Delayed-Onset Muscle Soreness Alters the Response to Postural Perturbations

HEDAYATPOUR, N., H. HASSANLOUEI, L. ARENDT-NIELSEN, U. G. KERSTING, and D. FALLA. Delayed-Onset Muscle Soreness Alters the Response to Postural Perturbations. Med. Sci. Sports Exerc., Vol. 43, No. 6, pp. 1010-1016, 2011. Introduction: Eccentric contractions induce muscle fiber damage that is associated with delayed-onset muscle soreness and an impaired ability of the muscle to generate voluntary force. Pain and pathophysiological changes within the damaged muscle can delay or inhibit neuromuscular responses at the injured site, which is expected to have an effect on reflex activity of the muscle. Purpose: The aim of the study was to investigate the reflex activity of knee muscles to rapid destabilizing perturbations, before, immediately after, and 24 and 48 h after eccentric exercise. Methods: Bipolar surface EMG signals were recorded from 10 healthy men with seven pairs of electrodes located on the knee extensor muscles (vastus medialis, rectus femoris, and vastus lateralis) and knee flexor muscles (the medial and lateral heads of the hamstring and the medial and lateral heads of gastrocnemius) of the right leg during rapid perturbations. Results: The maximal voluntary contraction force decreased by 24% +/- 4.9% immediately after exercise and remained reduced by 21.4% +/- 4.1% at 24 h and by 21.6% +/- 9.9% at 48 h after exercise with respect to baseline. During the postexercise postural perturbations, the EMG average rectified value of the knee extensor muscles was significantly lower than baseline (P < 0.001). Moreover, the decrease in average rectified value over time during postexercise sustained contractions was greatest compared with the session before exercise (P < 0.0001). Conclusions: Reflex activity in leg muscles elicited by rapid destabilizing perturbations is reduced after exercise-induced muscle soreness.