Too much high-intensity exercise may adversely affect heart health

Two new studies indicate that prolonged high-intensity exercise could lead to adverse CV consequences.

In one study, researchers found increased risk for adverse CV outcomes for adults who engage in daily strenuous physical activity, as well as adults who are physically inactive. Another study demonstrated that men who participated in more than 5 hours per week of endurance exercise had an elevated risk for developing atrial fibrillation, especially if they quit exercising later in life.

Exercise and CV events, death

Ute Mons, MA, from the German Cancer Research Center, and colleagues analyzed the association of self-reported physical activity level with CV prognosis in a prospective cohort of 1,038 patients with stable CHD. They analyzed the frequency of strenuous leisure-time physical activity during a 10-year follow-up period and correlated activity levels to outcomes such as major CV events, CV mortality and all-cause mortality.

The highest levels of incidence of poor outcomes per 1,000 person-years occurred among patients who rarely or never exercised (major CV events, 46.4; 95% CI, 32.3-66.8; nonfatal CV events, 18.9; 95% CI, 9.8-36.3; CV mortality, 29.1; 95% CI, 19.4-43.8; all-cause mortality, 44.3; 95% CI, 31.8-61.7). Compared with patients who exercised two to four times per week, those who rarely or never exercised had an increased risk for major CV events (HR=2.05; 95% CI, 1.2-3.51), nonfatal CV events (HR=2.51; 95% CI, 1.38-4.56), CV mortality (HR=3.3; 95% CI, 1.61-6.78) and all-cause mortality (HR=3.92; 95% CI, 2.26-6.79).

However, when the researchers’ analysis included time-dependence of physical activity, a reverse J-shaped association of physical activity with CV mortality was observed. Compared with patients who exercised two to four times per week, the HR for CV mortality for those exercising daily was 2.36 (95% CI, 1.05-5.34).

“Consistent with results of previous studies … we found that higher frequencies of physical activity did not confer additional benefit beyond that of physical activity of moderate frequency and duration, which suggests the existence of an upper limit for benefits,” Mons and colleagues wrote.

Exercise and AF

Nikola Drca, MD, from Karolinska University Hospital in Stockholm, and colleagues obtained information about physical activity from 44,410 men aged 45 to 79 years who were free of AF at baseline in 1997. Each participant was polled on leisure-time exercise and walking/biking at age 15 years, 30 years, 50 years and at baseline.

During a median follow-up of 12 years, the researchers determined who was diagnosed with AF and compared that outcome by level of physical activity.

Compared with men who engaged in moderate to intense physical activity for less than 1 hour per week at age 30 years, 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 engaged in moderate to intense physical activity for more than 5 hours per week at age 30 years, but for less than 1 hour per week at baseline (RR=1.49; 95% CI, 1.14-1.95).

Men who reported walking or bicycling for more than 1 hour per day at baseline had a lower risk for developing AF compared with men who almost never did so (RR=0.87; 95% CI, 0.77-0.97). The results did not change when men with previous CHD or HF at baseline were not included, according to the researchers.

Although exercise can protect against AF through positive effects on CV risk factors such as obesity, hypertension, hypercholesterolemia and diabetes, “there are many mechanisms through which frequent high-intensity exercise might increase the risk of AF, including left atrial enlargement, left ventricular hypertrophy, [LV] dilation, inflammatory changes in the atrium, and … an increase in parasympathetic tone,” Drca and colleagues wrote.

In a related editorial, Eduard Guasch, MD, and Lluis Mont, MD, PhD, from the University of Barcelona, Spain, noted that an important limitation of both studies is that they relied on self-administered questionnaires to determine physical activity.

“Research aiming at providing a safety threshold that avoids ‘exercise overdose’ and permits maximization of benefits is warranted,” they wrote. “In the clinical setting, an individualized mechanistic approach aiming to identify individuals at risk and detect the development of a deleterious substrate might better serve to titrate an optimal individualized dose of exercise” than the thresholds from both studies.

For more information:

Drca N. Heart. 2014;doi:10.1136/heartjnl-2013-305304.

Guasch E. Heart. 2014;doi:10.1136/heartjnl-2014-305780.

Mons U. Heart. 2014;doi:10.1136/heartjnl-2013-305242.

Disclosure: One researcher from the AF study reports consulting for Medtronic. The other researchers, Guasch and Mont report no relevant financial disclosures.