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Exercise, serum free tryptophan, and central fatigue
John D Fernstrom1, Madelyn H Fernstrom
1Department of Psychiatry, University of Pittsburgh School of Medicine, Pittsburgh PA 15213, USA. fernstromjd@upmc.edu
The Journal of Nutrition
|January 21, 2006
Summary
Exercise increases brain tryptophan and serotonin, potentially causing fatigue. However, the exact mechanism driving this brain tryptophan increase during running remains unknown, challenging current theories on central fatigue.
Area of Science:
- Neuroscience
- Exercise Physiology
- Biochemistry
Background:
- Running increases brain tryptophan (TRP) and serotonin (5HT) synthesis and release.
- Elevated 5HT function during exercise may contribute to central fatigue and reduced physical performance.
Purpose of the Study:
- To critically evaluate the prevailing hypothesis that exercise-induced increases in serum nonesterified fatty acids (NEFA) elevate free TRP, thereby increasing brain TRP uptake.
- To explore alternative explanations for the rise in brain TRP during exercise.
- To clarify the relationship between brain TRP and 5HT synthesis/release in the context of exercise-induced central fatigue.
Main Methods:
- Review and synthesis of existing dietary and pharmacological data.
- Analysis of evidence regarding serum free TRP and competing amino acid effects on brain TRP uptake.
- Discussion of the neuron-specific regulation of 5HT synthesis and release during exercise.
Main Results:
- Evidence suggests that the serum free TRP pool does not directly control brain TRP uptake during exercise.
- Changes in competing amino acid levels also do not adequately explain the rise in brain TRP.
- The precise mechanism driving increased brain TRP during exercise is currently unknown.
Conclusions:
- The widely accepted mechanism linking NEFA, free TRP, and brain TRP uptake during exercise is not supported by current evidence.
- The link between elevated brain TRP and increased 5HT synthesis/release is neuron-dependent, requiring active firing of 5HT neurons.
- Identifying specific 5HT pathways activated during exercise is crucial for understanding their contribution to central fatigue and optimizing physical performance.