[[alternative]]The Effects of The Repeated Bout Effect on Muscle Damage

Abstract

[[abstract]]BACKGROUND: Previous studies have shown that repeating the same bouts of 30 maximal voluntary eccentric contractions at 1 to 6 days or 3 and 6 days after the first maximal eccentric exercise (ECC1) did not cause further muscle damage. This is referred to as the “repeated bout effect”. However, the amount of total work done during each of the subsequent bouts could only reach about 57%-76% of that done during the ECC1. It may be possible that the repeated bout of 30 maximal eccentric contractions was not stressful enough to produce further damage. What if one were to do the subsequent bout of intensive eccentric exercise, at what intensity would this second bout produce no further muscle damage or retard the recovery process? PURPOSE: This study examined the effects of the repeated bout effect after second bout of intensive eccentric exercise (80%, 90%, and 100% of the pre-ECC1 MVC level) on the indicators of muscle damage. METHODS: Fifty-one college-age males and females were randomly assigned into 100% maximal isometric voluntary contraction strength (MVC)(E100; n =12), 90% MVC (E90; n =13), 80% MVC (E80; n =14), and control (CON; n = 12) groups. The initial exercise was 30 maximal eccentric contraction (ECC1) on non-dominant elbow flexors using a dumbbell that was set at 100% of the pre-ECC1 MVC level. Three days after ECC1, the E80, E90, and E100 groups repeated this same exercise of 30 repetitions, but using a dumbbell that was set at 80%, 90%, and 100%, respectively, of the pre-ECC1 MVC level. This second bout was hereafter referred to as ECC2. Upper arm circumference (CIR), range of motion (ROM), MVC, serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities were measured before, immediately after, and every 24 hours or 9 consecutive days after ECC1. In the E80, E90, and E100 groups, CIR, ROM, MVC, CK, and LDH were also tested immediately after ECC2. Muscle soreness was assessed before and for 9 consecutive days after ECC1. Ultrasound imagines were taken from the upper arm immediately before ECC1, and at 2, 4, and 9 days after ECC1 for all groups. RESULTS: There were significant changes (p < 0.05) in all criterion measures following ECC1 for all groups. Moreover, the E80 to E100 subjects who repeated the second bout of eccentric contraction training at varying intensities 3 days after ECC1, no further muscle damage was observed when the indirect indicators of muscle damage were used. However, the ultrasound imagine showed a significant increased (p < 0.05) in muscle damaged area after ECC2 for the E100 group when compared to the E80, E90, and CON groups. CONCLUSION: 1.When the indirect indicators of muscle damage (e.g. MVC, ROM, CIR, soreness, CK, LDH) were used for the evaluation of eccentric-training effect after repeating a second bout of eccentric exercise on the damaged muscle, at the intensity of 80~100% pre-ECC1 MVC level, no signs of deterioration or retardation in the recovery process were observed. 2.However, when ultrasound images were used for the evaluation of eccentric-training at 100% of pre-ECC1 MVC level, the damage was much more evident. This suggest that the upper limit of repeated bout effect is approximately at 90% of pre-ECC1 MVC. 3.The results of this study may provide new information and serve as a practical reference to strength training for coaches, athletes and the general public during muscle damage and muscle soreness. KEY WORDS: eccentric contraction training, repeated bout effect, ultrasound imagines, muscle damage.