Exercise volume and aerobic fitness in young adults: the Midwest Exercise Trial-2

To examine the effect of exercise volume at a fixed intensity on changes in aerobic fitness. Ninety-two overweight/obese individuals (BMI 25–40 kg m²), age 18–30 years, 50 % women, completed a 10 mo, 5 d wk⁻¹ supervised exercise intervention at 2 levels of exercise energy expenditure (400 or 600 kcal session⁻¹) at 70–80 % heart rate (HR) max. Exercise consisted primarily of walking/jogging on motor-driven treadmills. The duration and intensity of all exercise sessions were verified by a downloadable HR monitor set to collect HR in 1-min epochs. All participants were instructed to continue their typical patterns of non-exercise physical activity and dietary intake over the duration of the 10 mo intervention. Maximal aerobic capacity (indirect calorimetry) was assessed on a motor-driven treadmill using a modified Balke protocol at baseline, mid-point (5 mo), and following completion of the 10 mo intervention. VO₂ max (L min⁻¹) increased significantly in both the 400 (11.3 %) and 600 kcal session⁻¹ groups (14 %) compared to control (−2.0 %; p < 0.001); however, the differences between exercise groups were not significant. Similar results were noted for change in relative VO₂ max (mL kg⁻¹ min⁻¹); however, the magnitude of change was greater than for absolute VO₂ max (L min⁻¹) (400 group = 18.3 %; 600 group = 20.2 %) due to loss of body weight over the 10-mo intervention in both exercise groups. Our results indicate that exercise volume was not associated with change in aerobic fitness in a sample of previously sedentary, overweight and obese young adults.