Issue: May 2016
May 09, 2016
11 min read

Physical activity beneficial for CV health, but excessive exercise may confer harm

Issue: May 2016
You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

We were unable to process your request. Please try again later. If you continue to have this issue please contact

There is a growing body of literature on the benefits of physical activity and an active lifestyle on CV health, but in the past 10 to 15 years, data have accumulated on CV risks associated with intense and prolonged exercise.

The literature on the CV benefits of exercise is plentiful, but some studies have shown that certain people who exercise at vigorous levels experience a flattening out of CV benefits or an increase in CVD mortality risk. With tragic stories of extreme-endurance athletes experiencing sudden cardiac death during a marathon or exercise training that appear frequently in the media, some experts have posed the question of whether physical activity can be too much of a good thing.

Experts told Cardiology Today that there is some evidence that the risk for sudden cardiac death increases during exercise and for 1 hour afterward, but regular physical activity offers protective CV benefits in the long term. The experts noted, however, that only a small portion of the general population reaches the level of excessive exercise at which long-term CV risks potentially increase, most of the data have been observational and the literature is not definitive.

“Every time somebody goes out and exercises, their risk for a cardiac event is a little higher while exercising, but over the long term, that risk is much lower the other 23 hours of the day than if you weren’t exercising for that hour,” Michael Scott Emery, MD, FACC, cardiologist at Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, said in an interview.

Michael Scott Emery, MD, FACC, from Krannert Institute of Cardiology, University of Indiana, says for most people, regular exercise reduces long-term risk for CV events.
Michael Scott Emery, MD, FACC, from Krannert Institute of Cardiology, University of Indiana, says for most people, regular exercise reduces long-term risk for CV events.

Image credit: Tim Yates, Indiana University School of Medicine; printed with permission.

Overall, exercise is good for heart health and must be a priority, experts told Cardiology Today.

“My advice for sedentary patients is to go for a walk, even just 5 to 10 minutes at a time,” said Michael J. Joyner, MD, professor of anesthesiology at Mayo Clinic in Rochester, Minnesota. “Do something. It doesn’t take much, just 10 to 15 minutes per day, to see a difference.”

There is an ongoing discussion on whether people who exercise and their physicians should be more mindful of the intensity and duration of their workouts to attain maximum CV health benefit, and how health care professionals can encourage sedentary patients to exercise despite the negative headlines they might see.

The exercise paradox

Most current research suggests that moderate exercise reaps the most benefit when it comes to CV health, with extremes on either side associated with potential dangers.

Research published in Heart in 2014 by Ute Mons, MA, PhD, from the German Cancer Research Center, and colleagues demonstrated that physical activity decreased CV mortality in patients who never or rarely exercise. However, in patients who exercised daily, the CV mortality risk was higher than for those who only exercised two to four times per week.

In a study published in Mayo Clinic Proceedings,P.T. Williams, PhD, of the Lawrence Berkeley National Laboratory in Berkeley, California, and Paul Thompson, MD, of Hartford Hospital, Connecticut, focused on the CV benefits of running or walking for survivors of MI. Here again, the dose of exercise determined the CV benefits. The researchers observed that CVD mortality risk, especially related to ischemic heart disease, increased in patients who ran more than 7.1 km per day (4.4 miles per day) or took a brisk walk for at least 10.7 km per day (6.6 miles per day). The risk for ischemic heart disease-related mortalities more than tripled in this group.

Research by Miranda E.G. Armstrong, MPhil(Cantab), PhD, from Oxford University, and colleagues published in Circulation in February 2015 reported similar results. In examining the lifestyle habits of 1 million women from the United Kingdom in the Million Women Study, the researchers found that physical activity up to two or three times per week was associated with a 20% lower risk for CHD, stroke and venous thromboembolism events compared with sedentary women (P < .001 for all). Further, physical activity more than three times per week did not offer further benefits. Compared with participants who exercised two or three times per week, more frequent physical activity increased risk for CHD (P = .002), cerebrovascular disease (P < .001) and VTE events (P < .001).


Data from the Copenhagen City Heart study published in the Journal of the American College of Cardiology the same month showed that light jogging (1 to 2.5 hours per week) was associated with the lowest HR for mortality (HR = 0.29; 95% CI, 0.11-0.8), whereas strenuous runners seemed to have a similar mortality rate to those more sedentary.

Emery said in an interview that the dose-response curves for physical activity and CVD mortality are different for moderate and vigorous exercise.

Emery and colleagues from the American College of Cardiology Sports and Exercise Cardiology Leadership Council conducted a literature review of population studies from around the world and recommended in JACC that 41 metabolic equivalent of task hours per week (MET-h/week), about 547 minutes/week of moderate-intensity exercise or 289 minutes per week of vigorous-intensity exercise, offers optimum CV risk reduction (HR = 0.55; 95% CI, 0.46-0.66), with the response curve flattening out after 11 MET-h/week.

Effects on the body

The question remains whether vigorous exercise can be dangerous. According to Emery, the risk appears low in the long term, but slightly higher in the short term.

“There is a slightly higher risk for more intense physical activity than for lower intensity,” he said. “In the short term, you have just not given your body time to adapt to these kinds of intense stresses, so the ability of the body to respond in the short term takes more out of you when you are not in shape than it does when you are. Catecholamines and adrenaline levels are higher and the heart has not had time to adapt and learn what that means.”

These added stresses that extreme exercise causes the body can also lead to transient increases in systemic inflammation and a depression of LV function, according to Kerry J. Stewart, EdD, professor of medicine at Johns Hopkins School of Medicine.

Kerry J. Stewart, EdD
Kerry J. Stewart

In a study published in the Canadian Journal of Cardiology in 2013, researchers evaluated the cardiac risk of 20 amateur long-distance runners who were participating in the Quebec City Marathon. Approximately half of the participating runners had decreased function in left and right ventricles, as well as myocardial edema, but all changes were temporary.

John Swartzberg, MD, FACP, clinical professor at the University of California, Berkeley School of Public Health, told Cardiology Today that there also is an association between arrhythmia disorders, most commonly atrial fibrillation, and excessive exercise. This association also was investigated in a study by Nikola Drca, MD, from Karolinska University Hospital in Stockholm, and colleagues published in Heart in 2014. In that study, men who exercised for more than 5 hours per week at age 30 years had an elevated risk for developing AF (RR = 1.19; 95% CI, 1.05-1.36). This elevated risk was higher in those who at baseline worked out for less than 1 hour per week, but then quickly intensified their workout (RR = 1.49; 95% CI, 1.14-1.95).

Endurance events and sudden cardiac death

The general population is perhaps most aware of the CV risks from excessive exercise when deaths of endurance athletes are reported, but these deaths are not necessarily proof that prolonged, intense exercise is harmful for everyone, experts told Cardiology Today.

Every year there are cases of sudden cardiac death at marathons or other endurance events, but the death is “usually traced back to a previously undiagnosed underlying cardiac disease, be it ischemic disease or cardiomyopathy or some other abnormality that just wasn’t detected or, perhaps, even ignored,” Stewart said.

He gave as an example the case of Jim Fixx, author of The Complete Book of Running, who died in 1984 at age 52 years from MI while running. It was discovered that all men in his family had died of CHD at a young age, and he was running with chest pain.


“We ran a symposium here at Johns Hopkins a couple years ago — the ‘Jim Fixx: What do you tell your patients about exercises?’ symposium — with the pathologist who did Fixx’s autopsy,” Stewart said. “One can make the case that the exercise actually prolonged his life because he lived maybe 10 years more than any of his male relatives, but he had CHD. As I recall, he was advised to be evaluated for revascularization, but decided not to do it and kept running anyway.”

Benefits vs. risks

The data on excessive exercise are not all negative, however. Joyner told Cardiology Today that vigorous exercise also has been associated with positive cardiac changes. He referred to work by Benjamin D. Levine, MD, FACC, at the Institute for Exercise and Environmental Medicine in Dallas, in which master athletes maintained greater LV compliance and distensibility as they aged.

Michael J. Joyner, MD
Michael J. Joyner

Robert H. Eckel, MD, professor of medicine at the University of Colorado, Denver, and co-chair of the committee that wrote the 2013 AHA/ACC Guideline on Lifestyle Management to Reduce Cardiovascular Risk, told Cardiology Today that clinicians should encourage their patients to exercise but inform them about the CV risks from extreme exercise.

“Exercise is good and should be encouraged in the primary and secondary prevention of CVD, but on the extreme level I think it is important to caution our patients about the possibly of slightly higher risk for an adverse event,” said Eckel, a past president of the AHA. “There is a cautionary note that a health care professional should provide to his or her sedentary patient who is at risk for CVD when they advise them about physical activity and the cardiac benefits vs. risk of being physically active.”

Emery agreed. “The point is to show patients that you don’t have to go run marathons and triathlons and 5Ks just to gain the most benefit you are going to get from exercise,” he said.

One strategy to minimize risk for CV events from exercise is to increase activity gradually, Emery said. He noted that people who are just starting to exercise and jump right into an intense workout have a higher cardiac risk than those who have been doing it for a while.

“Take the weekend warrior or the couch potato who suddenly decides to run a 5K this weekend or decides to start CrossFit after sitting on the couch for the past year. His risk is probably 10-fold higher than someone who has been doing it a long time and training properly for it,” Emery said.

From sedentary to active

Robert H. Eckel, MD
Robert H. Eckel

A bigger challenge is encouraging sedentary patients to engage in physical activity, according to the experts Cardiology Today interviewed. The AHA/ACC guideline written by Eckel and colleagues states that the optimal length and duration of exercise for maximum CV health is 150 minutes per week of moderate exercise or 75 minutes per week of vigorous exercise; this also is the position of the Physical Activity Guidelines for Americans, issued by HHS in 2008. However, Emery said these are goals to eventually work up to, not necessarily the starting point for someone who has not been exercising before.

People first must be assessed for medical conditions. Eckel said conditions such as stroke, asthma and joint-related disabilities may medically limit how much exercise a patient can perform.

“The physician or health care professional must first assess the ability to exercise, and if they are concerned that heart disease may be [present] — either HF, cardiac rhythm disturbance, ischemic heart disease, or angina with exercise, cold or stress — then these patients should be evaluated by a cardiologist,” he said.


For a truly sedentary person, Eckel recommends beginning with 10-minute pauses throughout the day to increase time spent walking.

“Let’s begin by spending 10 to 15 minutes a day on a behavioral change that is modest and easily put into a schedule, even a very busy schedule. From there, gradual increases in physical activity are recommended as tolerated,” he said.

It is important, Swartzberg said, that clinicians use positive reinforcement, not negative reinforcement, to encourage their patients to exercise.

“My attitude ... with my patients is not to badger them, but to have a positive attitude and offer encouragement,” he said. “You have to explain that this [change] is a marathon, not a sprint. People who have not exercised [on a regular basis] are incredibly intimidated about exercising, so it is a process that should begin with just getting out of the chair. With general encouragement, you want to get people to lose the habit of sitting and adopt the habit of moving.”

For patients with known heart disease, extreme exercise is never advised, Stewart said.

“I work with patients with known heart disease, and we have to limit the intensity of exercise. We try to get people to exercise up to what we think is a safe threshold, and when that happens, activities like cardiac rehab are extremely safe,” Stewart said.

“By having patients exercise under our supervision, we will monitor their ECG, BP and heart rate during at least the first several months of cardiac rehab, so we can build up their confidence that they can be active without further damaging their heart,” he said. “As they get accustomed to training, we start weaning them off the intense monitoring to go out on their own and stay active with minimum worry.”

Sometimes, according to Stewart, a certain subset of patients will exercise too intensely, ignoring the parameters set for them. “These are the ones who are more likely to have an adverse event,” he said.

Call for future research

The story on the dangers of excessive exercise is not complete.

But, “from a health perspective, you don’t need to do extreme exercise to gain all the CV benefits,” Stewart said.

He called for future research in this area; specifically, studies that recruit a better caliber of control population.

“It is hard to do because people who don’t exercise may not exercise because they are not well for other reasons, and as a result they will have a higher mortality rate. We need to put a tremendous effort into good control groups. That is going to be tricky, but I think that is probably where research should go,” he said.

Eckel also suggested a focus on developing tools in the clinic that can assess cardiorespiratory fitness.

“Assessing cardiorespiratory fitness is not something that we can routinely do, and that came up when we dealt with the [AHA/ACC] guidelines. It would be nice if we could assess something measurable that we know predicts benefit from physical activity,” he said. “By making fitness measurable by the clinician in the clinic, we could better assess how fit people are in relation to their ability to improve their overall health, including cardiac health.”

Another area for future research is a focus on public health initiatives to get people to continue to understand the risk of not exercising, particularly “the risks of prolonged sitting and how we can adapt the workplace to improve patients’ health in meaningful measures,” Emery said.

These issues are bigger priorities than further refining the risks presented by excessive exercise, he said.

“I think the controversy over excessive exercise, while interesting, is not a large public health initiative.” – by Tracey Romero

Disclosures: Eckel, Emery, Joyner, Stewart and Swartzberg report no relevant financial disclosures.