Bonnie Knutson, age 75, works out with a personal trainer three times a week.

At 5-feet, 3-inches tall, she can bench press her weight of 105. A business professor at the Michigan State University, Knutson works hard and plays hard, regularly getting down on the floor to wrestle with her grandchildren.

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“I’m always moving,” Knutson said. “Before I started weight training about 20 years ago, I was pre-osteoporosis, and within 18 months my bone density was back in the normal range. I attribute it to weight training.”

A new study finds that weight lifting is good for the body and the brain. Research from of the University of British Columbia in Vancouver shows lifting weights can help cognitive function in older adults.

Related: Stairway to Longevity

During the study, researchers looked at three groups of women between the ages of 65 to 75 — women who pumped iron once a week, women who lifted twice a week, and those who did nothing at all. After a year, they did brain scans on the entire group and found that the women who worked out twice a week had fewer signs of common aging.

At 75 years old, Knutson can leg press 485 pounds.

“There have been studies showing it’s good for the bones,” Teresa Liu-Ambrose, director of the Vancouver lab, told LifeZette. “But now we see in older adults that it improves brain health and brain function.”

Other studies show you can put some spring in your step, and possibly extend your life, by reducing calories and by strength training.

“Like our thyroid or adrenal glands, muscle produces unique messengers,” said Dr. Robert Huizenga, a Los Angeles physician in Los Angeles and a consultant on the television show “The Biggest Loser.”

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“Specifically, muscles send signals that combat diabetes and depression, and basically let us live longer and stay smarter,” he said.

Related: Pump it in the P.M.

Personal trainer Lori Michiel agrees. Michiel’s runs a thriving fitness business in West Hills, California, that specializes in keeping older adults and seniors in shape.

“Weight training, especially on the lower body, is critical because it can strengthen the muscles supporting the hips,” said the 61-year-old National Academy of Sports Medicine certified personal trainer.

The woman behind Lori Michiel Fitness warned that while lifting weights is critical for seniors, every client must be evaluated for his or her particular health needs. Whether a client is perfectly healthy or dealing with ailments like arthritis or a heart condition, it’s critical to take that information into account before starting a workout routine.

“As we get older, it’s important to stay in good shape, but it’s more important to be safe before anything else,” she said.