Gravity is good for your bones. Weight-bearing exercise is perhaps the single most important thing you can do to slow the loss of bone density that comes with age.

Gravity is good for your bones. Weight-bearing exercise is perhaps the single most important thing you can do to slow the loss of bone density that comes with age.

Osteoporosis is a severe weakening of the bones that can lead to fractures and complications that often shorten a person's lifespan. One in two women and one in eight men aged 50 and older will have osteoporosis-related fractures, according to the National Osteoporosis Foundation.

Eighty percent of osteoporosis patients are women.

"You deposit into your 'bone bank' through diet and exercise until you're about 30. So teens who don't get enough calcium and don't exercise are at risk," says Kathy Bowlin, a physical therapist with Jackson County Physical Therapy in Medford, who has worked with many women to prevent osteoporosis and rehabilitate from bone fractures.

"Forces put upon the bone create new bone," Bowlin explains.

While basketball, volleyball and running are some of the best bone-building exercises, they are not advised for individuals who already have osteoporosis. Swimming and bicycling are great for the cardiovascular system but do very little for bone health.

"It's also a myth that walking 30 minutes a day will prevent osteoporosis," Bowlin says. "You'd need to walk five to six miles per hour to get that benefit. You can get bone-building benefits from walking by weighting yourself down with either a weight vest or carrying hand weights. Stepping up and down can also help."

Stronger muscles also help build stronger bones, says Carol Lee Rogers, a fitness trainer in Ashland.

"Strength to your muscles promotes solid bone density," says Rogers, who has been teaching osteoporosis prevention for more than five years through the Ashland Parks and Recreation Department. Strength training is the key to her program.

"The greatest bone density comes with a medium-intensity workout," Rogers adds. "You need to fatigue the muscles to gain strength. If you use too high a weight, you'll overstress or damage the joints. If it's too light, you won't get as much of a benefit."

While a person with osteoporosis should consult a doctor before beginning a new exercise regimen, Rogers finds the ideal strength program for most people involves two to three sessions a week. Increases in weight and number of repetitions should occur slowly, she says.

Rogers' program includes squats, forward and sideways lunges, chair raises, heel/toe raises, and step up/down — all designed to strengthen the hip joint. Hips, vertebrae and wrists are by far the three areas where fractures occur most often in some seniors.

"I also recommend wrist curls — both palm-up and palm-down — holding the weight by resting your forearm on your thigh," Rogers says. "Keep your back straight. For the spine, I use lateral raises with palms behind you."

Falls and improper body mechanics cause most fractures in seniors, so Bowlin stresses good form.

"If you bend forward with bad mechanics, you can get a bone fracture. I teach people to bend forward at the waist and to bend down with knees, keeping the spine straight," says Bowlin.

"Try to eliminate twisting. Keep away from golf: twisting under force is a risk for fracturing the vertebrae," Bowlin adds.

Our bones are continually dissolving and rebuilding. Weight-bearing exercise is critical to maintaining that balance, and making use of gravity is essential. Astronauts have learned this the hard way.

Studies at NASA found astronauts lose 1 percent of their bone mass per month when they are robbed of gravity during a space mission. Five years later, their bones had not completely recovered.

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Next month: The role of diet and other factors in preventing osteoporosis