One sneaker fits all.
Or according to government recommendations, you should do at least 2 1/2 hours of moderate aerobic activity per week and twice-weekly sessions of strength training to improve your health, no matter your age.
But don't physical fitness needs change as we grow older?
Not that much, it turns out.
Todd Miller, an associate professor in the Department of Exercise Science at George Washington University, says whether you're 20 years old or 60, you will need a combination of cardio and strength training to keep your heart and muscles in good shape and your weight under control.
The one difference may be that strength training becomes more crucial for everyday functional fitness as you get older.
"A big issue as you age is the risk of falling. And strength training that builds muscle power helps prevent falls," he says.
"People should do a combination of both cardio and strength" to meet those fitness goals, he says, but in general he sees an "overemphasis on cardio and underemphasis on strength."
The challenge, Miller says, is not deciding whether fitness needs are age-specific. It's getting people to do what they should do, at any age, to stay healthy and fit.
Only about 20 percent of Americans follow the government recommendations.
As you try to figure out a regime that keeps you healthy, here's some advice from three people — Miller, a trainer and tennis great Martina Navratilova — that may help you at any age.
The professional athlete
"As we age, we should exercise more often but for shorter periods of time," says Navratilova, 56, who writes a health and fitness column for AARP.
"And mix up your routine. Do strength, cardio, yoga. Do what feels good in the body, go easy on the joints," she says.
That's actually pretty much in line with government recommendations. "We know 150 minutes each week sounds like a lot of time, but you don't have to do it all at once. Not only is it best to spread your activity out during the week, but you can break it up into small chunks of time during the day. As long as you're doing your activity at a moderate or vigorous effort for at least 10 minutes at a time," says the Centers for Disease Control and Prevention, which recommends "a 10-minute brisk walk, 3 times a day, 5 days a week. This will give you a total of 150 minutes of moderate-intensity activity."
Navratilova says that when she was in her 20s, she worked out six hours a day and could do 70-pound triceps presses. No more. "Daily exercise? I don't do anything daily except eat and sleep," she says, joking.
"But I do think if you can do functional fitness — exercises designed to help someone better handle daily tasks — for an hour a day, that is great," she says. But for aging bodies, she adds, don't overdo it. "Be nice to yourself and listen to your body."
Navratilova says she recently began running again after a hiatus. "Nothing feels better than when you can run," she says. "But every day? Absolutely not. It's hard on your joints."
Now living in Miami, she mixes it up by adding bicycling and paddleboarding to her running and tennis cardio regimen.
Mike Fantigrassi, a trainer at the National Academy of Sports Medicine in Chandler, Ariz., says he makes balance and flexibility exercises a regular part of sessions with clients, but it's different for younger and older people.
"If we have 60 minutes, we would do about five minutes of flexibility for someone in their 20s or 30s," he says. "For someone 65 or older, we might do up to 15 minutes of flexibility."
It's not that the 20- or 30-year old should go completely without stretching (particularly of the postural muscles — chest, core, neck and shoulders — that get tight from sitting at a desk all day) or working on balance, he says. But younger bodies, generally speaking, are naturally looser than older ones and have not been subjected to as much wear and tear.
So when a 20-year-old reaches down to pick something up off the floor, he probably won't notice anything, but a 60-year-old may feel a tight hamstring.
Fantigrassi, who is 40, adds that the ability to generate muscle power suffers as we age, but we can slow the process down with such exercises as jumps — from foot to foot, or up and down from a bench or box. Eventually you're going to lose your basketball jump shot, but you can keep it alive longer by training the leg muscles that generate power.
Miller, 45, says that while building stronger muscles is protective for older people, strength training is important for everyone.
People begin to lose muscle mass and strength in their 30s, which slows metabolism. WebMD.com says that "each extra pound of muscle you carry can burn up to 50 additional calories — per day — just to maintain itself. Others, however, suggest that the muscle effect is probably much smaller.
Lifting weights can counteract muscle loss. Of course, you still may not be able to lift as much weight in your 60s as you could in your 20s, but you can slow muscle loss, which otherwise can decline by 5 percent per decade after age 30.
"The only difference between 20 and 60 is that you might be lifting less weight at 60. But the exercises themselves shouldn't change unless you have an injury, but that isn't age related," says Miller.
Strength training will also improve bone density, says Miller, who advocates the type of strength exercises where the feet are planted on the floor and generate force into the spine. It could be a regular squat. It could be a squat with dumbbells in your hands, resting on your shoulders. It could be one of those squat machines with padding on top of the shoulders.
Given that most Americans gain roughly a pound per year starting in their 20s, it's important at all ages to have cardio workouts in your week.
"If running feels good, then run," Miller says. Just make sure it feels OK in your joints. Whatever you choose, he says, the point is to get regular exercise no matter what age you are.