The effect of velocity of contraction on the repeated bout effect

Abstract

The 'repeated bout effect' (RBE) is an adaptation whereby a single eccentric (ECC) exercise session protects against muscle damage during subsequent ECC exercise bouts and is characterized by faster strength recovery and a reduction in soreness and inflammation. The purpose was to determine if the protective capacity of the RBE is greater when both bouts of ECC exercise are performed at the same compared to a different velocity of contraction as well as at a fast or slow velocity. Thirty-one right handed participants were randomly assigned to perform an initial unilateral bout of either fast (180°/s) or slow (30°/s) maximal isokinetic ECC elbow flexion. Three weeks later 16 participants completed a repeated bout of ECC exercise at the same velocity as the initial bout (SAME)(FAST-FAST[n=8] and SLOW-SLOW[n=8]), while 15 participants completed a bout at the corresponding different velocity (DIFF) (FAST-SLOW[n=8] and SLOW-FAST[n=7]). Elbow flexor function and damage was measured prior to, immediately after, and at 24, 48, and 72 hours post exercise. Dependant variables included maximal voluntary contraction (MVC) isometric strength (Dynamometer), muscle thickness (MT; Ultrasound), delayed onset muscle soreness (DOMS; Visual Analog Scale), biceps and triceps electromyography (EMG), percent activation (Interpolated twitch), and twitch torque. There were no group differences for height, weight, training experience, or total work performed during the ECC bouts (p>0.05). After the repeated bout, there was a significant reduction in MVC strength, MT, and DOMS at 24, 48, and 72 hours, pooled across participants (p<0.05). After the repeated bout, MVC strength recovered faster only for the SAME group. There were no differences between groups for MT, DOMS, EMG, ITT, and TT. The analysis revealed neither fast nor slow contractions offered greater protection against muscle damage when the repeated bout was not completed at the same velocity. Since a faster recovery of strength is velocity specific this suggests there may be a neural contribution to the repeated bout effect.