Effect of central and peripheral muscle fatigue contribution after ankle submaximal fatiguing contractions on muscle synergies and postural control

Although the effect of ankle muscles on postural control and muscle synergies has well been investigated, it is needed to study more about the contribution of central and peripheral fatigue of submaximal contractions on postural control and muscle synergies. The aim of this study was to investigate the effect of submaximal fatiguing exercise that induce preferentially central fatigue on muscle synergy and postural control. For this purpose, 12 volunteer subjects participated in this study. The tibia nerve was electrically stimulated to assess the M-wave, central fatigue (voluntary activation) and peripheral fatigue (rest imposed twitch) during voluntary maximal contractions on dynamometer. Moreover, electromyography activity of ten muscles and COP were recorded to assess muscle synergy and postural stability respectively during anterior-posterior voluntary sway on force plate. In order to induce fatiguing exercise the subjects performed submaximal fatiguing contractions on dynamometer and all of the mentioned variables again were measured. The effect of the fatiguing protocol tested with paired-samples T Test and Z Fisher Test. Submaximal contractions induced greater increases of COP sway area. Muscles activation, muscle synergies variance decreased and the number of co-contractions increased significantly after submaximal contractions (P = 0.01). Contribution of central fatigue (16.64%) significantly greater than peripheral fatigue (2.32%) after submaximal contractions (P = 0.02). The results of this study showed that more central fatigue after submaximal contraction leads to more COP changes. Therefore, investigating central and peripheral mechanisms following ankle fatiguing contractions may be useful for scheduling rehabilitation and balance training programs.