Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO_2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials

Enhancing cardiovascular fitness can lead to substantial health benefits. High-intensity interval training (HIT) is an efficient way to develop cardiovascular fitness, yet comparisons between this type of training and traditional endurance training are equivocal.

Our objective was to meta-analyse the effects of endurance training and HIT on the maximal oxygen consumption (VO_2max) of healthy, young to middle-aged adults.

Six electronic databases were searched (MEDLINE, PubMed, SPORTDiscus, Web of Science, CINAHL and Google Scholar) for original research articles. A search was conducted and search terms included ‘high intensity’, ‘HIT’, ‘sprint interval training’, ‘endurance training’, ‘peak oxygen uptake’, and ‘VO_2max’. Inclusion criteria were controlled trials, healthy adults aged 18–45 years, training duration ≥2 weeks, VO_2max assessed pre- and post-training. Twenty-eight studies met the inclusion criteria and were included in the meta-analysis. This resulted in 723 participants with a mean ± standard deviation (SD) age and initial fitness of 25.1 ± 5 years and 40.8 ± 7.9 mL·kg⁻¹·min⁻¹, respectively. We made probabilistic magnitude-based inferences for meta-analysed effects based on standardised thresholds for small, moderate and large changes (0.2, 0.6 and 1.2, respectively) derived from between-subject SDs for baseline VO_2max.

The meta-analysed effect of endurance training on VO_2max was a possibly large beneficial effect (4.9 mL·kg⁻¹·min⁻¹; 95 % confidence limits ±1.4 mL·kg⁻¹·min⁻¹), when compared with no-exercise controls. A possibly moderate additional increase was observed for typically younger subjects (2.4 mL·kg⁻¹·min⁻¹; ±2.1 mL·kg⁻¹·min⁻¹) and interventions of longer duration (2.2 mL·kg⁻¹·min⁻¹; ±3.0 mL·kg⁻¹·min⁻¹), and a small additional improvement for subjects with lower baseline fitness (1.4 mL·kg⁻¹·min⁻¹; ±2.0 mL·kg⁻¹·min⁻¹). When compared with no-exercise controls, there was likely a large beneficial effect of HIT (5.5 mL·kg⁻¹·min⁻¹; ±1.2 mL·kg⁻¹·min⁻¹), with a likely moderate greater additional increase for subjects with lower baseline fitness (3.2 mL·kg⁻¹·min⁻¹; ±1.9 mL·kg⁻¹·min⁻¹) and interventions of longer duration (3.0 mL·kg⁻¹·min⁻¹; ±1.9 mL·kg⁻¹·min⁻¹), and a small lesser effect for typically longer HIT repetitions (−1.8 mL·kg⁻¹·min⁻¹; ±2.7 mL·kg⁻¹·min⁻¹). The modifying effects of age (0.8 mL·kg⁻¹·min⁻¹; ±2.1 mL·kg⁻¹·min⁻¹) and work/rest ratio (0.5 mL·kg⁻¹·min⁻¹; ±1.6 mL·kg⁻¹·min⁻¹) were unclear. When compared with endurance training, there was a possibly small beneficial effect for HIT (1.2 mL·kg⁻¹·min⁻¹; ±0.9 mL·kg⁻¹·min⁻¹) with small additional improvements for typically longer HIT repetitions (2.2 mL·kg⁻¹·min⁻¹; ±2.1 mL·kg⁻¹·min⁻¹), older subjects (1.8 mL·kg⁻¹·min⁻¹; ±1.7 mL·kg⁻¹·min⁻¹), interventions of longer duration (1.7 mL·kg⁻¹·min⁻¹; ±1.7 mL·kg⁻¹·min⁻¹), greater work/rest ratio (1.6 mL·kg⁻¹·min⁻¹; ±1.5 mL·kg⁻¹·min⁻¹) and lower baseline fitness (0.8 mL·kg⁻¹·min⁻¹; ±1.3 mL·kg⁻¹·min⁻¹).

Endurance training and HIT both elicit large improvements in the VO_2max of healthy, young to middle-aged adults, with the gains in VO_2max being greater following HIT when compared with endurance training.