Davis' law
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Davis' law is used in anatomy to describe how soft tissue models along imposed demands. It is the corollary to Wolff's law. It is used in part to describe muscle-length relationships and to predict rehabilitation and postural distortion treatments as far as muscle length is concerned.
This is not necessarily describing myohypertrophy (muscle growth)—the shortening of muscle in response to resistance—but it explains also how a muscle will lengthen in response to stretching. Because most major muscles have an opposite, the protagonistic and antagonistic muscles (and their related syntergistic and groups of muscles) will end up reciprocating each other's length. A strong and inflexible gastrosoleus complex (calf) will therefore result in a weak and flexible tibialis anterior (shin muscle).
The origin of the name Davis' law is unclear, but it may be a reference to Nathan Smith Davis, the first editor of the Journal of the American Medical Association.
[edit] Soft Tissue Examples
Tendons are soft tissue structures that respond to changes in mechanical loading. Bulk mechanical properties, such as modulus, failure strain, and ultimate tensile strength, decrease over long periods of disuse as a result of micro-structural changes on the collagen fiber level. In micro-gravity simulations, human test subjects can experience gastrocnemious tendon strength loss of up to 58% over a 90-day period. [1] Test subjects who were allowed to engage in resistance training displayed a smaller magnitude of tendon strength loss in the same micro-gravity environment, but modulus strength decrease was still significant.
Conversely, tendons that have lost its original strength due to extended periods of inactivity can regain most of its mechanical properties through gradual re-loading of the tendon, [2] due to the tendon's reponse to mechanical loading. Biological signaling events initiate re-growth at the site, while mechanical stimuli further promote rebuilding. This 6-8 week process results in an increase of the tendon's mechanical properties until it recovers its original strength. [3] However, excessive loading during the recovery process may lead to material failure, i.e. partial tears or complete rupture. Additionally, studies show that tendons have a maximum modulus of approximately 800 MPa; thus, any additional loading will not result in a significant increase in modulus strength. [2] These results may change current physical therapy practices, since aggressive training of the tendon does not strengthen the structure beyond its baseline mechanical properties; therefore, patients are still as susceptible to tendon overuse and injuries.
[edit] See also
[edit] References
- ^ N. Reeves, C. Maganaris, G. Ferretti, M. Narici (2005). "Influence of 90-day simulated microgravity on human tendon mechanical properties and the effect of resistive countermeasures". J Appl Physiol. 98: 2278-2286.
- ^ a b T. Wren, S. Yerby, G. Beaupré, C. Carter (2001). "Mechanical properties of the human Achilles tendon". Clinical Biomechanics 16: 245-251.
- ^ R. James, G. Kesturu, G. Balian, B. Chhabra (2008). "Tendon: biology, biomechanics, repair, growth factors, and evolving treatment options". J Hand Surg 33: 102-112.
- Nutt, John Joseph, Diseases and deformities of the foot. New York: E. B. Treat & Co.; 1915, pp. 157-158. (Out of copyright. Available as a pdf in total via Google books).
- Spencer AM, Practical podiatric orthopedic procedures. Cleveland: Ohio College of Podiatric Medicine; 1978.
- Tippett, Steven R. and Michael L. Voight, Functional Progression for Sport Rehabilitation. Champaigne IL: Human Kinetics; 1995, ISBN 0-873-22660-7, p. 4.
