Search results for " Muscle"
showing 10 items of 1495 documents
Electrical and mechanical H(max)-to-M(max) ratio in power- and endurance-trained athletes.
2001
The aim of this study was to compare the mechanical and electromyographic (EMG) characteristics of soleus motor units activated during maximal H reflex and direct M response among subjects with different histories of physical activity. Power-trained athletes produced stronger twitches, with a higher rate of twitch tension buildup and relaxation, than their endurance counterparts for both maximal H-reflex and maximal M-wave responses. The maximal H-reflex-to-maximal M-wave ratios for both force output (twitch) and EMG wave amplitude were significantly lower in power-trained than endurance-trained athletes. However, power-trained athletes exhibited a significantly greater twitch-to-EMG ratio…
Alterations of neuromuscular function after an ultramarathon.
2002
Neuromuscular fatigue of the knee extensor (KE) and plantar flexor (PF) muscles was characterized after a 65-km ultramarathon race in nine well-trained runners by stimulating the femoral and tibial nerves, respectively. One week before and immediately after the ultramarathon, maximal twitches were elicited from the relaxed KE and PF. Electrically evoked superimposed twitches of the KE were also elicited during maximal voluntary contractions (MVCs) to determine maximal voluntary activation. MVC and maximal voluntary activation decreased significantly after the ultramarathon (−30.2 ± 18.0% and −27.7 ± 13.0%, respectively; P < 0.001). Surprisingly, peak twitch increased after the ultramara…
Enzyme activities in muscle and connective tissue of M. vastus lateralis in habitually training and sedentary 33 to 70-year-old men
1975
A cross-sectional study was carried out to examine the activities of certain enzymes representing aerobic and anaerobic energy metabolism as well as the biosynthesis of collagen of M. vastus lateralis in 23 male endurance athletes in habitual training, aged 33 to 70 years. 23 sedentary healthy men of corresponding ages were selected for the control group. The mean maximal oxygen uptake of the trained subjects was 53.6 ml · kg−1 · min−1 and that of the control subjects 36.3 ml · kg−1 · min−1. As compared to the control group the trained subjects had significantly higher values in the muscle malate dehydrogenase, succinate dehydrogenase and prolyl hydroxylase activities, whereas the opposite …
Afferent contribution to locomotor muscle activity during unconstrained overground human walking:an analysis of triceps surae muscle fascicles
2010
Plantar flexor series elasticity can be used to dissociate muscle–fascicle and muscle–tendon behavior and thus afferent feedback during human walking. We used electromyography (EMG) and high-speed ultrasonography concomitantly to monitor muscle activity and muscle fascicle behavior in 19 healthy volunteers as they walked across a platform. On random trials, the platform was dropped (8 cm, 0.9 g acceleration) or held at a small inclination (up to ±3° in the parasagittal plane) with respect to level ground. Dropping the platform in the mid and late phases of stance produced a depression in the soleus muscle activity with an onset latency of about 50 ms. The reduction in ground reaction force…
Isometric muscle contractions after double pulse stimulation. comparison of healthy subjects and patients with myotonic dystrophy.
1996
Isometric contractions of the adductor pollicis muscle were studied in healthy subjects and patients with myotonic dystrophy after single and double stimuli of the ulnar nerve using a wide range of interstimulus intervals (ISI, 0.4-180 ms). In healthy subjects, the force contributed by a second stimulus was greater than the single twitch force being maximal (mean + 140%) at 12-ms ISI. In myotonic dystrophy, the force contributed by the second stimulus was (relative to a reduced twitch amplitude) increased (mean + 204%) with a maximum at 4.8-ms ISI. An abnormal increase of force was only recorded if the single twitch force was clearly reduced. The absolute refractory period of muscle contrac…
Neuromuscular fatigue during a long-duration cycling exercise
2002
The effects of prolonged cycling on neuromuscular parameters were studied in nine endurance-trained subjects during a 5-h exercise sustained at 55% of the maximal aerobic power. Torque during maximal voluntary contraction (MVC) of the quadriceps muscle decreased progressively throughout the exercise ( P < 0.01) and was 18% less at the end of exercise compared with the preexercise value. Peak twitch torque, contraction time, and total area of mechanical response decreased significantly ( P < 0.05) after the first hour of exercise. In contrast, changes in M-wave characteristics were significant only after the fourth hour of the exercise. Significant reductions ( P < 0.05) in electro…
Skeletal muscle blood flow and flow heterogeneity during dynamic and isometric exercise in humans
2002
The effects of dynamic and intermittent isometric knee extension exercises on skeletal muscle blood flow and flow heterogeneity were studied in seven healthy endurance-trained men. Regional muscle blood flow was measured using positron emission tomography (PET) and an [15O]H2O tracer, and electromyographic (EMG) activity was recorded in the quadriceps femoris (QF) muscle during submaximal intermittent isometric and dynamic exercises. QF blood flow was 61% ( P = 0.002) higher during dynamic exercise. Interestingly, flow heterogeneity was 13% ( P = 0.024) lower during dynamic compared with intermittent isometric exercise. EMG activity was significantly higher ( P < 0.001) during dynamic e…
The association between muscle EMG and perfusion in knee extensor muscles
2006
The relationships between electromyographic (EMG) activity and force as well as muscle blood flow and work have been well established. However, the association between muscle blood flow and EMG activity remains unsolved. Thus, to test the hypothesis that muscle EMG activity relates to muscle perfusion in different compartments of the quadriceps femoris (QF) muscle, 12 healthy male subjects were studied. During two very submaximal exercise bouts, at different exercise intensities, oxygen labelled radiowater and positron emission tomography were used to measure muscle perfusion. In addition, produced force of knee extensors and muscle EMG activity in the vastus lateralis (VL), vastus medialis…
Torque decrease during submaximal evoked contractions of the quadriceps muscle is linked not only to muscle fatigue.
2015
International audience; The aim of this study was to analyze the neuromuscular mechanisms involved in the torque decrease induced by submaximal electromyostimulation (EMS) of the quadriceps muscle. It was hypothesized that torque decrease after EMS would reflect the fatigability of the activated motor units (MUs), but also a reduction in the number of MUs recruited as a result of changes in axonal excitability threshold. Two experiments were performed on 20 men to analyze 1) the supramaximal twitch superimposed and evoked at rest during EMS (Experiment 1, n = 9) and 2) the twitch response and torque-frequency relation of the MUs activated by EMS (Experiment 2, n = 11). Torque loss was asses…
Fast increase of motor cortical inhibition following postural changes in healthy subjects.
2012
BACKGROUND AND AIMS: Postural reactions are associated with changes in the excitability of the motor system. In the present study we investigated the presence of neurophysiological changes of motor cortical areas targeting muscles of the inferior limbs following treatment with a physiotherapy technique aimed to treat postural dysfunctions by stretching postural muscles, global postural reeducation (GPR). METHODS: Twenty healthy subjects were evaluated with paired-transcranial magnetic stimulation (TMS) of the motor cortex and recording of motor evoked potentials (MEPs) from peripheral muscles of the inferior limb before and after two GPR manoeuvres applied in different experiments (1 and 2)…