You've probably heard it said that weight training is good for your bones. Particularly if you're a woman, you've probably also heard that it's great for safeguarding you against osteoporosis. But do you know why?
Increasing what is known as bone mineral density via resistance training is a long process (6 months or more), but the mechanics of adaptation occur after just a few workouts. When we overload our bones with enough load, we eventually reach the point of minimal essential strain (MES); an indicator to the body that it's skeletal threshold has been reached and that new bone formation is potentially required. Reaching this threshold on a regular basis initiates the transit of collagen secreting cells called osteoblasts to the area of stress on the bone surface. On reaching the outer surface of the bone(periosteum), the osteoblasts deposit collagen molecules into the spaces between the existing bone cells, thus increasing it's strength. These proteins form a bone matrix, which in turn becomes mineralised as hydroxyapatite (calcium phosphate crystals), thus increasing the bone's diameter and strength.
Formation of new bone occurs only in stressed areas, so when training to elicit maximal osteogenic stimuli (variables that promote new bone formation) and corresponding increases in bone mineral density (BMD), exercise selection is key.
The biggest bang for your buck exercises when it comes to increasing BMD are multi-joint, structural exercises like the back squat, deadlift, power clean, snatch and overhead press (the latter for upper body). Conveniently, these are also some of the most effective exercises for reducing body fat and developing strength and power.
As with the development of all facets of fitness it's important to overload the body/skeleton progressively by following a well structured programme. Studies have also indicated that exercises presenting varying directional forces on the bone leads to the laying down of collagen fibres at different angles in order to dissipate the imposed forces and conform to the lines of stress experienced, thus resulting in a stronger internal architecture.
The take home message then, is to weight train using exercises that present a variety of distributional and directional force vectors in order to maximise your bone mass, increase your skeletal strength, and protect yourself from osteoporosis.
Plus you'll burn fat, get fit and look hot with it! :)
