Repeated bout effect and muscle damage at variable eccentric exercise intensities in active young men: a longitudinal repeated measures investigation

Abstract Exercise-induced muscle damage (EIMD) and repeated bout effect (RBE) are widely researched across various populations and at various intensities. Despite the existence of vast literature, there is lack of comparison of low versus submaximal versus maximal intensity required for preconditioning. The aim of the study was to compare the muscle damage and RBE at various intensities of eccentric exercise in active young men. Thirty-six healthy, physically active men were recruited and randomly assigned to three different groups low-high (L-H, n = 12), submaximal-high (M-H, n = 12) and maximal-high (H-H, n = 12). All participants performed 2 exercise bouts separated by 14 days. L-H, M-H and H-H groups performed low (10% of 1RM), moderate (50% of 1RM) and high (90% of 1RM) intensity eccentric exercise for knee extensors, respectively, in the 1st bout followed by high (100% of 1RM) intensity in the second bout. Muscle soreness (SOR), thigh circumference (CIR), maximal voluntary isometric contraction (MVIC), range of motion (ROM) and blood lactate (Bl Lac) were measured before, immediately, at 24 h, at 48 h and at 72 h after exercise. A significant effect of time appeared for MVIC ( ), CIR ( ), ROM ( ) and Bl Lac ( ). The bout × time interaction, as well as bout × time × group interaction was also found significant indicating changes in muscle strength and ROM. Circumference changed significantly with a significant bout × group interaction effect . SOR ( ) was significant between the bouts. Therefore, exhibiting attenuation of muscle damage markers after the second bout. Findings of the present study showed that muscle damage was evident at all three intensities. Moreover, it was greater after moderate and high intensity as compared to low intensity eccentric exercise. RBE was elicited after three intensities indicating their role in preconditioning the muscles of active men.