The virtues of exercising cannot be extoled enough. Doctors have time and again recommended physical activity to remain heart healthy and to combat conditions like diabetes, arthritis, depression, and even to improve one’s sex life. While the less initiated among us consider a 30-minute workout session at the gym or a walk in the outdoors as sufficient, there are some who exercise to the point that it actually starts having a negative impact on their body. Such people include heart attack survivors for whom excess exercise can actually cause death, as reported in a study in the Mayo Clinic Proceedings.

The Physical Activity Guidelines for Americans recommends 150 minutes per week of moderate-intensity exercise or about 75 minutes of vigorous-intensity exercise for cardiovascular benefits. Researchers Dr. Paul T. Williams of the Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, Calif., and Dr. Paul D. Thompson of the Department of Cardiology, Hartford Hospital, Hartford, Conn., used the National Walkers' and Runners' Health Studies databases to find how walking and running impact cardiovascular health. Their findings corroborate with previous research stating that as long as energy expenditures were the same, both modes of exercise benefit cardiovascular health, although calories are burnt much faster with running.   

The researchers also assessed the relationship between exercise and cardiovascular disease-related deaths in about 2,400 physically active heart attack survivors. They found that dose-dependent death due to cardiovascular events had reduced by up to 60 percent in patients who were running less than 30 miles or walking less than 46 miles per week. But any exercise more than this actually negated the benefits of exercise, a process called reverse J-curve pattern.

"These analyses provide what is to our knowledge the first data in humans demonstrating a statistically significant increase in cardiovascular risk with the highest levels of exercise," said Williams and Thompson in a statement. "Results suggest that the benefits of running or walking do not accrue indefinitely and that above some level, perhaps 30 miles per week of running, there is a significant increase in risk. Competitive running events also appear to increase the risk of an acute event." However, they pointed out that the study population consisted of heart attack survivors, so the research findings could not be applied to a general population of people who overexercise. 

The same issue of the journal also carries a report on a meta-analysis of 10 cohort studies aimed at understanding how life-expectancy in professional athletes differs from the general population. The studies were based on the health records of more than 42,000 top athletes (707 women) who had participated in a range of sports, including football, baseball, track and field, and cycling, including Olympic level athletes and participants in the Tour de France.

"What we found on the evidence available was that elite athletes (mostly men) live longer than the general population, which suggests that the beneficial health effects of exercise, particularly in decreasing cardiovascular disease and cancer risk, are not necessarily confined to moderate doses," said senior investigator Alejandro Lucia, of the European University Madrid, Spain. "More research is needed, however, using more homogeneous cohorts and a more proportional representation of both sexes."

In another study published in the same issue, author James H. O'Keefe and his colleagues from the Mid America Heart Institute in Kansas City, Mo., state that from the general population about one in 20 people are overexercising. This overexercising leads to what he terms as "cardiac overuse injury." At the same time, 10 out of every 20 people are not exercising for the time recommended for a healthy lifestyle that is more than 150 minutes of moderate exercise per week.

The researchers report that no more than five hours per week of rigorous exercise is recommended for long-term heart health and life expectancy. Also vigorous exercise should not be carried out on a daily basis and taking a few days of extreme exercise is considered safer.

Instead of being on either extremes of the exercise spectrum, a moderate routine will be most beneficial, say the researchers.

"For patients with heart disease, almost all should be exercising, and generally most should be exercising 30-40 minutes most days, but from a health stand-point, there is no reason to exercise much longer than that and especially not more than 60 minutes on most days," Lavie said.

Source: Williams P, Thompson P. Increased Cardiovascular Disease Mortality Associated With Excessive Exercise in Heart Attack Survivors. Mayo Clinic Proceedings. 2014.