Australasian Science: Australia's authority on science since 1938

Being Physically Active Became Twice as Hard

By Tim Olds

How much exercise do we need to remain healthy? A group of experts has now upped the ante dramatically.

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The last Australian Physical Activity Guidelines were in 2004, when it was recommended that adults get 30 minutes of exercise five times per week. In February the new guidelines were published, with the Australian government now recommending that we get 60 minutes of exercise five times per week. We also need two muscle strengthening sessions, and we need to reduce our sitting.

A 100% increase seems a bit beyond the normal rate of inflation, especially given that about half of all Australian adults didn’t get even 30 minutes per day. So how do experts decide on these guidelines?

One thing they normally do, or should do, is to look at dose–response curves. The idea of a dose–response curve started with drug studies: it showed the relationship between a drug dosage and the effect it had on some aspect of health (e.g. X dosage of statins reduces cholesterol by Y). But it doesn’t have to be a drug: the “dosage” could be a certain number of cigarettes, a given intake of dairy, sun exposure, years of schooling, or an amount of physical activity.

The accompanying figure shows a typical dose–response curve relating all causes of mortality to hours of physical activity. You can see that the more physical activity you do, the lower your risk of dying in any given year (in the long run we all have a 100% risk of dying).

You can also see that the biggest...

The full text of this article can be purchased from Informit.