Effects of different protocols of high intensity interval training for VO 2 max improvements in adults: A meta-analysis of randomised controlled trials.

OBJECTIVES: To examine the effects of different protocols of high-intensity interval training (HIIT) on VO2 max improvements in healthy, overweight/obese and athletic adults, based on the classifications of work intervals, session volumes and training periods.

DESIGN: Systematic review and meta-analysis.

METHODS: PubMed, Scopus, Medline, and Web of Science databases were searched up to April 2018. Inclusion criteria were randomised controlled trials; healthy, overweight/obese or athletic adults; examined pre- and post-training VO2 max/peak; HIIT in comparison to control or moderate intensity continuous training (MICT) groups.

RESULTS: Fifty-three studies met the eligibility criteria. Overall, the degree of change in VO2 max induced by HIIT varied by populations (SMD=0.41-1.81, p<0.05). When compared to control groups, even short-intervals (≤30s), low-volume (≤5min) and short-term HIIT (≤4weeks) elicited clear beneficial effects (SMD=0.79-1.65, p<0.05) on VO2 max/peak. However, long-interval (≥2min), high-volume (≥15min) and moderate to long-term (≥4-12weeks) HIIT displayed significantly larger effects on VO2 max (SMD=0.50-2.48, p<0.05). When compared to MICT, only long-interval (≥2min), high-volume (≥15min) and moderate to long-term (≥4-12weeks) HIIT showed beneficial effects (SMD=0.65-1.07, p<0.05).

CONCLUSIONS: Short-intervals (≤30s), low-volume (≤5min) and short-term (≤4weeks) HIIT represent effective and time-efficient strategies for developing VO2 max, especially for the general population. To maximize the training effects on VO2 max, long-interval (≥2min), high-volume (≥15min) and moderate to long-term (≥4-12weeks) HIIT are recommended.