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Neuromuscular responses to explosive and heavy resistance loading
V Linnamo1, R U Newton, K Häkkinen
1Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, 40351 Jyväskylä, Finland. linnamo@pallo.jyu.fi
Summary
Explosive exercise (EE) may enhance neuromuscular function more than heavy resistance exercise (HRE) by increasing muscle activation and potentially utilizing fast-twitch muscle fibers. This type of training appears to facilitate the neuromuscular system rather than induce fatigue.
Area of Science:
- Exercise Physiology
- Neuromuscular Physiology
- Sports Science
Background:
- Electromyography (EMG) power spectrum shifts to higher frequencies with increased movement velocity.
- Muscle fatigue is associated with a decrease in EMG frequency components.
- Understanding the acute effects of different exercise intensities on neuromuscular responses is crucial for optimizing training.
Purpose of the Study:
- To investigate the acute effects of explosive (EE) versus heavy resistance (HRE) concentric leg press exercise.
- To analyze changes in muscle force, EMG parameters (average EMG and power spectrum), and blood lactate levels.
- To correlate muscle fiber composition with physiological responses to exercise.
Main Methods:
- Participants performed five sets of ten repetitions of leg press exercise under either EE (40% isometric maximum, explosive intent) or HRE (67% isometric maximum) conditions.
- Maximal isometric and concentric actions, along with an isometric fatigue test, were assessed pre- and post-exercise.
- Surface EMG from the vastus medialis, muscle fiber composition of the vastus lateralis, and blood lactate were measured.
Main Results:
- Mean and median power frequencies were significantly higher during EE compared to HRE.
- EMG frequencies increased during EE but remained unchanged or decreased during HRE.
- No significant signs of fatigue were observed after EE, and limited fatigue was noted after HRE.
- A positive correlation was found between fast-twitch fiber percentage and blood lactate changes during HRE.
Conclusions:
- Explosive exercise appears to preferentially recruit fast-twitch motor units.
- EE may facilitate neuromuscular system function rather than induce fatigue, unlike HRE.
- The specific parameters of the concentric actions in EE might contribute to neuromuscular facilitation.