THYROID-HORMONE CONCENTRATIONS AND SKELETAL-MUSCLE METABOLISM DURING EXERCISE IN ANOREXIC FEMALES

Food restriction has been shown to result in an impairment of thyroid status, as the body attempts to conserve energy. In turn, hypothyroidi sm has been associated with impaired oxidative muscle metabolism, whic h could negatively affect one's ability to perform exercise. The purpo se of this study was to examine the relationship between thyroid statu s and muscle metabolism during exercise in anorexic (n = 8) and contro l (n = 13) female subjects. Thyroid status was evaluated by measuring resting serum triiodothyronine (T-3) and thyroxine (T-4) concentration s, and muscle metabolism was evaluated by (31)phosphorus magnetic reso nance spectroscopy during plantar flexion exercise. Concentrations of T-3 and T-4 in anorexics were significantly lower than in controls. Th e ratio of inorganic phosphate to phosphocreatine (P-i/PCr) was signif icantly higher in the anorexic compared with the control subjects at l ower (p < 0.05), but not higher, relative exercise intensities. Rates of PCr recovery were not different between anorexics (tau = 50.2 +/- 1 5.8 s) and controls (tau = 42.6 +/- 16.7 s). In conclusion, despite lo wer circulating thyroid hormones in anorexic compared with control sub jects, differences in oxidative metabolism between these groups were s mall.