Even a Little Exercise Yields Big Benefits, but Harm Unlikely at High Activity Levels

A little goes a long way when it comes to being physically active, according to a group of experts tasked with evaluating the benefits of habitual physical activity and regular training on cardiovascular morbidity and mortality. And while increasing the amount of physical activity and upping its intensity can provide further benefit, researchers say just small changes to our daily routine can add years to our lives.

“One of the key points is the value of very small amounts of exercise,” senior researcher Paul Thompson, MD, of Hartford Hospital in Connecticut, told TCTMD. “Simply standing more than 2 hours per day is associated with a lower risk of cardiovascular events than sitting all day. I think that’s important because, as we’ve become more mechanized and computerized, some of us spend nearly all of our time sitting.”

The new report, from the American College of Cardiology Sports and Exercise Cardiology Leadership Council, includes Thijs Eijsvogels, MD, of Liverpool John Moores University in the United Kingdom as its first author and was published this week in the January 2016 issue of the Journal of the American College of Cardiology (JACC). While the cardiovascular benefits of exercise are well documented, their research attempts to shed light on the dose-response relationship between physical activity and mortality, as well as the importance of exercise intensity on cardiovascular outcomes. 

The Physical Activity Guidelines Advisory Committee Report, published in 2008 by the US Department of Health and Human Services, recommends 150 minutes per week of moderate-intensity exercise or 75 minutes per week of vigorous-intensity exercise. Moderate-intensity aerobic exercise includes brisk walking (covering 3 or more miles per hour), bicycling, water aerobics, doubles tennis, ballroom dancing, or gardening. Vigorous-intensity exercise includes uphill walking/race walking, running or jogging, bicycling (more than 10 miles per hour), singles tennis, aerobic dancing, or heavy gardening.

“For moderate types of exercise, there doesn’t seem to be any limit to the amount of benefit,” said Thompson. “The more you do, the more benefit you get. Now, I’m sure there is some point where the benefit plateaus off, but we can’t see it from the studies. You can’t see it from the studies because not everybody walks all day.”

With a seemingly limitless benefit of moderate physical activity on cardiovascular risk, the dose-response curve does hint at a slight U-shaped association between vigorous physical activity and cardiovascular/all-cause mortality. This might occur, in part, because vigorous physical exercise transiently increases the risk of cardiovascular events. That said, Thompson is cautious in interpreting the limited data, especially since what constitutes a high-volume of vigorous amount of exercise is achieved by a very small segment of the population.

“We can’t be sure yet, but there is the possibility that in doing a lot, lot, lot, lot of exercise, you get diminishing benefits, and you might even get an increased risk,” he said. “But the part about diminishing benefits is probably also true with regard to modest and vigorous exercise—you probably get the most benefit from a modest amount of both of those types of activities and then the curve flattens out. The steep decrease in cardiovascular events occurs in going from doing nothing to doing something and then it flattens out. With vigorous exercise, it might increase [risk] at the other end, but there are too few studies to show it.”

JACC Editor-in-Chief Valentin Fuster, MD, of the Icahn School of Medicine at Mount Sinai (New York, NY), notes in an audio commentary accompanying the paper that half of Americans don’t meet the weekly recommended exercise targets, yet the number of participants in long-distance endurance events, such as marathons, is growing. Overall, the shift from an inactive to a moderately active lifestyle yields large reductions in cardiovascular risk, including a reduction in cardiovascular mortality, with further increases in exercise volume providing further benefit. Like Thompson, Fuster characterizes the volume-mortality benefit relationship as L-shaped, flattening out with increasing volumes. The data suggest that approximately 550 minutes of moderate-intensity exercise per week, or 290 minutes per week of vigorous-intensity exercise, is the volume in which maximal cardiovascular mortality reductions are observed, he says.

Potential Harm With Lifelong Endurance Exercise

Speaking with TCTMD, Thompson noted that the risk of acute events does increase when individuals are engaged in physical activity. For example, he pointed to a study he first conducted in 1982, when he collected data on people who died while jogging in Rhode Island. In that study, the runners were 7 times more likely to die while running than when participating in less vigorous activity. Participating in exercise increases the acute risk of MI and sudden cardiac death, he said, but the overall lifelong effects and changes are beneficial.

In recent years, studies have also raised the issue that lifelong endurance exercise, such as participating in marathons, Ironman-distance triathlons, or long-distance cycling or cross-country ski races, increases the risk of cardiovascular events. For example, studies and reports have documented exercise-induced elevations in cardiac troponin, evidence of myocardial fibrosis, increased coronary calcification, and an increased incidence of arrhythmias, namely atrial fibrillation, among those who participate in large amounts of exercise compared with those who engage in light-to-moderate amounts of exercise.

“In medicine, usually where there is a lot of smoke, there is some fire,” said Thompson. “One of the areas that looks smoky is with atrial fibrillation. There is a growing number of articles suggesting that atrial fibrillation goes up in the most active people. We know that exercise seems to reduce the risk when you go from no exercise to some exercise—atrial fibrillation risk goes down. But when you get into high amounts of exercise, it looks like the risk of atrial fibrillation goes up.”

That said, the exercise council is not warning individuals to not participate in these types of athletic events. While there is the possibility that too much exercise can produce harmful effects, these findings are not conclusive and need to be studied further. Moreover, individuals who run marathons or participate in Ironman triathlons are doing so not only for their health but for other very legitimate reasons. “For most Americans, too much exercise is not a problem,” said Thompson. “It’s a problem of no exercise. We want to make sure in papers such as this that we never discourage anybody from doing exercise. It’s very rare for people to have problems [with exercise] and it’s very few people who will do too much.”

Commenting on the review, Carl ‘Chip’ Lavie, MD, of the John Ochsner Heart and Vascular Institute (New Orleans, LA), agreed that the benefits of exercise occur at low doses, and like Thompson, did not wish to sound any alarms.

“There are risks of high-dose exercise, but the risks are relatively low,” he told TCTMD. “The reason to do high-exercise doses, however, is not due to health but generally fun, competition, ego, stress release, and [because] more exercise burns more calories and allows for a higher caloric intake. The evidence for toxicity of high exercise is not strong enough that we should be overly frightening high exercisers or athletes.”

The amount of vigorous exercise where there is potential harm is achieved only by “real athletes,” added Fuster, noting that the clinical significance of fibrosis, calcification, or these other markers is unknown. As to whether extreme exercise affects mortality, Fuster said “probably not.”

Secondary Prevention and Cardiac Rehabilitation

In addition to examining the data on exercise in primary prevention, the new review also outlines the benefits of cardiac rehabilitation. Most cardiac rehabilitation programs use a relatively standard exercise protocol, exercising patients 3 times per week for 30 to 40 minutes at 60% to 85% of their maximal heart rate. Randomized controlled trials testing cardiac rehabilitation in secondary-prevention patients have shown the programs to be beneficial. Following MI, for example, cardiac rehabilitation has been shown to reduce the risk of cardiovascular death and hospital admissions.   

These secondary-prevention patients are also at increased risk of cardiac events, particularly cardiac arrest, when exercising compared with being at rest but the overall risk during supervised rehabilitation is very low, according to the experts. “The point is that cardiac rehabilitation helps,” Thompson told TCTMD. “One of the reasons it may help is that even though you’ve had a heart attack, you’re exercising with people who can resuscitate you.”

While the advantages and benefits of exercise are widespread, Thompson did note it might cause harm in a small group of patients with a genetic predisposition for cardiac disease. Patients with genetic defects in the desmosomal proteins associated with right ventricular cardiomyopathy, he said, tend to present early in life and have more aggressive disease than patients with similar defects who are less active.

 

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Source: 
Eijsvogels TM, Molossi S, Lee DC, et al. Exercise at the extremes: the amount of exercise to reduce cardiovascular events. J Am Coll Cardiol. 2016;67:316-329.  

 

Disclosures: 

• Thompson reports receiving research support from Amarin, Aventis, Esperion, Genomas, the NIH, Pfizer, Regeneron, Roche, and Sanofi; serving as a consultant for Abbott, Amgen, AstraZeneca, Esperion, Genomas, Merck, Pfizer, Regeneron, and Sanofi; receiving speaking fees from Amgen, AstraZeneca, Merck, Regeneron, and Sanofi; and owning stock in Abbott Laboratories, Abbvie, CVS, General Electric, J.A.Wiley, Johnson & Johnson, and Medtronic.
• Lavie reports no conflicts of interest.

 

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