Wednesday April 6 2011
Researchers claim that “sprints are better than marathons for improving health, especially in children”, reported The Daily Telegraph. It said a study has found that “a number of brief bursts of exercise were better for your heart and circulation than the equivalent long distance training”.
The news story is based on a small study comparing the effects of bouts of intense exercise with moderate, steady exercise sessions in a group of 57 volunteer schoolchildren over a seven-week period.
Contrary to the newspaper reports, the study did not find that brief, intense exercise was better for heart health, but that teenagers on either type of exercise showed improvements in different measures of cardiorespiratory fitness. The high-intensity group had reductions in blood pressure, while the moderate group had greater improvements in aerobic fitness. Moderate exercise also had the greatest effect on other factors that can predict heart risk (body fat, insulin levels and levels of blood clotting factors).
In conclusion, this study is too small to make any robust statements about whether short periods of high-intensity exercise are better than longer periods of moderate exercise, either for teenagers or adults. Further research is needed in larger groups of people over a longer period.
Where did the story come from?
The study was carried out by researchers from the University of the West of Scotland, Swansea Univesity, Cardiff School of Sport, Hong Kong Baptist University, the Macao Polytechnic Institute in China, and the University of Texas in the US. Funding information is not given. The study was published in the peer-reviewed American Journal of Human Biology.
The reports in the Daily Mail and The Daily Telegraph inaccurately portray the results of this study. This misrepresentation appears to originate from the press release for the research. The study actually found that both high- and moderate-intensity interventions improved measures of cardiorespiratory fitness. While high-intensity exercise was associated with lowered BP, the moderate exercise group had better overall measures of cardio fitness.
It is also important to note that this research looked at the effects of exercise in teenagers. Different effects may be found in older people, and those who are actually at risk of heart disease.
What kind of research was this?
This was a randomised controlled trial designed to examine the effects of high-intensity exercise compared to moderate exercise on traditional markers of cardiovascular health in young people. The researchers point out that regular exercise in childhood and youth is known to protect against future cardiovascular disease (CVD) risk. But little is known about the effectiveness of different programmes to increase activity levels in young people, and there is little evidence on the amount of physical activity necessary to reduce the risk of CVD.
What did the research involve?
The researchers recruited 47 boys and 10 girls from two school PE classes in Years 5 and 6 at school (average age 16). The Year 5 pupils acted as a control group who carried on with their normal levels of activity, while those in Year 6 were randomly assigned to take part in either high (the HIT group) or moderate (MOD group) intensity training. The two groups performed exercise sessions three times a week over seven weeks. The HIT group’s training session consisted of four to six 20-metre “maximal effort” sprints (as much as they could run in 30 seconds) with 30 seconds’ rest in between. The MOD group were told to run steadily for 20 minutes, at an intensity of about 70% maximal oxygen intake. This was defined as the volunteer running at a speed that was individually set for them according to their cardiorespiratory fitness, as determined in a previous 20m multi-stage fitness test.
Various physiological and metabolic measurements were carried out on all the volunteers before, during and after the interventions. These included measurements of height, weight, BMI, body fat and blood pressure. Researchers also took blood samples and measured various markers for cardiovascular health, including insulin, measures of blood clotting (fibrinogen and plasminogen activator inhibitor-1) and blood lipid (fat) concentrations. Cardiorespiratory fitness was re-measured using the multi-stage fitness test during and after the intervention.
The effects of each exercise regime (compared with the controls) were then analysed using conventional statistical methods.
What were the basic results?
Of the 21 exercise sessions over the seven-week period, participants attended an average of 17-18 sessions, with no differences in attendance between groups. Over the seven weeks, the MOD group spent a total of 420 minutes on exercise, while the HIT group had 63 minutes in total. The total estimated energy expenditure was about 907.2 kcal for the HIT group and about 4,410 kcal for the MOD group.
After the seven weeks, the HIT group had significant improvements in systolic blood pressure, aerobic fitness, and body mass index (BMI) compared to the control group.
The MOD group also had significant improvements in aerobic fitness, percentage and BMI, but without the improvements in systolic blood pressure. However, it was associated with significant improvements in percentage body fat, and in the markers fibrinogen, plasminogen activator inhibitor-1, and insulin concentrations.
Overall, moderate exercise had the greatest effect on cardiorespiratory health. Volunteers in the MOD group improved their aerobic fitness by 26.8%, compared to an 8.3% improvement in the HIT group.
How did the researchers interpret the results?
The researchers say that “significant improvements” in CVD risk factors occurred in the HIT group in only 15% of the exercise time, compared to the MOD group. This makes it a “time efficient” way of improving CVD risk factors in adolescents.
However, the researchers say that HIT sessions seemed too short to adequately challenge the heart’s pumping ability, to produce the magnitude of improvements in aerobic fitness seen in the MOD group.
This small, short-term study of high- or moderate-intensity exercise in adolescents did not find that brief, intense exercise was better for heart health, as has been reported in the news. It actually found that both types of exercise were associated with a reduction in various measures of cardiorespiratory health and fitness. High-intensity exercise saw reductions in blood pressure. The moderate exercise group had a greater improvement in aerobic fitness and had the greatest overall effect on other physiological and metabolic factors that may predict cardiovascular disease risk.
The researchers argue that high-intensity exercise is better because it uses less time and energy to demonstrate a reduction in cardiovascular risk factors than moderate-intensity exercise. However, as they point out, it may be the length of time spent doing moderate exercise that places a greater demand on the heart and is therefore responsible for improved aerobic fitness.
The research has some limitations that should be highlighted:
- There were some imbalances between the groups that could undermine the reliability of the results: 25% of children in the MOD group were overweight, compared with only 6% of those in the HIT group.
- The trial cannot tell us the cardiovascular effects of continuing with either high- or moderate-intensity exercise in the longer term. Most importantly, although the results have demonstrated changes in certain markers of cardiovascular health and respiratory fitness in adolescents, they cannot tell us whether these would affect risk of cardiovascular disease in adult life. Likewise, we do not know what the effects of high or moderate exercise on these cardiorespiratory measures would be, had these tests been carried out in a sample of older adults.
In conclusion, this study is too small and too short to tell us much about the type of exercises that best help to protect adolescents against future heart problems. It cannot conclude that high-intensity exercise is better for blood pressure than longer periods of moderate exercise. Larger scale, longer term research is needed to evaluate the effects of different types of exercise in this age group, and in other age groups.
It is important for adolescents to exercise regularly, in a way they enjoy, whether sprinting or marathon training. More information on fitness can be found in our Live Well pages.