Effects on muscle damage of a single bout of intensive eccentric contractions at varying repetitions

Introduction

Many previous studies used a single bout of 24, 30, 50, or 70 repetitions of eccentric contractions of the elbow flexors or knee extensors to induce muscle damage and muscle soreness [1,2,3,4], and these previous studies have shown that this protocol can result in significant changes in all indicators of muscle damage. However, there is no study to examine whether a single bout of eccentric exercise, using different repetitions, can produce the different extent of muscle damage and result in the different recovery rate from muscle damage. Therefore, the purpose of this study was to examine whether subjects who perform the different repetitions of a single bout of eccentric contractions would cause the different extent of muscle damage and result in the different recovery rate from muscle damage.

Methods

A group of college-age male students (N=36; 20.6±1.8yrs) was recruited in the study, and then randomly assigned into 24 (EC24; n=12), 50 (EC50; n=12), and 70 eccentric exercise groups (EC70; n=12). A single bout of intensive eccentric exercise (ECC1) was 24, 50, and 70 repetitions for EC24, EC50, and EC70, respectively, on non-dominant elbow flexors using a dumbbell that was set at 80% of the pre-ECC1 MIF level. Upper arm circumference (CIR), ROM, MIF, serum CK activity were measured before and immediately after ECC1, and every 24 hours for 9 consecutive days after ECC1 for all groups. DOMS was assessed before and for 9 consecutive days after ECC1 for all groups.

Results

There were significant changes (P < 0.05) in all criterion measures following ECC1 for all groups. There were dramatic changes (P < 0.05) in MIF, ROM, CIR, and CK for EC70 than EC50 and EC24 following ECC1. Moreover, there were more significant changes (P < 0.05) in MIF, ROM, CIR, and CK for EC50 than for EC24 following ECC1. However, there were no significant changes (P > 0.05) in DOMS after ECC1 among the groups.

Discussion/Conclusion

The results of the present study showed that the larger the number of eccentric contractions, the greater the changes (P < 0.05) in criterion measures (MIF, ROM, CIR, CK) and the slower the recovery rate (P < 0.05) of muscle damage after ECC1. Furthermore, use of DOMS may not be a good indicator of eccentric exercise-induced muscle damage, and changes in indirect indicators of muscle damage are not necessarily accompanied with DOMS [4].

References

[1]. Brown,S. J., et al. (1997). J Sports Sci 15, 215-222.
[2]. Clarkson, P. M., & Tremblay, I. (1988). J Appl Physiol 65, 1-6.
[3]. Nosaka, K, & Clarkson, P. M. (1995). Med Sci Sports Exerc 27, 1263-1269.
[4]. Nosaka, K., et al. (2003). Scand J Med Sci Sports 12, 337-346.