Top 12 Weight-Training Tips for Women

June 17 -- It usually starts when a woman enters her mid-30s. Muscles begin to fade. A quarter to a third of a pound of muscle is lost per year — every year.

"Women become disabled. We get osteoporosis, diabetes, and obesity largely because we're losing this muscle," Miriam Nelson, an associate professor of nutrition at Tufts University, told ABCNEWS' John McKenzie.

But recent research assures women that they need not give in to aging. Pumping iron is now a proven prescription.

A recent study, published in the Journal of the American Medical Association, found that post-menopausal women can reduce their body fat, increase muscle mass, build up their bones, and improve their balance by lifting moderately heavy weights on a regular basis.

"Biologically, these women were about 20 years younger then they were at the start of the year," says Nelson, expert and lead author of the study.

Experts say the benefits of weight training are now indisputable, to both prevent the effects of aging in pre-menopausal women and reverse the effects of aging in post-menopausal women.

To find out how women can get the most out of weight-training sessions, ABCNEWS.com asked three exercise experts — Johanna Hoffman, an exercise physiologist at the Johns Hopkins Weight Management Center in Lutherville, Md.; Dr. Edward Laskowski, co-director of the Mayo Clinic Sports Medicine Center in Rochester, Minn., and a specialist in physical medicine and rehabilitation; and Dr. Paul D. Thompson, director of preventive cardiology at Hartford Hospital in Hartford, Conn. — their top training tips. Here are their top 12 tips:

1) Set a Goal. Decide what you want to get out of your workout. Are you after Jennifer Aniston's arms or a job with World Wrestling Entertainment? Are you lifting weights to improve function, health, appearance, or sports performance? Once this has been determined, you can better tailor your routine, choosing exercises that will target the proper muscles.