Fatigue-related adaptations in muscle coordination during a cyclic exercise in humans

Abstract

SUMMARYMuscle fatigue is an exercise-induced reduction in the capability of a muscle to generate force. A possible strategy to counteract the effects of fatigue is to modify muscle coordination. We designed this study to quantify the effect of fatigue on muscle coordination during a cyclic exercise involving numerous muscles. Nine human subjects were tested during a constant-load rowing exercise (mean power output: 217.9±32.4W) performed until task failure. The forces exerted at the handle and the footstretcher were measured continuously and were synchronized with surface electromyographic (EMG) signals measured in 23 muscles. In addition to a classical analysis of individual EMG data (EMG profile and EMG activity level), a non-negative matrix factorization algorithm was used to identify the muscle synergies at the start and the end of the test. Among the 23 muscles tested, 16 showed no change in their mean activity level across the rowing cycle, five (biceps femoris, gluteus maximus, semitendinosus, trapezius medius and vastus medialis) showed a significant increase and two (gastrocnemius lateralis and longissimus) showed a significant decrease. We found no change in the number of synergies during the fatiguing test, i.e. three synergies accounted for more than 90% of variance accounted for at the start (92.4±1.5%) and at the end (91.0±1.8%) of the exercise. Very slight modifications at the level of individual EMG profiles, synergy activation coefficients and muscle synergy vectors were observed. These results suggest that fatigue during a cyclic task preferentially induces an adaptation in muscle activity level rather than changes in the modular organization of the muscle coordination.

Comparison of muscle synergies before and after 10 minutes of running

“…Additionally, our intervention was not a fatigue protocol. Thus, our data was different from those obtained by Turpin et al29 ) .…”

“…Turpin et al29 ) reported that there was no change for the modules due to muscle fatigue during rowing exercise although our results showed a couple of different modules. Rowing exercise is performed in a stable condition in the sitting position.…”

Between-subject variability of muscle synergies during a complex motor skill

“…EMG signals were band-pass filtered (20–450 Hz, Butterworth filter, 2nd order), rectified, smoothed with a zero lag low-pass filter (9 Hz, Butterworth filter, 2nd order), and time-normalized in order to obtain 200 data points for each giant swing. EMG was normalized to the maximum level of activity across all giant swings (Turpin et al, 2011a). Therefore, as is classically done in studies focusing on muscle synergies, the degree of muscle activity was not taken into consideration.…”

Bio-mechanical aspects of elite cyclists’ motor system adaptation in process of competition activity

“…These factors determine external and internal conditions of realization of athletes' motor potential in the process of competition activity [13,27]. Winners of elite competitions in kinds of sports for endurance do not reduce speed at the end of distance but increase it in state of rising fatigue [29]. With it, technique of main sport movement changes [4,18].…”