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Moderate levels of exercise are often prescribed for people recovering from a heart attack or heart surgery, but pumping up workouts to high-intensity level may also be a safe option, according to a Norwegian study.
"The results of the current study indicate that the risk of a cardiovascular event is low after both high-intensity exercise and moderate-intensity exercise," wrote Oelvind Rognmo, lead author of the study and a researcher at the Norwegian University of Science and Technology, in the journal Circulation.
Rognmo said there is plenty of evidence that the harder people work out, the more benefit they gain in cardiovascular function. His team wanted to see if heart patients could benefit from high-intensity exercise, too.
The concern for heart patients, though, is that the higher exertion may carry an increased risk of heart malfunction.
Rognmo and his colleagues tracked 4,846 patients at three cardiac rehabilitation centres in Norway who racked up a combined total of more than 170,000 hours of aerobic exercise.
More than 129,450 hours was spent working out at moderate intensity and the rest was at high intensity. All people in the study participated in both types of exercise.
The moderately paced workouts included an hour of walking or other exercise at 60 to 70 per cent of their maximum heart rate.
At high intensity, people trained at repeated four-minute intervals alternating high-impact exercise such as cycling, jogging or cross-country skiing, to get their heart rate up to 85-95 per cent of capacity followed by four minutes of more relaxed activity, such as walking.
During the more than 129,000 hours people spent exercising moderately, one person died from cardiac arrest. During more than 46,000 hours of high-intensity workouts, two people had cardiac arrests but survived.
"We found that both types of intensities were involved with low event rates," Rognmo said. "I think (high-intensity training) should be considered for patients with coronary heart disease."
But he and his colleagues wrote that the differences in the numbers of cardiac arrests was too small to conclude whether high-intensity exercise is more dangerous than less demanding workouts.
"I think we're on the right track, but before we make it a standard recommendation, let's get our safety data," said Steven Ketevian, the director of preventive cardiology at Henry Ford Hospital in Michigan, who was not involved in the study.