It’s official. Research proves low-volume high intensity interval training involving less than 15 minutes can induce even greater improvements in overall health and fitness.

Scientists and exercise physiologists have devoted years of research to prove the benefits of short bursts of intensive exercise aka high intensity interval training (HIIT). Recently, researchers have been studying whether shorter variations of HIIT, involving less than 15 minutes of high intensity exercise per session also improve health.

A review paper* published in the Journal of Physiology collated and critically appraised over a decade’s worth of research on the topic of this so-called low-volume HIIT for health. Here’s what the authors found:

‘The findings from recent trials suggest that low-volume HIIT can induce similar, and at times greater, improvements in cardiorespiratory fitness, glucose control, blood pressure and cardiac function when compared to more traditional forms of aerobic exercise training including high-volume HIIT and moderate intensity continuous training, despite requiring less time commitment and lower energy expenditure.

‘… There is an ever-growing body of evidence supporting the utility of low-volume HIIT for improving cardiometabolic health in both clinical and general populations. The available evidence from randomised trials indicates that when compared to higher volume continuous training, low-volume HIIT leads to similar, and sometimes greater, cardiometabolic improvements despite lower energy expenditure and time requirement. Further studies involving long-term interventions are required to determine whether low-volume HIIT is sustainable in the long-term.’

Why low-volume HIIT works

Low-volume HIIT, typically involving less than 15 minutes of high-intensity exercise per session, is being increasingly investigated in healthy and clinical populations due to its time-efficient nature and purported health benefits.

The current World Health Organisation (WHO) physical activity guidelines (150 to 300 minutes of moderate activity per week or 75 to 100 minutes of vigorous activity per week) may be unattainable for a large portion of the population who are time-poor due to family or work commitments. This hypothesis is supported by the increasing rates of physical inactivity amongst adults in high- income countries.

The findings of the Journal of Physiology review show that low-volume HIIT (typically involving less than 20 minutes total exercise time – inclusive of warm up and cool down) yields comparable improvements to interventions meeting the current guidelines despite requiring significantly less time.

Beyond its effect on metabolic health, the new review reported that low-volume HIIT can also improve heart function and arterial health.

‘While the WHO guidelines may serve their purpose at a populational level, individualised and tailored low-volume HIIT interventions delivered by appropriately trained exercise professionals may be more effective at an individual level, especially for time-poor individuals,’ says Dr Angelo Sabag, corresponding author of the study.

‘This research is especially important now as people are looking for new and exciting ways to engage in regular exercise.’

Is HIIT more effective for fat loss?

Exercise scientists previously believed that ‘steady state’ cardio exercise was superior for fat loss because relatively more fat is used by the body as fuel at lower exercise intensities than at higher intensities. It’s now been shown there are several reasons HIIT may be more effective for fat loss compared to traditional steady-state cardio.

Firstly, HIIT increases your metabolic rate for hours after your workout, a phenomenon known as the afterburn effect, or excess post-exercise oxygen consumption (EPOC). The intense nature of the exercise stimulates your body to repair and rebuild muscles, which requires extra energy from stored fat. As a result, you continue to burn calories even when at rest post workout.

In addition, HIIT can help improve insulin sensitivity, which plays a crucial role in fat loss and overall health. Better insulin sensitivity means your body can process carbohydrates more efficiently, using them for energy and muscle growth instead of storing them as fat. This ultimately helps with managing body weight and reducing fat storage.

Moreover, HIIT has been shown to enhance fat oxidation during workouts, especially when compared to traditional steady-state cardio. This means that a greater proportion of the energy used during exercise comes from fat stores, leading to a more significant reduction in body fat percentage over time.

Lastly, HIIT workouts tend to be shorter in duration, making them more time-efficient. You can get the same, if not better, results in a 20-minute HIIT session compared to an hour of steady-state cardio. This can be highly motivating and easier to incorporate into your busy lifestyle, increasing the likelihood of being consistent and achieving long-term fat loss goals. CBM

*Sabag, A., Little, J.P. and Johnson, N.A. (2021), Low-volume high-intensity interval training for cardiometabolic health. J Physiol.