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The effect of endurance training on serum triiodothyronine kinetics in man: physical conditioning marked by enhanced thyroid hormone metabolism *
Author(s) -
Rone James K.,
Dons Robert F.,
Reed H. Lester
Publication year - 1992
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1992.tb02332.x
Subject(s) - endocrinology , medicine , triiodothyronine , thyroid , hormone , metabolism , endurance training , reverse triiodothyronine
OBJECTIVE We studied the relationship between endurance training, aerobic capacity, and T3 metabolism in healthy euthyroid men. DESIGN T3 kinetic studies performed on two groups of subjects differentiated on the basis of physical activity status and aerobic capacity. SUBJECTS Five endurance‐trained athletes and five sedentary controls (mean±SD Vo 2 max = 48.2 ± 7.1 vs 23.2±4.5 ml/kg/min, respectively) matched for age, body surface area, lean body mass, and baseline thyroid function. MEASUREMENTS Kinetic analysis performed using serial serum T3 levels measured following oral T3 administration. Metabolic clearance rate, total volume of distribution, disposal rate, and total body pool calculated using non‐compartmental analysis. RESULTS When normalized for lean body mass, all kinetic parameters were 25–38% greater in the athletic group compared to controls ( P <0.05). Total volume of distribution, disposal rate, and total body pool were positively correlated with aerobic capacity ( r =+0.69 to +0.79; P <0.05). Metabolic clearance rate was positively correlated to a non‐significant degree. CONCLUSIONS These results confirm the findings of prior studies that thyroid hormone metabolism is altered by physical conditioning. In addition, we demonstrated a positive correlation between aerobic capacity and several parameters of T3 kinetics. Differences in absolute lean body mass cannot explain these findings; rather it appears that there is something qualitatively different in the way endurance‐trained tissue processes thyroid hormone, compared to untrained tissue. The study was not designed to elucidate these differences at the cellular level; however, it does support a link between muscle physiology and T3 activity and may suggest a physiological role for thyroid hormone in physical conditioning.