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Adaptations in coactivation after isometric resistance training.
1Department of Physical Education, Faculty of Pure and Applied Science, York University, Toronto, Ontario, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|September 1, 1992
Summary
This study found that isometric knee extensor training significantly reduced hamstring muscle coactivation in both trained and untrained legs. This neuromuscular adaptation occurred early in training, indicating improved muscle coordination without muscle growth.
Area of Science:
- Neuromuscular Physiology
- Exercise Science
- Muscle Adaptation
Background:
- Sedentary individuals often exhibit inefficient muscle activation patterns.
- Understanding neuromuscular adaptations to resistance training is crucial for optimizing exercise protocols.
- Co-contraction of antagonist muscles can influence force production and joint stability.
Purpose of the Study:
- To investigate the effects of isometric knee extensor training on muscle activation and coactivation patterns.
- To determine if resistance training alters hamstring coactivity during quadriceps contractions.
- To examine neuromuscular adaptations in both trained and untrained limbs.
Main Methods:
- Twenty sedentary male university students were divided into experimental and control groups.
- The experimental group performed 30 isometric knee extensor maximal voluntary contractions (MVC) daily, three times weekly for 8 weeks.
- Electromyography (EMG) measured vastus lateralis and biceps femoris activity during MVCs.
Main Results:
- Isometric knee extensor strength increased by 32.8% in the trained leg and 16.2% in the untrained leg.
- Hamstring coactivation during extension MVC decreased by 20% in the trained leg after 1 week and 13% in the untrained leg after 2 weeks.
- No significant changes in vastus lateralis maximal integrated EMG (IEMGmax) were observed, suggesting a neural adaptation rather than hypertrophy.
Conclusions:
- Isometric resistance training leads to a rapid, non-hypertrophic reduction in hamstring coactivation during knee extension.
- This decreased coactivation suggests improved neuromuscular efficiency and reduced antagonist muscle cocontraction.
- These findings highlight early neural adaptations in response to static resistance training.