Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials

Abstract

Background: 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. Objective: Our objective was to meta-analyse the effects of endurance training and HIT on the maximal oxygen consumption (VO2max) of healthy, young to middle-aged adults. Methods: 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 ‘VO2max’. Inclusion criteria were controlled trials, healthy adults aged 18–45 years, training duration ≥2 weeks, VO2max 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 VO2max. Results: The meta-analysed effect of endurance training on VO2max 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). Conclusion: Endurance training and HIT both elicit large improvements in the VO2max of healthy, young to middle-aged adults, with the gains in VO2max being greater following HIT when compared with endurance training.