Understand the effort and recovery format
High-intensity interval training, or HIIT, alternates brief periods of hard exercise with lower-intensity recovery periods. Work duration, recovery duration, effort and the number of repetitions can all vary. HIIT describes this structure rather than one fixed list of exercises.
A timed workout is not automatically HIIT. Look for a clear difference between the demanding work and the recovery, and understand what the session asks you to do during each. Running, cycling and exercise circuits can use intervals, but the activity and its difficulty need to suit the person doing them.
Choose an effort you can repeat
Start by identifying the purpose of the interval session and how it fits with your other training. Ask an instructor what "hard" means for the chosen activity and your current ability. A classmate's pace or resistance is not a useful instruction for everyone in the room.
Learn the plan before starting: the activity, work periods, recovery periods and when the session ends. The recovery is part of that plan. Trying to make every segment equally demanding changes the workout and removes the contrast that defines the interval format.
Know the movement before adding intensity
Practise the selected movement at an easier effort first. Include a warm-up that prepares you for the activity, and learn any easier variations before the hard intervals begin. This gives you a usable adjustment when the original version becomes difficult to sustain.
ACE describes reducing movement speed, load or range as ways an instructor can scale a demanding interval. Ask which adjustment suits the activity instead of improvising a new exercise while following a timer. Keep the intended movement under control; the clock is a guide to the session, not a reason to ignore its instructions.
Adjust the session and plan recovery
Record the activity, interval structure and your impression of effort, along with any adjustments. Compare how consistently you completed the planned work. Changing work duration, recovery, resistance and pace at the same time makes the next session harder to interpret.
There is no single interval ratio that establishes the right starting point for every activity and ability. Adjust the plan deliberately, and account for demanding exercise elsewhere in the week. ACE emphasises recovery between HIIT sessions; making every day a hard interval day is not the goal. Choose a format that remains practical to repeat and review.
Sources & further reading.
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