Mechanical Efficiency of Normal-Weight Prepubertal Boys Predisposed to Obesity

Purpose: To compare 1) energy expenditure during rest and during submaximal exercise, and 2) the mechanical efficiency of normal-weight boys liable to obesity with normal-weight boys who are not liable to obesity. Methods: Two groups of prepubertal boys, aged 9-12 yr were compared, one with both parents of normal weight (NP, 20 ≤ BMI ≤ 27, N = 20) and the other (N = 20) with one obese parent (OP, BMI ≥ 30). Results: No significant differences were found between the two groups in the anthropometric measurements (means ± SD): body mass (32.9 ± 5.4 and 31.5 ± 3.1 kg, NP and OP, respectively), stature (141.0 ± 6.2 and 140. 0 ± 5.5 cm, NP and OP, respectively), and body fat (16.6 ± 3.5 and 15.1 ± 3.5%, NP and OP, respectively). Likewise, there were no differences in the reported physical activity habits. No differences were observed in the resting metabolic rate values between the two groups (5.071 ± 0.351 and 4.956 ± 0.386 MJ·d^-1, NP and OP, respectively). Submaximal V̇O₂ at 30, 45, and 60 W was similar in the two groups (0.63 ± 0.05, 0.78 ± 0.06, and 0.92 ± 0.08; and 0.63 ± 0.06, 0.78 ± 0.08, and 0.95 ± 0.08 L·min^-1, NP and OP, respectively). Likewise, the mechanical efficiency, calculated at 30, 45, and 60 W was similar in both groups (19.5 ± 2.3, 21.8 ± 2.2, 23.4 ± 2.5%; and 19.5 ± 3.0, 21. 9 ± 2.9, 22.6 ± 2.5%, NP and OP, respectively. No differences were found between groups in their V̇O_2peak (38.4 ± 3.8 and 40.4 ± 4.9 mL·kg^-1·min^-1, NP and OP, respectively). Conclusion: These data suggest that energy expenditure during rest and exercise may not be used to predict future obesity in normal-weight prepubertal boys predisposed to obesity.