Researchers at Harvard have found the optimal amount of exercise is between 150 and 600 minutes a week, with no harm done by intensity, but with a ceiling when it comes to impact.

Adults who perform two to four times the recommended amount of moderate or vigorous physical activity each week have a significantly reduced risk of premature death. Levels in excess of this do not provide any additional protection, according to new research published in the American Heart Association journal, Circulation.

Researchers looked at mortality data and medical records of more than 100,000 participants and had a 30-year follow-up period. It found a reduction of 21-23 per cent for people who engaged in two-to-four-times the recommended amount of vigorous physical activity (75-150 minutes/week), and a 26-31 per cent reduction for those undertaking moderate physical activity (150-300 minutes/week). Moderate activity included walking, weightlifting and calisthenics. Jogging, running, swimming, cycling and aerobic exercise was considered vigorous.

Participants in the study were 63 per cent female, 37 per cent male, had an average age of 66 and an average BMI of 26 kg/m2. Physical activity was self-reported every two years in a survey, which also asked questions surrounding health and habits.

Good news on extreme exercise

No harmful cardiovascular health effects were found among the adults who reported engaging in more than four times the recommended minimum activity levels. Previous studies have found evidence that long-term, high-intensity endurance exercise, such as marathons, triathlons and long-distance bike races, may increase the risk of adverse cardiovascular events such as myocardial fibrosis, coronary artery calcification, atrial fibrillation and sudden cardiac death.

“This finding may reduce concerns around the potential harmful effect of engaging in high levels of physical activity which was observed in previous studies,” said Dong Hoon Lee, study lead and research associate at the Harvard TH Chan School of Public Health.

Researchers also found engaging in long-term, high intensity (300 minutes/week) or moderate intensity physical activity (600 minutes/week) at levels more than four times the recommended weekly minimum did not provide additional reduction in risk of premature death, meaning they found an upper limit when it comes to these measures of exercise.

The report Long-term leisure-time physical activity intensity and all-cause and cause-specific mortality: a prospective cohort of US adults, was funded by the National Institutes of Health (NIH), the US’s medical research agency, and is accessible here www.hcmmag.com/circulation.