch reflex size

Introduction: The short latency stretch reflex (SLR) is well described, but the stimulus that evokes the SLR remains elusive. One hypothesis states that reflex size is proportional to muscle fiber stretch, so this study examined the relationship between these 2 parameters in human triceps surae muscles. Methods: Achilles tendon taps and dorsiflexion stretches with different amplitudes and preactivation torques were applied to 6 participants while electromyography and muscle fascicle length changes were recorded in soleus and medial gastrocnemius (MG). Results: In response to tendon taps, neither fascicle length nor velocity changes were correlated with SLR size in either muscle, but acceler…

Innervation zone shift at different levels of isometric contraction in the biceps brachii muscle

Experiments were carried out to examine whether innervation zone (IZ) location remains stable at different levels of isometric contraction in the biceps brachii muscle (BB), and to determine how the proximity of the IZ affects common surface electromyography (sEMG) parameters. Twelve subjects performed maximal (MVC) and submaximal voluntary isometric contractions at 10%, 20%, 30%, 40%, 50% and 75% of MVC. sEMG signals were recorded with a 13 rows x 5 columns grid of electrodes from the short head of BB. The IZ shifted in the proximal direction by up to 2.4 cm, depending upon the subject and electrode column. The mean shift of all the columns was 0.6+/-0.4 cm (10% vs. 100% MVC, P0.001). This…

Reduced stretch reflex sensitivity and muscle stiffness after long-lasting stretch-shortening cycle exercise in humans

It has been suggested that during repeated long-term stretch-shortening cycle (SSC) exercise the decreased neuromuscular function may result partly from alterations in stiffness regulation. Therefore, interaction between the short latency stretch-reflex component (M1) and muscle stiffness and their influences on muscle performance were investigated before and after long lasting SSC exercise. The test protocol included various jumps on a sledge ergometer. The interpretation of the sensitivity of the reflex was based on the measurements of the patellar reflexes and the M1 reflex components. The peak muscle stiffness was measured indirectly and calculated as a coefficient of the changes in the…

Decreased motor unit firing rate and force control in older men

Introduction Ageing is related to muscle atrophy that leads to decreases in muscle force. The largest changes are found in fast muscle fibres and fast force production, reducing the capability to recover from sudden balance disturbances. Also ageing-related decrease in force control has been found, as indicated by an increase in force fluctuations and motor unit (MU) firing variability (Galganski et al. 1993). Possibly due to differences in measurement protocols and muscles, the results concerning the effects of ageing on motor unit firing rate are, however, somewhat contradictory (for review, see Roos et al. 1997). The purpose of the present study was to investigate the age-related changes…

Older Age Increases the Amplitude of Muscle Stretch-Induced Cortical Beta-Band Suppression But Does not Affect Rebound Strength

Healthy aging is associated with deterioration of the sensorimotor system, which impairs balance and somatosensation. However, the exact age-related changes in the cortical processing of sensorimotor integration are unclear. This study investigated primary sensorimotor cortex (SM1) oscillations in the 15–30 Hz beta band at rest and following (involuntary) rapid stretches to the triceps surae muscles (i.e., proprioceptive stimulation) of young and older adults. A custom-built, magnetoencephalography (MEG)-compatible device was used to deliver rapid (190°·s−1) ankle rotations as subjects sat passively in a magnetically-shielded room while MEG recorded their cortical signals. Eleven young (age…

High Responders to Hypertrophic Strength Training Also Tend to Lose More Muscle Mass and Strength During Detraining Than Low Responders.

Räntilä, A, Ahtiainen, JP, Avela, J, Restuccia, J, Kidgell, DJ, and Häkkinen, K. High responders to hypertrophic strength training also tend to lose more muscle mass and strength during detraining than low responders. J Strength Cond Res 35(6): 1500-1511, 2021-This study investigated differences in individual responses to muscle hypertrophy during strength training and detraining. Ten weeks of resistance training was followed by 6 weeks of detraining in men (n = 24). Bilateral leg press (LP) one-repetition maximum (1RM) and maximal electromyography (EMGs) of vastus lateralis (VL) and vastus medialis, maximal voluntary activation (VA), transcranial magnetic stimulation for corticospinal exci…

Effects of power training on muscle structure and neuromuscular performance

The present study examines changes in muscle structure and neuromuscular performance induced by 15 weeks of power training with explosive muscle actions. Twenty-three subjects, including 10 controls, volunteered for the study. Muscle biopsies were obtained from the gastrocnemius muscle before and after the training period, while maximal voluntary isometric contractions (MVC) and drop jump tests were performed once every fifth week. No statistically significant improvements in MVC of the knee extensor (KE) and plantarflexor muscles were observed during the training period. However, the maximal rate of force development (RFD) of KE increased from 18,836+/-4282 to 25,443+/-8897 N (P0.05) durin…

Walking and Running Require Greater Effort from the Ankle than the Knee Extensor Muscles.

The knee and ankle extensors as human primary antigravity muscle groups are of utmost importance in a wide range of locomotor activities. Yet, we know surprisingly little about how these muscle groups work, and specifically, how close to their maximal capacities they function across different modes and intensity of locomotion. Therefore, to advance our understanding of locomotor constraints, we determined and compared relative operating efforts of the knee and ankle extensors during walking, running, and sprinting.Using an inverse dynamics biomechanical analysis, the muscle forces of the knee and ankle extensors during walking (1.6 m·s), running (4.1 m·s), and sprinting (9.3 m·s) were quant…

Mechanical and neural stretch responses of the human soleus muscle at different walking speeds

During human walking, a sudden trip may elicit a Ia afferent fibre mediated short latency stretch reflex. The aim of this study was to investigate soleus (SOL) muscle mechanical behaviour in response to dorsiflexion perturbations, and to relate this behaviour to short latency stretch reflex responses. Twelve healthy subjects walked on a treadmill with the left leg attached to an actuator capable of rapidly dorsiflexing the ankle joint. Ultrasound was used to measure fascicle lengths in SOL during walking, and surface electromyography (EMG) was used to record muscle activation. Dorsiflexion perturbations of 6 deg were applied during mid-stance at walking speeds of 3, 4 and 5 km h(-1). At eac…

Neuromuscular mechanics and hopping training in elderly.

Purpose The present study examined the effects of repetitive hopping training on muscle activation profiles and fascicle–tendon interaction in the elderly. Methods 20 physically active elderly men were randomly assigned for training (TG) and control groups (CG). TG performed supervised bilateral short contact hopping training with progressively increasing training volume. Measurements were performed before the training period (BEF) as well as after 2 weeks (2 W) and 11 weeks (11 W) of training. During measurements, the gastrocnemius medialis–muscle (GaM) fascicle and its outer Achilles tendon length changes during hopping were examined by ultrasonography together with electromyographic (EMG…

Effects of ageing on motor unit activation patterns and reflex sensitivity in dynamic movements.

Both contraction type and ageing may cause changes in H-reflex excitability. H reflex is partly affected by presynaptic inhibition that may also be an important factor in the control of MU activation. The purpose of the study was to examine age related changes in H-reflex excitability and motor unit activation patterns in dynamic and in isometric contractions. Ten younger (YOUNG) and 13 elderly (OLD) males performed isometric (ISO), concentric (CON) and eccentric (ECC) plantarflexions with submaximal activation levels (20% and 40% of maximal soleus surface EMG). Intramuscular EMG data was analyzed utilizing an intramuscular spike amplitude frequency histogram method. Average H/M ratio was a…

Modulations of corticospinal excitability following rapid ankle dorsiflexion in skill- and endurance-trained athletes

Abstract Purpose Long-term sports training, such as skill and endurance training, leads to specific neuroplasticity. However, it remains unclear if muscle stretch-induced proprioceptive feedback influences corticospinal facilitation/inhibition differently between skill- and endurance-trained athletes. This study investigated modulation of corticospinal excitability following rapid ankle dorsiflexion between well-trained skill and endurance athletes. Methods Ten skill- and ten endurance-trained athletes participated in the study. Corticospinal excitability was tested by single- and paired-pulse transcranial magnetic stimulations (TMS) at three different latencies following passive rapid ankl…

Age-related muscle activation profiles and joint stiffness regulation in repetitive hopping

It is well documented that increasing effort during exercise is characterized by an increase in electromyographic activity of the relevant muscles. How aging influences this relationship is a matter of great interest. In the present study, nine young and 24 elderly subjects did repetitive hopping with maximal effort as well as with 50%, 65%, 75% and 90% intensities. During hopping joint kinematics were measured together with electromyographic activity (EMG) from the soleus, gastrocnemius medialis, gastrocnemius lateralis and tibialis anterior muscles. The results showed that agonist activation increased in both age groups with increasing intensity. The highest jumping efficiency (EMG ratio …

Neuromuscular fatigue induced by an isotonic heavy-resistance loading protocol in knee extensors.

Abstract The main aim of this study was to assess neuromuscular fatigue during a typical high-load, low-repetition loading protocol. Muscle stimulations were used to assess maximum voluntary contraction, resting single- and double-pulse twitch characteristics, and superimposed double-pulse twitch force (used to calculate voluntary activation) before and after an acute knee extension loading protocol. In our participants, who had previous resistance training experience, the mean voluntary activation level was 96.2% in an unfatigued state. Maximum voluntary contraction (−11.8%), resting double-pulse twitch force (−10.6%), and voluntary activation (−2.1%) were markedly decreased as a consequen…

Tracking the corticospinal responses to strength training

Purpose\ud The motor cortex (M1) appears to be a primary site of adaptation following both a single session, and repeated strength-training sessions across multiple weeks. Given that a single session of strength-training is sufficient to induce modification at the level of the M1 and corticospinal tract, this study sought to determine how these acute changes in M1 and corticospinal tract might accumulate across the course of a 2-week heavy-load strength-training program.\ud \ud Methods\ud Transcranial magnetic stimulation (TMS) was used to infer corticospinal excitability (CSE), intracortical facilitation (ICF), short and long-interval intracortical inhibition (SICI and LICI) and silent per…

Modulation of H-reflex and V-wave responses during dynamic balance perturbations

AbstractMotoneuron excitability is possible to measure using H-reflex and V-wave responses. However, it is not known how the motor control is organized, how the H-reflex and V-wave responses modulate and how repeatable these are during dynamic balance perturbations. To assess the repeatability, 16 participants (8 men, 8 women) went through two, identical measurement sessions with ~ 48 h intervals, where maximal isometric plantar flexion (IMVC) and dynamic balance perturbations in horizontal, anterior–posterior direction were performed. Soleus muscle (SOL) neural modulation during balance perturbations were measured at 40, 70, 100 and 130 ms after ankle movement by using both H-reflex and V-…

Neuromuscular adaptations to constant vs. variable resistance training in older men.

This study examined the effects of constant or variable external resistance training on neuromuscular adaptations in the lower limbs of older men. 37 subjects (age 65±4 year) were quasi-randomly assigned to the constant or variable training group, or a non-training control group. Training consisted of a 20-week medium-intensity, high volume resistance training program. Maximum bilateral concentric and isometric force production of the leg extensors as well as repetitions-to-failure test were performed pre-, mid- and post-training. Vastus lateralis muscle cross-sectional area was assessed by ultrasound and lean leg mass was assessed by dual-energy x-ray absorptiometry. Both training groups s…

Neuromuscular responses to different resistance loading protocols using pneumatic and weight stack devices

The purpose of this study was to examine single repetition characteristics and acute neuromuscular responses to typical hypertrophic (HL), maximal strength (MSL), and power (PL) loadings performed with two of the most common resistance modes; pneumatic and weight stack. Acute responses were assessed by measuring maximal voluntary contraction (MVC), corresponding quadriceps-EMG and resting and superimposed twitch torques. Activation level was calculated from the twitch torques. Decreases in MVC were greater during HL and MSL than during PL. During HL, resting twitch force decreased 8% (P < 0.05) more on the weight stack than on the pneumatic device. Furthermore, loading using the weight stac…

Kinetic and electromyographic analysis of single repetition constant and variable resistance leg press actions

During a multi-joint leg press action, maximal force capabilities increase with increasing knee angle. In typical resistance exercises, constant resistance is used, which does not stress the neuromuscular system at large knee angles. The purpose of this study was to compare constant and variable resistance settings using a range of contraction loads and velocities. Nine healthy, untrained males performed single contractions using four different resistance settings (constant resistance, two settings that increased resistance at large knee angles and one setting that reduced resistance at large knee angles). Single contractions using 40%, 60%, and 80% of one repetition maximum with both stead…

Neuromuscular adaptations to combined strength and endurance training: order and time-of-day

AbstractThe present study examined the effects of 24 weeks of morning vs. evening same-session combined strength (S) and endurance (E) training on neuromuscular and endurance performance. Fifty-one men were assigned to the morning (m) or evening (e) training group, where S preceded E or vice versa (SEm, ESm, SEe and ESe), or to the control group. Isometric force, voluntary activation, EMG and peak wattage during the maximal cycling test were measured. Training time did not significantly affect the adaptations. Therefore, data are presented for SEm+e (SEm+SEe) and ESm+e (ESm+ESe). In the morning, no order specific gains were observed in neuromuscular performance. In the evening, the changes …

Reduced reflex sensitivity persists several days after long-lasting stretch-shortening cycle exercise

The mechanisms related to the acute and delayed secondary impairment of the stretch reflex function were investigated after long-lasting stretch-shortening cycle exercise. The results demonstrated a clear deterioration in muscle function immediately after fatigue, which was accompanied by a clear reduction in active and passive reflex sensitivity. For active and passive stretch reflexes, this reduction was biphasic ( P &lt; 0.05 to P &lt; 0.001). However, for the ratio of the electrically induced maximal Hoffmann reflex to the maximal mass compound action potential, only one significant reduction was seen immediately after fatigue (71.2%, P &lt; 0.01). A similar significant ( P &lt; 0.01) d…

Reliability of transcranial magnetic stimulation and H-reflex measurement during balance perturbation tasks

Following ankle movement, posterior balance perturbation evokes short- (SLR ∼30–50 ms), medium- (MLR ∼50–60 ms), and long-latency responses (LLR ∼70–90 ms) in soleus muscle before voluntary muscle contraction. Transcranial magnetic stimulation (TMS) and Hoffmann-reflex (H-reflex) measurements can provide insight into the contributions of corticospinal and spinal mechanisms to each response. Motor evoked potential (MEP) and H-reflex responses have shown good reliability in some dynamic muscle contraction tasks. However, it is still unclear how reliable these methods are in dynamic balance perturbation and corticospinal modulation during long amplitude balance perturbation tasks. 14 subjects …

Predictors of lower extremity injuries in team sports (PROFITS-study): a study protocol.

Introduction Several intrinsic risk factors for lower extremity injuries have been proposed, including lack of proper knee and body control during landings and cutting manoeuvres, low muscular strength, reduced balance and increased ligament laxity, but there are still many unanswered questions. The overall aim of this research project is to investigate anatomical, biomechanical, neuromuscular, genetic and demographic risk factors for traumatic non-contact lower extremity injuries in young team sport athletes. Furthermore, the research project aims to develop clinically oriented screening tools for predicting future injury risk. Methods Young female and male players (n=508) from nine basket…

Achilles tendon length changes during walking in long-term diabetes patients

Diabetes leads to numerous side effects, including an increased density of collagen fibrils and thickening of the Achilles tendon. This may increase tissue stiffness and could affect stretch distribution between muscle and tendinous tissues during walking. The primary aim of this study was to examine stretch distribution between muscle and tendinous tissues in the medial gastrocnemius muscle-tendon unit in long-term diabetes patients and control subjects during walking.Achilles tendon length changes were investigated in 13 non-neuropathic diabetes patients and 12 controls, whilst walking at a self selected speed across a 10 m force platform. Electromyographic activity was recorded in the me…

Maturation-Related Differences in Neuromuscular Fatigue After a Short-Term Maximal Run

AbstractPurpose. This study investigated maturation-related differences in neuromuscular fatigue after a short-term maximal run. Methods. Eight male children, eight adolescents, and eight adults performed a maximal ca. 50-s run (300/350/400 m, respectively). Mechanisms of neuromuscular fatigue were assessed through isometric plantar flexor tests, electrical stimulation of the posterior tibial nerve, soleus electromyography, and blood tests. Results. All the groups showed a decrease in the running speed (children: -12.2 ± 6.5%; adolescents: -9.8 ± 5.1%; adults: -12.2 ± 3.1%), but only adults revealed a decline in the maximal isometric plantar flexor torque (-16.1 ± 13.0%). On the other hand,…

Interaction between muscle stiffness and stretch reflex sensitivity after long-term stretch-shortening cycle exercise

The short latency stretch-reflex component (M1) and its interactions with muscle stiffness and with muscle performance were investigated before and after long-term stretch-shortening cycle (SSC) exercise. Dramatic fatigue induced reduction in maximal SSC performance capability, and electromyographic activity was accompanied by a consistent decrease in the M1 reflex component and eccentric peak stiffness of the muscle. It can be suggested, therefore, that the decreased muscle performance is not simply a direct effect of central or peripheral fatigue, but is partly due to impairment of the ability to utilize stiffness-related elastic energy.

Neomuscular fatigue to power loading using a weight-stack device fitted with or without additional rubber band resistance

The addition of a rubber band (RB) to traditional weight-based resistance may be beneficial regarding the deceleration phase common during explosive power actions with light weights. This would lead to greater force and muscle activity during the latter part of the movement, but this may influence the distribution of neuromuscular fatigue. Fifteen men performed 2 knee extension power loadings (5 × 5 × 40% of 1 repetition maximum [1RM]) using a typical weight-stack device without (WS) and with the addition of a RB (WS + RB) in a crossover design. Concentric contractions were performed as fast as possible, and analyzed for torque, velocity, power, and vastus lateralis and medialis surface ele…

Age-related muscle activation profiles and joint stiffness regulation in repetitive hopping

Abstract It is well documented that increasing effort during exercise is characterized by an increase in electromyographic activity of the relevant muscles. How aging influences this relationship is a matter of great interest. In the present study, nine young and 24 elderly subjects did repetitive hopping with maximal effort as well as with 50%, 65%, 75% and 90% intensities. During hopping joint kinematics were measured together with electromyographic activity (EMG) from the soleus, gastrocnemius medialis, gastrocnemius lateralis and tibialis anterior muscles. The results showed that agonist activation increased in both age groups with increasing intensity. The highest jumping efficiency (E…

Ipsilateral corticomotor responses are confined to the homologous muscle following cross-education of muscular strength

Cross-education of strength occurs when strength-training 1 limb increases the strength of the untrained limb and is restricted to the untrained homologous muscle. Cortical circuits located ipsilateral to the trained limb might be involved. We used transcranial magnetic stimulation (TMS) to determine the corticomotor responses from the untrained homologous (biceps brachii) and nonhomologous (flexor carpi radialis) muscle following strength-training of the right elbow flexors. Motor evoked potentials were recorded from the untrained left biceps brachii and flexor carpi radialis during a submaximal contraction from 20 individuals (10 women, 10 men; aged 18–35 years; training group, n = 10; c…

Determining the Corticospinal Responses to Single Bouts of Skill and Strength Training

Mason, J, Frazer, AK, Jaberzadeh, S, Ahtiainen, JP, Avela, J, Rantalainen, T, Leung, M, and Kidgell, DJ. Determining the corticospinal responses to single bouts of skill and strength training. J Strength Cond Res 33(9): 2299-2307, 2019-Neuroplastic changes in the primary motor cortex accompany performance improvements following motor practice. Recent evidence suggests that the corticospinal responses to strength and skill training are similar, following both a single session and repeated bouts of training, promoting discussion that strength training is a form of motor learning. However, these findings are limited by the lack of a light-load strength training group. Therefore, the aim of the…

Neural Compensation Within the Human Triceps Surae During Prolonged Walking

During human walking, muscle activation strategies are approximately constant across consecutive steps over a short time, but it is unknown whether they are maintained over a longer duration. Prolonged walking may increase tendinous tissue (TT) compliance, which can influence neural activation, but the neural responses of individual muscles have not been investigated. This study investigated the hypothesis that muscle activity is up- or down-regulated in individual triceps surae muscles during prolonged walking. Thirteen healthy subjects walked on a treadmill for 60 min at 4.5 km/h, while triceps surae muscle activity, maximal muscle compound action potentials, and kinematics were recorded…

Acute Neuromuscular Adaptations in Response to Low-Intensity Blood-Flow Restricted Exercise and High-Intensity Resistance Exercise: Are There Any Differences?

Fatela, P, Reis, JF, Mendonca, GV, Freitas, T, Valamatos, MJ, Avela, J, and Mil-Homens, P. Acute neuromuscular adaptations in response to low-intensity blood flow restricted exercise and high-intensity resistance exercise: are there any differences? J Strength Cond Res 32(4): 902-910, 2018-Numerous studies have reported similar neuromuscular adaptations between low-intensity (LI) blood-flow restricted exercise (BFRE) and high-intensity (HI) resistance training. Unfortunately, none of these experimental designs individualized blood flow restriction (BFR) levels to each participant. Thus, their findings are difficult to interpret. We aimed at comparing the acute effects of LI BFR (80% of abso…

Knee extensor and flexor dominant gait patterns increase the knee frontal plane moment during walking

High gait-induced knee frontal plane moment is linked with the development of knee osteoarthritis. Gait patterns across the normal population exhibit large inter-individual variabilities especially at the knee sagittal plane moment profile during loading response and terminal stance phase. However, the effects of different gait patterns on this moment remain unknown. Therefore, we examined whether different gait patterns are associated with atypically high knee frontal plane moments. Profiles of knee joint moments divided a sample of 24 subjects into three subgroups (11, 7, 6) through cluster analysis. Kinetics, kinematics, and spatio-temporal parameters were compared among clusters. Subjec…

Effect of electrode location on surface electromyography changes due to eccentric elbow flexor exercise.

Experiments were carried out to determine whether the location of electrodes has an effect on eccentric exercise–induced changes in surface electromyography (sEMG) variables in the biceps brachii muscle. sEMG signals were recorded with a grid of 64 electrodes before and up to 4 days post-exercise. Root mean square (RMS) and mean power frequency (MNF) were calculated for: (1) each channel; (2) as an average of all channels; and (3) as an average of individual channel rows and columns. Mean muscle-fiber conduction velocity (CV) was estimated similarly but was based on double-differential channels. Maximal isometric voluntary torque decreased 21.3 ± 5.6% post-exercise. The average sEMG variabl…

Functional test measures as risk indicators for low back pain among fixed-wing military pilots.

Purpose The purpose of this study was to find out the risk value of functional fitness test (FFT) results for low back pain (LBP) among fixed-wing military pilots. Methods A total of 104 male military pilots were recruited for this study. The study was conducted with a self-administered questionnaire and FFT. The functional tests were performed in the beginning of study (baseline). The questionnaire was carried out at the baseline and 5 years later. Results The isometric low back endurance test result was associated with physical activity-related LBP experienced 5 years later. Demographic information was not associated with LBP. The prevalence of overall LBP was 71% and the flight-related L…

Corticospinal and intracortical excitability is modulated in the knee extensors after acute strength training.

The corticospinal responses to high-intensity and low-intensity strength-training of the upper limb are modulated in an intensity-dependent manner. Whether an intensity-dependent threshold occurs following acute strength training of the knee extensors (KE) remains unclear. We assessed the corticospinal responses following high-intensity (85% of maximal strength) or low-intensity (30% of maximal strength) KE strength-training with measures taken during an isometric KE task at baseline, post-5, 30 and 60-min. Twenty-eight volunteers (23 ± 3 years) were randomized to high-intensity (n = 11), low-intensity (n = 10) or to a control group (n = 7). Corticospinal responses were evoked with transcra…

Changes in corticospinal excitability during an acute bout of resistance exercise in the elbow flexors

Purpose Hypertrophic resistance exercise (HRE) induces central and peripheral fatigue. However, more detailed information about changes in corticospinal excitability remains to be elucidated. Methods Eleven volunteers participated in the upper arm HRE which included one repetition maximum (1 RM) control contractions and three sets of 13 RM (SET1–3). Transcranial magnetic stimulation (TMS) was applied during maximal isometric voluntary contraction (MVC) at the end of each set and during control contractions to study changes in corticospinal excitability. Electrical stimulation was used in order to measure peripheral changes. Results MVC decreased after each set when compared to control contr…

Motor unit discharge rate in dynamic movements of the aging soleus

Aging is related to changes at the muscular level, leading to a decline in motor performance increasing the risk of falling and injury. It seems that the age-related changes in motor unit activation are muscle- and intensity dependent. The purpose of this study was to examine possible differences in soleus motor unit discharge rate (MUDR) in both isometric and dynamic contractions between young and elderly adults. 11 young (YOUNG) and 8 elderly (OLD) males participated in the study. The subjects performed isometric and dynamic plantar flexions while seated in an ankle dynamometer. The force levels studied were 10, 20, 40, 60, 80 and 100% of the isometric (ISO) MVC in ISO and 10, 20 and 40% …

NMR relaxation times of trabecular bone—reproducibility, relationships to tissue structure and effects of sample freezing

Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T(2), Carr-Purcel-T(2), T(1ρ)) for fat and water and relate those to the structural parameters obtained by micro-computed tomography (μCT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 °C for 7 days and measured by NMR spec…

Neural and mechanical responses of the triceps surae muscle group after 1 h of repeated fast passive stretches

Experiments were carried out to examine interaction between mechanical changes of the muscletendon unit and reduced reflex sensitivity after repeated and prolonged passive muscle stretching (RPS). There is some evidence that this interaction might be relevant also during active stretch-shortening cycle type of fatigue tasks. The results demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions after RPS. Maximal voluntary contraction (MVC), average electromyographic activities of the gastrocnemius and soleus muscles, and maximal twitch contraction decreased on average by 13.8, 10.4, 7.6, and 16.8%, respectively. In addition, there was a 14% lengthening …

Differences in contractile behaviour between the soleus and medial gastrocnemius muscles during human walking

The functional roles of individual lower limb muscles during human walking may differ depending on walking speed or duration. In this study, 11 volunteers walked on a treadmill for 60 min at speeds corresponding to both optimal and 20% above optimal energetic cost of transport whilst oxygen consumption and medial gastrocnemius (MG) and soleus fascicle lengths were measured. Although energetic cost of transport was ∼12% higher at the faster speed, it remained constant over 60 min at both speeds, suggesting that humans can walk for prolonged periods at a range of speeds without compromising energetic efficiency. The fascicles of both muscles exhibited rather ‘isometric’ behaviour during the e…

Which muscles compromise human locomotor performance with age?

Ageing leads to a progressive decline in human locomotor performance. However, it is not known whether this decline results from reduced joint moment and power generation of all lower limb muscle groups or just some of them. To further our understanding of age-related locomotor decline, we compare the amounts of joint moments and powers generated by lower limb muscles during walking (self-selected), running (4 m s −1 ) and sprinting (maximal speed) among young, middle-aged and old adults. We find that age-related deficit in ankle plantarflexor moment and power generation becomes more severe as locomotion change from walking to running to sprinting. As a result, old adults generate more pow…

Leg stiffness modulation during exhaustive stretch-shortening cycle exercise.

The present study examined the effects of muscle activity modulation on leg stiffness during an exhaustive stretch-shortening cycle (SSC) exercise in eight male subjects. Reaction force, electromyography (EMG) of the soleus (Sol), gastrocnemius (Ga) and vastus lateralis (VL) muscles and sledge seat position were recorded during the SSC exercise, consisting of 100 maximal intermittent drop jumps followed by a continuous submaximal jumping until exhaustion, on a sledge apparatus. Metabolic loading was determined by measuring blood lactate (La). No change was found in leg stiffness during the maximal jumps, whereas the subsequent submaximal jumping induced a significant reduction by 27+/-12% (…

Effects of caffeine on neuromuscular function in a non‐fatigued state and during fatiguing exercise

New findings What is the central question of the study? What are the effects of caffeine on neuromuscular function in a non-fatigued state and during fatiguing exercise? What is the main finding and its importance? In a non-fatigued state, caffeine decreased the duration of the silent period evoked by transcranial magnetic stimulation. Caffeine-induced reduction of inhibitory mechanisms in the central nervous system before exercise was associated with an increased performance. Individuals who benefit from caffeine ingestion may experience lower perception of effort during exercise and an accelerated recovery of M-wave amplitude postfatigue. This study elucidates the mechanisms of action of …

Association between frontal plane knee control and lower extremity injuries : a prospective study on young team sport athletes

Background/aimPoor frontal plane knee control can manifest as increased dynamic knee valgus during athletic tasks. The purpose of this study was to investigate the association between frontal plane knee control and the risk of acute lower extremity injuries. In addition, we wanted to study if the single-leg squat (SLS) test can be used as a screening tool to identify athletes with an increased injury risk.MethodsA total of 306 basketball and floorball players participated in the baseline SLS test and a 12-month injury registration follow-up. Acute lower extremity time-loss injuries were registered. Frontal plane knee projection angles (FPKPA) during the SLS were calculated using a two-dimen…

Ankle and knee extensor muscle effort during locomotion in young and older athletes : Implications for understanding age-related locomotor decline

AbstractAge-related reduction in muscle force generation capacity is similarly evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function. To better understand why ageing has the largest detrimental effect on ankle joint function during locomotion, we examined maximal ankle and knee extensor force development during a two-leg hopping test in older and young men, and used these forces as a reference to calculate relative operating efforts for the knee and ankle extensors as participants walked, ran and sprinted. We found that, across locomotion modes in both age groups, ankle ex…

REGIONAL DIFFERENCES IN BICEPS FEMORIS FASCICLE LENGTH AND PENNATION ANGLE AFTER A SIMULATED SOCCER MATCH

Background Hamstring Strain Injuries (HSIs) represent 12% of all injuries in soccer players, and their incidence has increased in recent years. Between 53%-84% of HSIs involve the Biceps femoris muscle (BF). Recent studies have shown that soccer players with shorter BF fascicle length (FL) suffer more HSIs and exhibit regional differences in FL and pennation angle (PA) along BF. It is unclear whether there is any regional difference in the degree of change of these parameters after a soccer match. Objective Describe changes in BF muscle architecture after a simulated soccer match. Design Controlled laboratory study. Pre and Post single session. Setting Laboratory. Amateur Level. Participant…

Corrigendum to “Increased cross-education of muscle strength and reduced corticospinal inhibition following eccentric strength training” [Neuroscience 300 (2015) 566–575]

Cortical Proprioceptive Processing Is Altered by Aging

Proprioceptive perception is impaired with aging, but little is known about aging-related deterioration of proprioception at the cortical level. Corticokinematic coherence (CKC) between limb kinematic and magnetoencephalographic (MEG) signals reflects cortical processing of proprioceptive afference. We, thus, compared CKC strength to ankle movements between younger and older subjects, and examined whether CKC predicts postural stability. Fifteen younger (range 18-31 years) and eight older (66-73 years) sedentary volunteers were seated in MEG, while their right and left ankle joints were moved separately at 2 Hz (for 4 min each) using a novel MEG-compatible ankle-movement actuator. Coherence…

Isometric parameters in the monitoring of maximal strength, power, and hypertrophic resistance-training.

This study monitored strength-training adaptations via isometric parameters throughout 2 × 10 weeks of hypertrophic (HYP I–II) or 10 weeks maximum strength (MS) followed by 10 weeks power (P) training with untrained controls. Trainees performed bilateral isometric leg press tests analyzed for peak force (maximal voluntary contraction (MVC)) and rate of force development (RFD) every 3.5 weeks. These parameters were compared with dynamic performance, voluntary and electrically induced isometric contractions, muscle activity, and cross-sectional area (CSA) in the laboratory before and after 10 and 20 weeks. RFD increased similarly during the first 7 weeks (HYP I, 44% ± 53%; MS, 48% ± 55%, P &l…

Effects of plyometric and pneumatic explosive strength training on neuromuscular function and dynamic balance control in 60–70year old males

The present study compared neuromuscular adaptations to 12weeks of plyometric (PLY) or pneumatic (PNE) power training and their effects on dynamic balance control. Twenty-two older adults aged 60-70 (PLY n=9, PNE n=11) participated in the study. Measurements were conducted at Pre, 4, 8 and 12weeks. Dynamic balance was assessed as anterior-posterior center of pressure (COP) displacement in response to sudden perturbations. Explosive isometric knee extension and plantar flexion maximal voluntary contractions (MVCs) were performed. Maximal drop jump performance from optimal dropping height was measured in a sledge ergometer. Increases in knee extensor and ankle plantar flexor torque and muscle…

Neck and Shoulder Muscle Activation Among Experienced and Inexperienced Pilots in +Gz Exposure

Background The aim of the present study was to compare differences in electromyography (EMG) activation of the neck and shoulder muscles between groups of inexperienced and experienced pilots during controlled +Gz exposure in a centrifuge. Methods The subjects were volunteer cadets (inexperienced group) and lieutenants (experienced group) undergoing their first centrifuge training. The first group did not have any high performance aircraft (HPA) experience, while the latter one had a 1-yr experience of intense flying of HPA. During the centrifuge run, EMG activity was recorded from the left and right shoulder, neck flexor, and neck extensor muscles. Results The pilots without HPA experience…

Exercise-induced changes in tendinous tissue compliance: Outer tendon or aponeurosis?

Bimodal Recovery Pattern in Human Skeletal Muscle Induced by Exhaustive Stretch-Shortening Cycle Exercise:

Introduction/Purpose: Recovery of force and stretch reflex from exhaustive stretch-shortening cycle (SSC) exercise is usually bimodal, characterized as immediate exercise-induced performance reduction, with its quick recovery followed by a longer-lasting reduction in performance. A clear parallel exists between the respective changes in performance, neural activation, and metabolic or structural exercise-induced changes. This implies the existence of potential coupling between muscle failure and the induced neural adjustments that take place along its recovery. The present study was designed to explore the evidence of this coupling more thoroughly. Methods: H- and stretch reflexes were meas…

Motor Unit Firing Behaviour of Soleus Muscle in Isometric and Dynamic Contractions

Introduction. Understanding the detailed control of human locomotion and balance can be improved, when individual motor units can be isolated and their firing rates followed in natural movement of large, fuctionally important muscles. For this reason the present study investigated the motor unit discharge rate (MUDR) in isometric and dynamic contractions of the soleus muscle. Methods: Eleven males performed isometric (10–100% MVC) and dynamic (10–40% MVC) plantar flexions. Intramuscular EMG was measured from Soleus with bipolar wire-electrodes and decomposed with custom built “Daisy” software. Results. The Soleus MUDR was significantly higher in concentric compared to isometric or eccentric…

STUDY OF LEG MOVEMENT IN ONE- AND TWO-LEGGED HOPPING

This study was based on the previous research where mechanics of the leg-pushing phase in shot put was studied. The present paper examined the functional mechanics of leg movements during the ground contact of the jumps on one leg and on two legs. The principle of the measuring method was to photograph the movement in series of subject images on one frame where the marker lights attached to the subject can be seen as broken light-lines. The measuring accuracy of the system (time and distance) proved to be very high. This new measuring method is a useful complement to the existing methods. The aim of the study was to approximate the measured points by a suitable curve. Two equations (represe…

Viscoelastic properties of the Achilles tendon in vivo

It has been postulated that human tendons are viscoelastic and their mechanical properties time-dependent. Although Achilles tendon (AT) mechanics are widely reported, there is no consensus about AT viscoelastic properties such as loading rate dependency or hysteresis, in vivo. AT force-elongation characteristics were determined from 14 subjects in an ankle dynamometer at different loading rates using motion capture assisted ultrasonography. AT stiffness and elongation were determined between 10 – 80% of maximum voluntary contraction (MVC) force at fast and slow loading rates. As subjects were unable to consistently match the target unloading rate in the slow condition, AT hysteresis was on…

Comparison of impact characteristics of four different ice hockey arena dasher boards

During recent years the incidence of ice hockey related concussions has increased. Therefore, the main aim of this study was to determine how dasher board materials and structures affect impact characteristics and thereby concussion risk. The measurements were divided into two parts; 1. physiological characteristics of body checks were determined in real game measurements, and 2. simulation of body checks in the laboratory. Peak forces and stopping distances were determined from the high-speed camera data, and stiffness values were subsequently calculated. Dasher board materials and structures had a clear effect on impact characteristics. Flexible protective shielding material resulted in 1…

Exercise intervention protocol in children and young adults with cerebral palsy : the effects of strength, flexibility and gait training on physical performance, neuromuscular mechanisms and cardiometabolic risk factors (EXECP)

Abstract Background Individuals with cerebral palsy (CP) have problems in everyday tasks such as walking and climbing stairs due to a combination of neuromuscular impairments such as spasticity, muscle weakness, reduced joint flexibility and poor coordination. Development of evidence-based interventions are in pivotal role in the development of better targeted rehabilitation of CP, and thus in maintaining their motor function and wellbeing. Our aim is to investigate the efficacy of an individually tailored, multifaceted exercise intervention (EXECP) in children and young adults with CP. EXECP is composed of strength, flexibility and gait training. Furthermore, this study aims to verify the …

Stiff landings are associated with increased ACL injury risk in young female basketball and floorball players

Background: Few prospective studies have investigated the biomechanical risk factors of anterior cruciate ligament (ACL) injury. Purpose: To investigate the relationship between biomechanical characteristics of vertical drop jump (VDJ) performance and the risk of ACL injury in young female basketball and floorball players. Study Design: Cohort study; Level of evidence, 3. Methods: At baseline, a total of 171 female basketball and floorball players (age range, 12-21 years) participated in a VDJ test using 3-dimensional motion analysis. The following biomechanical variables were analyzed: (1) knee valgus angle at initial contact (IC), (2) peak knee abduction moment, (3) knee flexion angle at …

Deteriorated stabilization of walking in individuals with spastic cerebral palsy revealed by a simulated tripping perturbation

Abstract. The aim of this study was to make use of a pr eviously introduced method of a simulated tripping perturbation to examine stability of walking in individuals with and with out cerebral palsy. This tripping perturbation is a forward-dynamics analys is, and it works so that in a subjec t-specific muscle-driven simulation of walking, created from experimental gait data, a force is applied to the swin g-foot, and resulting changes in the kinematics are observed. Here, changes in the fore-aft position of the trunk were analyzed. Subjects were 10 children with spastic diplegic cerebral palsy and eight un impaired children walking at their self-sel ected speed. Several tripping perturbati…

Aging and strength training influence knee extensor intermuscular coherence during low- and high-force isometric contractions

Aging is associated with reduced maximum force production and force steadiness during low-force tasks, but both can be improved by training. Intermuscular coherence measures coupling between two peripheral surface electromyography (EMG) signals in the frequency domain. It is thought to represent the presence of common input to alpha-motoneurons, but the functional meaning of intermuscular coherence, particularly regarding aging and training, remain unclear. This study investigated knee extensor intermuscular coherence in previously sedentary young (18–30 years) and older (67–73 years) subjects before and after a 14-week strength training intervention. YOUNG and OLDER groups performed maximu…

Modeling the force – velocity relationship in arm movement

Modeling the force-velocity dependence of a muscle-tendon unit has been one of the most interesting objectives in the field of muscle mechanics. The so-called Hill’s equation [1,2] is widely used to describe the force-velocity relationship of muscle fibers. Hill’s equation was based on the laboratory measurements of muscle fibers and its application to the practical measurements in muscle mechanics has been problematic. Therefore, the purpose of this study was to develop a new explicit calculation method to determine the force-velocity relationship, and test its function in experimental measurements. The model was based on the motion analysis of arm movements. Experiments on forearm rotatio…

The effect of paired associative stimulation on fatigue resistance

Paired associative stimulation (PAS) is a non-invasive stimulation method developed to induce bidirectional changes in the excitability of the cortical projections to the target muscles. However, very few studies have shown an association between changes in motor evoked potentials (MEP) after PAS and behavioral changes in healthy subjects. In the present study we hypothesized that the functional relevance of PAS can be seen during fatiguing exercise, since there is always a central contribution to the development of fatigue. Transcranial magnetic stimulation was applied over the motor cortex to measure changes in the MEPs of the soleus muscle before and after PAS. Furthermore, fatigue resis…

On-Ice and Off-Ice Fitness Profiles of Elite and U20 Male Ice Hockey Players of Two Different National Standards

Vigh-Larsen, JF, Haverinen, MT, Panduro, J, Ermidis, G, Andersen, TB, Overgaard, K, Krustrup, P, Parkkari, J, Avela, J, Kyröläinen, H, and Mohr, M. On-ice and off-ice fitness profiles of elite and U20 male ice hockey players of two different national standards. J Strength Cond Res 34(12): 3369-3376, 2020-Differences in body composition and performance were investigated between elite and U20 male ice hockey players of 2 different national standards. One hundred seventy-nine players were recruited from the highest Finnish (n = 82) and Danish (n = 61) national level, as well as from 1 U20 team from Finland (n = 19) and Denmark (n = 17). Body composition and countermovement jump performance (CM…

In vivo mechanical response of human Achilles tendon to a single bout of hopping exercise

SUMMARY Stiffness of the human Achilles tendon (AT) was determined in vivo before and after a single bout of hopping exercise. It was hypothesized, based on published data using in vitro specimens, that a reduction in AT stiffness may occur after just 1000 loading cycles at physiological stress levels. Ten healthy subjects performed two-legged hopping exercise consisting of 1150–2600 high impacts. Tendon stiffness was determined in several isometric ramp contractions [20%, 40%, 60%, 80% and 100% maximum voluntary contraction (MVC)] during which tendon elongation was measured using ultrasonography and two cameras. Tendon force was calculated by dividing measured ankle torque by magnetic reso…

Changes in motor unit characteristics after eccentric elbow flexor exercise

Morphological evidence suggests that fast-twitch fibers are prone to disruption of their membrane structures by eccentric exercise. However, it is unclear how this is reflected in the discharge rate and action potential propagation of individual motor units, especially at high contraction levels. High-density surface electromyograms were recorded from biceps brachii muscle and decomposed to individual motor unit action potentials at isometric contraction levels between 10% and 75% of maximal voluntary contraction (MVC) before intermittent maximal elbow flexor eccentric exercise, and two hours (2H), two days (2D) and four days (4D) post-exercise. Maximal voluntary force decreased by 21.3±5.6…

Neuromuscular control in landing from supra-maximal dropping height.

International audience; The present study utilized high-impact supra-maximal landings to examine the influence of the pre-impact force level on the post-impact electromyographic (EMG) activity and, in particular, on the short latency EMG reflex (SLR) component. Unilateral-leg landings were performed in a sitting position on a sledge apparatus after release from high, but individually constant dropping height. A lower limb guiding device fixed to the front of the sledge seat allowed the subjects to sustain a given pre-set force level up to impact. This force level was either freely chosen or set at 20, 35, and 50% of maximal isometric plantarflexion force. EMG activity was recorded from eigh…

Changes in motor unit characteristics after eccentric elbow flexor exercise

Morphological evidence suggests that fast-twitch fibers are prone to disruption of their membrane structures by eccentric exercise. However, it is unclear how this is reflected in the discharge rate and action potential propagation of individual motor units, especially at high contraction levels. High-density surface electromyograms were recorded from biceps brachii muscle and decomposed to individual motor unit action potentials at isometric contraction levels between 10% and 75% of maximal voluntary contraction (MVC) before intermittent maximal elbow flexor eccentric exercise, and two hours (2H), two days (2D) and four days (4D) post-exercise. Maximal voluntary force decreased by 21.3±5.6…

Sarcolemmal excitability as investigated with M-waves after eccentric exercise in humans

It has been shown that intensive eccentric muscle actions lead to prolonged loss of muscle force and sarcolemmal damage. This may lead to a reduction in the excitability of the sarcolemma and contribute to the functional deficit. Experiments were carried out to test sarcolemmal excitability after eccentric elbow flexor exercise in humans. Electrically elicited surface compound muscle action potential (M-wave) properties from 30s stimulation trains (20Hz) were analyzed in biceps brachii muscle immediately after, 1h and 48h after the exercise. M-wave area, amplitude, root mean square and duration were reduced immediately after the eccentric exercise. However, no such reduction could be observ…

Effects of marathon running on running economy and kinematics.

The present study was designed to investigate interactions between running economy and mechanics before, during, and after an individually run marathon. Seven experienced triathletes performed a 5-min submaximal running test on a treadmill at an individual constant marathon speed. Heart rate was monitored and the expired respiratory gas was analyzed. Blood samples were drawn to analyze serum creatine kinase activity (S-CK), skeletal troponin I (sTnI), and blood lactate (B-La). A video analysis was performed (200 frames · s−1) to investigate running mechanics. A kinematic arm was used to determine the external work of each subject. The results of the present study demonstrate that after the …

Older adults show elevated intermuscular coherence in eyes‐open standing but only young adults increase coherence in response to closing the eyes

New Findings: What is the central question of this study? Can a 14-week strength-training programme modify intermuscular coherence levels during bipedal standing tasks with eyes open and eyes closed and reduce age-related differences? What is the main finding and its importance? Older adults had more prominent common input over 4–14 Hz with eyes open, but during the eyes-closed task the young adults were able to further enhance their common input at 6–36 Hz. This indicates that young adults are better at modulating common input in different motor tasks. Abstract: Understanding neural control of standing balance is important to identify age-related degeneration and design interventions to ma…

Altered reflex sensitivity after repeated and prolonged passive muscle stretching.

Experiments were carried out to test the effect of prolonged and repeated passive stretching (RPS) of the triceps surae muscle on reflex sensitivity. The results demonstrated a clear deterioration of muscle function immediately after RPS. Maximal voluntary contraction, average electromyographic activity of the gastrocnemius and soleus muscles, and zero crossing rate of the soleus muscle (recorded from 50% maximal voluntary contraction) decreased on average by 23.2, 19.9, 16.5, and 12.2%, respectively. These changes were associated with a clear immediate reduction in the reflex sensitivity; stretch reflex peak-to-peak amplitude decreased by 84.8%, and the ratio of the electrically induced m…

Effects of gait speed on stability of walking revealed by simulated response to tripping perturbation

The objective of this work was to study stability of walking over a range of gait speeds by means of muscle-driven simulations. Fast walking has previously been related to high likelihood of falling due to tripping. Various measures of stability have shown different relationships between walking speed and stability. These measures may not be associated with tripping, so it is unclear whether the increase in likelihood of falling is explicable by an increase in instability. Here, stability with respect to a constant tripping perturbation was quantified as the immediate passive response of torso to the perturbation. Subject-specific muscle-driven simulations of eight young healthy subjects wa…

Contributions of individual muscles to the sagittal- and frontal-plane angular accelerations of the trunk in walking.

This study was conducted to analyze the unimpaired control of the trunk during walking. Studying the unimpaired control of the trunk reveals characteristics of good control. These characteristics can be pursued in the rehabilitation of impaired control. Impaired control of the trunk during walking is associated with aging and many movement disorders. This is a concern as it is considered to increase fall risk. Muscles that contribute to the trunk control in normal walking may also contribute to it under perturbation circumstances, attempting to prevent an impending fall. Knowledge of such muscles can be used to rehabilitate impaired control of the trunk. Here, angular accelerations of the t…

Effects of long- and short-term fatiguing stretch-shortening cycle exercises on reflex EMG and force of the tendon-muscle complex

This study examined the fatigue effects of stretch-shortening cycle exercises of different intensity and duration on stretch reflex EMG and mechanical responses of the triceps surae muscle. Twelve subjects performed either a 10-km run ( n=6) or short but exhaustive rebound exercise on a sledge apparatus ( n=6). Passive reflex tests (mechanically induced ankle dorsiflexions) were examined before, after as well as 2 h, 2 and 7 days after exercise. Mechanical reflex responses were recorded from the ergometer torque signal. An acute contractile failure was observed as large reductions in twitch responses, especially in the sledge subgroup who showed high post-exercise peak blood lactate and an …

Neuromuscular fatigue during dynamic maximal strength and hypertrophic resistance loadings

The purpose of this study was to compare the acute neuromuscular fatigue during dynamic maximal strength and hypertrophic loadings, known to cause different adaptations underlying strength gain during training. Thirteen healthy, untrained males performed two leg press loadings, one week apart, consisting of 15 sets of 1 repetition maximum (MAX) and 5 sets of 10 repetition maximums (HYP). Concentric load and muscle activity, electromyography (EMG) amplitude and median frequency, was assessed throughout each set. Additionally, maximal bilateral isometric force and muscle activity was assessed pre-, mid-, and up to 30 min post-loading. Concentric load during MAX was decreased after set 10 (P<0…

Doublet potentiation in the triceps surae is limited by series compliance and dynamic fascicle behavior.

Activation of skeletal muscle twice in quick succession results in nonlinear force summation (i.e., doublet potentiation). The force contributed by a second activation is typically of augmented amplitude, longer in duration, and generated at a greater rate. The purpose of this study was to examine force summation in a muscle attached to a compliant tendon, where considerable internal shortening occurs during a fixed-end contraction. The triceps surae of 21 ( Experiment 1) and 9 ( Experiment 2) young adults were maximally activated with doublet stimulation of different interstimulus intervals (ISIs) (5-100 ms) at several muscle lengths. Ultrasound images acquired from lateral gastrocnemius …

Age-related decreases in motor unit discharge rate and force control during isometric plantar flexion.

Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software "Daisy". DR was lower in OLD in RECR-10% (17.9%, p0.001), RECR-20% (15.8%, p0.05), ISO-10% (17.7%, p0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p0.001)…

Neuromuscular Behaviour of the Triceps Surae Muscle-Tendon Complex during Running and Jumping

The present study examined the behaviour of the Achilles tendon (AT) - triceps surae (TS) muscle complex during running and long jump take-off. High AT forces were measured in the push-off phase in running even with very low EMG activity. In the long jump, high rate of stiffness development was a characteristic of the braking phase of the jump. The results suggest that high and well-coordinated activation patterns of the leg extensor muscles during the preactivation and eccentric phases together with high stretching velocities of muscle-tendon complex provide basis for appropriate tendomuscular stiffness. This together with high force at the end of the eccentric phase enables an effective p…

Multi-channel electromyography during maximal isometric and dynamic contractions.

Motor unit behavior differs between contraction types at submaximal contraction levels, however is challenging to study during maximal voluntary contractions (MVCs). With multi-channel surface electromyography (sEMG), mean physiological characteristics of the active motor units can be extracted. Two 8-electrode sEMG arrays were attached on biceps brachii muscle (one on each head) to examine behavior of sEMG variables during isometric, eccentric and concentric MVCs of elbow flexors in 36 volunteers. On average, isometric (364 ± 88N) and eccentric (353 ± 74N) MVCs were higher than concentric (290 ± 73N) MVC (p0.001). Mean muscle fiber conduction velocity (CV) was highest during eccentric MVC …

Bone rigidity to neuromuscular performance ratio in young and elderly men.

Given the adaptation of bone to prevalent loading, bone loss should follow, but lag behind, the decline in physical performance during aging. Furthermore, bone responsiveness to load-induced strains is believed to decrease with aging. However, the relationship between bone and lean body ( approximately muscle) mass appears to remain rather constant throughout adulthood. The purpose of this study was to examine the association between age and bone to neuromuscular performance ratio. Young (N=20, age 24 SD+/-2 years, body mass 77+/-11 kg, height 178+/-6 cm) and elderly (N=25, 72+/-4 years, 75+/-9 kg, 172+/-5 cm) men served as subjects. Bone structural traits were measured at the right distal …

Age-related neuromuscular function and dynamic balance control during slow and fast balance perturbations.

This study investigated age-related differences in dynamic balance control and its connection to reflexes and explosive isometric plantar flexor torque in 19 males (9 Young aged 20–33 yr, 10 Elderly aged 61–72 yr). Dynamic balance was measured during Slow (15 cm/s) and Fast (25 cm/s) anterior and posterior perturbations. H/M-ratio was measured at 20% of maximal M-wave (H/M20%) 10, 30, and 90 ms after perturbations. Stretch reflexes were measured from tibialis anterior and soleus during anterior and posterior perturbations, respectively. In Slow, Elderly exhibited larger peak center-of-pressure (COP) displacement (15%; P &lt; 0.05) during anterior perturbations. In Fast, Young showed a tren…

Corticospinal and intracortical excitability is modulated in the knee extensors after acute strength training

The corticospinal responses to high-intensity and low-intensity strength-training of the upper limb are modulated in an intensity-dependent manner. Whether an intensity-dependent threshold occurs following acute strength training of the knee extensors (KE) remains unclear. We assessed the corticospinal responses following high-intensity (85% of maximal strength) or low-intensity (30% of maximal strength) KE strength-training with measures taken during an isometric KE task at baseline, post-5, 30 and 60-min. Twenty-eight volunteers (23 ± 3 years) were randomized to high-intensity (n = 11), low-intensity (n = 10) or to a control group (n = 7). Corticospinal responses were evoked with transcra…

Assessment of Muscular Fitness as a Predictor of Flight Duty Limitation.

Introduction The high acceleration (Gz) exposure among military pilots flying fighter aircraft has been associated with an increased risk for cervical and lumbar disorders. It has been suggested that an adequate level of physical performance could reduce the risk of experiencing these disorders. The Finnish Air Force has for several years used aerobic (bicycle ergometer) and muscular fitness tests (battery of five tests) in the selection process of military pilot candidates in order to evaluate their physical fitness level. The aim of the study was to determine if these selection phase tests and anthropometry measures can predispose those individuals who might be at risk of developing sever…

Increased cross-education of muscle strength and reduced corticospinal inhibition following eccentric strength training.

Aim: Strength training of one limb results in a substantial increase in the strength of the untrained limb, however, it remains unknown what the corticospinal responses are following either eccentric or concentric strength training and how this relates to the cross-education of strength. The aim of this study was to determine if eccentric or concentric unilateral strength training differentially modulates corticospinal excitability, inhibition and the cross-transfer of strength. Methods: Changes in contralateral (left limb) concentric strength, eccentric strength, motor-evoked potentials, short-interval intracortical inhibition and silent period durations were analyzed in groups of young ad…

EFFECTS OF STRIKING STRATEGY ON LOWER EXTREMITY LOADING DURING RUNNING

Backround It is expected that every second runner has a running-related overuse injury each year. The knee joint and Achilles tendon are the most commonly injured sites covering both about one fifth of all running related injuries. 1 Runners can be categorized into rearfoot strikers, mid-foot strikers or forefoot strikers based on the landing strategy at the instant of initial ground contact. Forefoot or mid-foot striking has been shown to reduce impact peak and loading rate of the ground reaction force during early stance phase. 2 Furthermore, the finding of the recent study suggest that forefoot striking may potentially decrease the risk of running-related injuries. 3 However, the effect …

Impaired action potential conduction at high force levels after eccentric exercise

High-density surface electromyography was used to examine whether gross sarcolemmal function is impaired in m. biceps brachii after intensive eccentric elbow flexor exercise, when measured at wide range of isometric contraction levels. Root mean square (RMS), mean power frequency (MNF) and mean muscle fibre conduction velocity (CV) were calculated before and up to four days post-exercise. Maximal isometric voluntary (MVC) force decreased by 21.3+/-5.6% two hours after exercise, and by 12.6+/-11.1% two days post-exercise. CV and MNF decreased both during MVC (CV from 4.1+/-0.3m/s to 3.8+/-0.4m/s and MNF from 92.6+/-10 Hz to 85.2+/-11 Hz) and during electrically evoked maximal M-wave (CV from…

The Effects of Cold Water Immersion on the Recovery of Drop Jump Performance and Mechanics : A Pilot Study in Under-20 Soccer Players

Cold water immersion (CWI) is a popular method used for enhancing recovery from exercise. However, the efficacy of this approach is inconclusive and studies investigating variables contributing to overall performance are scarce. Additionally, few studies have investigated the recovery of stretch-shortening cycle (SSC) performance after a fatiguing SSC task. The SSC occurs naturally in human locomotion and induces a recovery pattern different from isolated muscle contractions (e.g., pure eccentric exercise). Therefore, the main aim of this study was to investigate the effects of a single CWI on jumping performance and mechanics after exhaustive SSC exercise. On a sledge apparatus, 10 male un…

Acute and prolonged reduction in joint stiffness in humans after exhausting stretch-shortening cycle exercise.

The purpose of the present study was to examine the acute and long-term fatigue effects of exhausting stretch-shortening cycle (SSC) exercise on the stiffness of ankle and knee joints. Five subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Neuromuscular fatigue ef- fects were examined in submaximal hopping (HOP) and in maximal drop jumps (DJ) from 35 (DJ35) and 55 cm (DJ55) heights on a force plate. Additional force and reflex measurements were made using an ankle ergom- eter. Jumping tests and ankle ergometer tests were car- ried out before, immediately after, 2 h (2H), 2 days and 7 days (7D) after…

Effects of prolonged walking on neural and mechanical components of stretch responses in the human soleus muscle

After repeated passive stretching, tendinous tissue compliance increases in the human soleus (SOL) muscle–tendon unit. During movement, such changes would have important consequences for neural and mechanical stretch responses. This study examined the existence of such effects in response to a 75 min walking intervention. Eleven healthy subjects walked on a treadmill at 4 km h−1 with a robotic stretch device attached to the left leg. Ultrasonography was used to measure SOL fascicle lengths, and surface EMG activity was recorded in the SOL and tibialis anterior (TA) muscles. Perturbations of 6 deg were imposed at three different measurement intervals: Pre (immediately before the walking inte…

Effects of medially posted insoles on foot and lower limb mechanics across walking and running in overpronating men.

Anti-pronation orthoses, like medially posted insoles (MPI), have traditionally been used to treat various of lower limb problems. Yet, we know surprisingly little about their effects on overall foot motion and lower limb mechanics across walking and running, which represent highly different loading conditions. To address this issue, multi-segment foot and lower limb mechanics was examined among 11 over-pronating men with normal (NORM) and MPI insoles during walking (self-selected speed 1.70 +/- 0.19 m/s vs 1.72 +/- 0.20 m/s, respectively) and running (4.04 +/- 0.17 m/s vs 4.10 +/- 0.13 m/s, respectively). The kinematic results showed that MPI reduced the peak forefoot eversion movement in …

Revising the stretch reflex threshold method to measure stretch hyperreflexia in cerebral palsy

Funding Information: This work was supported by the Olvi Foundation, Research Foundation of Cerebral Palsy Alliance (PHD00321), Finnish Cultural Foundation, University of Jyväskylä, Academy of Finland (grants #296240, #307250, #327288, #311877, #326988), including “Brain changes across the life-span” profiling funding to University of Jyväskylä, Jane and Aatos Erkko Foundation (#602.274), and the Netherlands Organization for Scientific Research (NWO-016.186.144). Ministry of Education and Culture (OKM/28/626/2022). Hyper-resistance is an increased resistance to passive muscle stretch, a common feature in neurological disorders. Stretch hyperreflexia, an exaggerated stretch reflex response, …

Test-retest reliability of motor-evoked potentials at 20% and 60% of maximum isometric voluntary contraction in rectus femoris muscle

Effects of Combined Strength and Endurance Training on Treadmill Load Carrying Walking Performance in Aging Men

Holviala, J, Hakkinen, A, Karavirta, L, Nyman, K, Izquierdo, M, Gorostiaga, EM, Avela, J, Korhonen, J, Knuutila, V-P, Kraemer, WJ, and Hakkinen, K. Effects of combined strength and endurance training on treadmill load carrying walking performance in aging men. J Strength Cond Res 24(6): 1584-1595, 2010—The present study examined the effects of twice weekly total body strength training (ST), endurance cycling (ET), and combined ST and ET (2 + 2 times a week) (SET) training on the load carrying walking test performance on the treadmill (TM) and changes in neuromuscular and endurance performance during a 21-week training period in aging men. Forty healthy men (54.8 6 8.0 years) were divided in…

Neuromuscular changes after long-lasting mechanically and electrically elicited fatigue

Central fatigue was investigated under an isolated active condition whereby the possible effects of supraspinal fatigue were minimized. Therefore, ten subjects were fatigued by simultaneously and repeatedly mechanically stretching and electrically stimulating their calf muscles for 1 h. This was performed using an ankle ergometer. The active fatigue task included a total of 2400 muscle stretches with an intensity of 10% of the maximal voluntary contraction (MVC). This protocol clearly impaired neuromuscular function, as revealed by a significant reduction in MVC (P < 0.01) and the neural input to the muscle (average EMG) (P < 0.01-0.001). The interpolated nerve stimulation compensated for t…

Effects of muscle action type on corticospinal excitability and triceps surae muscle-tendon mechanics.

This study investigated whether the specific motor control strategy reported for eccentric muscle actions is dependent on muscle mechanical behavior. Motor evoked potentials, Hoffman reflex (H-reflex), fascicle length, pennation angle, and fascicle velocity of soleus muscle were compared between isometric and two eccentric conditions. Ten volunteers performed maximal plantarflexion trials in isometric, slow eccentric (25°/s), and fast eccentric (100°/s) conditions, each in a different randomized testing session. H-reflex normalized by the preceding M wave (H/M) was depressed in both eccentric conditions compared with isometric ( P &lt; 0.001), while no differences in fascicle length and pe…

The Stretch-Shortening Cycle

Neuromuscular fatigue has traditionally been examined using isolated forms of either isometric, concentric or eccentric actions. However, none of these actions are naturally occurring in human (or animal) ground locomotion. The basic muscle function is defined as the stretch-shortening cycle (SSC), where the preactivated muscle is first stretched (eccentric action) and then followed by the shortening (concentric) action. As the SSC taxes the skeletal muscles very strongly mechanically, its influence on the reflex activation becomes apparent and very different from the isolated forms of muscle actions mentioned above. The ground contact phases of running, jumping and hopping etc. are example…

Achilles tendon stiffness is unchanged one hour after a marathon

Overuse-induced injuries have been proposed as a predisposing factor for Achilles tendon (AT) ruptures. If tendons can be overloaded, their mechanical properties should change during exercise. Because there data are lacking on the effects of a single bout of long-lasting exercise on AT mechanical properties, the present study measured AT stiffness before and after a marathon. AT stiffness was determined as the slope of the force–elongation curve between 10 and 80% of maximum voluntary force. AT force–elongation characteristics were measured in an ankle dynamometer using simultaneous motion-capture-assisted ultrasonography. Oxygen consumption and ankle kinematics were also measured on a trea…

Effects of power training on mechanical efficiency in jumping.

The present study investigates the effects of power training on mechanical efficiency (ME) in jumping. Twenty-three subjects, including ten controls, volunteered for the study. The experimental group trained twice a week for 15 weeks performing various jumping exercises such as drop jumps, hurdle jumps, hopping and bouncing. In the maximal jumping test, the take-off velocity increased from 2.56 (0.24) m.s(-1) to 2.77 (0.18) m.s(-1) ( P<0.05). In the submaximal jumping of 50% of the maximum, energy expenditure decreased from 660 (110) to 502 (68) J.kg(-1).min(-1) ( P<0.001) while, simultaneously, ME increased from 37.2 (8.4)% to 47.4 (8.2)% ( P<0.001). Some muscle enzyme activities of the ga…

Priming the Motor Cortex With Anodal Transcranial Direct Current Stimulation Affects the Acute Inhibitory Corticospinal Responses to Strength Training.

Frazer, AK, Howatson, G, Ahtiainen, JP, Avela, J, Rantalainen, T, and Kidgell, DJ. Priming the motor cortex with anodal transcranial direct current stimulation affects the acute inhibitory corticospinal responses to strength training. J Strength Cond Res 33(2): 307-317, 2019-Synaptic plasticity in the motor cortex (M1) is associated with strength training (ST) and can be modified by transcranial direct current stimulation (tDCS). The M1 responses to ST increase when anodal tDCS is applied during training due to gating. An additional approach to improve the M1 responses to ST, which has not been explored, is to use anodal tDCS to prime the M1 before a bout of ST. We examined the priming effe…

Leg Extension Power and Walking Speed in Very Old People Living Independently

BACKGROUND Leg extension power can be determined as the product of the force and velocity of movement. Its association with maximal walking speed was studied in 131 80- and 85-year-old men and women. METHODS Leg extension power was measured with the help of a sledge ergometer in a sitting position using a facilitated "jump test." The participant was attached by belts to a sliding chair on rails inclined at 12.6 degrees to the floor. The feet were placed on the force plate attached perpendicularly to the rails, and the knee angle was 90 degrees at the starting position. The participant was advised to extend his or her legs powerfully. The highest value of five to eight attempts was accepted …

Whole body frontal plane mechanics across walking, running, and sprinting in young and older adults

This study investigated the whole body frontal plane mechanics among young (26 ± 6 years), early old (61 ± 5 years), and old (78 ± 4 years) adults during walking, running, and sprinting. The age-groups had similar walking (1.6 m/s) and running (4.0 m/s) speeds, but different maximal sprinting speed (young 9.3 m/s, early old 7.9 m/s, and old 6.6 m/s). Surprisingly, although the old group exerted much lower vertical ground reaction force during running and sprinting, the hip frontal plane moment did not differ between the age-groups. Kinematic analysis demonstrated increased hip adduction and pelvis drop, as well as reduced trunk lateral flexion among old adults, especially during sprinting. …

Muscle fascicle stretch velocity in relation to stretch reflex activation at different contraction levels in human triceps surae

Transcranial Magnetic Stimulation as a Tool to Study the Role of the Motor Cortex in Human Muscle Function

Blood Flow Restriction Alters Motor Unit Behavior During Resistance Exercise.

AbstractWe aimed to determine whether blood flow restriction (BFR) alters the characteristics of individual motor units during low-intensity (LI) exercise. Eight men (26.0±3.8 yrs) performed 5 sets of 15 knee extensions at 20% of one-repetition maximum (with and without BFR). Maximal isometric voluntary contractions (MVC) were performed before and after exercise to quantify force decrement. Submaximal isometric voluntary contractions were additionally performed for 18 s, matching trapezoidal target-force trajectories at 40% pre-MVC. EMG activity was recorded from the vastus lateralis muscle. Then, signals were decomposed to extract motor unit recruitment threshold, firing rates and action p…

Neuromuscular Adaptations to Different Modes of Combined Strength and Endurance Training

The present study investigated neuromuscular adaptations between same-session combined strength and endurance training with 2 loading orders and different day combined training over 24 weeks. 56 subjects were divided into different day (DD) combined strength and endurance training (4-6 d·wk(-1)) and same-session combined training: endurance preceding strength (E+S) or vice versa (S+E) (2-3 d·wk(-1)). Dynamic and isometric strength, EMG, voluntary activation, muscle cross-sectional area and endurance performance were measured. All groups increased dynamic one-repetition maximum (p<0.001; DD 13±7%, E+S 12±9% and S+E 17±12%) and isometric force (p<0.05-0.01), muscle cross-sectional area (p<0.0…

Age dependency of neuromuscular function and dynamic balance control

Abstract The purpose of the present study was to examine whether static and dynamic balance control are related to neuromuscular function and ageing. For this purpose, we constructed a new dynamic balance measurement system that simulates natural falling. Ten young (age 21–31 years) and 20 elderly (age 60–70 years) men participated in the experiment. Maximal isometric torque (MVC) and activation level were measured from the quadriceps and plantar flexor muscles. The H-reflex, V-wave, and maximal M-wave were measured from the soleus muscle. In dynamic balance control, anterior-posterior centre-of-pressure swaying was 74±8.1 mm in the young men and 91.5±19.4 mm in the elderly men (P<0.05), wh…

Effects of differently induced stretch loads on neuromuscular control in drop jump exercise

The neuromuscular characteristics of the triceps surae and vastus lateralis muscles and interactions between the pre-activation of these muscles and the muscle output itself during ground contact were investigated during various types of stretch-shortening cycle muscle loading. The loading of the muscles was effected by using three different types of drop jump exercise. These jumps allowed separate modifications of the loading of the leg extensor muscles by changing the velocity of the centre of gravity (CG) or by changing directly the body mass, which was also affected by changing artificially the acceleration of the CG. It was found that the eccentric peak angular velocity of the ankle jo…

Older Age Increases the Amplitude of Muscle Stretch-Induced Cortical Beta-Band Suppression But Does not Affect Rebound Strength

Healthy aging is associated with deterioration of the sensorimotor system, which impairs balance and somatosensation. However, the exact age-related changes in the cortical processing of sensorimotor integration are unclear. This study investigated primary sensorimotor cortex (SM1) oscillations in the 15–30 Hz beta band at rest and following (involuntary) rapid stretches to the triceps surae muscles (i.e., proprioceptive stimulation) of young and older adults. A custom-built, magnetoencephalography (MEG)-compatible device was used to deliver rapid (190°·s−1) ankle rotations as subjects sat passively in a magnetically-shielded room while MEG recorded their cortical signals. Eleven young (age…

Voluntary activation and mechanical performance of human triceps surae muscle after exhaustive stretch-shortening cycle jumping exercise.

The purpose of this study was to examine neuromuscular factors that may contribute to post exercise force loss and subsequent recovery after exhaustive stretch-shortening cycle (SSC) exercise. Six subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Exercise-induced changes in neuromuscular performance were followed up to 7 days post exercise. The total number of jumps in the SSC exercise ranged from 336 to 1392. The SSC exercise induced a significant immediate plantarflexion torque decline of 29, 38 and 44% (P<0.05) in maximal voluntary contraction and evoked maximal twitch and low-frequency (LF) stim…

Effect of body composition on the neuromuscular function of Finnish conscripts during an 8-week basic training period.

The dropout rate in the Finnish military service has increased during the past two decades. At the same time, the physical fitness level of young Finnish males has decreased, possibly leading to overtraining in new conscripts. The purpose of the present study was to examine whether body composition would influence neuromuscular function during the 8-week basic training (BT) period. Eighteen healthy male subjects (19 +/- 1 years) were divided into three different groups according to their body fat %. Group 1 (10%), group 2 (10-13%) and group 3 (13%). The soleus H-reflex response was measured in the standing position. In the seated position (knee 160 degrees and hip 110 degrees), the V-wave r…