Not a good idea to run more than 7 k a day if you've had a heart attack
If you have survived a heart attack exercise is certainly good for you. It improves your cholesterol balance, rejuvenates your blood vessels and strengthens your heart. But there is something like an optimal amount of exercise for heart attack survivors, statistician Paul Williams reports in the Mayo Clinic Proceedings. If they run more than 50 km or walk more than 75 km a week, the positive health effects of exercise disappear.
Between 1990 and 2009 Williams monitored 2377 men and women who had had a heart attack. He used data that had been gathered in the National Walkers and Runners Health Studies. So most of the participants in the study were walkers or runners.
Those who walked or ran were less likely to die than inactive participants, Williams noticed. But he also discovered that the protective effect of running was optimal among those who ran about 3-7 MET hours a day. At more than 7.1 MET hours a day the positive effect of running disappeared.
1 MET hour is roughly equivalent to 1 km running or 20 minutes of walking. Running more than 7 km or walking more than 10 km a day made the people who had had a heart attack just as unhealthy as the people who did almost no exercise.
There are in fact few people who exercise more than the optimal amount indicated by this study. In Williams' study only 6 percent of the participants exercised so much that the health benefits disappeared. On the other hand, half of the American population is not even capable of walking for half an hour a day – the minimal amount of physical exercise that is recommended for everyone.
"Exercise is unparalleled for its ability to improve cardiovascular health, quality of life, and overall longevity", writes cardiologist James O'Keefe in a comment on Williams' study. O'Keefe has been warning for years about the dangers of too much intensive exercise. [Heart. 2013 Apr;99(8):516-9.] "If the current mantra 'exercise is medicine' is embraced, physical activity might be best analogized as a drug, with indications and contraindications, as well as issues related to underdosing and overdosing."
"As with any powerful therapy, establishing the safe and effective dose range is fundamentally important - an insufficiently low dose may not bestow full benefits, whereas an overdose may produce dangerous adverse effects that outweigh its benefits."
"Fortunately, the exercise dose-response range that is safe and effective for improving cardiovascular health and longevity is broad."
Mayo Clin Proc. 2014 Sep;89(9):1187-94.
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