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 < or = BMI < or = 27, N = 20) and the other (N = 20) with one obese parent (OP, BMI > or = 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 x d(-1) , NP and OP, respectively). Submaximal VO2 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 x 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 VO2peak (38.4 +/- 3.8 and 40.4 +/- 4.9 mL x kg(-1) x 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.