Thursday April 28 2016
Sprint interval training is increasingly popular
"Researchers have found that short bursts of intense exercise produce similar results to traditional longer-duration workouts," the Mail Online reports.
Researchers compared two types of exercise programme over a 12-week period with a control. The two programmes were:
- a 10-minute "intense" workout, three times a week (referred to as Sprint Interval Training)
- a 50-minute moderate intensity workout, once a week
At the end of the study, they found similar improvements in reliable fitness markers in both groups, such as the body's response to insulin, peak uptake of oxygen and the functioning of muscle cells. However, it is uncertain that the changes seen would have an effect on cardiovascular disease risk and outcomes in the long term.
The study was also quite small (just 25 young men), and the results ideally need verifying in a larger trial, including a study of wider population groups, such as women and different age groups. The study showed no effect on the men's weight or body mass index (BMI), and did not include information about any adverse effects or risks.
The message that your health may benefit from a 10-minute workout is welcome for anyone who struggles to find time to exercise. However, the researchers warn that very high-intensity exercise is not suitable for everyone.
There are also questions over its safety. Famously, in 2013, the broadcaster and journalist Andrew Marr blamed high-intensity training for triggering his stroke.
If you think you are very unfit, it is probably best to build up your fitness gradually, rather than trying to go all-out straight away.
Where did the story come from?
The study was carried out by researchers from McMaster University in Canada and was funded by the Natural Sciences and Engineering Research Council and McMaster University.
The study was published in the peer-reviewed journal Public Library of Science (PLOS) One on an open access basis, so it is free to read online.
The Mail Online's headline that you only need a "minute of exercise" is a bit disingenuous, as the intervals of high-intensity exercise were within a 10-minute session, which included a warm-up and warm-down, and was done three times a week. However, the full text of the story quickly makes that clear, and reports the study reasonably accurately.
What kind of research was this?
This was a randomised controlled trial (RCT), which is a good way of finding out if a treatment works. Researchers wanted to know whether very short, high-intensity exercise could improve health measures as much as moderate-intensity exercise, when compared to a group who did a "no exercise" programme.
What did the research involve?
Researchers recruited 27 men (two later dropped out) who did little exercise and whose average age was 27. They matched them for similar age, BMI and peak oxygen uptake. They were then randomly assigned to either high-intensity sprint interval training (SIT), traditional moderate-intensity continuous training (MICT), or to a control group which was not given an exercise programme.
They carried out a number of tests on their cardiovascular and metabolic health at the start, during, then again after they finished the 12-week programme. They then compared results of the two exercise groups to the control group.
The tests included:
- peak oxygen uptake (VO2 peak), measured through a mask worn while cycling on an exercise bike – high oxygen uptake shows the heart and lungs are working efficiently
- insulin sensitivity index (CS1) measured by monitoring how quickly the body clears glucose from the blood, after it's been infused into a blood vessel – poor insulin sensitivity can lead to type 2 diabetes
- muscle mitochondrial content, measured by taking a muscle biopsy – mitchondiral content gives an indication of how efficient the muscle is at using energy
Both exercise programmes were carried out using exercise bikes and included a two-minute warm-up and three-minute cool-down, cycling at low intensity. For the SIT programme, men cycled three 20-second bursts of "all out" effort, separated by periods of two minutes of low-intensity cycling, adding up to 10 minutes in total. For the MICT programme, they cycled for 45 minutes at approximately 70% of maximal heart rate, adding up to 50 minutes total.
What were the basic results?
Both exercise groups improved on the three tests, while the control group did not show much difference on any test.
Maximum oxygen uptake improved by about 19% for both exercise groups. Insulin sensitivity improved by 53% for men in the SIT programme and 34% for men in the MICT programme, while the measure of mitochondrial content in muscle cells rose 48% after the SIT programme and 27% after MICT.
None of the men showed much change in their weight or BMI, although body fat percentage decreased for men on either exercise programme.
How did the researchers interpret the results?
The researchers said their study showed that a weekly exercise programme of 30 minutes, including three minutes of intense intermittent exercise, was as effective as 150 minutes a week of moderate-intensity, continuous training on three measures of cardiovascular and metabolic health.
"Considering that a large number of individuals do not meet the current physical activity recommendations, there is value in exploring the potential benefits of exercise strategies that involve reduced time commitment," they say. However, they warn that, "this type of exercise requires a very high level of motivation and is clearly not suited for everyone."
The idea that a 10-minute workout could have the same benefits as spending 45 minutes in the gym is tempting. The researchers found it may improve specific markers of health, in one group of young men.
However, this is a small study in a specific population, and we don't know whether it would have comparable effects in older people or women. Also, we don't know the long-term effects of this type of training programme on people's health.
Studies that look at the effects of an intervention, whether it's exercise, diet or medicine, on health measures such as insulin resistance and oxygen uptake, can only give us a short-term, partial picture. What we really want to know is whether an intervention will reduce your chances of having a heart attack or stroke, or of getting diabetes, or dying earlier. Unfortunately, that information can only come from very long-term studies, which are expensive.
One gap in the study is assessment of safety or negative effects of this type of exercise. High-intensity exercise has been linked in the media to the risk of stroke, especially after broadcaster Andrew Marr suffered a stroke shortly after completing an intense session of exercise.
This study doesn't report any adverse effects, nor does it address safety issues. It is probably too small and of too short a duration to be able to detect any. Ideally, some comparison of the risks of strokes or heart attacks with different types of exercise would be needed. However, this would require a large trial and with long enough duration to identify differences.
There's no doubt that most of us need to do more exercise than we do, and that exercise has many health benefits. If you're concerned about the safety of a new exercise programme, it's best to talk to your doctor. You might need to start slowly and build up the amount and intensity of exercise you do, especially if you already have a medical condition.
Government guidelines recommend that adults in the UK should do at least 150 minutes a week of moderate-intensity exercise, or 75 minutes of vigorous exercise, as well as exercise to strengthen muscles. Read more about health and fitness.