By Dominique Wood-Ward – Physiotherapist
Bone remodelling is happening constantly in the skeletal system. Normal sites of microdamage occur throughout bony structure all the time.
In the normal process of bone remodelling, microcracks will form in bone tissue and osteocytes (bone cells) will die around an area where a microcrack has formed, in a process called apoptosis; cells called osteoclasts move towards the microcrack in bone to resorb the tissue. Osteoblasts then move into the area and create new bony tissue, creating new osteocyte cells. This is how the skeleton continues to stay strong and serve its functions of supporting body movement, protecting internal organs, and serving as a storage unit for minerals.
Bone stress injuries occur when there is an imbalance of microdamage, resorption, and formation on new bone tissue. An increase in microdamage can occur when there is an increase in stress/strain on bone tissue through a high or a sudden change in exercise load that does not match the ability of the bone to tolerate that load. If this is left to progress, it can escalate to a stress fracture. Not all athletes have healthy skeletons.
Factors than can influence skeletal bone properties:
- Rates, repetition, and magnitude of mechanical load
- Quantity, quality, and organisation of bone tissue
- Genetics
- Physical activity history
- Nutrition
- Hormonal status
- Injury history
- Primary or secondary bone disease
Risk factors for bony stress injury:
- Low bone density
- High exercise load (> 12 hours per week)
- Low body mass index
- Oligo-amenorrhea (infrequent periods)
- High dietary restraint
- Participation in sport/activity that promotes leanness
- Poor calcium and vitamin D levels
- Premature sports specialisation in young athletes equal to/greater than 8 months per year in sport to the exclusion of other sport
When is a bone stress injury likely to occur?
When you have had a change in exercise load (duration, frequency, intensity), surface, equipment, or training type.
What can you do? Manage your load.
Finding the appropriate load is about balancing the bone loading with its capacity to cope with that load.
Building the capacity of bone to handle load must be done in a gradual progressive process. As the load on your shins is progressed, so too is the capacity to manage that load.
Do osteogenic loading!
Activities that promote greater adaptation to bone tissue are called osteogenic. Some examples of these include progressive resistance training, plyometrics (jumping), sprinting, high-intensity resistance training (high load and high rates of loading), and jump rope.
Running is an example of an activity that has a low-moderate osteogenic effect.
Sports that have a very low osteogenic effect (i.e. that bone tissue will have very little strengthening response to) include yoga, cycling, swimming, and walking.
The reason some activities are better than others for bone health is due to the accommodation of cells to a stimulus. After that stimulus has occurred, the bone tissue responds. Tissue adapts and sensor cells accommodate and then a new threshold is established. Effectively, if the activity is repetitive and low load, the tissue does not see the need to continue to adapt.
Symptoms you might be experiencing:
- Pinpoint activity-induced bone pain (e.g. on initial ground contact when running or landing from a jump) that is present throughout whole aggravating activity.
- Lasting pain once ceasing activity, often with night pain.
These tend to go along with a history of load change, usually one month prior.
If you think you are suffering from a bone stress injury, see one of our physiotherapists to assess the contributing factors, guide your load management, address weaknesses and biomechanical factors, and help you get back to the activities you love.
