Lower fatigability of locomotor than non-locomotor muscles in endurance runners

Knee extensor and elbow flexor muscles have been demonstrated to have similar fatigability, i.e. time to task failure at submaximal force level, in healthy non-trained individuals. This experiment investigated if continuative endurance training can influence the fatigability of these two muscle groups in amateur runners. Surface electromyography was used to assess fatigability in twelve amateur runners. Participants were requested to sustain for 30 s the 70 % of their maximum voluntary contraction of knee extensor and elbow flexor muscles. During contractions, electromyographic signals were recorded, respectively, from vastus lateralis and biceps brachii muscles with linear array of eight electrodes. Muscle fiber conduction velocity (CV), mean power spectral frequency (MNF), and fractal dimension (FD) of electromyographic signals were calculated. During the sustained contraction vastus lateralis muscle showed smaller decrease of CV (p = 0.006), MNF (p = 0.001), and FD (p = 0.001) than biceps brachii muscle. The lower fatigability found in knee extensors than in elbow flexors suggests that the physiological adaptation promoted by the endurance training was specific to the musculature involved in the training (i.e. the lower limbs).