Did you know that most of the adult skeleton is completely replaced about every 10 years? We tend to think of our bones as constants, like a steel framework for a building. In actuality, throughout life the human skeleton is being continuously broken down and restored. This process of continual reshaping and rebuilding is called remodeling. This is an apt term. Just like a dilapidated old house or an outdated room, we can actually redesign, restore and renew our skeleton to a level equal or greater than before.
Why do we care?
Bone strength (measured as bone mineral density) is directly tied to issues such as osteoporosis, increased fractures (particularly of the hips), and postural problems such as a hunched back. As people age and/or become more sedentary, the risks of reduced bone density and brittle bones increases.
Remodeling is vital for bone health for several reasons (ACE Essentials of Exercise Science):
- repairs damage to skeleton that can result from repeated or traumatic stresses
- prevents accumulation of "old bone" which may have lost its resilience and become brittle
- plays a role in releasing key nutrients, calcium and phosphorus, from the bones into the blood stream when these minerals are deficient in the diet (or in higher demand due to pregnancy or nursing)
> 50% of women and >20% of men over 50 will suffer an osteoporotic fracture at some time in their lives
(US Department of Health & Human Services)
What's the secret to remodeling our skeleton?
While nutrition plays a vital role in bone health, the primary mechanism to maintain or improve bone density is applying repeated "stresses" through exercise. According to Wolff's law, when bone is subject to stressful forces such as those of weight bearing exercise, it stimulates the effected bones to lay down more bone tissue, thereby increasing density. Conversely, prolonged bed rest or sedentary lifestyle yields reductions in density or bone weakening.
The key is to do exercise that is weight bearing with repeated application of forces. Our own body weight and gravity are the perfect "equipment".
Running, walking and standing can all impact bone density, with running being the most effective. As noted in a recent NY Times Personal Health article by Jane E. Brody, swimming and cycling are not very effective at building bone because they are not weight bearing. Very little compressive force is applied to the skeleton in swimming or cycling. For those with joint issues such that running isn't feasible, try walking hills, steps, or jumping jacks
Body weight exercises such as chair squats, standing squats, calf raises or lunges help strengthen lower body muscles and improve bone density.
For the upper body: push ups, desk push ups, tricep dips and planks are great weight bearing exercises that strengthen, tone and build bone without equipment.
According to WebMD and other expert sources, Pilates and core conditioning is great for strengthening the spine while also serving to tone the muscles hat support the spine and good posture. BONUS!!!!
Of course lifting free weights & dumbbells is also effective, especially exercises you do standing such as standing shoulder press, squats, etc...
Time to go pound my bones on the pavement for a strong & healthy skeleton and teach Pilates in Central Park to save some spines!