In Reply: Dr Short inquires about the rationale for the intervention duration, whether fatness was adjusted, and the effects of pubertal development in our trial of exercise and diabetes risk in overweight children. It was important that the stimulus be strong enough to affect outcomes; therefore we elicited vigorous intensity physical activity (7.5 metabolic equivalents) with a frequency of every day after school for about 3 months, modeled after prior effective interventions.1,2 It was necessary to repeat the testing and intervention with additional children each semester for several years to power the study; this limited the intervention's duration. We agree with Short that the intervention could be feasible in other settings, and that analyzing the time course of improvements was beyond the study's scope. A briefer intervention period would probably result in improved insulin resistance,3 but would result in less fat loss due to lower cumulative energy expenditure. Given the similar effects of 20 minutes and 40 minutes of daily exercise, a longer program might result in greater loss of fat with similar effects on fitness and diabetes risk.
Davis CL, Waller JL, Pollock NK. Exercise for Overweight Children and Diabetes Risk—Reply. JAMA. 2013;309(2):133–134. doi:10.1001/jama.2012.148059
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