What is Wolff’s Law and where does it come from?

Wolff’s law comes from the German anatomist and surgeon Julius Wolff (1836-1902). He stated that the bone in an animal will adapt to loads it is placed under.

This adaptation will increase the strength of the bone over time to resist the stress from loading. Osteoblasts are bone cells that receive stimulation of the stress and build new stronger bone, eventually turning into osteocytes (mature permanent bone cell). Osteoblasts are also activated to heal fractures where too much stress was provided to the bone. Your body will lay down stronger cortical bone as a result and it may also be thicker. This can be seen with martial arts where a sensei may have their students punch trees or other hard surfaces to thicken the bone in their hands. This will eventually lead to them being able to punch through boards or even bricks without breaking their hand.

Wolff’s law also works the opposite way.

The less stress you put on a bone or joint the weaker and less dense your bone will become over time. This is seen in the disease osteopenia where a loss of bone density occurs. Osteopenia is quite common with joint replacement surgery because the bone is shielded from stress due to the prosthetic implant. Its designed to take stress off the bone. Which in turn causes that part of the bone to become weak and less dense. The more advanced stage of bone density loss is called Osteoporosis. Osteoporosis is caused from lack of calcium, vitamin D, and Vitamin B12 over a long period of time. There are hormone imbalances that may also cause osteoporosis as well. Most commonly from menopause. When the bone density is changing to a softer less dense bone osteoclasts are more active. Osteoclasts are a bone cell that will dissolve hard bone. This is due to the lack of stress to that specific bone.

So, your bone is constantly in a battle of building bone and dissolving bone depending on your activity levels and stress to your body. This is commonly called bone remodeling and it occurs every day and every minute of our lives. This is a perfect example of the saying “If you don’t use it, you lose it.” If you do not stress your bones with exercise you will lose your bone density. Therefore, it is more important for patients with osteoporosis to do light weightlifting to help rebuild bone they have lost.

So, go exercise and have those osteoblasts get to work. You have bone to build.