Wolff's law

Wolff's law is a theory developed by the German Anatomist/Surgeon Julius Wolff (1835-1902) in the 19th century that states that bone in a healthy person or animal will adapt to the loads it is placed under. If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading. The external cortical portion of the bone becomes thicker as a result. The converse is true as well: if the loading on a bone decreases, the bone will become weaker due to turnover as it is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass.

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Associated laws

In relation to soft tissue, Davis's Law explains how soft tissue remolds itself according to imposed demands.

Examples

• The racquet-holding arm bones of tennis players become much stronger than those of the other arm. Their bodies have strengthened the bones in their racquet-holding arm since it is routinely placed under higher than normal stresses.

• Astronauts who spend a long time in space will often return to Earth with weaker bones, since gravity hasn't been exerting a load on their bones. Their bodies have reabsorbed much of the mineral that was previously in their bones.

• Weightlifters often display increases in bone density in response to their training.

• Fighters who punch or kick objects with increasing intensity (or of increasing hardness) to develop striking power to damage opponents, often display increases in bone density in the striking area. Others may do this specifically to reduce pain response in the nerve endings of the striking tissue and to increase the bone density. Due to the ballistic and inconsistent nature of striking practise, load-bearing exercises are generally a safer form of measurable progression for increases in both bone and muscle strength.

Many fighters will do things like knuckle push-ups as a form of conditioning, for example, so the impacts of strikes are only supplementary conditioning, as ideally in both sparring and striking practise as well as competitive contest your body should not be experiencing adequate stress for microtrauma adaptation. This is so the body can solely focus on technique and nervous recruitment and not tissue adaptation which can be distracting. Not including supplementary exercise does however guarantee that the body will not over-adapt and develop toughness specifically in response to training demands, which can be a factor for those concerned with making weight, and not wanting to develop bone or muscle weight they may not need for contest.