Moderate levels of exercise are often prescribed for people recovering from a heart attack or heart surgery, but the authors of a recent paper are suggesting that pumping up workouts to high intensity levels might be a safe option too.
Among 4800 Norwegian heart patients, who racked up a combined total of over 170 000 hours of aerobic exercise, researchers found three cardiac arrests occurred during workouts and only one - during moderate exercise - was fatal. There were no myocardial infarctions at all.
The number was too small to say for sure that high intensity workouts are just as safe as moderate ones, but they show the overall risk of exercise bringing on cardiac arrest is fairly low, according to the researchers.
"I think we're on the right track, but before we make it a standard recommendation, let's get our safety data," said Dr Steven Keteyian, the director of preventive cardiology at Henry Ford Hospital in Michigan, who was not involved in the study.
There is plenty of evidence that the harder people work out, the more benefit they gain in cardiovascular function, said Dr Oeivind Rognmo, a researcher at the Norwegian University of Science and Technology in Trondheim and lead author of the study.
It's therefore appealing to see whether heart patients could benefit from high-intensity exercise, he says.
A needed data required
Dr Rognmo and his colleagues tracked 4 846 patients at three cardiac rehabilitation centres in Norway. They found that those patients spent a combined total of 129 456 hours working out at moderate intensity and 46 364 hours 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 that resulted in exertion at about 60-70% of maximum heart rate.
At high intensity, people trained with repeated four-minute intervals - four minutes of high impact exercise, such as cycling, jogging or cross country skiing, to get the heart rate up to 85-95% of maximum exertion, followed by four minutes of a more relaxed activity, such as walking.
Dr Rognmo and his colleagues analysed how many times people experienced a heart attack or cardiac arrest during exercise or within an hour afterward.
During the more than 129 000 hours the patients spent exercising moderately, one person died from cardiac arrest. During over 46,000 hours of high-intensity workouts, two people had cardiac arrest but survived.
"We found that both types of intensities were associated with low event rates," said Dr Rognmo. "I think (high intensity training) should be considered for patients with coronary heart disease."
The rates of heart events seen translate to one per 129 456 hours of moderate exercise by patients and one per 23 182 hours of high intensity exercise.
Dr Rognmo and his colleagues wrote in their report in Circulation, published online, that the differences in the number of cardiac arrests during moderate and high intensity exercise were too small to conclude whether high intensity exercise is more dangerous than less demanding workouts.
"I don't think we're ready for prime time because there's a little bit of a difference between the two groups, but it's too small to even say from their study (whether it's meaningful), so we just need more data," Dr Keteyian said.
(Reuters Health, September 2012)
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