Heart disease continues to be one of the country's most serious health problems and the leading cause of death. Approximately 84 million people in the U.S. suffer from some form of cardiovascular disease, causing about 2,200 deaths per day, with one-third of cardiovascular disease deaths occurring before age 75. About half of those who develop heart failure die within five years of diagnosis.

Aging impacts the cardiovascular system as the structures of the heart become more rigid. The muscles of the left ventricle get thicker, the heart may increase slightly in size, and the volume of the left ventricle may decline.

As a result, the heart may both fill and empty more slowly, thus putting less blood into circulation. Sedentary aging can lead to a stiffening of the muscle in the heart's left ventricle (LV), which causes high pressure and an inability of the heart chamber to fill with blood, with a possible result of heart failure.

According to the findings by researchers at the Institute for Exercise and Environmental Medicine (IEEM), which is a collaboration between UT Southwestern Medical Center and Texas Health Presbyterian Hospital Dallas, exercise can reverse damage to sedentary, aging hearts, especially if begun by late middle age (before age 65) when the heart retains some plasticity and ability to remodel itself.

In this study, healthy, sedentary, middle-aged participants (53±5 years, 48 percent male) were randomly assigned to either two years of exercise training or a control group that participated in yoga and balance training.

Right heart catheterization and three-dimensional echocardiography were performed with preload manipulations to define LV end-diastolic pressure-volume relationships and Frank-Starling curves. LV stiffness was calculated by curve fit of the diastolic pressure-volume curve. Maximal oxygen uptake (Vo2max) was measured to quantify changes in fitness.

The regimen included exercising four to five times a week, generally in 30-minute sessions, plus warmup and cooldown. One of the weekly sessions included a high-intensity 30-minute workout, such as aerobic interval sessions in which heart rate tops 95 percent of peak rate for four minutes, with three minutes of recovery, repeated four times. Each interval session was followed by a recovery session performed at relatively low intensity.

One day's session lasted an hour and was of moderate intensity. According to Dr. Benjamin Levine, Director of the Institute and Professor of Internal Medicine at UT Southwestern, and lead author, this longer session could be a fun activity such as tennis, aerobic dancing, walking or biking. One or two other sessions were performed each week at a moderate intensity, meaning the participant would break a sweat, be a little short of breath, but still be able to carry on a conversation.

Exercise sessions were individually prescribed based on exercise tests and heart rate monitoring. One or two weekly strength training sessions using weights or exercise machines were included on a separate day or after an endurance session. Study participants built up to those levels, beginning with three, 30-minute, moderate exercise sessions for the first 3 months and peaked at 10 months when two high-intensity aerobic intervals were added.

At the end of the two-year study (53 participants completed), those who had exercised showed an 18 percent improvement in their maximum oxygen intake during exercise and a more than 25 percent improvement in elasticity of the left ventricular muscle of the heart.

In previously sedentary healthy middle-aged adults, two years of exercise training improved maximal oxygen uptake and decreased cardiac stiffness, suggesting that regular exercise training may provide protection against the future risk of heart failure.