Current physical activity guidelines for adults by the World Health Organization recommend 2.5 hours of moderate exercise – or 1.25 hours of vigorous exercise – a week. But just how frequently you need to work out to achieve optimum health, and how hard, remains unclear. Neither is it clear if there’s an upper limit – how much is too much?

Two new studies, both published in the JAMA Internal Medicine journal in April, reveal some interesting facts.

Exercise frequency
In the larger of the two studies*, data on physical activity levels among 661,137 men and women from Europe and the US was collated. They had an average age of 62 and were categorised by the amount of exercise they did each week. The researchers then looked at death rates over a 14-year follow-up period.

People who did no exercise faced the highest risk of mortality. No surprises there.

However, even those whose moderate activity levels fell below the recommended guidelines of 2.5 hours a week – people who were at least doing something – still benefited from exercise. Their risk of dying was reduced by 20 per cent.

Longevity increased among those who met the minimum levels of exercise, or who did twice as much – between 2.5 and 5 hours a week. This group were 31 per cent less likely to pass away. But the optimal results from exercise were seen among the people who engaged in three to five times the recommended amount – equating to 7.5-12.5 hours of leisurely activity a week. They had a 39 per cent lower risk of death.

The few who took it to the extreme, working out 10 times more than the guidelines – or 20.5 hours a week – saw no additional mortality benefit. But neither was there an increased risk of death.

Exercise intensity
In another study**, researchers focused on the intensity of exercise and mortality rates over more than six years. It was based on 204,542 men and women in Australia who were aged 45 and older.

Participants were categorised not only by how often they exercised, but also by how hard they pushed themselves. The researchers compared those who engaged in moderate activity – such as a gentle swim, social tennis or household chores – to those who included at least some vigorous activity in their routine, such as jogging, aerobics or competitive tennis.

The results showed that achieving the recommended levels of exercise a week – even if it was just moderate intensity – lowered the risk of premature death.

Yet premature death was significantly lower for those who stepped it up a gear. People who spent up to 30 per cent of their weekly exercise time doing vigorous activity were 9 per cent less likely to die prematurely than those who only opted for more leisurely activities. Meanwhile, those who spent more than 30 per cent of their exercise time working out strenuously saw a 13 per cent reduction in mortality risk.

As with the other study, the researchers found no increased risk of early death when people exercised – even among those who worked out the most frequently and the most vigorously.

The take-home message? Any amount of exercise is good. But 7.5-12.5 hours of physical activity a week reaps the highest benefits in terms of life expectancy. And if up to 30 per cent of that time is spent working out vigorously, even better.

*Arem H et al. Leisure Time Physical Activity and Mortality: A Detailed Pooled Analysis of the Dose-Response Relationship. JAMA Intern Med, April 2015

**Gebel K et at. Effect of Moderate to Vigorous Physical Activity on All-Cause Mortality in Middle-aged and Older Australians. JAMA Intern Med, April 2015