On Tuesday evening this week, television viewers in the UK got to see a BBC programme investigating claims that just three minutes intensive exercise a week could give significant health and fitness benefits. Presented by medically-trained Michael Mosley, the research presented seems to be counter to current recommendations for "at least 150 minutes (2½ hours) of moderate intensity activity in bouts of 10 minutes or more" or "75 minutes of vigorous intensity activity spread across the week", which are the guidelines in the UK.
For a lot of people, lack of time after work and family commitments are met is either a genuine reason for not getting enough exercise, or alternatively a convenient excuse for not exercising regularly. An alternative is offered by High Intensity Training (HIT), which some researchers claim can improve aerobic fitness, burn fat and improve insulin sensitivity in just a few 20-30 second bursts of maximum effort a week.
Although billed as "three minutes a week" in the BBC programme, a little more time is actually required, as the exercise sessions also include warmup and recovery periods. If doing the three minutes of HIT split between two sessions a week, each of the three 30 seconds of highly intensive exercise (for example on an exercise bike) per session is preceded by 2 minutes of gentle cycling to warm up before the first high-speed burst and recover before the subsequent flat-out periods. As the 30 seconds does have to be at maximum intensity, it is hard work, and shouldn't be attempted by people with medical conditions without checking with a doctor first.
But how does it work? There are a number of mechanisms reported to be involved.
- When you perform high intensity exercise, you use a lot more of your body's muscles; around 80% of your body's muscles are active (compared with 20-40% from jogging or moderate intensity cycling).
- It moves sugar from blood into the muscle so that it can be readily burned.
- It releases adrenaline which acts as an appetite suppressant.
- You can release hormones that break down fat.
- High intensity exercise causes microscopic tears in your muscles as it strengthens. This healing uses up calories.
- Insulin regulation occurs due to release of growth factors such as IGF-1.
- Metabolic rate increases, which means you will burn more calories when resting.
One catch is that some people's genes will prevent them from increasing their aerobic fitness, but this is the case for other forms of exercise too. According to the BBC programme, the benefit people receive from exercise in terms of increasing aerobic fitness varies widely, with 15% of people making great improvement and about 20% little or no improvement, with the differences linked to a small number of genes.
It's probably also best not to see HIT as sufficient in itself and an excuse to spend the rest of the week in front of the TV or PC. Dr Mosley also reported on how we can all benefit from incorporating more movement into our everyday lives, through simple things such as taking the stairs rather than a lift, or walking short distances rather than using the car.
I took a quick look at CAB Abstracts to see what papers on HIT were indexed there, and found quite a few. Interestingly, many of them investigate HIT as a supplementary form of training for athletes that may help them get more benefit from their normal endurance training. In some of the studies, it's also combined with dietary supplements such as creatine. But for those for whom even 30 seconds of intensive exercise may be too much to start with, a study by Metcalfe et al. in the European Journal of Applied Physiology shows benefits from a program which begins with just 10-second all-out sprints and builds up to 20 seconds.
HIT probably isn't for everyone, and for those of us who enjoy sport or outdoor activities then cramming exercise into just a couple of very short bursts a week may seem a strange way to go about things. But it does seem to offer either a way of getting some health benefits in limited time, or a method for the more active or serious athletes to improve their training.
Links to a few relevant studies, and to an article about the BBC programme, are given below.
Towards the minimal amount of exercise for improving metabolic health: beneficial effects of reduced-exertion high-intensity interval training. Metcalfe, R.S.; Babraj, J.A.; Fawkner, S.G.; Vollaard, N.B.J. European Journal of applied Physiology [DOI: 10.1007/s00421-011-2254-z]
Effect of sprint interval training on circulatory function during exercise in sedentary, overweight/obese women. Trilk, J. L.; Singhal, A.; Bigelman, K. A.; Cureton, K. J, European Journal of Applied Physiology, 2011, 111, 8, pp 1591-1597, [DOI: 10.1007/s00421-010-1777-z.]
High-intensity interval training attenuates the exercise-induced increase in plasma IL-6 in response to acute exercise. Croft, L.; Bartlett, J. D.; MacLaren, D. P. M.; Reilly, T.; Evans, L.; Mattey, D. L.; Nixon, N. B.; Drust, B.; Morton, J. P.; Applied Physiology, Nutrition and Metabolism, 2009, 34, 6, pp 1098-1107, [DOI: 10.1139/H09-117]
High-intensity interval training increases SIRT1 activity in human skeletal muscle. Gurd, B. J.; Perry, C. G. R.; Heigenhauser, G. J. F.; Spriet, L. L.; Bonen, A.; Applied Physiology, Nutrition and Metabolism, 2010, 35, 3, pp 350-357, [DOI: 10.1139/H10-030]
High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals. Sartor, F.; Morree, H. M. de; Matschke, V.; Marcora, S. M.; Milousis, A.; Thom, J. M.; Kubis, H. P.; European Journal of Applied Physiology, 2010, 110, 5, pp 893-903, [DOI: 10.1007/s00421-010-1571-y]