What to watch with FT4 and Sport?

FT4 (free thyroxine) is a thyroid hormone that regulates basal metabolic rate and energy availability. In athletes, intense exercise can transiently alter FT4 levels, especially during overtraining or caloric deficit. Persistently low FT4 may indicate hypothyroidism, impairing recovery and performance. Conversely, high FT4 (hyperthyroidism) can cause muscle wasting and cardiac strain. Key point: a single FT4 value is not diagnostic; it should be interpreted alongside TSH and free T3. MyBody-X does not directly measure FT4; for hormone assessment in a sports context, a clinical blood test is necessary. Evidence for exercise effects on FT4 is moderate (human-observational). Caveat: home tests may be affected by time of day, food intake, or recent exercise. Always consult a doctor for abnormal results.