"People with heart failure can regain 70% of their exercise capacity if they stick to an exercise program," says Axel Linke, MD, an assistant professor of medicine at the University of Leipzig in Germany. Linke worked on both studies.
"These studies show that the benefits come from both the regeneration of muscle cells and the formation of blood vessels," he says.
The research was presented here at the American Heart Association's (AHA) Scientific Sessions 2007.
Heart Failure and Skeletal Muscles
About 5 million Americans have chronic heart failure, a condition in which the heart is unable to pump blood properly and keep up with the body's demand for oxygen.
The condition weakens more than just the heart: The skeletal muscles also deteriorate, says past AHA president Robert Bonow, MD, chief of the division of cardiology at Northwestern Memorial Hospital in Chicago.
One reason for this is the patient's weak condition makes it difficult to exercise, he says.
But there are also cellular-level changes in the muscles that make patients weaker, even prone to shrinkage, Bonow says.
Exercise Builds Skeletal Muscle
In one study, the researchers investigated whether exercise training could activate progenitor cells, a pool of immature cells in skeletal muscle that can divide into mature cells as needed for muscle repair.
People with heart failure have about half as many progenitor cells in their muscles as healthy people, Linke says.
The six-month study involved 50 people with moderate to severe heart failure -- a level at which any exercise is uncomfortable. Half remained inactive and half participated in an individualized, doctor-supervised exercise program. They rode a stationary bicycle at least 30 minutes a day at about half their peak exercise capacity.
Biopsies of their thigh muscles showed that levels of progenitor cells stayed the same in the inactive group.
In the exercise group, though, the number of progenitor cells actively dividing to form new cells and repair muscle damage increased sixfold.
"That's exactly what patients with heart failure need -- replacement of muscle cells," Linke says.
Linke says this translates into appreciable benefits. He recalls one patient whose son had to carry him up the stairs. When he started the exercise program, he could barely pedal on a stationery bike.
After three months, the man could climb the stairs again. "No medication can do this," Linke tells WebMD.
Exercise Helps Blood Vessels
In the second study, researchers found that a 12-week exercise program increased the production and activity of progenitor cells that spur new vessels to form in skeletal muscle.
The study involved 37 men with severe heart failure who were randomly assigned to three months of exercise or to remain inactive.
Linke says that before they started exercising, participants' exercise capacity was similar to that of people in need of heart transplants.
The exercise program boosted their exercise capacity by an average of 35%, giving the men about three-fourths the capacity of healthy men their age.
Bonow says that despite AHA recommendations, many heart failure patients fail to exercise and enter a cardiac rehabilitation program. "Here's some evidence showing exercise works," he says.
Nevertheless, this is a surrogate measure of improvement, he says. The real question, which is being tested in a trial sponsored by the National Institutes of Health, is whether exercise actually prevents hospitalizations and deaths, Bonow says.
Linke stresses that people with heart failure need to check with their doctor before embarking on an exercise regimen.