In studying why people opt to exercise or not, scientists often and understandably focus on individual psychology and situations. But increasingly, exercise scientists are also looking into broader factors that can have a bearing, including our social relationships and whether being single, married, childless or employed is likely to affect exercise behaviour.

The results of past studies on this subject have been alternately predictable and startling. Single men and women, for instance, generally exercise far more than do married people, although divorce can change that. Men typically exercise more after a marriage ends; women in that situation frequently exercise less. Meanwhile, employed men, even those with desk jobs, usually exercise more than men who are unemployed.

Parenthood, though, has the greatest downward pull on planned exercise time. In a number of studies in recent years, scientists have found that mothers of even one child exercise considerably less than do the childless, although, perhaps not surprisingly, they often complete more light activity, which would include cooking, cleaning and scrambling after streaking toddlers, than do the childless. Meanwhile, fathers of a single child often exercise as much as they did before becoming a parent, but fathers of more than one child experience a large and rapid decline in their formal exercise time. There has been surprisingly little examination, however, of how marriage affects exercise in the years after a couple’s children have grown, and especially whether and how changes in one spouse’s exercise routine at that point affect the other spouse.

So, for the new study, which was presented this month at a scientific meeting of the American Heart Association in Baltimore, researchers from Johns Hopkins University and other institutions turned to data from the large-scale Atherosclerosis Risk in Communities Study, which includes answers to health-related questionnaires from thousands of middle-aged American adults. Most of the participants answered the questionnaires

multiple times, beginning in the late 1980s.

The researchers looked for data related to exercise from 3,261 healthy, middle-aged, married couples with an average age of about 55, each of whom had filled out the questionnaires at least twice, with about six years between their answers.

As a benchmark, the researchers focused on whether, according to their first questionnaire, each husband or wife had met the standard recommendation for exercise to improve health, which amounts to 30 minutes of moderate exercise at least five times a week. (These married couples consisted of a man and a woman.) Then the scientists determined whether either of the middle-aged spouses had altered his or her exercise habits between questionnaires, and whether the couple’s exercise routines had converged or grown more different during those years.

What they found was that the older couples’ exercise routines tended to become strikingly similar at this point in their lives.

If a woman met the standard recommendation for exercise during her first questionnaire and her husband did not, he was 70 percent more likely to be meeting those recommendations six years later than were men whose spouses did not exercise much, so long as the woman was still exercising regularly. Similarly, if a husband met the recommendations during his first questionnaire and his wife did not, she was about 40 percent more likely to be meeting those recommendations a few years later than were women whose husbands were and remained sedentary.

Less encouraging, if one spouse eased off or eschewed exercise during the years between questionnaires, his or her spouse usually followed suit. The implication, says Laura Cobb, a graduate student at Johns Hopkins who led the study, is that “spouses can play an outsized role” in exercise behaviour during middle age.

Of course, the study relies on self-reported, prospective information, she says, and so “can’t prove” that one spouse’s exercise habits directly affect the other’s. “It’s equally possible,” she says, “that other shared lifestyle factors,” such as retirement or a move to a new neighbourhood, could be influential. (The scientists controlled for health problems by not including couples if one spouse had or developed a major disease.)

But the neat alignment between one middle-aged spouse’s workouts and, after a few years, the

other’s does suggest, Cobb says, that to inspire your spouse to work out more, you should probably begin by ramping up your own routine. And if you hope to maintain that regimen into the future, nudge a sedentary spouse to join you. Otherwise it can be sorely tempting to settle onto the couch yourself.

—©2015 The New York Times