Older Americans who exercise strenuously are more mentally nimble, have better memories and process information more rapidly than their more sedentary peers, new research suggests. And as they continued to age, participants who were very physically active at the start of a five-year study lost less ground cognitively than did couch potatoes.

The study, published Wednesday in the journal Neurology, underscores the importance of moderate to intensive exercise in healthy aging. In addition to keeping diabetes, heart disease and osteoporosis at bay or in check, several studies suggests a good workout prevents and treats depression and shores up cognitive function.

The study parses out the cognitive benefits of moderate to intensive physical activity in an ethnically diverse group of New York City residents with an average age of 71 upon entry into the study. Most were followed for about five years, at the end of which their performance in a range of cognitive domains was compared with their baseline scores.

Intensive exercisers were 10 percent of the study participants. They reported engaging in activities several times a week that were likely to get their heart rates. Those who reported light or no leisure-time physical activity made up the remaining 90 percent of participants.

“If you're thinking strolling, you're not going to make it” into that top 10 percent category, said Clinton B. Wright, a University of Miami neurologist and study's lead author. “You need to do a significant amount of exercise and get your heart rate up to fit into the moderate-to-heavy category.”

When researchers looked only at subjects who had no evidence of cognitive impairment when they enrolled in the study, they found a stark difference in memory function between the highly active and the non-active and lighty active: After five years, exercisers were the equivalent of 10 years younger than the light- and non-exercisers on measures of “episodic memory” function, the ability to recall past experiences and autobiographical information.