Half of our bone density is laid down by early puberty: 95% is present at the age of 17 for females and at the age of 19 for males. By the age of 40, our bone density is typically declining by 0.5% per year. For women, this rate speeds up to a 2-3% annual decline after menopause.
Stress fractures are micro-trauma that accumulates in bone from frequent unaccustomed repetitive activity. These can develop into full fractures that keep us out of action for 8 weeks to 8 months, and occur in adults of any age including athletes. Running and marching have risks and benefits - they increase bone density, but may also cause stress fractures due to repetition if you do not slowly increase the distance or intensity.
What To Do?
Encourage youngsters to be active:
Build a strong base skeleton for a lifetime of health. Encourage play that is intermittently intense. Soccer and basketball, to name a few, are very effective at strengthening bone. Research shows another effective exercise to increase bone density for school aged children would be to jump 5-15 times, three times a day.1
Stay active through all of life:
Soccer, basketball, high intensity interval activities, jumping, yoga, dancing, gymnastics, and running all help increase bone density, especially in the lower body.
Weightlifters have the densest bones compared to runners; however both groups of athletes are equally strong compared to their relative size.2 Calf raises will protect against stress fractures in shin bones. Lifting weights will also help increase upper body bone density. Therefore, in addition to less intense exercises like swimming, aquafit, cycling, using an elliptical and walking, consider adding some weight lifting or calf raises to your exercise routine. If you are a runner, reducing your stride length by 10% may reduce your risk of stress fractures by 3-6%.
Bone is a living tissue, in a constant state of breakdown and repair. In adulthood, we actually have new bones every 8-10 years! The ratio of breakdown shifts as we progress through life, which is why we need to build strong bones when we are young, and maintain them throughout our whole lifespan. However, it is still not too late and we can reduce the decline by implementing a few new exercises.
1. H.M. Macdonald et al., "Is school-based physical activity intervention effective for increasing tribial bone strength in boys and girls?"Journal of Bone and Mineral Research, 2007, 22(3), 434-446.
2. Scott Rector et al., "Lean body mass and weight-bearing activity in the prediction of bone mineral density in physically active men," Journal of Strength and Conditioning Research, 2009, 23(2), 427-435.