Exercise and the Heart: Setting Limits
Written by Editor   
Friday, May 16, 2014 03:41 PM

Exercise is good for the heart, but too much of a good thing could be bad for healthy adults and patients with cardiovascular disease, according to two observational studies that suggest a J-shaped curve for the dose-response effects of intense physical activity.

Research involving stable chronic heart disease (CHD) patients found daily strenuous exercise to be associated with a more than twofold increased risk for cardiovascular mortality compared with moderate (two- to four-times a week) exercise, and high-intensity physical activity early in adulthood, but not in middle-age, was found to be associated with an increased risk for atrial fibrillation later in life in a Swedish trial. The study is one of several linking regular strenuous exercise early in life to increased afib risk.

"The literature over the last 50 years overwhelmingly point toward moderate exercise being extremely beneficial from a cardiovascular standpoint, but it is also increasingly clear that extremes on both ends of the exercise spectrum might be detrimental,"

Widely accepted joint guidelines for patients with stable heart disease, which call for 30 to 60 minutes of moderate intensity aerobic activity, such as brisk walking, 5 to 7 days a week, are based on research showing regular exercise to have a clear positive impact on outcomes in heart patients. But only a few studies have examined the potential benefit of physical activity under real-life conditions.

"These (studies) consistently found the highest risk for adverse outcomes in the most inactive patients, yet the exact dose-response relationship with different levels of physical activity is still unclear," they wrote.

For all outcomes, the highest hazards were consistently found in the least active patient group, with a roughly twofold risk for major cardiovascular events and a roughly fourfold risk for all-cause mortality  in comparison to the reference group of patients who were moderately active (exercised two- to four-times per week).

Patients who reported engaging in strenuous physical activity on a daily basis had a 62% to 78% increased risk for death and a 65% to 2.37% increased risk for CVD death compared with the two- to four-time a week exercising group, in various models.

"When taking time-dependence of physical activity into account, our data indicated reverse J-shaped associations of physical activity level with cardiovascular mortality, with the most frequently active patients also having increased hazards."

Source:  http://www.medpagetoday.com/Cardiology/Prevention/45785