Aging while exercising? Great. Just be sure to reevaluate your routine.

It’s smart to follow Fonda’s lead and adjust your approach to physical activity as you age. But you needn’t—and shouldn’t—wait till you’re an octogenarian to do so. Instead, think about recalibrating by about 55.

“I think we have to make peace with the fact that we’re getting older and our bodies are changing. You can’t beat yourself up about that, because it’s useless,” Joan Pagano, a New York City–based exercise physiologist and personal trainer with 35 years of experience in the field, tells Fortune. “You have to say, ‘I don’t have the same body as I did when I was 30, but want to look the best that I can. Let’s find the good things about our bodies.” 

To that end, she says, “We need to think about changing the program to be effective and to be safe.” And women, she adds, need “to address that we start losing protective estrogen, which is a magic superpower in our bodies.” 

It’s this need to change the fitness program with age that inspired kinesiologist and trainer Dan Ritchie, cofounder of the Functional Aging Institute, an Indiana-based fitness facility and trainer certification program. “We saw, 20 years ago, there was a massive shift in our population: The biggest number of people in U.S. history were beginning to turn 60 … So we looked at what the fitness industry was doing and it was woefully unprepared,” Ritchie tells Fortune. “This generation wants to age better than their parents and grandparents did. Now, if you’re 70, you might not even think of yourself as a senior yet.” 

But that doesn’t mean you should be working out with abandon. “Our primary goal is that we want to help you move better, improve balance, and reduce your risk of injury,” he says.

Below, Pagano and Ritchie sound off on what to keep in mind with exercise as you age.

Be open to change—and then mix it up

“People get into a routine that they’re comfortable with, which is understandable,” says Ritchie. “But you have to constantly change your routine, or else your body adapts to it very quickly,” rendering it ineffective.

Pagano, who is 78 and sticks to a combination of strength training, core work, stretching and a run-walk program, advises being well-rounded. She often works one-on-one with clients (who have included Caroline Kennedy and also her mom Jackie Onassis, who wanted to get stronger for equestrianism) who come to her feeling frustrated because their longtime tried-and-true routine no longer seems to be doing its job.

“Strength training, cardio, and stretching are three aspects of a well-rounded fitness program,” she says. 

“There are a lot of different ways you can do that,” notes Ritchie. “You can move resistance with bands and pneumatic equipment, but you have to be stressing the muscular system so bones will grow and stay dense.”

For cardio, Pagano advises doing intervals of higher intensity—which doesn’t need to be a hardcore HIIT class, but could instead be an approach to a walking program. Instead of doing a 30-minute walk five days a week, for example, you’d break it up into 3 minutes at a moderate pace and 3 minutes at a faster pace or jogging, and do that five times in a row.  

But whatever your routine, she cautions against slamming into anything. “You need to warm up, you need to protect joints and work out in proper form, plus develop a progressive program with a gradual progression of strength training exercises. Just adhering to certain precautions, because if you do get injured, you’ll get pulled off course.”

Ritchie adheres to what he calls a functional approach, based on what a client wants to be able to do in day-to-day life. “It doesn’t make any sense for me to put you through an NFL combine prep workout for an athlete if you like to hike and play tennis,” he says. “Instead, let’s look at the activities you want to do well and design a program around that … One 55-year-old might say, ‘I want to compete in track and field,’ and the other might want to be able to play with their granddaughter on the playground. Those goals are different.” 

Others might be motivated by vanity, he says. “If that’s really important then we’ve got to be working on the nutritional component, because I think people make a big mistake of thinking, ‘exercise will help me get back into shape like when I was 30,’ which is really overselling fitness’s ability.” Also necessary: eating, sleeping, and managing stress well, all of which are important as your body composition and hormones change with age—including for men, who typically see these shifts a bit later in life than women. 

Finally, says Ritchie, by sticking to the same routine for years and years, you run the risk of avoiding “progressive overloading,” in which you overload the system, in a positive way, to continually stimulate it and help it adapt. “If all you’re doing is the treadmill and some strength machines, why would you expect any results after 10 years?” he says. Instead, it’s important to try “new games, new challenges, a new dance step, with an exercise program tailored toward that.” 

Be aware of personal risks and be your own advocate

The specifics of a well-rounded routine should be based on your personal health risks and issues. “Ask, what do I need for cardio if I’m at risk for heart disease? Am I stretching enough? What about my bones? Look at those areas and personalize the routine, and find a professional who could give you some sort of an assessment,” Pagano advises. “Once you see the goals and take into account your medical history, that’s a good start.” She adds that women should aim for a baseline bone-density scan at 50.

“Especially because when women lose estrogen in the five to seven years post-menopause, we can lose two to three percent of bone density per year—which means we lose 21% of our skeleton,” she says. “And strength training is one thing that has been proven, over and over, to preserve and even regain bone density.” 

After getting a thorough physical assessment, Pagano advises finding support in your workout—and choosing an instructor or trainer wisely. “Ask them: ‘What is your background? What are you certified in? Do you have experience working with older women or women with osteoporosis?’ Some of these young guys don’t relate and they will push, but you have to respect your body’s wisdom.” 

There are some specific movements that are ill-advised for women with osteoporosis, for instance, such as twisting, crunching or bending all the way over. So knowing your specific risks is important, Pagano says, stressing that there are plenty of modifications for every issue, as long as you go slow, and not to abandon movement altogether for fearing of getting hurt.

“You have to push back against the aging process to make headway, but you have to do it in a safe way, understanding your own personal limitations and what lack of estrogen, for example, can cause, or incipient heart disease,” she says. “You have to know your risk factors.” 

But bottom line, as Fonda advised on Louis-Dreyfus’s podcast: “Keep exercising. You’ve got to stay strong.”

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