A COMPARISON OF INTERVAL VS. STEADY-STATE EXERCISE ON SUBSTRATE UTILIZATION IN OVERWEIGHT WOMEN

Abstract

PURPOSE: This study investigated changes in substrate utilization during exercise following 8 weeks of interval versus steady-state training in 15 obese women. (Age: 33.8 ± 8.2 yr; HT: 165.7 ± 6.8 cm; WT: 88.0 ± 21.4 kg; BMI: 31.8 ± 6.6 kg/m2; % body fat: 42.9 ± 6.8%). METHODS: Subjects were randomized to either a high intensity interval group (IT (n = 7): 2 minutes at 95% of VO2 max alternating with 3 minutes of 25% of VO2 max) or a lower intensity steady state training group (ST (n = 8): 50% of VO2 max). There were no statistical differences between the IT and ST group prior to training in fitness or body composition. During training, each group was monitor by indirect calorimetry so they had the same mean intensity, duration, and caloric expenditure (300 kcals) during the workouts. VO2 (1/min and ml/kg/min), kcal/min, kcal/min/kgBW, and kcal/min/kgFFW were calculated at specific RER values 0.80, 0.85, 0.90, 0.95, and 1.00 both prior to and following training. RESULTS: The results indicated, that despite similar average exercise training intensities, only the IT group showed significant improvements after training. Using the 0.85 RER value (The cross-over point for fat to CHO usage), the IT showed a significant increase in VO2 (13.59 ± 3.85 to 16.53 ± 2.70 ml/kg/min; p < 0.05), kcal/min/kgBW (0.066 ± 0.18 to 0.081 ± 0.013; p < 0.05), and kcal/min/kgFFW (0.113 ± 0.026 to 0.143 to 0.018; p = 0.01) and trends toward significance in absolute VO2 (1.21 ± 0.26 to 1.49 ± 0.28 L/min; p = 0.08) & kcal/min (5.88 ± 1.27 to 7.26 ± 1.35; p = 0.08). Similar improvements were observed at 0.90 and 1.0 RER values. In contrast, no significant changes were found in the ST group. CONCLUSIONS: These results suggest that high intensity interval training independent of total workload, significantly improved caloric expenditure at a given RER value. Consequently, a significant increase in absolute fat utilization during submaximal exercise resulted which lead to improvements in fat losses in the IT group as we've previously reported (King, 2001 ACSM annual meeting).