Do we really need to exercise five times more than we’re told?

For decades, public health guidelines around the world have recommended that adults get at least 30 minutes of moderate physical activity on most days of the week. This is roughly equivalent to 150 minutes of moderate activity per week or 75 minutes of vigorous activity.

That is why many were surprised, and perhaps even horrified, when they read headlines last week claiming that “we have to practice five times more than we were told” These claims come from a study published in British Medical Journal (BMJ), which stated:

People who achieve levels of total physical activity that are several times higher than the recommended minimum level have a significantly lower risk of developing the five diseases studied.

Indeed, the more exercise you do, the better. But an crucial point that has been overlooked is that the BMJ study based its findings on self-reported physical activity time collected across a range of life domains. These include incidental physical activities such as lifting boxes at work and washing windows, as well as running and playing tennis. Yet most studies that examine the relationship between disease risk and exercise rely on specific physical activities.

By using a self-reported multidomain measure of physical activity, this study generated estimates — approximately 13 to 16 hours of brisk walking or 6 to 8 hours of running per week — that are significantly higher than studies using measures focused on specific types of exercise, such as jogging or weightlifting.

How was the study conducted?

The BMJ study was a systematic review, in which researchers analyze a range of existing studies and articles on a specific topic. In this case, the authors looked at studies from 1980 to 2016 that examined the link between physical activity and the risk of five common diseases: breast cancer, colon cancer, diabetes, heart disease and stroke.

In the 174 articles reviewed, the authors extracted data on total minutes of physical activity per week. Activity in these studies was performed in multiple domains, including work activities, such as carrying lithe loads; transportation, such as walking to work or to the shops; and leisure activities, such as walking the dog or playing tennis.

Many of these studies focused solely on leisure-time activity. In these studies, the authors used statistical methods to estimate what the equivalent total physical activity would be in different domains.

These estimates were based on data from nationally representative surveys that used The World Health Organization’s Global Physical Activity Questionnaire (GPAC), which also measures physical activity in many areas.

What were the results?

The study confirmed that physical activity, even moderate exercise, equal to 150 minutes a week of 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 can be gained by taking more physical activity, including reducing the risk of breast and colon cancer.

For diabetes, heart disease, and stroke, the authors found a fairly huge risk reduction (14–16%) in adults who engaged in physical activity for 30 to 99 minutes per day compared with those who engaged in physical activity for less than 30 minutes per day.

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

How should we read the results?

This study examined in detail the associations of total physical activity across multiple domains with chronic disease risk. The exploit of this multidomain approach resulted in overestimating activity levels. For example, the highest levels of physical activity in the article correspond 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 showing higher numbers than those that exploit questionnaires that focus solely on leisure time. This is for several reasons.

Leisure-time activity tends to be purposeful and more vigorous than the random activity typically performed in other domains. For this reason, it is easier for study participants to recall and report their leisure-time activity.

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

Recall that the BMJ study used the World Health Organization’s questionnaire, which measures physical activity in multiple areas, as the basis for estimates of physical activity.

This survey may be a reasonable tool for classifying participants from the least to the most vigorous – in different domains of their lives – or for monitoring physical activity in populations. However, the minutes per week estimates obtained from this survey cannot be considered accurate representation amount of physical activity associated with disease risk.

The only conclusion we can draw from this study is that moderate amounts of physical activity provide health benefits, and additional physical activity may provide additional benefits.

What else should we consider?

When health agencies first recommended specific levels of physical activity to the public, the focus was on intense exercise and heart function. The recommendation of 150 minutes of moderate-intensity activity per week came about in the 1990s in response to evidence showing the benefits of lower-intensity physical activity.

Australian Government reviewed national guidelines for physical activity in 2014, which are enough to provide many health benefits. Australians are now encouraged to aim for 300 minutes of moderate (or 150 minutes of vigorous) activity a week, to include strength training at least twice a week and to try to reduce the amount of time they spend sitting each day.

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

Reports that people should exercise five times more risk discouraging most people from adopting achievable behaviours that are clearly good for their health. – Brigid Lynch and Paul Gardiner

Expert review

I generally agree with the research findings that the BMJ study has methodological problems with measuring physical activity.

The most sedate problem with this study is the exploit of self-report measures that measure all areas of physical activity. They are known to significantly overestimate the amount of physical activity performed.

This overestimation weakens the dose-response effects of physical activity, suggesting that we need to do much more to achieve the same health outcomes. The study’s results would be more reliable if the authors had used objective measures of total physical activity (assessed with accelerometers, which are instruments that measure the acceleration of the body) in their meta-analysis.

Several others outstanding researchers of physical activity also raised this issue and other, more technical, methodological issues in their response published in the BMJ. -Corneel Vandelanotte