High-intensity interval training (HIIT) uses short, intense bursts of activity followed by quick recovery periods. It can be performed with bodyweight movements, strength exercises, cycling, walking, swimming or running and often needs little equipment.
Work intervals are commonly challenging—around 80–95% of estimated maximum heart rate—while recovery periods reduce the intensity. HIIT may improve conditioning, metabolism and insulin sensitivity, but it also creates more fatigue than steady-state exercise.
Begin with one session per week if needed, avoid back-to-back hard sessions and increase frequency only when recovery is good. People with medical conditions should seek appropriate professional guidance before starting.