What’s the best way to exercise if you want to remain healthy? Men who exercised moderately had a lower risk of heart failure than men who exercised either more or less strenuously, a new Karolinska Institutet study finds.

Heart failure, also referred to as congestive heart failure, sounds like the heart stops completely, but that isn't the case. This condition occurs when the heart becomes too weak to pump as much blood as the body needs, causing shortness of breath and difficulty walking. Around the globe, 23 million people suffer from heart failure each year, including almost six million Americans. On average, the researchers note, each of us has a 20 percent lifetime risk for developing heart failure. What can be done to prevent it?

To understand whether exercise would help or hurt — past studies show conflicting evidence — the Karolinska researchers tracked 33,012 men from the Cohort of Swedish Men from 1998 through 2012. To begin the study, participants from just two counties in Sweden completed a questionnaire about their level of activity at work and at home. An average age of 60, the participants listed the amount they had exercised in the year prior as well as the year they turned 30. Specifically, they focused on how much they walked and biked. Collecting these surveys, the researchers assigned each type of physical activity an intensity score and then they analyzed data.

Surprisingly, they found what they referred to as a “U-shaped association” between exercise and heart failure. Surprisingly, men who had the lowest and highest levels of physical activity had a higher risk of heart failure, 47 percent and 51 percent respectively, than men at the median level.

Walking or bicycling just 20 minutes per day was associated with a 21 percent lower risk of heart failure, the researchers discovered. And, this very same level of activity accounted for the largest difference in heart failure-free survival. Looking only at the men diagnosed with heart failure during the study, the researchers noticed a trend. Those who had spent at least 20 minutes each day walking or bicycling were approximately eight months older than the heart failure cases who walked or biked less than 20 minutes each day.

Occupation, household work, and physical inactivity were not significantly associated with heart failure development. Researchers also found that men who were active at 30 years old but were inactive at the time of study enrollment did not have a decreased risk of heart failure.

Analyzing the different types of activities, the researchers found walking or bicycling for 20 minutes per day was associated with the largest risk reduction. Only “certain types of physical activity are associated with a protective effect on heart failure in men,” concluded the authors.

Source: Rahman I, Bellavia A, Wok A, Orsini N. Physical Activity and Heart Failure Risk in a Prospective Study of Men. Journal of the American College of Cardiology: Heart Failure. 2015.