Weight training has gained attention in recent years as a way to prevent bone loss in postmenopausal women. Now experts say that this type of exercise is crucial for everyone.

In issuing updated, broad exercise guidelines for children and adults, the American College of Sports Medicine emphasized not just the benefits of cardiovascular exercise but the advantages of resistance training, as well. Resistance training doesn’t always mean weight workouts — it also refers to using one’s own body weight in exercises such as push-ups.

Children, especially those who are pre-pubescent, should do impact activities such as jumping, combined with moderate resistance training at least three days a week for 10 to 20 minutes, the guidelines suggest. However, kids shouldn’t adopt a “no pain, no gain” policy — the organization suggests not lifting more than 60 percent of the maximum amount one can lift.

“These types of exercise have been shown to increase bone mineral during pre-puberty,” says Wendy M. Kohrt, professor of Medicine at the University of Colorado Health Sciences Center and lead author of the guidelines, published in this month’s issue of Medicine & Science in Sports & Exercise. Those years are critical, she says, “because the system is primed to grow.”

Adults should do weight-bearing endurance activities (tennis, jogging) three to five times a week, and resistance training (weight lifting) two to three times a week at a moderate to high intensity for 30 to 60 minutes a day combined, the organization recommended.

Kohrt also encourages the elderly to keep physically active. Although evidence isn’t conclusive that moderate exercise later in life will build bone density, older people can reduce their chances of falling, which, says Kohrt, “has the same outcome as preventing fractures due to osteoporosis.”