Finding time for exercise isn’t always easy, so the idea of getting fitter with just a few minutes of training a week has obvious appeal. High-intensity interval training (HIIT) is often presented as the answer. But what can it realistically offer?

HIIT has a reputation for delivering results in short sessions. Research suggests that it can improve cardiorespiratory fitness, but claims about transforming your fitness or health in just a few minutes need closer examination. Here’s what’s worth knowing.

What is HIIT?

HIIT alternates demanding bursts of exercise with periods of rest or lower-intensity activity. The length and intensity of the intervals vary between programmes, as do the recovery periods. Sessions can involve activities such as cycling, running or rowing.

“High intensity” is relative to the person exercising. It does not mean that every interval has to be an all-out sprint.

How does HIIT differ from steady-paced endurance training?

Steady-paced endurance training involves maintaining a relatively consistent effort over a longer period. HIIT breaks the session into harder efforts and recovery intervals, often allowing a shorter overall workout.

The distinction is not simply “anaerobic versus aerobic”. Both energy systems contribute during exercise, and HIIT can place substantial demands on the body’s ability to take in and use oxygen.

Is HIIT a new idea?

Alternating harder efforts with recovery is a long-established training approach. Modern HIIT programmes apply this principle in different ways, with sessions adapted to particular activities, fitness levels and training goals.

Why does HIIT appeal to so many people?

Time is part of the attraction. Some programmes can improve fitness with shorter sessions than the endurance training used for comparison. However, there is no universal rule that HIIT delivers the same benefits in a tenth of the time.

It’s also important to count the whole session. Warming up, recovering between intervals and cooling down all take time, even when the demanding bursts themselves are brief. Some people enjoy the variety of intervals; others prefer a steadier pace.

What does the research show?

Studies have found that HIIT can improve cardiorespiratory fitness. In some comparisons, improvements have been similar to or greater than those achieved with moderate-intensity continuous training. Results depend on the programme, the participants and the outcome being measured.

HIIT is not one standardised workout. Studies use different activities, intensities, interval lengths and training schedules, so findings from one programme cannot automatically be applied to another.

Research also extends beyond people who are already fit. Adapted programmes have been studied in older adults and people with certain health conditions, often with screening and supervision. This does not mean that every HIIT workout is suitable for everyone.

There is no single ideal programme for all goals and abilities. How often to train, how hard to work and how much recovery to allow should reflect the individual and the rest of their activity.

HIIT can be one option within a varied exercise routine. It need not replace all steady-paced activity, and it does not cover every aspect of fitness. The most useful approach is one that suits your needs and that you can keep up.

Please note: Build up gradually and choose a programme appropriate to your current fitness. If you have a health condition, symptoms during exercise or concerns about vigorous activity, seek advice from a healthcare professional before starting. A qualified exercise professional can help you adapt the sessions and allow appropriate recovery.