The Unknown Mechanism of the Overtraining Syndrome Clues from Depression and Psychoneuroimmunology Lawrence E. Armstrong and Jaci L. VanHeest Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, Connecticut, USA Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 1. The Training Continuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 2. The Complexities of Overtraining Syndrome (OTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 3. The Search for a Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 3.1 Initiating Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 3.2 Biological Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 3.3 Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 3.4 Nutrition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 3.5 Bodily Responses to Stressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 3.6 Hormonal Perturbations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 3.7 Immune Responses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 3.8 Disturbances of Mood State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 4. OTS and Depression: A Case Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 5. Depression and OTS: Shared Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 5.1 The Role of Neurotransmitters in Major Depressive Disorder (MD) and OTS . . . . . . . . . . . 195 5.2 Neuroendocrine Responses in MD and OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 5.3 Receptors in MD and OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 5.4 Synaptic Plasticity in MD and OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 5.5 Immune System Activation in MD and OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 6. A Novel Perspective on OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 6.1 Autonomic Balance and the Sympathetic-Adrenal Medullary Axis . . . . . . . . . . . . . . . 202 6.2 Cortisol and the Hypothalamic-Pituitary-Adrenocortical Axis . . . . . . . . . . . . . . . . . . . 202 7. Potential Pharmacologic Therapies for OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 7.1 Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 8. Considerations for Coaches and Physicians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 8.1 OTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 8.2 MD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 9. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Abstract When prolonged, excessive training stresses are applied concurrent with in- adequate recovery, performance decrements and chronic maladaptations occur. Known as the overtraining syndrome (OTS), this complex condition afflicts a large percentage of athletes at least once during their careers. There is no objective biomarker for OTS and the underlying mechanism is unknown. However, it is REVIEW ARTICLE Sports Med 2002; 32 (3): 185-209 0112-1642/02/0003-0185/$25.00/0 © Adis International Limited. All rights reserved.