Getting inactive middle-aged women and men to stick to an aerobic workout may reduce or reverse their risk of heart failure, a new study shows.

Sedentary people — such as those who spend hours sitting while working or lying on the couch while watching TV — are at greater risk of having their heart muscle shrink and stiffen in late-middle age, which can increase their risk for heart failure.

It wasn’t known if this heart stiffness could be stopped or reversed. To find out, researchers randomly assigned a group of more than 50 sedentary women and men between the ages of 45 and 64 to an aerobic exercise training program or to a yoga, balance and strength training program. The participants exercised for two years.

In the study, published Monday in the American Heart Association’s journal Circulation, the aerobic exercise group took part in high- and moderate-intensity aerobic exercise at least four days a week. This included, for example, four sets of four minutes of exercise, at 95 percent of their maximum heart rate — the hardest they could exercise for four minutes. This intense activity was followed by three minutes of recovery at 60 percent to 75 percent of their peak heart rate. The other group did yoga, balance training or weight training three times a week.

The researchers conducted tests to assess heart health at the beginning and end of the study. They found that the individuals assigned to the aerobic exercise program showed significant improvements in how their body used oxygen and had less cardiac stiffness — two markers of a healthier heart. Among the women and men who took part in the yoga, balance and strength training program, cardiac stiffness and the body’s use of oxygen remained unchanged.

“We found what we believe to be the optimal dose of the right kind of exercise, which is four to five times a week, and the ‘sweet spot’ in time (late middle age) when the heart risk from a lifetime of sedentary behavior can be improved,” said the study’s lead author and cardiologist Dr. Benjamin Levine in a press release.

Levine is the founder and director of the Institute for Exercise and Environmental Medicine, a joint program between Texas Health Resources and UT Southwestern Medical Center in Dallas. His study was funded by the National Institutes of Health.

Because the study included volunteers who were willing to take part in a two-year intensive exercise program, the findings may not be applicable to the general adult population. Also, most of the study participants were white, and whether other racial groups would benefit equally is not known.

Levine said he recommends people make exercise a regular part of their personal routine. The optimal weekly program, he said, would include at least one hour of an aerobic exercise such as tennis, cycling, running or brisk walking; one aerobic session that includes interval training; two or three days of moderate intensity exercise; and at least one strength training session.

“That’s my prescription for life,” Levine said.

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