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Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations
Published on: May 1, 2018
Time course of neuromuscular adaptations to knee extensor eccentric training
B M Baroni1, R Rodrigues, R A Franke
1School of Physical Education, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
International Journal of Sports Medicine
|March 26, 2013
Summary
Eccentric training enhances knee extensor strength, with neural and muscle adaptations contributing differently over time. Early gains are linked to neural activation and muscle growth, while later gains involve other mechanisms.
Area of Science:
- Exercise Physiology
- Muscle Adaptation
- Neuromuscular Training
Background:
- Eccentric training is known to increase muscle strength.
- Understanding the timeline of neural and morphological adaptations is crucial for optimizing training programs.
- The specific contributions of these adaptations to different types of muscle actions (isometric, concentric, eccentric) require further investigation.
Purpose of the Study:
- To investigate the chronology of neural and morphological adaptations to knee extensor eccentric training.
- To determine the contribution of these adaptations to strength gains in isometric, concentric, and eccentric muscle actions.
- To differentiate the adaptation timelines for strength, neural activation, and muscle mass.
Main Methods:
- 20 healthy male subjects underwent a 12-week isokinetic eccentric training program for knee extensors.
- Neuromuscular evaluations, including torque, electromyography (EMG), muscle thickness, and anatomical cross-sectional area (ACSA), were conducted every 4 weeks.
- Data analysis focused on tracking changes over the 12-week period and correlating them with strength outcomes.
Main Results:
- Significant increases in isometric (24%), concentric (15%), and eccentric (29%) torques were observed after 12 weeks.
- Neural adaptations (isometric: 29%, eccentric: 33%) and morphological adaptations (muscle thickness: 10%, ACSA: 19%) also increased significantly.
- Concentric strength and muscle mass gains plateaued after 8 weeks, unlike progressive increases in eccentric and isometric strength and activation.
Conclusions:
- Concentric strength gains are minimal and not driven by neural adaptations.
- Early strength improvements (up to 8 weeks) in eccentric and isometric actions result from combined neural and morphological adaptations.
- Later strength gains (weeks 8-12) in eccentric and isometric actions may be attributed to mechanisms beyond neural activation and muscle hypertrophy.
