Aerobic endurance, energy expenditure, and serum leptin response in obese, sedentary, prepubertal children and adolescents participating in a short-term treadmill protocol

Objective We analyzed aerobic endurance, energy expenditure, and serum leptin concentrations during programmed, short-term exercise in a group of untrained, obese children and adolescents. Methods This was a prospective, controlled study of prepubertal males and females ages 6 to 11 y. Group 1 (n = 40) comprised obese children, and group 2 comprised similarly aged non-obese children (n = 16). The children completed a stepwise maximal aerobic endurance test (Bruce protocol) on a treadmill. The variables measured included anthropometric indexes, serum leptin, and physiologic indexes. Results Maximal oxygen consumption (corrected for body weight) values were 29.9 ± 6.7 mL · kg−1 · min−1 in group 1 and 47.2 ± 5.3 mL · kg−1 · min−1 in group 2 (P < 0.05). The number of exercise steps was smaller in group 1 (3.7 ± 0.7 versus 5.3 ± 0.4, P < 0.05), as was time to exhaustion (9.3 ± 1.9 min versus 15.1 ± 1.9 min, P < 0.05). However, the energy cost of the exercise did not differ significantly between groups (57.7 ± 17.8 kcal versus 65.2 ± 17.6 kcal), indicating greater energy expenditure for less performance in the obese children. Initial leptin concentrations were higher in group 1 (24.0 ± 13.1 ng/mL versus 1.6 ± 1.7 ng/mL, P < 0.001), and exercise did not significantly modify these findings. Conclusions Obese children were seriously unfit and paid a high energy price for the treadmill test. Initial leptin concentrations were very high in the obese children, in the range of concentrations found in obese adults. No significant change in leptin concentration was observed at the end of the test, probably because of the short duration of the activity.