Interval Training in the Fed or Fasted State Improves Body Composition and Muscle Oxidative Capacity in Overweight Women

Objective: To investigate the effects of low-volume high-intensity interval training (HIT) performed in the fasted (FAST) versus fed (FED) state on body composition, muscle oxidative capacity, and glycemic control in overweight/obese women. Design and Methods: Sixteen women (27 +/- 8 years, BMI: 29 +/- 6 kg/m(2), VO2peak: 28 +/- 3 ml/kg/min) were assigned to either FAST or FED (n=8 each) and performed 18 sessions of HIT (10 x 60-s cycling efforts at similar to 90% maximal heart rate, 60-s recovery) over 6 weeks. Results: There was no significant difference between FAST and FED for any measured variable. Body mass was unchanged following training; however, dual energy X-ray absorptiometry revealed lower percent fat in abdominal and leg regions as well as the whole body level (main effects for time, P <= 0.05). Fat-free mass increased in leg and gynoid regions (P <= 0.05). Resting muscle biopsies revealed a training-induced increase in mitochondrial capacity as evidenced by increased maximal activities of citrate synthase and beta-hydroxyacyl-CoA dehydrogenase (P <= 0.05). There was no change in insulin sensitivity, although change in insulin area under the curve was correlated with change in abdominal percent fat (r = 0.54, P <= 0.05). Conclusion: Short-term low-volume HIT is a time-efficient strategy to improve body composition and muscle oxidative capacity in overweight/obese women, but fed-versus fasted-state training does not alter this response.