Physiology

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 modeling 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 with in 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 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 breaking force needed to fracture the bone. Training effects have a positive relationship to 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
  • Proper exercise selection
  • Progressive overload
  • Variation

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, dead lifts, and straight leg dead lifts.

Exercise selection

This will promote osteogenic stimuli (factors that stimulate new bone formation) and will exhibit these characteristics: Compound exercise muscle movements consisting of multi joint, structural loading and varying force vectors. Such exercises are the squat, dead lift, military press and the bench press along with the Olympic style moves.

Progressive overload

Greater than normal loads force the body to adapt in a positive manner regarding new bone formation. This response is greater if the load changes are dramatic and repetitive in nature. 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. In order to prevent accommodation the exercises need to be varied on a periodic basis. 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.

Mechanical load consists of the following:

  • Magnitude of force - Magnitude of the load density or the intensity of the load will generally be above eighty to ninety percent of repetition maximum (RM) in order to see improvements in the tissue response.
  • Speed of force development - The rate or speed of loading means how fast the force is being applied to move the load in a concentric muscle contraction (force applied against a weight with the muscles shortening). Think speed during the lift.
  • The direction of forces -Varying the direction and pattern of movement will stress the bone and the attaching musculature. Full range of motion in all exercises ensures to a certain extent that the forces are applied as required.
  • Volume of force applied - The first three mentioned above are primarily responsible for bone mineral improvements. Typically the repetitions do not need to exceed thirty to thirty five to see improvements when the load is within the correct intensity zone (80% to 90% RM).

Exercise prescriptions for bone growth stimulation [1]

Volume 3 to 6 sets of 10 repetitions
Load 80% to 90% repetition maximum (RM)
Rest 1 to 4 minutes between sets
Variation Undulating periodisation patterns
Exercise selection Structural, multi-joint, large muscle groups

Summary

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.

Exercise suggestions

To increase lean body mass, add strength and power

  1. Warm up for 5 to 8 minutes
  2. Squats
  3. Calf raises
  4. Dead lifts
  5. Military presses
  6. Shoulder shrugs
  7. Abdominal work - two sets of 15 to 20 reps
  8. Bench presses
  9. Bar bell rows
  10. Barbell curls
  11. Triceps extensions
  12. Abdominal work again to end the session - two sets of 15 to 20 reps

Notes

  • Full body resistance training program on a schedule of at least two times per week, with three times to optimize the results
  • Utilize correct exercise technique at all times
  • Three sets of ten to twelve repetitions each exercise unless other wise noted
  • Work to rest ratio is 1:2, meaning if you work out for ten seconds you then rest for twenty seconds
  • If you are able to add weight after completing the series three times, then do so the next session
  • If you have increased the weight then do only ten repetitions and work up to twelve

About the Author

Danny O`Dell is a NSCA Certified Strength and Conditioning coach from the USA. He is the author of a number of 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 the healthy fitness lifestyle. Danny can be contacted through his website at www.Explosivelyfit.com

Article Reference

  • O'Dell D. (2004), "Adaptation of bone to exercise", Brian Mackenzie's Successful Coaching (ISSN 1745-7513), Issue 14

Associated Pages

The following Sports Coach pages should be read in conjunction with this page: