Changes in Motor Coordination Induced by Local Fatigue during a Sprint Cycling Task

AbstractPurposeThis study investigated how muscle coordination is adjusted in response to a decrease in the force-generating capacity of one muscle group during a sprint cycling task.MethodsFifteen participants were tested during a sprint before and after a fatigue electromyostimulation protocol was conducted on the quadriceps of one leg. Motor coordination was assessed by measuring myoelectrical activity, pedal force and joint power.ResultsThe decrease in force-generating capacity of the quadriceps (-28.0±6.8%) resulted in a decrease in positive knee extension power during the pedaling task (-34.4±30.6 W; P=0.001). The activity of the main non-fatigued synergist and antagonist muscles (triceps surae, gluteus maximus and hamstrings) of the ipsilateral leg decreased, leading to a decrease in joint power at the hip (-30.1±37.8 W; P=0.008) and ankle (-20.8±18.7 W; P=0.001). However, both the net power around the knee and the ability to effectively orientate the pedal force were maintained during the extension by reducing the co-activation and the associated negative power produced by the hamstrings. Adaptations also occurred in flexion phases in both legs, exhibiting an increased power (+17.9±28.3 [P=0.004] and +19.5 ± 21.9 W [P=0.026]), associated with an improvement in mechanical effectiveness.ConclusionThese results demonstrate that the nervous system readily adapts coordination in response to peripheral fatigue by i) decreasing the activation of adjacent non-fatigued muscles to maintain an effective pedal force orientation (despite reducing pedal power) and ii) increasing the neural drive to muscles involved in the flexion phases such that the decrease in total pedal power is limited. Purpose This study investigated how muscle coordination is adjusted in response to a decrease in the force-generating capacity of one muscle group during a sprint cycling task. Methods Fifteen participants were tested during a sprint before and after a fatigue electromyostimulation protocol was conducted on the quadriceps of one leg. Motor coordination was assessed by measuring myoelectrical activity, pedal force and joint power. Results The decrease in force-generating capacity of the quadriceps (-28.0±6.8%) resulted in a decrease in positive knee extension power during the pedaling task (-34.4±30.6 W; P=0.001). The activity of the main non-fatigued synergist and antagonist muscles (triceps surae, gluteus maximus and hamstrings) of the ipsilateral leg decreased, leading to a decrease in joint power at the hip (-30.1±37.8 W; P=0.008) and ankle (-20.8±18.7 W; P=0.001). However, both the net power around the knee and the ability to effectively orientate the pedal force were maintained during the extension by reducing the co-activation and the associated negative power produced by the hamstrings. Adaptations also occurred in flexion phases in both legs, exhibiting an increased power (+17.9±28.3 [P=0.004] and +19.5 ± 21.9 W [P=0.026]), associated with an improvement in mechanical effectiveness. Conclusion These results demonstrate that the nervous system readily adapts coordination in response to peripheral fatigue by i) decreasing the activation of adjacent non-fatigued muscles to maintain an effective pedal force orientation (despite reducing pedal power) and ii) increasing the neural drive to muscles involved in the flexion phases such that the decrease in total pedal power is limited. Correspondence and reprints: Sylvain DOREL, PhD, University of Nantes, Laboratory "Motricité, Interactions, Performance" (EA4334), 25 bis boulevard Guy Mollet, BP 72206, 44322 Nantes cedex 3, France. Email: sylvain.dorel@univ-nantes.fr Project support was provided by the Region Pays de la Loire (ANOPACy project) and the French Ministry of Sport (14-R-23). Francois Hug was supported by a fellowship from the Institut Universiatire de France (IUF). The authors report no conflict of interest. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation Accepted for Publication: 6 February 2018 © 2018 American College of Sports Medicine

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