Endoh, T., Nakajima, T., Sakamoto, M., Tazoe, T., Ogawa, H, Yoneda, T., & Komiyama, T. (2006). Exercise-induced muscle damage exacerbates muscle fatigue. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 2006.

This study examined how the muscle damage induced by repetitive eccentric exercise with maximal voluntary effort affects the time course of central and peripheral fatigue during sustained maximal voluntary contraction. Healthy male volunteers (N = 10) were asked to perform brief (control maximal voluntary contraction) and sustained (fatigue test of 60 seconds duration) maximal voluntary contraction with elbow flexion before and 2 and 4 days after maximal voluntary effort. In addition, another 10 healthy male volunteers were asked to perform these tasks before and after injection of isotonic saline (0.9%, 1.0 ml, ISO) or hypertonic saline (5.25%, 1.0 ml, HYP) into the left biceps brachii. During the fatigue test, transcranial magnetic stimulation of the motor cortex was used to determine the changes in voluntary activation, size of the motor evoked potential, and length of electromyographic (EMG) silencing.

Control maximal voluntary contraction was significantly decreased and muscle soreness was significantly increased, 2 and 4 days after maximal voluntary effort in comparison with that before maximal voluntary effort. During the fatigue test, voluntary activation, which was determined as a phasic increase in the twitch force after transcranial magnetic stimulation, decreased significantly 2 and 4 days after maximal voluntary effort in comparison with that beforehand. In addition, the RMS/F was significantly increased 2 and 4 days after maximal voluntary effort. Although the degree of facilitation of the motor evoked potential was increased significantly, the length of EMG silencing was less affected by maximal voluntary effort. However, during the fatigue test, there was no significant difference in these parameters between HYP and ISO (P > 0.05).

Implication. The muscle damage induced by repetitive eccentric exercise with maximal effort, and not delayed-onset muscle soreness, may be a strong modifier of central and peripheral fatigue experienced during subsequent sustained maximal exercise.

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