Studies confirm any amount of exercise helps
Sudden death after exertion is extremely rare, and even irregular exercise is better than none
Is it safe to exercise?
There can be very little doubt that exercise is good for you. In the constant back and forth of which foods are good for you and which foods are bad for you (if you’ve been keeping track, eggs are bad for you again), exercise is the one thing that seems to survive unscathed.
Some people simply cannot exercise. It is hard to run a marathon with bad knees or a bad hip, although swimming might be a good alternative. And it might be inadvisable to go for a walk outside on ice-covered sidewalks, given that gravity is an implacable foe.
But otherwise able-bodied people may be worried that exercise itself may prove to be dangerous. Media reports of runners dying during or after a marathon are obviously frightening, as are papers like the Copenhagen City Heart Study, which showed that strenuous jogging increases your chance of dying as compared to light jogging. What was often neglected in the broad coverage of the Copenhagen City Heart Study was that there were only two deaths in the strenuous jogger group, and the cause of death was not available to researchers who analyzed the data. Those two individuals could have died from cancer, in car accidents or from the flu. With such small numbers, random events are always a possibility.
Other data is far more reassuring. A 2000 NEJM study found that the risk of sudden death in the 30 minutes after a vigorous bout of exercise was 17 times higher than at rest. That sounds worrisome until you crunch the numbers and realize that amounts to about one death for every 1.5-million episodes of exercise, which would certainly make it one of the least likely ways to die.
Still, people are concerned that if you do not exercise regularly, you might be putting yourself at risk by going all-out with vigorous but infrequent bouts of physical activity. The weekend warrior is the obvious example. This intrepid individual, who does nothing all week then pours their heart and soul into a pickup hockey game on Saturday, might put undue strain on an untrained heart. But the evidence seems to suggest that such fears are unjustified. An analysis of U.K. health data compared sedentary individuals, regularly active people and weekend warriors who got all their exercise in one intense bout per week. In the end, being a weekend warrior was not dangerous, and was in fact better than being a sedentary couch potato. In other words, some exercise is better than none, even if you can’t do it daily.
But what about people with actual heart disease? A recent analysis in JAMA cardiology is very interesting for exactly that reason. This paper examined not simply healthy subjects, but also those with high levels of coronary artery calcium (CAC). While the clinical value of measuring CAC with a CT scan is debatable (and, in my opinion, often not necessary), in a research setting it is a useful way to identify people who are at high risk for cardiovascular events.
In this analysis, those who reported high levels of exercise (more than five hours of vigorous exercise per week) did not have a higher risk of cardiovascular death or death overall despite having high levels of CAC. In fact, their risk of death was slightly but not significantly lower.
The American College of Sports Medicine does have guidelines on who should have a medical clearance before starting an exercise program, but in truth, very few people would actually be barred from exercising. For the vast majority of people, exercise is not just safe but possibly the healthiest thing you can do for yourself. Christopher Labos is a Montreal doctor and an associate with the McGill Office for Science and Society. He also co-hosts a podcast called The Body of Evidence.