Evidence check: TSH in the context of Sport

TSH (thyroid-stimulating hormone) is a blood biomarker of thyroid function, not a genetic test. In the context of sport, TSH can be affected by intense training, caloric restriction, or overtraining – often TSH decreases under high training load, suggesting central suppression of the hypothalamic-pituitary-thyroid axis. Evidence is moderate, based on human observational studies, not RCTs. A low TSH alone is not a clear indicator of overtraining, as other factors (diet, stress, sleep) also matter. MyBody-X does not measure TSH; it is a standard blood test requiring clinical interpretation. A single TSH value has limited predictive power – serial measurements and inclusion of fT3, fT4, and clinical symptoms are necessary. Athletes with abnormal TSH should consult an endocrinologist before changing training or nutrition. In summary: TSH in sport is a useful but non‑standalone biomarker; evidence is moderate, and individual variability is high.