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Differences in endocrine function with varying fitness capacity in postpubertal females across the weight spectrum.

OBJECTIVE
To relate endocrine and nutritional correlates of fitness in postpubertal physically active females across the normal weight spectrum to identify markers and how these might serve as associations of exercise-related endocrine disruption.


DESIGN
Cross-sectional study analyzed by repeated-measures analysis of variance for frequent blood sampling.


SETTING
A general clinical research center.


SUBJECTS
Twenty-two healthy postpubertal female subjects recruited 2 years or more after menarche.


MAIN OUTCOME MEASURES
Maximum oxygen consumption was determined as an index of fitness and daily caloric intake was calculated from a 3-day food diary. During the follicular phase of the cycle, luteinizing hormone was sampled every 10 minutes during a 24-hour period, while follicle-stimulating hormone and cortisol were sampled hourly.


RESULTS
For every 1-unit increase in maximum oxygen consumption, cortisol concentration increased by 2% (P =.005; 95% confidence interval, 1%-3%). However, there was no association between mean gonadotropin concentrations and fitness. Hormone concentrations were not significantly associated with body mass index or percentage of body fat. Higher mean caloric intake from a 3-day summary was inversely related to mean luteinizing hormone concentration, which decreased by 5.5% for every 100-kcal increase (P =.03; 95% confidence interval, 1%-10%). With every 1-year increase in age at menarche, follicle-stimulating hormone concentration decreased by 12% (P =.01; 95% confidence interval, 4%-19%) and cortisol concentration increased by 7% (P =.03; 95% confidence interval, 1%-12%).


CONCLUSIONS
In active adolescents, increased cortisol concentration may represent an adaptive change to exercise that may precede gonadotropin changes seen with higher levels of fitness.