When Barbara Hannah Grufferman was in her early 50s, a bone density scan showed that she was on a path to developing osteoporosis. If she didn’t change her lifestyle, her bones would become increasingly brittle, putting her at high risk for spine, hip and other life-altering fractures.

Grufferman had always been active, chasing after her two daughters and walking her dog around Manhattan. But she hadn’t done much formal exercise since “the Jane Fonda days” of her 20s, she said.

Once she learned about her low bone density, she began training to run-walk the New York City Marathon and started doing daily planks and squats. She practiced standing on one foot whenever she could, to improve her balance. Today, more than 15 years later, her bone density has held steady and she’s training for her 18th marathon.

“I’m a walking, talking, breathing example that it’s never too late to take action,” Grufferman, 67, said.

But you don’t have to run marathons to protect your bones. Simply adding a few strategic exercises to your routine can support them — now and in the future.

“People think of bone as this static thing,” said Dr. Andrea Singer, chief medical officer of the Bone Health and Osteoporosis Foundation. But “it’s a living, dynamic organ that is constantly remodeling.”

As with your muscles, the more you strategically stress your bones with exercise, the stronger they become, she said.

Everyone’s bones weaken with age, but 80% of Americans with osteoporosis are women, and half of women older than 50 will break a bone because of the disease. Women reach their peak bone density in their early 20s. The biggest decline happens in the five to seven years after menopause, when levels of estrogen, which help to keep bones robust, plummet.

The earlier in your life you start building bone strength, the better — but it’s also never too late, experts said. If you have already been diagnosed with low bone density, if you’ve fractured bones in the past or if you have osteoporosis, speak to your doctor about the best workout plan before starting anything new.

For cardio, gravity is your friend

While most exercise is good for your bones, workouts that require your body to support its own weight are especially effective for bone strength, experts said. This helps explain why astronauts’ bones weaken in space and why they spend two hours a day exercising.

“Bone is very, very adaptive,” said Rebekah Rotstein, a Pilates instructor and creator of Buff Bones, a fitness program to help women build bone strength, who has worked with hospitals across the country. “It responds to external forces by getting stronger, and the lack of force will weaken it.”

If you’re new to aerobic exercise, or getting back into the swing of it — or if you’ve already been diagnosed with low bone density — start by walking, said Dr. Mary O’Connor, emerita professor of orthopedics at the Mayo Clinic and the chief medical officer for the telehealth company Vori Health. Carrying hand weights can help to strengthen the bones in your upper body as well.

If you work out regularly and haven’t been diagnosed with low bone density, cardio that puts more force on your body is ideal for strengthening bone. Running and jumping exercises (for example, box jumps or jumping jacks) are good options. Workouts that involve moving in multiple directions — think dance, tennis or pickleball — are even better.

“Surprising your body with new movements, in different directions, has a better, more efficient effect in building bone than doing hours and hours of repetitive activity,” said Dr. Kathryn Ackerman, an associate professor of medicine at Harvard Medical School who studies bone health.

If your bones are already fragile, high-impact exercises may put you at greater risk of fracture “because they’re putting more stress on the bone,” O’Connor said. Talk to your doctor about what your body can handle.

Regularity is also key, since bones must be stressed constantly to stay strong. Rather than stacking workouts on the weekends, do roughly 30 minutes of daily weight-bearing cardio to support bone health.

Build muscle to build bone strength

Resistance training strengthens your bones in addition to your muscles — which, in turn, strengthen your bones more by putting additional force on them, experts said.

“We used to be really nervous about older women, in particular, and having them do too much” or lift too much, Ackerman said. “We did them a little disservice because they got nervous to move, because they thought they would break.”

As part of her Buff Bones program, Rotstein recommends regular squats, hip hinges, lunges, calf raises, planks and push-ups. Pay extra attention to form, so that your joints and bones are in proper alignment.

These exercises strengthen the muscles that are essential for daily activities, Rotstein said, including sitting, standing, bending to pick up objects and reaching for items on a shelf.

Consider free weights or machines as well, Ackerman said, but start slow. As you age, these daily activities can lead to fractures if your bones and muscles aren’t strong yet.

Boost your balance

A well-rounded bone health workout should include exercises designed to keep you stable on your feet. This can help to prevent falls, which can be particularly devastating to your bones as you age, Ackerman said.

Single-leg balances, weight shifts, Pilates and yoga are all helpful for cultivating balance, experts said. And research suggests tai chi may be effective, too.

If you have weak bones, avoid bending and twisting.

Finally, if you’ve already been diagnosed with osteoporosis, avoid movements that involve bending all the way forward from the waist and quick twists. “Most hip fractures in older, osteoporotic women — what we would call fragility hip fractures — happen before the fall,” O’Connor said. “So someone stands, they turn, their hip breaks, and they fall.

“Our bones are weakest in torsion.”

But try not to let fear of fracture discourage you from moving at all, she said. With a few precautions, staying active now is what will keep you active for years to come.