Reduced muscle lengthening during eccentric contractions as a mechanism underpinning the repeated-bout effect

Abstract

This study investigated biceps brachii distal myotendinous junction (MTJ) displacement during maximal eccentric elbow flexor contractions to test the hypothesis that muscle length change would be smaller (less MTJ displacement) during the second than the first exercise bout. Ten untrained men performed two eccentric exercise bouts (ECC1 and ECC2) with the same arm consisting of 10 sets of six maximal isokinetic (60°/s) eccentric elbow flexor contractions separated by 4 wk. Biceps brachii distal MTJ displacement was assessed using B-mode ultrasonography, and changes in the displacement (muscle length change) from the start to the end of each contraction during each set and over 10 sets were compared between bouts by two-way repeated-measures ANOVA. Several indirect muscle damage markers were also measured and compared between bouts by two-way repeated-measures ANOVA. The magnitude of MTJ displacement (average of six contractions) increased from set 1 (8.2 ± 4.7 mm) to set 10 (16.4 ± 4.7 mm) during ECC1 (P < 0.05), but no significant changes over sets were evident during ECC2 (set 1: 8.5 ± 4.0 mm; set 10: 9.3 ± 3.1 mm). Changes in maximal voluntary isometric contraction strength, range of motion, muscle thickness, ultrasound echo intensity, serum creatine kinase activity, and muscle soreness (visual analog scale) were smaller (P < 0.05) following ECC2 than ECC1, showing less damage in the repeated bout. These results indicate that the magnitude of muscle lengthening was less during the second than the first eccentric exercise bout, which appears to be a mechanism underpinning the repeated-bout effect.

Muscle damage and inflammation after eccentric exercise: can the repeated bout effect be removed?

“…; Lau et al. ). The successive application of concentric exercise followed by eccentric exercise renders the sarcomeres more vulnerable to stretch‐induced damage in the subsequent eccentric exercise overcoming the repeated bout effect (Fig.…”

“…; Lau et al. ). Conclusively, the alternating eccentric‐concentric exercise model exploits the finding that concentric only exercise renders the muscle more vulnerable to damage after any subsequent eccentric exercise (Ploutz‐Snyder et al.…”

“…However, indirect measures of muscle fiber length can be taken in vivo and a recent study has shown that the mechanism underpinning the repeated bout effect is the reduced magnitude of muscle fascicle lengthening during a repeated eccentric exercise bout compared to the first eccentric session (Lau et al. ). Other studies have shown that eccentric and concentric exercise training modes induce divergent adaptations in human muscle architecture.…”

“…What molecular re-arrangements at the sarcomere level may have caused the removal of the repeated bout effect? Based on relevant experimental evidence, a tempting hypothesis is that chronic eccentric exercise leads to sarcomerogenesis (i.e, addition of serial sarcomeres) leading to less stretch during an eccentric action, whereas the following chronic concentric exercise induces sarcomerolysis (i.e, removal of serial sarcomeres) leading to more stretch during the subsequent eccentric action (Williams and Goldspink 1971;Tabary et al 1972;Ploutz-Snyder et al 1998;Whitehead et al 1998;Gleeson et al 2003;Butterfield et al 2005;Timmins et al 2015;Lau et al 2015). The successive application of concentric exercise followed by eccentric exercise renders the sarcomeres more vulnerable to stretch-induced damage in the subsequent eccentric exercise overcoming the repeated bout effect (Fig.…”

“…Experimental measurements of sarcomere operating length in humans are invasive and impractical (Lieber and Friden 1998). However, indirect measures of muscle fiber length can be taken in vivo and a recent study has shown that the mechanism underpinning the repeated bout effect is the reduced magnitude of muscle fascicle lengthening during a repeated eccentric exercise bout compared to the first eccentric session (Lau et al 2015).…”