Is exercising three days a week as good as five?

Thursday August 16 2007

Walking for just 30 minutes a day three times a week can lower blood pressure and the risk of heart disease, The Daily Telegraph and the BBC have both reported. The current advice is that the minimum amount of exercise necessary for health benefits is 30 minutes, five days a week.

The newspaper reports were based on a study which found that people who performed less than the recommended weekly amount of exercise still gained some health benefits. The authors of the study suggested that a new minimum could be helpful for encouraging those with sedentary lifestyles to take up exercise.

Dr Mark Tully, lead author of the research, said, “Exercising five days a week should still be the minimum goal, as it had greater positive effects on blood pressure.” and, "To get to that goal the first hurdle could be to exercise three days a week,” reported the BBC.

The well-conducted study provides evidence that there are benefits to physical activity at lower levels than previously thought. As the BBC stated, “Doing any physical activity is better than none.” However, the study does not address the important question of whether doing more than the recommended amount of exercise is even better.

Where did the story come from?

Dr Mark Tully and colleagues from Queen’s University, Belfast, carried out this research. The lead author was supported by funding from the Department of Education and Learning in Northern Ireland. The study was published in the peer-reviewed medical journal The Journal of Epidemiology and Community Health .

What kind of scientific study was this?

This was a randomised controlled trial of a 12-week walking programme, in which 106 sedentary 40 to 61-year-old men and women from the Northern Ireland Civil Service were randomly allocated to one of three walking programmes. There was a 30-minute programme three days a week, a 30-minute programme five days a week, and a control group who maintained their current lifestyle for 12 weeks. Participants were given the option of completing the 30 minutes of activity in three 10-minute bursts or all at once.

All groups were asked to record their levels of activity (the control group recorded any exercise above what they would normally do) and they were all given pedometers to record the number of steps taken per day. A range of measurements were taken and a food questionnaire completed at the start and within one week of the end of the 12-week programme.. The researchers measured the participants’ ‘functional capacity’ by asking them to walk between two cones placed 10 metres apart at increasing speed until they stopped, and recording the total distance walked.

What were the results of the study?

Improvements in blood pressure, waist circumference, hip circumference and performance on the ‘functional capacity’ test were noted in both the three-times-a-week activity group and the five-times-a-week group, but not in the control (sedentary) group.

The study did not show any improvements in weight or body mass index in the group that exercised five days a week. Surprisingly, however, there was a decrease of these in the people who exercised three times a week. There were no clinically significant differences between the groups in their lipid levels (blood fats).

What interpretations did the researchers draw from these results?

There were some surprising differences between the groups. For example, the three–days-a-week group lost more weight than the five-days-a-week group. The authors suggest that the unequal distribution of men and women between the three-days and five-days groups may have accounted for this. They also suggested that as the three-days group walked slightly further (20 metres or 2.6 minutes per day), than the five-days group, this may account for the differences in weight gain.

The researchers conclude that, “This study shows short-term benefits of unsupervised, home-based walking programmes at and below the currently recommended minimum target levels of exercise.”

They suggest that this is valuable for sedentary people who feel they don’t have time to exercise and also point out that short bouts of exercise, that can be integrated into daily working routines, are valuable.

What does the NHS Knowledge Service make of this study?

This was a well-conducted study of a small number of people that showed statistically significant improvements over a relatively short time (12 weeks) for some of the outcomes measured.

The authors acknowledge that their study is limited by its small sample size, partly due to a low response rate from the civil servants invited to take part. A possible effect of this may be the result that the three-days group lost more weight than the five-days group. Such surprising findings are often found in studies with insufficient participants and this could be attributable to chance.

The reliance of these sorts of studies on the ‘self reporting’ of walking is a potential problem, which the authors acknowledge, although the use of pedometers and the reported acceptance of these by the participants is promising.

The study was not large enough to detect the health improvements demonstrated in other observational studies, which have shown links between the amount of physical activity people take, and reductions in the onset of heart disease and reductions in premature death. It also can’t provide the same level of assurance for the chances of improved survival associated with the recommended 30 minutes of moderate physical activity five days a week.

Single studies very rarely give clear results; the results of a single study should always be incorporated in a synthesis of all that is known about a topic.

The results of this study are completely consistent with the results of other studies; there is no threshold for exercise to be beneficial. Even five minutes once a week would have a beneficial effect compared with no exercise, but no study could ever demonstrate that benefit.

Sir Muir Gray adds...

It would be a positive result if this encourages people who are struggling to perform the recommended minimum amount of exercise. But it’s still advisable to try to meet the target of five days a week, and exceeding it is even better.

Analysis by Bazian
Edited by NHS Choices