Sweat Equity: How exercise can stall aging and help overall health. (ALAMY)

It’s inevitable: As you get older, you slow down. A 40-year-old runs more slowly than a 20-year-old. A 70-year-old can’t be expected to keep up with a 50-year-old on a bike or a hike. It’s only natural.

Well, no, it’s not.

While you can’t defy aging’s impact on your speed and fitness forever, research shows that you can push back, hard. You can markedly slow your decline and postpone tumbling off the fitness cliff that some people encounter in old age. And the gains may transfer from athletics to the tasks of daily life.

The tonic, you won’t be surprised to learn, is regular, lifelong exercise to condition your cardiovascular and neuromuscular systems. At least one study suggests the amounts, types and frequency of the workouts necessary to maintain speed and fitness. You’ll benefit from regular, several-times-a-week exercise whenever you start, but beginning early in life and sticking with a program appears to hold the greatest value.

When Scott Trappe, director of the human performance laboratory at Ball State University in Muncie, Ind., and colleagues tested nine elite, lifelong athletes older than 80, they found their cardiovascular fitness to be “comparable to non-endurance-trained men 40 years younger.” The level of conditioning of these athletes — all had been top-flight cross-country skiers, and one had been an Olympic champion — was “associated with lower risk for disability and mortality,” according to Trappe’s 2012 paper in the Journal of Applied Physiology.

A major reason for that is the strength of their well-conditioned hearts. “Once you get to late middle age, 45 to 60, the heart starts to shrink and stiffen,” said Benjamin Levine, director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital in Dallas. “And that makes it less able to expand when you start pumping blood back to it, and therefore you can’t send as much volume” to the muscles.

“People who have trained their whole lives, they can prevent that from happening,” he said.

Slowing a decline in fitness

Dee Nelson of Gaithersburg, 69, started racing at age 34 and ran her first Cherry Blossom 10-miler in 76:55 in 1985. Ten years later, she ran the same race in 73:32, according to meticulous records she has kept of the 1,490 road races she has run. She has begun to slow in recent years but has stayed ahead of most of her peers. She finished the 2013 Cherry Blossom April 7 in 87:11, good enough for third place in her age group.

“I pretty much run to exhaustion, but I don’t feel any pain,” Nelson said. “My health is the most important thing I have, and I think that’s why I’ve been running all these years.”

Nelson may be a genetic outlier — in 2009, she set an age-group record in the gold standard fitness test at Dallas’s Cooper Clinic — but she also has followed a training regimen developed by the clinic’s founder, Kenneth Cooper, that emphasizes the preventive power of fitness.

Four or five workouts a week — one of them speedwork, one of them a long, slow distance run — appears to provide the optimal defense against declining speed and cardiac strength, Levine said. (Most experts also recommend two weekly strength training sessions to maintain muscle and bone fitness, but Levine did not study that.)

Nelson trains only nine to 12 miles per week and races nearly every weekend. The competitions condition her heart, nervous system and the fast-twitch muscle fibers in her legs as if she were doing a tough speedwork session.

In one study, Levine examined casual exercisers, who worked out two to three days a week; committed exercisers, who participated in four to five sessions weekly; sedentary people, who exercised fewer than two times a week; and elite masters athletes, who worked out six or seven times a week. He tried to determine how much exercise prevented stiffening of the heart’s left ventricle, which has been linked to cardiovascular problems in the elderly.

“We found that two to three days, unfortunately, did almost nothing for you,” said Levine, who also is a professor of cardiology at the University of Texas Southwestern. “But four to five days a week got you most of the way there.”

In another study, Levine and colleagues compared the impact of 30 years of aging with the effects of three weeks of bed rest. He looked at five men who were put on three weeks of strict bed rest in 1966, at the age of 20, to study how that lack of activity affected healthy individuals. Thirty years later, he tested their ability to use oxygen (VO2 max), their cardiac output and their body fat composition.

The results of this study, which were published in 2001, clearly showed that the bed rest was far more damaging to their aerobic fitness than three decades of aging, reinforcing the notion that what we consider a normal decline in physical fitness is actually the result of too little activity.

“Much of the age-associated decline may be avoidable or reversible with regular exercise,” the researchers wrote.

Gaining speed, or slowing its decline, depends, of course, on how fast you are when you start. Someone who is doing no exercise will certainly improve his speed and fitness as he begins any form of cardiovascular training.

But such people aside, most exercisers can expect their fitness profiles to follow a rough bell curve over time, said Lisa Reichmann, a running coach and co-founder of Run Farther and Faster, a running program in Rockville.

Training makes a difference

Less naturally talented athletes and others who aren’t training efficiently can be boosted toward their proper spot on that curve, she said. “If you haven’t worked out in a while or you haven’t been properly trained, you’re going to be below” the curve, she said. “And if you get proper training, you can improve.”

As I have grown older and heavier, and concentrated on running longer distances, I have noticed how sharply my speed has fallen off. Ten-minute miles several years ago have become 10:45 or even 11:00 today at age 55, which makes a 10-mile run a nearly two-hour endeavor.

In preparing to do this story, I decided to see what Reichmann and program co-founder Julie Sapper could do for me in two months of training. I had only one request: “Make me faster.”

After I filled out a detailed questionnaire, they designed a six-day-per-week training schedule that included one day of speedwork, two days of core-strengthening exercises and three days of roadwork, including a weekly long run (seven to 10 miles) and a weekly medium-long run (five to seven miles). They also sent me recommendations on eating more healthfully, which I utterly failed to adopt.

The workouts sound like a major time investment, and they are, but they comprise the kind of regimen that research suggests is necessary to stave off the most debilitating conditions of old age.

I already was running long and slow perhaps three or four times a week. The core work was enjoyable, except for the lunges. I hate lunges.

Speedwork is another matter. “Neuromuscular capability and VO2 max [the best measurement of aerobic fitness] are intertwined,” Sapper said. “A lot of [improving] VO2 max is teaching your body to run in that uncomfortable place where you feel like you’re going to throw up.”

My seven weekly speedwork sessions started with four 400-meter runs, or one lap around an outdoor track, at a designated pace and ended with four 800s. In between I did five 1,000s and a “ladder” of various distances at designated paces, among others.

To measure the results of my work, I signed up for a way-too-hilly 6.2-mile run in Boonsboro, Md., and was pleased with the result: 59:27, significantly below the 10:20-per-mile target time the coaches had given me. Even if the course was a little short of 6.2 miles, as I suspect, I still finished in less than 10 minutes per mile on difficult terrain, considerably faster than I had been running only two months earlier.

“We’ve seen tremendous fitness gains from someone just adding speedwork to an endurance base,” Reichmann said.

Levine said that such gains are transferable to the tasks of everyday life. It stands to reason that if I can improve my running speed, housework or dancing also should be easier, he said.

Will this keep me young? It’s hard to say. A recent study by researchers at West Virginia University School of Medicine showed that while baby boomers are living longer than their parents, they are spending more of their lives with chronic illnesses and disabilities, most likely because they are more sedentary and obese than the previous generation.

It may be that exercise compresses that period of chronic illness and postpones the inevitable drop off the “fitness cliff” until we are very old. That seems like a chance worth taking.