Scientists have found the "optimal threshold" for athletic exertion

Regularly engaging in different types of physical activity may be more effective at prolonging life than "more of the same", according to a study published in BMJ Medicine. The authors concluded: variety was associated with a lower risk of death regardless of the total amount of exertion, although an active lifestyle in itself is still important.

The work is based on data from the two largest long-term US cohorts with repeated assessments of activity over more than 30 years: the Nurses' Health Study (121,700 women) and the Health Professionals Follow-Up Study (51,529 men). Participants completed regular questionnaires about their health and habits, and reported how much time per week they spent on different types of activity - from walking and running to swimming, tennis and strength training.

To compare the "load" of different activities, the researchers used MET (metabolic equivalent): activity time (hours per week) was multiplied by its MET value. More than 111,000 people were included in the analysis of total activity, and diversity was assessed by how many different types of activity a person practised (up to a maximum of double-digit number of activities, depending on the cohort).

What the results showed

During the follow-up period, 38,847 participants died; a proportion of deaths were due to cardiovascular causes, cancer and respiratory disease. And almost all individual leisure activities (swimming was the exception) were associated with a reduced risk of death from any cause.

But the key finding is that the relationship turned out to be non-linear. As the total activity increased, the risk of death decreased, but after reaching about 20 MET-hours per week, the effect "levelled off", indicating a possible optimal threshold: it is not always useful to add activity beyond this threshold.

Separately, the researchers compared people with a different "mix" of activities. After adjusting for the total amount of activity, those who practised the widest range of exercises had about 19 per cent lower risk of death compared to those with a monotonous activity. There were also lower risks for causes of death (cardiovascular, cancer, respiratory and other) - the range of effects was wider than for overall mortality.

Limitations

The authors emphasise that this is an observational study, so it does not prove causality. In addition, the activity data were self-reported and the sample was predominantly white participants, which may limit the transferability of the findings to other groups.