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Neural adaptations to fatigue: implications for muscle strength and training
D A Gabriel1, J R Basford, K N An
1Biomechanics Laboratory, Brock University, St. Catharines, Ontario, Canada L2S 3A1. dgabriel@arnie.pec.brocku.ca
Medicine and Science in Sports and Exercise
|July 28, 2001
Summary
Repeated isometric contractions enhance elbow extension strength by altering neural drive. This training stimulus down-regulates motor-unit firing frequency, leading to strength gains.
Area of Science:
- Neuroscience
- Exercise Physiology
- Biomechanics
Background:
- Serial isometric contractions can lead to strength gains.
- The underlying neural mechanisms require further investigation.
Purpose of the Study:
- To investigate the neural mechanisms behind strength increases during serial isometric contractions.
- To examine changes in motor unit activity and muscle activation patterns.
Main Methods:
- Thirteen subjects performed a 30-trial isometric elbow extension fatigue protocol across three sessions.
- Elbow extension torque and surface electromyography (EMG) of triceps and biceps brachii were recorded.
- Measures included torque, EMG amplitude, and mean power frequency (MPF).
Main Results:
- Maximal torque, EMG amplitude, and MPF decreased within each session.
- However, mean torque and the magnitude of torque decrease increased across sessions.
- Biceps and triceps EMG amplitude increased, while MPF decreased with repeated sessions.
Conclusions:
- The fatigue protocol acted as a training stimulus.
- This stimulus led to a downregulation of motor-unit firing frequency.
- This neural adaptation contributes to observed strength increases.
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