Too much sitting has been shown to increase the risk of chronic diseases, particularly diabetes, heart disease, and some types of cancer. Current guidelines suggest adults do 150 minutes of moderate intensity activity a week, but more than a third (35.6%) of adults worldwide are sufficiently inactive.

Furthermore, the proportion of time spent being inactive rises with age: from 55% (7.7 hours) at 20-29 years, to 67% (9.6 hours) in those aged 70-79 years.

Two articles published in The BMJ argue that the 150 minute target is beyond the reach of some, especially older people, and say we should be promoting the benefits of small increases in daily physical activity rather than focusing on meeting current recommendations.

Philipe de Souto Barreto at the University Hospital of Toulouse says studies show a dose-response relationship between physical activity and health, suggesting that benefits can be achieved by people doing less than the recommended amount of physical activity.

For example, a study of over 250,000 US adults aged 50-71 found that less than one hour of moderate physical activity a week or 20 minutes or more of vigorous physical activity less than once a week was associated with a reduced risk of all cause mortality of 15% and 23%, respectively.

And a review of six studies found a 19% decrease in the risk of all cause mortality among people walking for 1-74 minutes a week compared with people doing nothing.

Barreto believes that policies and actions to promote physical activity "should focus on people who are fully sedentary" and the main goal should be "to make small incremental increases in physical activities in their daily life rather than reaching current recommendations."

Achieving target physical activity recommendations "should remain a goal but not the core public health message surrounding physical activity," he concludes.

In a second article, Professor Phillip Sparling at the Georgia Institute of Technology and colleagues point out that older adults find it difficult to meet moderate and vigorous exercise targets.

They argue that focusing on the 150 minute recommendation "may mean that the benefits of lesser amounts of exercise are overlooked" and say a change in message to reduce sedentary time and increase light activities "may prove more realistic and pave the way to more intense exercise."

"We are not proposing that the 150 minute a week standard be abandoned," they write. "Rather, our purpose is to remind colleagues that a broad perspective to counselling is already embedded in the guidelines and that a whole data approach for older sedentary patients may help them move towards the recommended activity levels."