So-called "weight-bearing" exercise, which includes high-impact sports like soccer, may be best when it comes to helping girls build strong bones, researchers say.

"Beyond the basic premise that kids need exercise, our study suggests that weight-bearing exercise with skeletal impact needs to be promoted during youth to preserve future bone health," researcher James W. Bellew of Louisiana State University in Shreveport said in a prepared statement.

The study compared the bone mineral density (BMD) of three groups of adolescent female athletes: 29 swimmers, 16 soccer players, and 19 weightlifters. BMD is a standard measurement of bone strength.

The soccer players had the highest BMD levels, followed by weightlifters and swimmers. Not only is soccer a weight-bearing sport, it also places repetitive impact on the skeleton, which further promotes bone development, Bellew noted.

The average BMD values among the soccer players were higher than normal values for adult women -- even though the girls in the study weren't fully mature. The weightlifters' BMD values were similar to those of adult women, while the swimmers' BMD values were below adult norms.

"Like other sports that involve a lot of running and jumping, soccer is definitely a good sport to consider for building bone strength. Lacrosse and field hockey are other good examples of sports that place a continuous load on the skeleton," Bellew said.

"Swimmers can add other forms of exercise that will promote bone development -- for example, they can perform weight training in weight-bearing positions or add running as a cross training activity," Bellew added.

The study appears in the journal Pediatric Physical Therapy.