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December 17, 2003

Effect of Exercise Intensity on Body Composition—Reply

Author Affiliations

Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.

JAMA. 2003;290(23):3069. doi:10.1001/jama.290.23.3069-a

To the Editor: Dr Jakicic and colleagues1 concluded that vigorous exercise intensity was not superior to moderate exercise intensity for weight loss in a 12-month physical activity program with additional restriction in dietary fat and caloric intake.

To help explain this unexpected finding, we suggest that the intensity-dependent effect of physical activity on body composition should be taken into account. A higher intensity level of physical activity leads to a more pronounced shift in the relationship of fat mass with fat-free mass (specifically, skeletal muscle mass) with only minimal changes in body weight.2,3 Thus, the apparent lack of an effect of intensity may be due to higher postintervention fat-free mass in the individual who exercised vigorously. This potential benefit of higher exercise intensity could have been assessed with measurement of body composition.