OBJECTIVE: Lean body mass is a better determinant of thyroid size than body weight as demonstrated in a previous crosssectional study. We now evaluated if intra-individual changes in body composition and especially changes in lean body mass, due to physical training, could give rise to changes in thyroid volume. SUBJECTS AND METHODS: We investigated 17 freshmen (group 1) before and after six months of competition rowing; controls (group II) were 19 senior rowers, already participating in a training program for more than 2 years. RESULTS: In group I body weight (BW; p < 0.01), lean body mass (LBM; p 0.05), fat weight (FW; p < 0.05), body mass index (BMI; p < 0.01) and thyroid volume (TV; p = 0.08) all decreased; in group II body composition and thyroid volume did not change at all during the 6 months observation period. Whereas serum TSH and T3 did not change, free thyroxine (FT4) concentrations increased slightly in both groups (p < 0.01), presumably caused by the combination of exercise and insufficient energy intake. Taking together all subjects, baseline TV was directly related to BW (r = 0.35, p<0.05), to LBM (r=0.40, p<0.05) and to BMI (r=0.43, p < 0.01) but not to FW (r = - 0.06, NS). The decrease in thyroid volume was related to the decrease in LBM (r = 0.32, p = 0.05), in BW (r = 0.49, p < 0.005), in FW (r = 0.42, p = 0.01) and in BMI (r = 0.53, p = 0.001). CONCLUSIONS: After a six-month period of intensive physical training, changes in thyroid volume correlate directly with changes in body composition. Horm Metab Res 2001 Jul;33(7):423-7
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