Cross-training may be the key to a long life

Many sportspeople do a mixture of exercises to boost their performance. Now there’s evidence that this cross-training could extend their lives, too.

An analysis of two studies that followed people for more than 30 years has found that those who did a variety of activities were 19 per less likely to die of any cause during that time than those who were just as physically active but whose exercise was less varied.

“If the total amount of physical activity is kept constant, you will get additional benefits from doing a mix of physical activities,” says Han Han at Harvard University. But studies of this kind can’t establish cause and effect, she says, so the findings are suggestive rather than definitive.

Most exercise studies focus on the intensity or overall amount of physical activity, rather than the variety. Those that have looked at different exercise types tend to compare aerobic with strength exercises.

Han and her colleagues instead looked at nine kinds of mostly aerobic activities: walking; jogging (defined as a pace slower than 6.2 minutes per kilometre); running; cycling outside or on an exercise bike; climbing stairs; swimming laps; rowing or callisthenics (where you use your body weight as resistance, such as squats or pull-ups); tennis, squash or racquetball; and weight or resistance training.

The team got data on the activities of 70,000 women and 41,000 men between 1986 and 2018 from the Nurses’ Health Study and the Health Professionals Follow-Up Study, both done in the US. Study participants were asked to fill in questionnaires every two years detailing their physical activities.

The researchers then looked for associations between people’s activities and their chance of dying from any cause during the study period. People with illnesses that would have affected their ability to exercise were excluded.

The team found that, with all these exercise types, people seemed to reach a point of diminishing returns, in terms of a lower risk of dying during the study period, if they did more than a few hours a week.

This could be why doing a variety of exercises has additional benefits: once someone gets to the point of diminishing returns, they might gain more by spending their time doing a different exercise rather than more of the same, says Han. Another explanation could be that different types of physical activities have distinct physiological effects whose combined benefits are greater.

“We think that future studies could examine the possible synergistic effects of different activities,” says Han. “This will help to identify the optimal mix of activities.” The optimal mix may also change over people’s lifespans, she says.

Few studies have investigated the effect of different types and combinations of exercise on mortality, says Duck-chul Lee at the University of Pittsburgh in Pennsylvania. The findings should be interpreted cautiously because of the limitations of this kind of study, he says. These include the fact that people tend to report doing more exercise than they really do and that people who are healthier overall tend to be more active, which can bias the results.

“However, their findings are also somewhat supported by the current World Health Organization physical activity guidelines suggesting that doing both aerobic and resistance exercise provides a large and more comprehensive health and mortality benefit than doing either alone,” says Lee.

In the future, it should become possible to do this kind of study using data from wearable fitness trackers, rather than relying on self-reporting. “But for now, to get this length of time, you have to rely on the questionnaires,” says Han.