HIIT vs. SIT: What Is the Better to Improve V˙O₂max? A Systematic Review and Meta-Analysis

Lack of time is seen as a barrier to maintaining a physically active lifestyle. In this sense, interval training has been suggested as a time-efficient strategy for improving health, mainly due to its potential to increase cardiorespiratory fitness. Currently, the most discussed interval training protocols in the literature are the high-intensity interval training (HIIT) and the sprint interval training (SIT). Objective: We investigated, through a systematic review and meta-analysis, which interval training protocol, HIIT or SIT, promotes greater gain in cardiorespiratory fitness (V˙O₂max/peak). The studies were selected from the PubMed (MEDLINE), Scopus and Web of Science databases. From these searches, a screening was carried out, selecting studies that compared the effects of HIIT and SIT protocols on V˙O₂max/peak. A total of 19 studies were included in the final analysis. Due to the homogeneity between studies (I² = 0%), fixed-effects analyses were performed. There was no significant difference in the V˙O₂max/peak gains between HIIT and SIT for the standardized mean difference (SMD = 0.150; 95% CI = -0.038 to 0.338; p = 0.119), including studies that presented both measurements in mL·kg^-1·min^-1 and l·min^-1; and raw mean differences (RMD = 0.921 mL·kg^-1·min^-1; 95% CI = -0.185 to 2.028; p = 0.103) were calculated only with data presented in mL·kg^-1·min^-1. We conclude that the literature generates very consistent data to confirm that HIIT and SIT protocols promote similar gains in cardiorespiratory fitness. Thus, for this purpose, the choice of the protocol can be made for convenience.