Impact of a single exercise bout on energy expenditure and spontaneous physical activity of obese boys

The main objective of the present study was to determine whether a structur ed, laboratory-based exercise task would modify the energy expenditure (EE) and the pattern of spontaneous physical activity (PA) of obese boys on the clay of an exercise laboratory visit and on the following day. Fourteen 10 - to 15-y-old moderately obese (36.6 +/- 3.3% fat) boys volunteered. They e ach had three laboratory visits, 1 wk apart. In one visit, they performed a strenuous 50-min cycling task; in another, a 30-min medium-intensity cycli ng task; and in another (which served as placebo), they did not exercise. P A was monitored the day before (d 1), during (d 2), and after (d 3) each la boratory visit by use of a heart rate monitor and a 12-h recall interview. EE was calculated from minute-by-minute heart rate and each child's predete rmined relationship between oxygen uptake and heart rate. EE and PA were an alyzed from 1300 to 1900 h each day using 15-min intervals. EE tended to de crease (p < 0.087) in the afternoon of all d 2 compared with d 1, and it in creased on d 3 after the medium-intensity exercise (p < 0.0005). EE during d 2 and 3 combined, compared with d 1, decreased after the high-intensity e xercise (534.2 versus 564.3 kJ/h, p < 0.05). It increased after the medium- intensity exercise (561.8 versus 526.7 kJ/h, p = 0.052) and was not affecte d after the placebo visit (589.4 versus 574.3 kJ/h). Time spent outdoors wa s consistently reduced on the day of laboratory visit compared with the day before and after the visit, regardless of the contents of intervention. In conclusion, a single laboratory visit is followed by a reduction in EE, an d PA on the day of intervention. However, its effect on EE the following da y may be dose dependent: medium-intensity exercise induces an increase in E E, but high-intensity exercise causes a decrease in EE. One implication is that intervention by physical training should employ medium-intensity exerc ise to enhance the EE of obese boys.