Get fit with less than 5 min of exercise a week?

A few relatively short bursts of intense exercise, amounting to only a few minutes a week, can deliver many of the health and fitness benefits of hours of conventional exercise. Jamie Timmons, a professor in Ageing Biology at the University of Birmingham explains the science behind the revelation.

There are many good reasons for taking exercise. As well as improving fitness, there are long term health benefits in reducing risk factors associated with cancer, diabetes and cardiovascular disease and you may even feel better.

The problem is that most people don't follow the NHS/government advice to do several hours of exercise 5 times a week.

The reason may be because substantial amounts of physical activity has always been associated with work or survival, not leisure or enjoyment. But it is lack of time which is the most common reason people give for not doing any organised physical activity.

But an ever increasing body of research is showing that with far less time commitment, it is possible to get many of the benefits you get from traditional time-consuming aerobic training.

Short bursts

Imagine cycling as hard as possible on an exercise bike for 20-30 seconds, resting then doing the same twice more over a period of a few minutes. At our university laboratories in the UK and Canada, hundreds of volunteers have been performing that routine three times a week during the past 8 years

Medical tests have shown that those three minutes of exercise a week have delivered, on average, improvements in line with the benefits of several hours of conventional exercise such as walking or cycling a week.

These are measured in terms of improved endurance fitness, improved aerobic capacity (a measure of the maximal capacity of your heart, lungs and muscles) and an improvement in the body's response to insulin which is need to control your blood sugar during eating.

Most importantly these findings have been emerging from independent studies in several countries, notably by Professors Martin Gibala at McMaster University in Canada, Niels Vollaard at the University of Bath and Ulrik Wisloff in Norway.

So why is it working? The truthful answer is we do not fully understand why so little time is required.

Image caption High Intensity Training works most of the body's muscles.

But part of the explanation is (probably) that High Intensity Training (HIT) uses far more of our muscle tissue than classic aerobic exercise.

HIT cvcling really vigorously uses not just the leg muscles, but also the upper body including arms and shoulders so that 80% of the body's muscle cells can be activated, compared to 20-40% for walking or moderate intensity jogging or cycling.

Activating the muscle cells breakdown much of the stored glycogen (meaning the body is "primed" to respond to insulin, and this is one of the responses that fails in type II diabetes.

This explanation fits with decades of muscle biochemistry and in many ways is not so surprising to exercise scientists.

It is more difficult to explain why HIT also produces large improvements in aerobic capacity and endurance performance.

But a growing body of independent research shows this is the case and that the text book explanation of the science of exercise require revision.

While more research to do to understand the mechanisms, an explanation is not needed to enjoy the benefits from HIT already.

So where is the catch? For some people at risk of having vascular disease, any stress might be a problem, but there is no compelling data that HIT is any more dangerous that normal exercise and it has been used in patients with metabolic and cardiovascular disease. Indeed, statistically these patients are more likely to die in their sleep.

Like any exercise programme, you should ideally talk to your cardiologist first, if you have any concerns. They can confirm if you are potentially at risk. Your GP may also be able to advise you, although traditionally they are not qualified in exercise science.

Muscle inactivity can also have other negative consequences. Our bones and muscles become weaker more rapidly in old age if we are inactive, leaving us more likely to have falls and fractures.

For those able to do intensive exercise, HIT may build muscle and so combat aspects of human ageing. It is well established that intense muscle contractions are the best way of building muscle tissue. Many athletes exploit this by using exercise training that activates large amounts of muscle cells, like HIT, to build muscle.

Public health

So why is HIT not already part of current public health advice? Although the weight of evidence is building up, conventional wisdom takes time to overturn and longer term studies are needed

In addition, as well as 'fitness', public health advice also reflects concerns about obesity. Hours of aerobic exercise a week can "burn" 2000-4000 K-calories helping, it is argued, to battle against obesity.

The trouble is spending more time exercising means you also eat more, as your body strives to promote "energy balance". To lose weight you must eat less calories than you consume during exercise.

We think HIT will not stimulate appetite, while stimulating your basal metabolism (as you build some new muscle), stimulating fat break-down and burning a few K-calories into the bargain. We are now testing this idea across 6 international research centres in a new study funded by the European Union.

The new study is called Metapredict and you can follow our project on the web or via updates on Twitter at ♯metapredict during the next three years.