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Reduced neuromuscular activity and force generation during prolonged cycling
A St Clair Gibson1, E J Schabort, T D Noakes
1MRC/UCT Research Unit of Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town Medical School, Cape Town, 7725 South Africa. agibson@sports.uct.ac.za
Summary
Neuromuscular activity and power output decrease during prolonged high-intensity cycling. This suggests a central neural governor limits muscle recruitment to conserve energy during endurance exercise.
Area of Science:
- Exercise Physiology
- Sports Science
- Neuromuscular Function
Background:
- Endurance athletes face challenges maintaining high power output during prolonged exercise.
- Understanding neuromuscular adaptations is crucial for optimizing performance.
Purpose of the Study:
- To investigate changes in neuromuscular activity during high-intensity epochs within a 100-km cycling time trial.
- To examine the influence of dietary carbohydrate manipulation on these responses.
- To explore the potential role of a central neural governor in regulating muscle recruitment.
Main Methods:
- Seven endurance-trained cyclists completed two 100-km cycling time trials.
- High-intensity epochs (1-km and 4-km) were included within the trials.
- Measurements included power output, electromyogram (EMG) for neuromuscular activity, and muscle glycogen levels.
Main Results:
- Mean power output significantly decreased in 4-km high-intensity epochs throughout the trial (319 W to 278 W).
- Integrated EMG (IEMG) activity also significantly declined, falling from 16.4% to 11.1% of maximal voluntary contraction.
- These neuromuscular changes occurred with less than 20% of available muscle recruited.
Conclusions:
- Neuromuscular activity in peripheral skeletal muscle decreases in parallel with power output during prolonged high-intensity exercise.
- The findings support the existence of a central neural governor that limits muscle recruitment during extended exercise bouts.
- This neural regulation may be a protective mechanism to conserve energy and prevent fatigue.