Studies show that too much high-intensity exercise over a long period of time can result in an irregular heart beat, according to Medical News Today. Results of a study conducted in Sweden that looked at the exercising habits of 44,000 men between the ages of 45 and 79 showed that those who engaged in high-intensity exercise in excess of five hours per week were 19 percent more likely to have an irregular heartbeat by the time they turned 60.
In general, the exercise intensity that is considered safe for an individual is determined by age; the same exercise program might be moderate for a 30 year old and very intense for a 60 year old. The development of an irregular heart beat, also known as atrial fibrillation, increases the likelihood of fatality by stroke or heart attack. A graph of the effects of exercise form what is called a J-shaped curve, wherein the benefits of exercise are high in the low-to-moderate ranges and then decline or even reverse when exercise is overly strenuous. Individuals who engaged in low intensity exercise such as walking or riding a bicycle for an hour a day at age 60 were found to be 13 percent less likely to develop an atrial fibrillation than those who engaged in no exercise at all, states Medical News Today.