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 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.


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.
Wesche
M F
MF
Department of Internal Medicine, Hospital de Tjongerschans, Heerenveen, The Netherlands.
Wiersinga
W M
WM
D000328:Adult; D001823:Body Composition / Q000502:physiology*; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000378:metabolism; D008297:Male; D009929:Organ Size / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D013177:Sports / Q000502:physiology*; D013954:Thyroglobulin / Q000378:metabolism; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000502:physiology*; D013963:Thyroid Hormones / Q000097:blood; D014463:Ultrasonography
D013963:Thyroid Hormones; D013954:Thyroglobulin; D007453:Iodide Peroxidase