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Time course of muscle adaptation after high force eccentric exercise
K Nosaka1, P M Clarkson, M E McGuiggin
1Institute of Sports Medicine, Yokohama City University, Japan.
Summary
The repeated bout effect reduces muscle damage indicators like soreness and creatine kinase activity after exercise. This protective effect is observed with shorter (6 weeks) and longer (10 weeks) recovery periods between exercise bouts.
Area of Science:
- Exercise Physiology
- Sports Science
- Muscle Physiology
Background:
- The repeated bout effect (RBE) describes the protective phenomenon where a prior bout of exercise attenuates the response to subsequent bouts.
- Understanding the time course of RBE is crucial for optimizing training programs and injury prevention.
Purpose of the Study:
- To investigate the influence of different recovery intervals (6 and 10 weeks) between two bouts of eccentric exercise on muscle damage indicators.
- To assess the persistence of the repeated bout effect over longer time periods.
Main Methods:
- Two groups of female subjects (n=6 for 6-week interval, n=8 for 10-week interval) performed 70 maximal eccentric forearm flexions.
- Muscle damage indicators measured included isometric strength (STR), relaxed elbow joint angle (RANG), flexed elbow joint angle (FANG), perceived muscle soreness (SOR), and plasma creatine kinase (CK) activity.
- Measurements were taken pre-exercise and 5 days post-exercise for both bouts, with a follow-up measurement 6 months after the second bout for a subset of subjects.
Main Results:
- The second bout of exercise resulted in significantly smaller changes in RANG, SOR, and CK in the 6-week group, and smaller changes in RANG and CK in the 10-week group compared to the first bout.
- Faster recovery of STR and FANG was observed in the second bout for the 6-week group.
- Plasma CK levels remained significantly lower in the second bout even 6 months later, though other indicators did not show significant differences at this long-term follow-up.
Conclusions:
- A 6-week recovery interval appears sufficient to elicit a robust repeated bout effect, significantly reducing muscle damage markers and enhancing recovery.
- While the 10-week interval also showed protective effects, they were less pronounced for some indicators compared to the 6-week interval.
- The repeated bout effect, particularly concerning plasma creatine kinase levels, demonstrates considerable long-term persistence.