High-intensity interval training: Modulating interval duration in overweight/obese men

Abstract

Introduction: High-intensity interval training (HIIT) is a time-efficient strategy shown to induce various cardiovascular and metabolic adaptations. Little is known about the optimal tolerable combination of intensity and volume necessary for adaptations, especially in clinical populations.

Objectives: In a randomized controlled pilot design, we evaluated the effects of two types of interval training protocols, varying in intensity and interval duration, on clinical outcomes in overweight/obese men.

Methods: Twenty-five men [body mass index (BMI) > 25 kg · m(2)] completed baseline body composition measures: fat mass (FM), lean mass (LM) and percent body fat (%BF) and fasting blood glucose, lipids and insulin (IN). A graded exercise cycling test was completed for peak oxygen consumption (VO2peak) and power output (PO). Participants were randomly assigned to high-intensity short interval (1MIN-HIIT), high-intensity interval (2MIN-HIIT) or control groups. 1MIN-HIIT and 2MIN-HIIT completed 3 weeks of cycling interval training, 3 days/week, consisting of either 10 × 1 min bouts at 90% PO with 1 min rests (1MIN-HIIT) or 5 × 2 min bouts with 1 min rests at undulating intensities (80%-100%) (2MIN-HIIT).

Results: There were no significant training effects on FM (Δ1.06 ± 1.25 kg) or %BF (Δ1.13% ± 1.88%), compared to CON. Increases in LM were not significant but increased by 1.7 kg and 2.1 kg for 1MIN and 2MIN-HIIT groups, respectively. Increases in VO2peak were also not significant for 1MIN (3.4 ml·kg(-1) · min(-1)) or 2MIN groups (2.7 ml · kg(-1) · min(-1)). IN sensitivity (HOMA-IR) improved for both training groups (Δ-2.78 ± 3.48 units; p < 0.05) compared to CON.

Conclusion: HIIT may be an effective short-term strategy to improve cardiorespiratory fitness and IN sensitivity in overweight males.

Keywords: Exercise; VO2peak; body weight; insulin; lifestyle; metabolism; percent body fat.

Figure 1

Experimental design for inclusion criteria, pre-post assessments, and training protocol. Abbreviation: HIIT = High-intensity interval training.

Figure 2

Mean ± 95% confidence intervals and individual responses for the change in (a) Fat mass (kg), (b) Lean mass (kg), and (c) Percent body fat (%) for 1MIN-HIIT, 2MIN-HIIT, and CON from pre- to post-training. Abbreviation: HIIT = High-intensity interval training.

Figure 3

Mean ± 95% confidence intervals and individual responses for the change in (a) VO₂peak (ml·kg·min⁻¹) and (b) TTF, s. Abbreviation: TTF = Time to fatigue.