do we really need to do five times as much exercise as we are told?

For decades, public health guidelines around the world have recommended adults engage in at least 30 minutes of moderate-intensity physical activity most days of the week. This equates to approximately 150 minutes of moderate-intensity activity per week or 75 minutes of vigorous-intensity activity.

That’s why it surprised, and perhaps horrified, many people who read headlines last week claiming that “we have to do five times as much exercise as we were told“. These claims come from a study published in the journal British medical journal (BMJ), which stated:

In people who achieve a level of total physical activity several times higher than the currently recommended minimum level, a significant reduction in the risk of developing the five diseases studied is observed.

Indeed, the more exercise you do, the better. However, an important point that was missed is that the BMJ study based its findings on self-reported physical activity time accumulated across multiple areas of life. These include occasional physical activity, such as lifting boxes at work and washing windows, as well as jogging and playing tennis. However, most studies examining associations between disease risk and exercise rely on specifically designated physical activity.

Using self-reported, multi-domain measures of physical activity, the present study produced estimates—of approximately 13 to 16 hours of brisk walking or six to eight hours of running per week—that are significantly higher than studies using measures focusing on designated exercise, such as jogging or lifting weights.

How was the study conducted?

The BMJ study was a systematic review in which researchers analyzed a number of existing studies and articles on a specific topic. Here, the authors reviewed studies conducted between 1980 and 2016 that examined the relationship between physical activity and the risk of five common diseases: breast cancer, colorectal cancer, diabetes, heart disease and stroke.

In the 174 articles reviewed, the authors extracted data on the total number of minutes of physical activity per week. Activity in these studies covered many domains, including work time, such as carrying light loads; transportation, such as going to work or to the shops; and recreation, such as walking the dog or playing tennis.

Many of these studies reported only leisure-time activity. To do this, the authors used statistical methods to estimate what the equivalent of total physical activity would be in several domains.

These estimates were based on data from representative nationwide surveys using: World Health Organization Global Physical Activity Questionnaire (GPAC), which also measures physical activity in multiple domains.

What were the results?

The study confirmed that physical activity, even moderate physical activity of 150 minutes a week at a moderate intensity, is associated with a reduced risk of some of the leading causes of disease and premature death in Australia (diabetes, heart disease and stroke).

The study also found that additional health benefits could be gained by engaging in greater levels of physical activity, including reducing the risk of breast and colorectal cancer.

For diabetes, heart disease, and stroke, the authors found quite large risk reductions (14–16%) in adults who engaged in 30 to 99 minutes of physical activity per day, compared to less than 30 minutes per day.

However, a risk reduction of around 15% was only observed for colon cancer in adults who accumulated 100–199 minutes of activity per day. Even more physical activity – more than 200 minutes a day – was associated with a 15% reduction in the risk of breast cancer.

How should we read the findings?

This study specifically examined the associations of total physical activity across multiple domains with the risk of chronic disease. The use of this multi-domain approach resulted in an overestimation of activity levels. For example, the highest level of physical activity reported in the article is equivalent to more than 19 hours of moderate-intensity activity per day. This is clearly unrealistic.

Multi-domain physical activity questionnaires routinely overestimate physical activity, often shows higher numbers than those that use questionnaires focusing solely on free time. This happens for several reasons.

Activities performed in free time tend to be more purposeful and energetic than occasional activities typically performed in other areas. For this reason, it is easier for study participants to recall and describe their leisure activities.

Free time is also the area in which adults have the most freedom in how they spend their time and is therefore more susceptible to change.

As a reminder, the BMJ study used the World Health Organization’s questionnaire, which measures physical activity in many areas, as the basis for estimating physical activity.

This questionnaire may be a reasonable tool for ranking participants from least to most active – in many areas of their lives – or for monitoring physical activity in populations. However, the estimated minutes per week obtained from this questionnaire cannot be considered as estimates accurate representation amount of physical activity associated with disease risk.

All we can conclude from this study is that a small amount of physical activity provides health benefits and that additional physical activity may provide additional benefits.

What else should we consider?

When health agencies first recommended physical activity levels to the public, the emphasis was on vigorous exercise and heart efficiency. The recommendation of 150 minutes of moderate-intensity physical activity per week emerged in the 1990s in response to evidence showing the benefits of lower-intensity physical activity.

Australian Government revised its national physical activity guidelines in 2014, which are sufficient to grant many health benefits. Australians are now encouraged to aim for 300 minutes of moderate (or 150 minutes of vigorous) activity per week, incorporate strength training at least twice a week and try to limit the amount of time they spend being sedentary each day.

Just 56% of adult Australians and 25% of older Australians met the Australian Government’s 2014–2015 physical activity guidelines.

Reports stating that people need to exercise five times more may discourage most from engaging in achievable behaviors that are clearly good for their health. – Brigid Lynch and Paul Gardiner

Affiliate review

Overall, I agree with this study because there are methodological issues with how physical activity is measured in the BMJ study.

A major concern with this study is the use of self-report measures, which measure all domains of physical activity and are known to significantly overestimate the amount of physical activity performed.

This overestimation weakens the dose-dependent effects of physical activity, suggesting that we need to do much more to achieve the same health outcomes. The study’s results would have been more robust if the authors had used objective measures of total physical activity (assessed using accelerometers, i.e. devices that measure body acceleration) in their meta-analysis.

A few others outstanding researchers of physical activity in their response published in the BMJ also pointed out this and other more technical methodological issues. – Corneel Vandelanotte