Sensory and electromyographic mapping during delayed-onset muscle soreness

PURPOSE: The aim of this human study was to apply novel topographical mapping techniques to investigate sensory and EMG manifestations of delayed-onset muscle soreness (DOMS) in multiple locations of the quadriceps.

METHODS: Bipolar surface EMG signals were recorded from 11 healthy men with 15 pairs of electrodes located at 10, 20, 30, 40, and 50% of the distance from the medial, superior, and lateral border of the patella to the anterior superior iliac spine. Subjects performed sustained isometric knee extensions at 40% of the maximal force (MVC) until task failure before, 24 h, and 48 h after eccentric exercise. Pressure-pain thresholds (PPT) were assessed at the 15 locations where the EMG was recorded.

RESULTS: Time to task failure was reduced after the eccentric exercise (mean +/- SD, 56.6 +/- 23 s before the eccentric exercise; 34.3 +/- 18.9 s at 24 h after exercise; and 34.3 +/- 14.4 s at 48 h after exercise). During the postexercise sustained contractions, EMG average rectified value (ARV) significantly decreased over time (P < 0.001), but it did not change over time before the eccentric exercise. Moreover, the decrease in ARV over time during postexercise contractions was greatest in the distal region of the quadriceps, where the PPT were most reduced (P < 0.05).

CONCLUSION: Novel topographical mapping of both surface EMG and PPT of the quadriceps showed site-dependent effects of eccentric exercise, probably attributable to variations in the morphological and architectural characteristics of the muscle fibers. Greater manifestations of DOMS in the distal region of the quadriceps may indicate a greater susceptibility of this region to further injury after eccentric exercise.