If you increase your heart rate, will your life span follow?
That possibility is at the heart of an ambitious new study of exercise and mortality. The study, one of the largest and longest-term experimental examinations to date of exercise and mortality, shows that older men and women who exercise in almost any fashion are relatively unlikely to die prematurely. But if some of that exercise is intense, the study also finds, the risk of early mortality declines even more, and the quality of people's lives climbs.
Short bursts of intense exercise could be more beneficial than moderate training. Credit:iStock
Scientists have known for some time, of course, that active people tend also to be long-lived people. According to multiple past studies, regular exercise is strongly associated with greater longevity, even if the exercise amounts to only a few minutes a week.
But almost all of these studies have been observational, meaning they looked at people's lives at a moment in time, determined how much they moved at that point, and later checked to see whether and when they died. Such studies can pinpoint associations between exercise and life spans, but they cannot prove that moving actually causes people to live longer, only that activity and longevity are linked.
To find out if exercise directly affects life spans, researchers would have to enroll volunteers in long-term, randomised controlled trials, with some people exercising, while others work out differently or not at all. The researchers then would have to follow all of these people for years, until a sufficient number died to allow for statistical comparisons of the groups.
Such studies, however, are dauntingly complicated and expensive, one reason they are rarely done. They may also be limited, since over the course of a typical experiment, few adults may die. This is providential for those who enroll in the study but problematic for the scientists hoping to study mortality; with scant deaths, they cannot tell if exercise is having a meaningful impact on life spans.
Those obstacles did not deter a group of exercise scientists at the Norwegian University of Science and Technology in Trondheim, Norway, however. With colleagues from other institutions, they had been studying the impacts of various types of exercise on heart disease and fitness and felt the obvious next step was to look at longevity. So, almost 10 years ago, they began planning the study that would be published in October in The BMJ.
Their first step was to invite every septuagenarian in Trondheim to participate. Mortality studies involving older people are the most likely to return useful data, the scientists reasoned, since, realistically, there will be more deaths among the elderly than the young, making it possible to compare differences in longevity between study groups.
More than 1,500 of the Norwegian men and women accepted. These volunteers were, in general, healthier than most 70-year-olds. Some had heart disease, cancer or other conditions, but most regularly walked or otherwise remained active. Few were obese. All agreed to start and continue to exercise more regularly during the upcoming five years.
The scientists tested the subjects' current aerobic fitness as well as their subjective feelings about the quality of their lives and then randomly assigned them to one of three groups. The first, as a control, agreed to follow standard activity guidelines and walk or otherwise remain in motion for half an hour most days. (The scientists did not feel they could ethically ask their control group to be sedentary for five years.)
Another group began exercising moderately for longer sessions of 50 minutes twice a week. And the third group started a program of twice-weekly high-intensity interval training, or HIIT, during which they cycled or jogged at a strenuous pace for four minutes, followed by four minutes of rest, with that sequence repeated four times.
Almost everyone kept up their assigned exercise routines for five years, an eternity in science, returning periodically to the lab for check-ins, tests and supervised group workouts. During that time, the scientists noted that quite a few of the participants in the control had dabbled with interval-training classes at local gyms, on their own initiative and apparently for fun. The other groups did not alter their routines.
After five years, the researchers checked death registries and found that about 4.6 per cent of all of the original volunteers had died during the study, a lower number than in the wider Norwegian population of 70-year-olds, indicating these active older people were, on the whole, living longer than others of their age.
But they also found interesting, if slight, distinctions between the groups. The men and women in the high-intensity-intervals group were about 2 per cent less likely to have died than those in the control group, and 3 per cent less likely to die than anyone in the longer, moderate-exercise group. People in the moderate group were, in fact, more likely to have died than people in the control group.
The men and women in the interval group also were more fit now and reported greater gains in their quality of life than the other volunteers.
In essence, said Dorthe Stensvold, a researcher at the Norwegian University of Science and Technology who led the new study, intense training — which was part of the routines of both the interval and control groups — provided slightly better protection against premature death than moderate workouts alone.
Of course, exercise was not a panacea, she adds. Some people still sickened and died, whatever their workout program. (No one died while exercising.) This study also focused on Norwegians, who tend to be preternaturally healthy, and most of us, perhaps regrettably, are not Norwegians. We also may not yet be in our 70s.
But Stensvold believes the study's message can be broadly applicable to almost all of us. "We should try to include some exercise with high intensity," she said. "Intervals are safe and feasible for most people. And adding life to years, not only years to life, is an important aspect of healthy ageing, and the higher fitness and health-related quality of life from HIIT in this study is an important finding."
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