Aim: The aim of this study was to describe the impact of organized weekly exercise for 13 weeks on aerobic fitness, objectively assessed habitual physical activity and body weight in obese adolescents.
Methods: After inclusion and diagnostic evaluation, the adolescents were randomized to either an exercise group or to a control group which lasted for 13 weeks and consisted of a variety of group exercise activities. Out of 47 adolescents 31 (66%) could be evaluated, 16 in the exercise group and 15 in the control group.
Results: After the intervention, the exercise group had decreased the daily time spent in moderate activity by 17 (32) min/day (p < 0.05), and the average intensity by 60 (96) counts/min (p < 0.05). A tendency for increased time spent in inactivity was found (37 min/day). No differences were seen in the control group for any of the variables measured.
Conclusion: The exercise group showed, in contrast to expectations, a reduction in total daily physical activity with organized physical exercise compared to the control group. This may partly explain the failure of many intervention trials.