In general, regular exercise is safe and has countless physical and mental benefits. But could too much cardio be bad for your heart? Before beginning a new exercise routine, you should always talk to your doctor, but knowing the differences between moderate, vigorous, and extreme exercise can help you understand how each may affect you.
Moderate vs. vigorous
Moderate exercise refers to the intensity of the workout. Think of moderate exercise as requiring a medium amount of effort. Your heart will beat faster, and you'll breathe harder than expected, but you’ll be able to talk. Walking, jogging, and swimming are good examples of moderate exercise.
The American Heart Association recommends moderate exercise at least five days a week for 30 minutes or 15 minutes of vigorous exercise daily. Vigorous activities will push your body a little further. You’ll get warm and begin to sweat, and you won’t be able to talk much without getting out of breath.
Here are some examples of vigorous cardio activities:
What research says
After reviewing more than 300 studies, the AHA concluded that the benefits of exercise outweigh the risks for most people. For example, regular walkers and active people have a 50% less chance of having a heart attack. But the AHA warns of potential risks associated with intense exercise training if you're inactive or not trained.
In a small study on people participating in high-intensity or extreme exercises, like running a marathon or triathlon, almost 40% of heart problems happened in first-time participants. That indicates that inadequate training or existing heart problems were a factor.
Half of cardiac problems happen in the last mile of a marathon or half-marathon, so experts recommend that runners pace themselves rather than sprint.
The risk of cardiac problems is greater at high altitudes but can be reduced by spending at least one day adapting to the elevation before strenuous activity.
The risk of atrial fibrillation (AFib), a common heart arrhythmia that increases the risk of stroke, is reduced with moderate exercise volumes but is highest in people who are inactive and almost as high in people who are engaged in very high volumes of exercise training, that is, high-intensity training (such as running 60-80 miles a week)
When to stop or slow down
There’s a simple way to know if you’re doing too much or not enough. Your heart rate helps you hit the bullseye so you can get the most from every step, swing, and squat. Your maximum target heart rate is 220 minus your age. For example, if you’re 40, your maximum heart rate is 180–that is the number of times your heart beats per minute.
Once you know your maximum heart rate, you can calculate your desired target heart rate zone—the level at which your heart is being exercised and conditioned but not overworked. The American Heart Association generally recommends a target heart rate of:
For most people, the benefits of cardio exercise are extensive and far outweigh the risks. But competing in a marathon or triathlon can be risky if you aren't used to extreme exercise. Most people with no known risks and symptoms like chest pain can start a light exercise program. But experts recommend that they pace themselves and slowly increase the intensity.
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Exercise-Related Acute Cardiovascular Events and Potential Deleterious Adaptations Following Long-Term Exercise Training: Placing the Risks Into Perspective–An Update: A Scientific Statement From the American Heart Association | Circulation (ahajournals.org)
The “Extreme Exercise Hypothesis”: Recent Findings and Cardiovascular Health Implications - PMC (nih.gov)
Target Heart Rates Chart | American Heart Association
Slow, steady increase in exercise intensity is best for heart health — much more is not always much better | American Heart Association