title: Electromyographic analysis of exercise resulting in symptoms of muscle damage.
abstract: Surface electromyographic (EMG) signals were recorded from the hamstring muscles during six sets of submaximal isokinetic (2.6 rad x s(-1)) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions. The EMG per unit torque increased during eccentric (P < 0.01) but not during concentric exercise. Similarly, the median frequency increased during eccentric (P < 0.01) but not during concentric exercise. The EMG per unit torque was lower for submaximal eccentric than maximum isometric contractions (P < 0.001), and lower for submaximal concentric than maximum isometric contractions (P < 0.01). The EMG per unit torque was lower for eccentric than concentric contractions (P < 0.05). The median frequency was higher for submaximal eccentric than maximum isometric contractions (P < 0.001); it was similar, however, between submaximal concentric and maximum isometric contractions (P = 0.07). Eccentric exercise resulted in significant isometric strength loss (P < 0.01), pain (P < 0.01) and muscle tenderness (P < 0.05). The greatest strength loss was seen 1 day after eccentric exercise, while the most severe pain and muscle tenderness occurred 2 days after eccentric exercise. A lower EMG per unit torque is consistent with the selective recruitment of a small number of motor units during eccentric exercise. A higher median frequency during eccentric contractions may be explained by selective recruitment of fast-twitch motor units. The present results are consistent with the theory that muscle damage results from excessive stress on a small number of active fibres during eccentric contractions.
authors.affiliation: School of Sport, Health and Physical Education Sciences, University of Wales, Bangor, Gwynedd, UK. mchugh@nismat.org
authors.forename: M P
authors.initials: MP
authors.lastname: McHugh
authors.forename: D A
authors.initials: DA
authors.lastname: Connolly
authors.forename: R G
authors.initials: RG
authors.lastname: Eston
authors.forename: G W
authors.initials: GW
authors.lastname: Gleim
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000886:Anthropometry; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000293:injuries* / Q000503:physiopathology; D010147:Pain Measurement; D010807:Physical Endurance; D010809:Physical Fitness; D012016:Reference Values; D012680:Sensitivity and Specificity