Comparison of repeated bout protective effect between different eccentric contraction modes

Description

INTRODUCTION: Prior unaccustomed eccentric exercise can provide an adaptive protective effect commonly termed the repeated bout effect (RBE) [1], evidenced by the attenuation of the exercise-induced muscle damage symptoms in subsequent bouts of exercise [2]. As several eccentric exercise modes are frequently used in athletic settings and investigated in research, the purpose of this study was to compare the RBE of downhill running (DHR), drop jumps (DJ), and isokinetic eccentric contractions (ISOK) during maximal voluntary isometric contractions (MVIC) of the knee extensors.

METHODS: Thirty participants were stratified (using knee extensor torque) into three experimental groups (DHR [n = 10], ISOK [n = 10], DJ [n = 10]) with DHR performing a 30 min run at ~70%VO2max and 15% decline, ISOK performing 100 unilateral isokinetic eccentric contractions at 50% MVIC, and DJ performing 100 drop jumps from a height of 0.6 m (5 sets of 20 jumps with 1 min rest between sets). Maximum voluntary isometric knee extensor torque (N.m) was measured during MVIC tests before (Pre) and 24, 48, 72, 96 hr post-exercise [bout 1], with identical exercise and testing repeated a week later [bout 2]. The index of protection (RBE) was calculated as the change in torque from Pre to 24 hr post-exercise in the first bout, minus the change in the second bout, divided by the change in the first bout, multiplied by 100 [3].

RESULTS: Compared to baseline, there was a significant (P ≤ 0.05) reduction in knee extensor torque after bout 1 for DJ (24, 48, 72, 96 hr timepoints) and DHR (24hr) but no difference for ISOK. The greatest mean reductions in knee extensor torque occurred after bout 1 for all groups (DJ: Δ = 15% at 48 hr; DHR: Δ = 8.1% at 24 hr; ISOK Δ = 6.1% at 24 hr). There was no significant reduction in knee extensor torque after bout 2 in any group (Δ = 0.9% to 3.4%), with a significant difference between bout 1 and 2 percentage change at 24hr (P ≤ 0.01). The index of protection was greatest for DJ (93%) followed by ISOK (69%) and DHR (62%) groups, but there were no significant differences between groups index of protection (P ≥ 0.05).

CONCLUSION: This is the first study to compare these commonly used eccentric contraction modes to induce symptoms of muscle damage and assess the index of protection on maximal torque production. Whilst drop jumps reported the greatest mean index of protection, it was not significantly greater than other contraction modes. These data suggest that all contraction modes conferred similar levels of functional protection that may have implications for exercise prescription and injury risk during repeated performance over several days following intense exercise.

REFERENCES
1.Kwiecien et al. (2020). Eur J Appl Physiol, 120(2):413–423.
2.Howatson & van Someren (2008). Sports Med, 38(6):483–503.
3.Chen et al. (2007). J Appl Physiol, 102:992–999.

Period	7 Jul 2023
Event title	28th Annual Congress of the European College of Sport Science (ECSS)
Event type	Conference
Location	Paris, FranceShow on map
Degree of Recognition	International