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Quadriceps concentric and eccentric exercise 1: changes in contractile and electrical activity following eccentric
1Human Science Division, Lincoln University, Canterbury, New Zealand.
Journal of Science and Medicine in Sport
|May 8, 2001
Summary
Eccentric exercise causes muscle weakness due to contractile failure, not reduced neural excitation. Surface electromyography (EMG) confirms that muscle strength loss after eccentric contractions is not linked to central fatigue.
Area of Science:
- Exercise Physiology
- Neuromuscular Function
Background:
- Muscle fatigue is a complex phenomenon affecting both central and peripheral factors.
- Understanding the mechanisms of strength loss after different exercise types is crucial for training and rehabilitation.
Purpose of the Study:
- To investigate if reduced neural excitation contributes to strength and endurance losses after eccentric and concentric exercise.
- To differentiate between central and peripheral fatigue mechanisms following strenuous exercise.
Main Methods:
- 10 healthy males performed 20-minute bench-stepping with a dominant leg.
- Maximal voluntary isometric contractions (MVC) and surface electromyography (EMG) of the quadriceps were measured pre- and post-exercise.
- Analysis focused on force output and EMG amplitude during the initial 3 seconds (MVC0-3) and over 30 seconds.
Main Results:
- Eccentrically exercised muscles (ECC) showed immediate MVC0-3 decline to 88% of pre-exercise values, significantly lower than concentrically exercised muscles.
- Increased surface EMG amplitude during MVC0-3 in ECC suggested no reduction in neural drive.
- No significant changes in 30-second muscular fatigue were observed between exercise types.
Conclusions:
- Muscle weakness after eccentric exercise is primarily due to contractile failure, not central fatigue or reduced neural excitation.
- Eccentrically exercised muscles are weaker but not more fatigable compared to concentrically exercised muscles post-exercise.