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Eccentric strain at long muscle length evokes the repeated bout effect
Robert W Pettitt1, David J Symons, Patricia A Eisenman
1Human Performance Research Laboratory, Mesa State College, Grand Junction, Colorado, USA. bpettitt@mesastate.edu
Journal of Strength and Conditioning Research
|December 8, 2005
Summary
The repeated bout effect (RBE) reduces muscle soreness and weakness after exercise. Eccentric exercise at longer muscle lengths triggers this protective effect by shifting the optimal angle for muscle contraction, unlike exercise at shorter lengths.
Area of Science:
- Exercise Physiology
- Muscle Biology
- Biomechanics
Background:
- The repeated bout effect (RBE) mitigates muscle damage and soreness from subsequent exercise bouts.
- Previous research suggests optimal angle shifts mediate the RBE, but the role of initial exercise muscle length is unclear.
Purpose of the Study:
- To investigate if the RBE for elbow extensors is influenced by the initial eccentric exercise muscle length.
- To determine if strain at longer muscle lengths induces optimal angle shifts that mediate the RBE.
Main Methods:
- Untrained women performed two bouts of eccentric elbow extensor exercise, separated by one week.
- Initial bout was performed at either long (50-130°) or short (0-80°) muscle length.
- Muscle soreness (DOMS), torque, and optimal angle were measured before and after each bout.
Main Results:
- Exercise at long muscle length induced a greater shift in optimal angle immediately after the first bout compared to short muscle length.
- The RBE, characterized by reduced torque deficit and DOMS, was observed after the second bout only in the group initially exercising at long muscle length.
- Optimal angle shifts were sustained and correlated with the protective RBE.
Conclusions:
- Eccentric exercise at long muscle lengths, but not short, elicits immediate and sustained shifts in optimal angle.
- These angle shifts are the primary mechanism mediating the protective repeated bout effect for elbow extensors.
- Muscle length during initial eccentric exercise is a critical factor in developing the RBE.