Adaptation of bone to exercise
Danny O'Dell explains how exercise is beneficial to bone development.
Bone is considered a connective tissue that when stressed, deforms as a result of the load. To meet the strain imposed upon the external structure caused by the bending, compressive, torsional loads and the muscular contractions at the tendinous insertion points, osteoblasts migrate to the surface of the bone.
At the point of the strain, immediate modelling of the bone begins. Proteins form a matrix between the bone cells. This causes the bone to become denser due to the calcification process occurring during the growth response to the load.
The new growth occurs on the outside of the bone to allow the manufacture of new cells to continue in the limited space within the bone itself. This outer layer is commonly known as the periosteum.
Adaptations take place at different rates in the axial skeleton (skull/cranium, vertebral column, ribs, and sternum) and the appendicular skeleton (shoulder, hips, pelvis and the long bones of the upper and lower body - essentially the arms and legs). This is due to the differences in the bone types - trabecular (spongy) and cortical (compact) bone.
The stimulus for new bone formations
Minimal essential strain (MES) refers to the threshold amount of stress applied to the structure which is necessary to elicit the growth of new bone material. A force exceeding MES is required to signal the osteoblasts to move toward the periosteum and begin this transformation. MES is thought to be 1/10 of the braking force needed to fracture the bone. Training effects have a positive relationship with bone density, just as sedentary living habits play a role in the loss of bone density.
Training to increase bone formation
Programs designed to stimulate bone growth, also known as bone mineral density (BMS), will incorporate the following characteristics:
Specificity of loading
This will see the exercise patterns emphasizing specific areas in need of assistance. New or unusual forces in varying angles of stress will enable your bones to adapt to the greater intensities. Military presses, bench presses, upright shoulder shrugs, push-ups, chin-ups, plus other similar exercises would help develop stronger upper body bones. Lower body exercises selections would be along the lines of these types of movement patterns: squats, calf raises, deadlifts, and straight leg deadlifts.
This will promote osteogenic stimuli (factors that stimulate new bone formation) and will exhibit these characteristics: Compound exercise muscle movements consisting of multijoint, structural loading and varying force vectors. Such exercises are the squat, deadlift, military press and bench press along with the Olympic style moves.
Greater than normal loads force the body to adapt positively regarding new bone formation. This response is greater if the load changes are dramatic and repetitive. Younger bones may be more receptive to osteogenic changes in the load variance than older bones.
Variations of exercise selections
The body adapts quickly to imposed loads per the Specific Adaptation to Imposed Demands (SAID) principle. To prevent accommodation, the exercises need to be varied periodically. There are many individual differences in the same exercise, e.g. the squat has at least seventy variations, and these do not include any machine versions.
The mechanical load consists of the following:
Exercise prescriptions for bone growth stimulation
Baechle & Earle (2001) recommend:
The greater the magnitude or intensity, the higher and faster the power output and the direction of force all contribute to the successful laying down of new bone growth.
To increase lean body mass, add strength and power
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About the Author
Danny O`Dell is an NSCA Certified Strength and Conditioning coach from the USA. He is the author of several training manuals including The Ultimate Bench Press Manual, Wilderness Basics, Strength training Secrets, Composite training and Power up your Driving Muscles. Danny has published articles in national and international magazines describing the benefits of living a healthy fitness lifestyle.