Responses of human elbow flexor muscles to electrically stimulated forced lengthening exercise.
This study developed an electrical stimulation model for human elbow flexors to examine eccentric exercise-induced muscle damage and adaptation. Male students (n=17) were randomly placed into one of two groups; isometric (ES-ISO, n=8) and eccentric (ES-ECC, n=9). The elbow joint was fixed at 90 degrees (1.57 rad) and the elbow flexors stimulated percutaneously by an electronic muscle stimulator for 5 s through two electrodes placed over the muscles for ES-ISO. In ES-ECC, the muscles were stimulated similarly to the ES-ISO, but the elbow joint was forcibly extended from an elbow flexed (90 degrees 1.57 rad) to a full-extended position (180 degrees, 3.14 rad) in 3 s. Maximal voluntary isometric force, range of motion, upper arm circumference, muscle thickness by ultrasonography, muscle soreness, plasma creatine kinase and aspartate aminotransferase activities were assessed before and for 4 days after exercise. ES-ECC produced significantly larger changes in all criterion measures compared with ES-ISO (P < 0.01). These findings confirmed that eccentric muscle actions induced muscle damage, but isometric contractions resulted in little or no damage. Six subjects from the ES-ECC group repeated the same eccentric exercise (ECC2) 2 weeks after the first bout (ECC1), and changes in the criterion measures were compared between the bouts. Changes in all criterion measures after ECC2 were significantly smaller than ECC1 (P < 0.01). These results suggest that the first eccentric exercise produced a protective effect against muscle damage in the subsequent eccentric exercise bout, which does not involve adaptations in the central nervous system.
Nosaka
K
K
Exercise and Sports Science, Graduate School of Integrated Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan.
Newton
M
M
Sacco
P
P
D000222:Adaptation, Physiological; D000328:Adult; D001219:Aspartate Aminotransferases / Q000097:blood; D003402:Creatine Kinase / Q000097:blood; D004551:Elbow Joint / Q000502:physiology*; D004558:Electric Stimulation; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009126:Muscle Relaxation / Q000502:physiology; D018482:Muscle, Skeletal / Q000293:injuries / Q000473:pathology / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013314:Stress, Mechanical; D013997:Time Factors
D001219:Aspartate Aminotransferases; D003402:Creatine Kinase