For decades, public health guidelines around the world have recommended adults get at least 30 minutes of moderate-intensity physical activity most days of the week. This is roughly equivalent to 150 minutes of moderate-intensity activity per week, or 75 minutes of vigorous-intensity activity.
So it surprised, and perhaps dismayed, many to read headlines last week claiming “we need to do five times as much exercise as we’ve been told”. These claims came from a study published in the British Medical Journal (BMJ), that concluded:
People who achieve total physical activity levels several times higher than the current recommended minimum level have a significant reduction in the risk of the five diseases studied.
Indeed, the more exercise you do the better. However, the important issue that has been missed is that the BMJ study based its findings on self-reported physical activity time accumulated across multiple areas of life. These include such incidental physical activity as lifting boxes at work and cleaning windows, as well as going for jogs and playing tennis. But most studies that explore associations between disease risk and exercise are based on specifically designated physical activity.
By using a self-reported multiple-domain measure of physical activity, this study has generated estimates – of around 13 to 16 hours of brisk walking or six to eight hours of running per week – that are significantly higher than studies using measures focused on designated exercise activities, such as jogging or lifting weights.
How was the study conducted?
The BMJ study was a systematic review, where researchers analyse a number of existing studies and papers on a particular topic. In this case, authors reviewed studies between 1980 and 2016 that examined the association between physical activity and risk of five common diseases: breast cancer, colon cancer, diabetes, heart disease and stroke.