That’s the message from new research published this week in the Archives of Internal Medicine, which examined the connection between a person’s fitness level at midlife and their risk of chronic illness after the age of 65. “We’ve known for years that if you exercise, you’re likely to live longer,” says Jarett Berry, MD, an assistant professor of internal medicine at UT Southwestern Medical Center and senior author of the study. “But not as much is known, yet, about fitness’ influence on how healthy those last years are.” As it turns out, that influence appears to be profound. Researchers looked at health data of 18,670 study participants, all of whom performed a fitness test—based on their pace and endurance on a treadmill—around the age of 50. The team then tracked the Medicare claims of those same people from age 70 to 85. The results? Those who’d aced the fitness test were significantly less likely to have come down with a chronic illness, including heart disease, Alzheimer’s, and diabetes. More from Prevention.com: Would You Recognize The Signs Of Alzheimer’s?   And ladies, listen up: The incidence of chronic disease among fit women was a stunning 43% lower than their less-fit-at-middle-age counterparts. “It really comes down to quality of life,” says Dr. Berry. “And our study suggests that if you’re less fit now, there’s a greater risk that you’ll pay with reductions in quality of life later.” So if you aspire to be the grandma who’s still kicking butt at 90, how hard do you need to work now? Hard enough to break a serious sweat, Dr. Berry says. “In general, higher-intensity exercise boosts fitness levels more than lower intensity,” he says. “So jog, don’t walk.” (See how to turn your walk into a run—and drop a size in four weeks.)   And, of course, do it consistently: Federal guidelines recommend 75 weekly minutes of vigorous activity, which translates to three twenty-five minute sweat sessions. If that sounds like a slog now, consider how great it’ll leave you feeling in your golden years. “Don’t put it off, and tell yourself that you can get fit later,” says Dr. Berry. “The time to get started is now.” Ready to get started? Check out A Better Body For Busy Women  Follow her on Twitter: @katiedrumm Send news tips and positive vibes to: Katie.Drummond@rodale.com