What it’s for
- Improving aerobic fitness
Repeated hard exercise efforts separated by recovery periods.
Purpose, evidence and practical considerations.
Randomised trials support improvements in cardiorespiratory fitness and some metabolic measures. There is no single best interval format, and harder sessions need appropriate recovery.
Confidence: strong
HIIT can cause musculoskeletal injury, marked fatigue or cardiovascular symptoms when intensity exceeds readiness. Build an aerobic base, warm up, progress gradually and stop for chest pain, faintness or unusual breathlessness. People with cardiovascular, metabolic or orthopedic disease should seek individualized clearance and programming.
HIIT alternates repeated high-intensity work intervals with lower-intensity recovery. The cardiovascular and metabolic stimulus depends on exercise mode, work-to-rest ratio, total volume and how intensity is prescribed relative to individual fitness.
The evidence on this page does not automatically apply to:
How people use it, with their schedules, context and original sources.
Occasionally
2x/week
Reviewed session and timing context, separate from what public protocols report.
Session and schedule patterns reported in public protocols; these are observations, not instructions. Private and hidden usage is excluded.
These share a protocol with this intervention. This does not establish that they work together or are suitable alternatives.