Wolff's Law

There’s an underlying theme that I notice the more I study and it’s that however much it may look like things stay the same, they really don’t. In the same way that water erodes rock, so forces gradually shape us. We may find ourselves falling back on tired-old pronouncements such as,
“Oh, it’s inherited”,
“It’s genetic”,
“That’s just the way it is” or
“I’ve no idea how that could’ve happened to me”.
But if we take the time to trace things back we can see that it is often our actions (or inactions) that have contributed to where we find ourselves in this moment.

Wolff’s Law:
Bone grows and strengthens under pressure (in proportion to mechanical stress) and weakens when it is rarely used.

Our bones tell the story of ‘use it or lose it’ because the more physical activity we do, the denser and more mineralised our bones become. Runners have higher bone density in their legs and tennis players in their racquet-holding arm as bone is deposited and resorbed in accordance with the loads placed upon it. Bone is a dynamic tissue that is tightly regulated by a multitude of homeostatic controls, with one of the main key environmental regulators being mechanical stimulation.

Traditional martial arts recognised this ability of the body and developed conditioning regimes that included repetitively blocking and striking fingers, knuckles, forearms, abdomen, tips of toes, shins, thighs and calves to produce slight trauma to them to increase their strength. This phenomenon is known as Wolff’s Law, and it allows our body adapt to the stresses placed upon it.

Whether we like it or not, over time our body reflects the choices we make and it adapts to the demands that we place upon it every day.

Just as we can gain bone density, so we can lose it. Since no weight is acted on astronauts, their bone mass and mineral density diminishes as their bodies don’t have to fight gravity to move around. Cyclists suffer from this to a lesser extent and, to counter this, incorporate walking, running and weight-lifting into their training regimes. This is also seen in people who are bedridden or have a sedentary lifestyle; the lack of stimulus required for continued remodeling means their bones become less dense and weaker leading to a higher susceptibility to fractures and osteoporosis.

Stress fractures happen when a bone reduces in density and becomes weaker, or when the stresses applied to the bone exceed the bone’s ability to adapt and the larger the loads, the greater the strain. A common cause of this is overtraining, especially by people who run and jump on hard surfaces (think distance runners, basketball players and ballet dancers) and the femur, tibia, navicular and metatarsals are the most often affected. We all need to allow ourselves adequate rest and recovery to reduce the chance of this happening to us and if we want to avoid the dreaded shin-splints or runners knee we can increase training slowly and consistently. Please don’t think that as you get older you need to protect yourself from the world, because if you don’t use it you’ll lose it and increase the chance of things like osteoporosis because your body has adapted to less stress and less loads than it ideally needs.

Hip replacements can also lead to a reduction in bone density and weakness because the bone is shielded by an implant. The removal of typical stress from a bone causes it to remodel and lose bone mass.

This structural imbalance can be seen in people who suffer from musculoskeletal issues where some bones become overly strong and dense, leaving others with nothing to do and weakening over time. If weight is not distributed evenly then overly strong muscles fire first, leaving the weaker groups unaffected, but at the same time these groups, being over-proportionally dense and compact, will have the tendency to absorb most of the loads and stresses submitted to the body through weight-bearing.  Structures that need a balanced stress input - such as the shoulder joint - become ‘shielded’ from mechanical load and further reduce in strength in a vicious cycle unless intervention and re-integration of missing movements take place.

The changes in bone density, size and shape are the work of two specialised bone cells called osteoblasts and osteoclasts, which respectively form and resorb bone tissue. The bone remodeling occurs throughout life. During the process, resorption precedes formation, so as old bone tissue is replaced by new bone tissue. Remodeling can be in either ‘conservation mode’ with no change in bone mass, or ‘disuse mode’ with a net loss of bone mass characterised by an enlarged marrow cavity and thin cortex. The latter leads to osteoporosis, results from either excessive resorption or inadequate formation. The bone modeling occurs during growth and healing. Unlike remodeling, the osteoblasts predominate the activity (formation) with a net gain in bone mass.

Ulf H.Lerner

If you have suffered a fracture, placing specific stress in specific directions to the bone can help it remodel and become normal and healthy again.

During the first few weeks after an injury you may have had to use a cast or splint to immobilise bone as it healed. Once this is removed putting gradual and progressive weight back through it will ensure it will grow back into healthy bone. By gradually introducing new stressors you build up a tolerance to the loads you will encounter in everyday life and by building in weight-bearing and strength exercises you can prevent future reductions in bone density.

Bunions. An example of Wolff’s Law in action.

When we come to the feet, if there’s a lack of movement in some joints then others have bigger demands placed upon them and lay down extra bone to cope with the increased stress. Bunions are the most well-known example of this and they may have developed as a way for the body to adapt to keep moving. There are many reasons they devlelop including:

- As a way to decelerate over-pronation.
- Because the first metatarsal-cuneiform is unable to open.
- There is limited dorsiflexion in the ankle.
- The joint is stiff because it never gets to move.

There is no reason that bunions can’t reduce or even disappear over time if the bone remodels and adapts to a more efficient experience and it no longer needs to use that strategy. As Gary Ward said, “the bunion is not the problem but may actually be acting as a solution (giving you more at one joint to make up for less at another)”.

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