Metabolic and cardiorespiratory acute responses to fasting versus feeding during high-intensity interval training

Abstract

The aim of this study was to investigate the effects of sprint interval training (SIT) and feeding state [fasted (FAST) or fed (FED)] on metabolic and cardiorespiratory parameters. Twelve active men (age 23 ± 3 years; body mass 76.43 ± 4.06 kg; height 175.6 ± 4.98 cm; body mass index 24.78 ± 0.56 kg/m2; VO2peak 52.33 ± 4.87 mL/min/kg) volunteered to participate in this study. Participants completed a 2-week SIT intervention, comprising two randomized sessions (FAST, FED) of three bouts of 30-s Wingate anaerobic sprints on an electromagnetically braked cycle, with 4 min of rest interspersed between bouts. Metabolic and cardiorespiratory assessments were repeated every 10 min during the 1 h post-intervention time period. The rating of perceived exertion was higher in the FAST condition as compared to FED during bout 3 (20 ± 0.0 vs. 19.42 ± 0.51; p ≤ 0.05). There was no difference in peak power, mean power and minimum power during the SIT protocol in FAST and FED conditions. Glucose values were lower 10, 20, 30, 40 and 50 min following SIT than during bouts 1–3 in the FED condition, whereas glucose values remained stable during all time points in the FAST state. Triglycerides and cholesterol remained unchanged following SIT as compared to pre-exercise in both conditions. Compared to pre-exercise, respiratory exchange ratio was higher 10 and 20 min, and lower 40, 50 and 60 min post-exercise in the FAST condition and was higher at all time points in the FED condition. SIT in the fasted state does not decrease muscle performance and increase fat oxidation 30 min post-exercise without optimizing energy expenditure in healthy active men.