HIIT

Research summary

• High-intensity interval training (HIIT) is supported by several meta-analyses and randomized controlled trials showing improvements in cardiorespiratory fitness and body composition, including in clinical populations such as people with rheumatoid arthritis, stroke survivors, and adolescents with obesity.
• Head-to-head comparisons with moderate-intensity continuous training generally show HIIT delivers comparable or modestly greater fitness gains in less training time, though results vary by population and outcome measured.
• The evidence is reasonably strong and comes from controlled trials rather than only observational data, which supports causal interpretation, but most trials are short-term (weeks to months), so long-term and mortality-relevant outcomes are less established than for more broadly studied aerobic training.