Should I exercise harder, but in shorter bursts?

UK national guidelines say that adults should be active every day, and in a week do 150 minutes of moderate activity in bouts of 10 minutes of more. This means activities such as brisk walking, cycling, running or swimming.

However, only 5% of us get the recommended amount of exercise. Over two hours a week seems a big commitment, especially given that we spend half our lives being sedentary – a hugely unhealthy activity. Studies show that not moving much increases the risk of dying from diabetes, heart disease and some cancers.

If we are too idle to be active for 150 minutes a week, is there anything else we can do? Apparently so, according to new research published in The Journal of Physiology. Researchers from Liverpool John Moores University and the University of Birmingham claim that a way of exercising in short, intense bursts has the same metabolic benefits as longer regimes.

Sprint interval training (SIT) may have a sedentary sounding acronym, but it is anything but relaxing. It involves 30-second episodes of all-out exercise – sprinting or cycling as fast as possible – repeated four to six times. Between each bout of high-intensity exercise are four and a half minutes of low-intensity exercise. The research shows that three sessions, adding up to a more manageable 90 minutes a week, have the same effect as the current recommended guidelines.

So should you switch to a shorter, more intense programme?

The solution

The studies were small: 16 sedentary, 21-year-old men were used for both. But one of the authors, Matthew Cocks, a lecturer in muscle biochemistry, says it backs up previous research that showed short bursts of exercise have the same effect as more time-consuming regimens in reducing the body’s resistance to insulin, which is a risk factor in developing diabetes.

But the researchers also found their sedentary young men much preferred SIT to longer sessions. Cocks says that SIT works if your heart rate reaches 80-100% of its maximum rate during the intense bursts of activity. Not knowing your maximum heart rate is no excuse. You can estimate it by subtracting your age from 220. If you are a fit 20-year-old man your maximum heart rate is around 200 and 80% of that 160.

But most of us aren’t fit 20-year-olds. Is it safe to push ourselves that hard? For the more mature there is high intensity training (HIT) , which involves a more gentle 15 to 60 seconds intense exercise followed by two to four minutes of low intensity jogging or cycling. This works just as well as SIT because the intensity is relative. But the evidence base for both SIT and HIT is still weaker than the existing guidelines. And even if you have no known underlying medical condition, if you are older or have any concerns, you should still ask your doctor if these regimens are safe for you.

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