Resting metabolic rate and thermogenic effect of glucose in trained and untrained girls age 11-15 years

Twelve girls who trained in rowing were examined twice a year for 4 years. Their initial age was 11.7 +/- (SD) 0.2 yrs. Control groups consisted of 13 girls age 11.5 +/- 0.3 yrs and 18 girls age 14.4 +/- 0.3 yrs examined simu ltaneously with trained girls in the first and last year of the study, resp ectively. The examination involved basic anthropometry, estimation of sexua l maturation (Tanner scale), 2-day food records, measurements of resting me tabolic rate, energy expenditure following glucose ingestion (50 g), and de terminations of blood glucose and plasma insulin concentrations prior to an d 2 hrs after glucose load. Body mass, height, and fat content were slightl y greater in trained girls. None of the subjects reported disturbances in m enstrual function, and the age of menarche was similar for all. Both traine d and untrained girls reported similar daily energy intake closer to the lo wer limit or slightly below the estimates of energy requirements for adoles cents. Resting metabolic rate calculated per kg of total body mass or lean body mass was lower in trained girls, while the thermogenic effect of gluco se was greater. Plasma insulin concentrations measured 2 hrs after glucose ingestion were lower in trained girls. The results suggest that in circumpu bertal girls, increased physical activity leads to energy conservation at r est in postabsorptive state and a tendency toward enhancement of food-induc ed thermogenesis.