Researchers looked at the physical activity levels of over 800 Swedish men aged 19 to 24 and found that those who boosted their physical activity during that period also showed increased bone density in the hips, arms and lower legs and spine.
Young men whose physical activity decreased during that period had significantly more "brittle" bones, according to a University of Gothenburg news release.
Improved bone development, which occurs throughout childhood and into young adulthood, can reduce the risk for fractures and osteoporosis later in life.
The study was released online in advance of publication in an upcoming print issue of the Journal of Bone and Mineral Research.
"The men who increased or maintained high levels of physical activity also developed larger and thicker bones in their lower arms and legs," study author Mattias Lorentzon, of the Sahlgrenska Academy's Centre for Bone and Arthritis Research, said in a news release. "These findings suggest that maintaining or, ideally, increasing physical activity can improve bone growth in our youth, which probably reduces the risk of fractures later on."