An exercise prescription for obese individuals follows the same framework of mode, intensity, duration, and frequency already described. The volume of exercise needed for weight loss is greater than that which is necessary to improve fitness.1 Modifications to the standard fitness exercise prescription focus on greater overall energy expenditure. Initial training intensity should be modest (40%–60% Vo2 reserve or heart rate reserve), account for deconditioning, and emphasize duration and frequency rather than intensity. The Vo2max and heart rate during brisk walking are higher in obese persons; therefore, brisk walking may present difficulty as an activity.9 The ACSM recommends a training frequency of 5 to 7 days per week, with sessions lasting 45 to 60 minutes.5 Longer-duration training at lower intensity is based on the premise that glycogen is the predominant fuel source during the first 20 minutes of exercise, followed by a shift to fat stores after 30 minutes.9