Relation between lean body mass and thyroid volume in competition rowers before and during intensive physical training

Objective: Lean body mass is a better determinant of thyroid size than body weight as demonstrated in a previous cross-sectional study. We now evaluat ed if intra-individual changes in body composition and especially changes i n lean body mass, due to physical training, could give rise to changes in t hyroid volume. Subjects and Methods: We investigated 17 freshmen (group I) before and after six months of competition rowing; controls (group II) were 19 senior rowers, already participating in a training program for more tha n 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 compositi on 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) conc entrations increased slightly in both groups (p < 0.01), presumably caused by the combination of exercise and insufficient energy intake. Taking toget her all subjects, baseline TV was directly related to BW (r = 0.35, p < 0.0 5), 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 decre ase 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-mo nth period of intensive physical training, changes in thyroid volume correl ate directly with changes in body composition.