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Physiological responses to prolonged exercise in ultramarathon athletes
Journal of Applied Physiology (Bethesda, Md. : 1985)
|August 1, 1986
Summary
Ultramarathon runners primarily use fat for energy during prolonged exercise. While cardiovascular and thermal factors are not limiting, muscle force generation decreases post-exercise.
Area of Science:
- Exercise Physiology
- Sports Science
- Human Performance
Background:
- Ultramarathon running demands sustained high-intensity effort.
- Understanding physiological adaptations is crucial for optimizing performance and preventing fatigue.
Purpose of the Study:
- To examine the physiological responses of ultramarathon athletes during 4 hours of maximal sustained exercise.
- To identify potential limiting factors in prolonged high-intensity endurance events.
Main Methods:
- Monitored energy expenditure, substrate utilization (fat oxidation), and blood lactate levels.
- Measured oxygen intake (VO2), cardiac frequency, stroke volume, and body temperatures (rectal and skin).
- Assessed muscle force generation and mechanical properties post-exercise.
Main Results:
- Fat oxidation provided 63% of energy expenditure; glycogen stores were significantly depleted (37-53% of resting values).
- Oxygen intake increased over time, indicating rising relative intensity.
- Cardiac output was maintained via increased heart rate compensating for decreased stroke volume.
- Significant post-exercise reduction in voluntary muscle force (-25%) was observed, with no change in evoked mechanical properties.
Conclusions:
- Fat utilization is a key energy source for ultramarathon athletes.
- Thermal and cardiovascular systems appear capable of sustaining prolonged high-intensity exercise.
- Reduced voluntary muscle force post-exercise suggests neural or peripheral fatigue mechanisms, not solely metabolic depletion.