Substrate oxidation in overweight boys at rest, during exercise and acute post-exercise recovery

To compare substrate oxidation between normal weight (n = 10) and overweight (n = 10) boys at rest, during exercise at 50% VO(2peak) and during the first 30 minutes of recovery post-exercise.

Twenty boys (8-11 years) were tested over two separate occasions. At the first session, body composition was measured by Dual-Energy X-ray Absorptiometry and peak aerobic capacity (VO(2peak)) was assessed using an incremental treadmill protocol. At least one week later, substrate oxidation was determined via indirect calorimetry in the fasted state at rest, during 10 minutes of exercise at 50% VO(2peak) and during the first 30 minutes of acute recovery post-exercise.

There were no significant differences in substrate oxidation between the two groups at rest or during exercise. However, during early recovery, respiratory exchange ratio (RER) transiently increased in the overweight boys (p = 0.034) but not in the normal weight boys (p = 0.796), with a shift towards greater carbohydrate oxidation in the former group at 15-20 (p = 0.044) and 25-30 (p = 0.052) minutes post-exercise. In contrast, absolute post-exercise fat oxidation was similar between the two groups.

Overweight boys may oxidise fat less efficiently than normal weight boys during recovery post-exercise, deriving a greater proportion of energy from carbohydrate oxidation.