More does not always equal better, and exercise is a prime example of these wise words. Although recreational runners are shown to live years longer than the average couch potato, several studies suggest that overdoing the track or treadmill may actually reverse any health gains.

The Studies

The Mayo Clinic recently published an illuminating report showing that participating in excessive endurance exercises--like marathons, triathlons and long-distance bike races-- may actually change the structure of your heart and major arteries. The activity causes volume overload, and may result in stiff arteries, coronary artery calcification and other dangerous conditions that may ultimately lead to heart disease.

Another recent study followed runners and walkers who had already survived heart attacks. Although patients who continued to run or walk at moderate levels had a lower risk of repeat attacks, those who ran more than 7.1 kilometers or walked more than10.7 kilometers per day did not gain any cardiac benefits.

How Much is Too Much Exercise?

Even before this research, experts suspected that overexercise was a real and dangerous phenomenon. These fears were solidified for many after two Ironman Triathlon world champions faced heart surgery and experts unearthed a link between endurance sports and enlarged aortic roots. So how much is too much? Going by the research, running more than 30 miles per week may negate any cardiovascular benefits of exercise

That said, most people get nowhere near as much exercise as a marathon runner, and will do no harm by revving up their workout routine. The average American doesn't even meet the minimum aerobic exercise requirements set by the Centers for Disease Control and Prevention, which recommend 150 to 300 minutes per week of moderate cardio, or 75 to 150 minutes per week of vigorous cardio. That doesn't count strength-training exercises like lifting weights, which the CDC recommends performing at least twice weekly.

The Benefits of Regular Exercise

Excessive training aside, a regular exercise routine offers significant protection from cardiovascular disease. The activity helps lower blood pressure and reduces arterial plaque, and also makes your heart more efficient so it doesn't have to work as hard to deliver blood throughout your body. On top of that, exercise increases immune function to help stave off infections, builds stronger bones and muscles and even releases brain chemicals that make you happier. People who exercise regularly are also less susceptible to dementia in old age.

If you can't live without endurance sports, there is some hope. Although chronic overtraining leads to health concerns, you're probably not going to drop dead after participating in one or two marathons. According to epidemiological research, runners are only slightly more likely to suffer a heart attack during or just after a marathon as they are sitting quietly at home.
No matter what your exercise habits may be, factors like genetics and eating habits also help determine your likelihood of cardiac disease. The best you can do is stay physically active, reduce saturated fat intake and enjoy the things you love--including running--in moderation.