Effect of suspending exercise training on resting metabolic rate in women

We tested the hypothesis that enhanced resting metabolic rate (RMR) in highly trained endurance athletes is an acute effect of prior exercise induced by catecholamines and not serum thyroxine. RMR and energy-regulating hormones were studied in nine highly trained women runners during habitual training (period I), and suspension of training (period II). Data were collected during the follicular phase of two consecutive menstrual cycles, confirmed by serum progesterone and estradiol. Subjects maintained training between the two periods. Total energy intake and diet composition, body weight, and oral temperature did not change from period I to period II (P greater than 0.05). With suspension of training, urinary epinephrine and nonrepinephrine excretion dropped (P less than 0.022) while serum TSH rose (P = 0.011) and free T4 did not change (P = 0.182). RMR (mean +/- SEM) was 274 +/- 6.2 and 252 +/- 7.8 kJ.h-1 for periods I and II, respectively, with repeated measures ANOVA indicating a drop in RMR occurred with cessation of exercise (P = 0.048). The augmentation of RMR by exercise lasted more than 15 h but less than 39 h post-exercise. The results suggest that the drop in catecholamines may partly explain the lower RMR following suspension of training.