Middle aged and out of shape? It's not too late to get fit - and reduce your risk for heart failure, according to research presented at the American Heart Association's Quality of Care and Outcomes Research Scientific Sessions 2013.

Researchers ranked fitness levels of 9,050 men and women (average age 48) who took two fitness tests - eight years apart - during mid-life. After 18 years of follow-up, they matched the fitness information to Medicare claims for heart failure hospitalizations.

"People who weren't fit at the start of the study were at higher risk for heart failure after age 65," said Ambarish Pandey, M.D., lead author of the study and an internal medicine resident at the University of Texas Southwestern Medical Center in Dallas. "However, those who improved their fitness reduced their heart failure risk, compared to those who continued to have a low fitness level eight years later."

The researchers used metabolic equivalents (METs), a measure of how people do on a treadmill test. For each MET improvement in fitness, participants' heart failure risk dropped by 20 percent. For example, if a 40-year-old went from jogging 12 minutes per mile to running 10 minutes per mile - an increase of two METs - he or she reduced heart failure risk at a later age by 40 percent, Pandey said.

As more people survive heart attacks and live with heart disease, the number with heart failure is increasing. More than 5.1 million Americans live with heart failure, according to the American Heart Association, and by 2030, the prevalence of heart failure may increase 25 percent from 2013 estimates.

"Improving fitness is a good heart failure prevention strategy - along with controlling blood pressure and improving diet and lifestyle - that could be employed in mid-life to decrease the risk of heart failure in later years," Pandey said.