Search results for " FLEX"
showing 10 items of 320 documents
Neural activation after maximal isometric contractions at different muscle lengths.
2006
DESBROSSES K., N. BABAULT, G. SCAGLIONI, J.-P. MEYER, and M. POUSSON. Neural Activation after Maximal Isometric Contractions at Different Muscle Lengths. Med. Sci. Sports Exerc., Vol. 38, No. 5, pp. 937–944, 2006. Purpose: To investigate i) whether neural activation dependence on muscle length is preserved with neuromuscular fatigue and ii) whether fatigue induced by a maximal isometric exercise is muscle length dependent. Methods: Twelve male subjects performed two fatiguing quadriceps muscle exercises: FS is the fatigue carried out at short muscle length (S) (S = 40- of knee flexion) and FL is the fatigue at long muscle length (L) (L = 100-). Before and after each fatiguing exercise (i.e.…
Effects of plantar flexor muscle fatigue induced by electromyostimulation on postural coordination
2007
International audience; The aim of the present study was to investigate the influence of a modification of an intrinsic capacity (plantar flexor strength) on the implementation of in-phase and anti-phase mode of coordination. Analysis of hip and ankle relative phases during fore-aft tracking task was done before and after an electromyostimulation fatigue protocol on the soleus muscles. Results showed participants used exclusively in-phase and anti-phase modes of coordination, with a sudden switch from one to the other with target frequency increase. Regarding tracking tasks, fatigue induces a decrease of performance for lower frequencies, and a significant decrease of switch frequency (−0.0…
Age-related neuromuscular function and dynamic balance control during slow and fast balance perturbations.
2013
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 < 0.05) during anterior perturbations. In Fast, Young showed a tren…
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…
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…
Superimposing hip extension on knee flexion evokes higher activation in biceps femoris than knee flexion alone.
2021
Hamstring muscle function during knee flexion has been linked to hamstring injury and performance. However, it is unclear whether knee flexion alone (KF) requires similar hamstring electromyography (EMG) activity pattern to simultaneous hip extension and knee flexion (HE-KF), a combination that occurs in the late swing phase of sprinting. This study examined whether HE-KF maximal voluntary isometric contraction (MVIC) evokes higher (EMG) activity in biceps femoris long head (BFlh) and semitendinosus (ST) than KF alone. Effects of shank rotation angles were also tested. Twenty-one males performed the above-mentioned MVICs while EMG activity was measured along ST and BFlh. Conditions were com…
Neural drive preservation after detraining following neuromuscular electrical stimulation training
2006
The purpose of the study was to investigate the behaviour of the central nervous system when 5 weeks of neuromuscular electrical stimulation (NMES) training was followed by 5 weeks of detraining. Nineteen males were divided into the neuromuscular electrostimulated group (EG, n=12) and the control group (CG, n=7). The training program consisted of 15 sessions of isometric NMES over a 5-week period. The EG subjects were tested before training (PRE), after 5 weeks of NMES training (POST) and after 5 weeks of detraining (DE) while CG subjects were only tested at PRE and at POST. Soleus (SOL) and gastrocnemii (GAS) maximal H-reflex and M-wave potentials were evoked at rest (i.e., H(max) and M(ma…
Effect of bike-fit in the perception of comfort, fatigue and pain
2016
The aim of this study was to assess the influence of different bike positions on the perception of fatigue, pain and comfort. Twenty cyclists underwent three tests that involved cycling for 45 min at their individual 50% peak aerobic power output while adopting different positions on the bike. Participants performed the cycling tests adopting three positions defined by two parameters (knee flexion angle [20°, 30°, 40°] and trunk flexion angle [35°, 45°, 55°]) in random order. Angles were measured using a 2D motion analysis system during cycling and applying Fonda's correction factor. Perceptions of comfort, fatigue and pain were reported before the end of each test. The combination of 40° k…
Time of day effects on isometric and isokinetic torque developed during elbow flexion in humans
2001
The aim of this study was, firstly, to confirm or refute the existence of circadian rhythms during several velocities of concentric action of the elbow flexor muscles and, secondly, to compare the characteristics of these circadian rhythms with those obtained during isometric actions. Eight volunteer subjects participated in this study. The circadian rhythms were obtained from six test sessions (TS) carried out at different times of day over 6 days with only one TS a day. During each TS, oral temperature and the torque of the muscle action were measured. The subjects made, on an isokinetic ergometer, two maximal isokinetic concentric elbow flexions at five angular velocities (60, 120, 180, …
Neural Activation During Submaximal Contractions Seems More Reflective of Neuromuscular Ageing than Maximal Voluntary Activation
2016
International audience; This study aimed at testing the hypothesis that differences in neural activation strategy during submaximal but not maximal plantarflexions exist between young and older men. Eleven young men (YM, 26 +/- 4 years) and thirteen old men (OM, 76 +/- 3 years) volunteered for the investigation. Maximal voluntary torque (MVT) was 38.2%, lower (p < 0.001) in OM than in YM, while voluntary activation was equivalent (similar to 97%). The relationship between the interpolated twitch torque and the voluntary torque (IT-VT relationship) was composite (curvilinear + exponential) for both age-groups. However, the OM showed accentuated concavity, as attested by the occurrence of the…