Insights gained into eccentric exercise-induced muscle damage from high-density surface electromyography

Abstract

The purpose of this thesis was to investigate whether exercise-induced muscle damage (EIMD) leads to local changes in the amplitude of supramaximal M waves detected along biceps brachii. Ten healthy male subjects were submitted to the following measurements conducted immediately before and four consecutive days after 3x10 eccentric elbow flexions: evaluation of muscle soreness; acquisition of ultrasound images proximally and distally from biceps; recording of surface electromyograms with a 64- electrodes grid while 10 supramaximal pulses were applied to the musculocutaneous nerve; two isometric, maximal voluntary elbow flexion contractions (MVCs). The innervation zone (IZ) longitudinal location, the number of electrodes detecting the largest M waves (segmented channels) and the centroid longitudinal coordinate of these electrodes were assessed in order to characterize the distribution of M-waves amplitude. After EIMD, the MVC torque decreased while the perceived muscle soreness increased at 24, 48, 72 and 96 h (P<0.004 for both cases). The echo intensity of ultrasound images increased at 48, 72 and 96 h with respect to baseline for both regions (P<0.001) while no differences were observed between regions at any time (P=0.136). No time effect was observed for IZ location (P=0.283). The number of segmented channels significantly decreased (P<0.032) and the centroid longitudinal coordinate shifted towards the distal region at 24, 48 and 72 h (P<0.032). EIMD consistently changed supramaximal M waves detected mainly proximally from biceps brachii, suggesting a local effect of EIMD on muscle excitation.