Homeostasis and the Envelope of Function

Overload and overuse are very common and often correctable causes of musculoskeletal pain. When tissues are exposed to overload and overuse there is a natural reparative process that tries to occur. If the body’s ability to heal from the micro-damage resulting from overload and overuse is overwhelmed by the amount and/or duration of overload damage, then tissue damage results in inflammation and loss of tissue balance or "homeostasisi" occurs. It has been documented scientifically when overload is relieved that cells have a remarkable ability to return to a “homeostatic” or asymptomatic state. This can happen even in the presence of structurally damaged tissue such as an arthritic joint. This is the principle which is both logical and effective in managing orthopedic problems related to overload. An excellent example of this is the not uncommon situation where a joint looks arthritic on x-ray but does not hurt. That joint is at homeostasis. It is a well-documented but under-appreciated fact that x-ray appearance does not predict the presence or severity of symptoms. It is very important to realize that overload can be related to one single episode of severe injury or to a very large amount of small injuries over an extended period of time. This understanding led Dr. Scott Dye, an orthopedist in San Francisco, to develop the concept of an "envelope of function."

As long as tissue is exposed to loads which it can handle metabolically without damage, tissue homeostasis is maintained. When overload occurs (either in a single acute episode or by repetitive overuse) a healing response is initiated. If this tissue has not been loaded so severely as to produce complete disruption (and even sometimes when there is), there is an ability to return to homeostasis. In situations where the tissue is more damaged the ability to return fully to homeostasis can be more limited.

The concept of an envelope of function describes the amount of load considering both intensity and frequency. This is best understood by the diagram above. The concept is very simple. Once understood it seems like common sense. Its application is extremely important and consistently successful. As long as loads are within the envelope of function (below the line on the graph) tissue remains healthy happy and no pain results. In some cases the envelope of function is very small and only very light activities are tolerated. For example, walking up stairs may be painful or impossible. With time and gradual increases in activity just exceeding the envelope of function, this stimulus can lead to strengthening and ultimately the envelope of function can increase. Think of an athlete training. As the strength, flexibility and endurance increase, he or she gets in better shape, can do more, and the envelope increases.

When the absolute amount or duration of load is excessive tissue enters the area described on the diagram as the zone of supra-physiological overload. Tissue can recover from this zone. If however, the load persists at an unacceptable level, exceeding the tissues ability to restore homeostasis, then the zone of structural failure occurs. When structural failure occurs, surgical repair or other significant medical care (bracing/casting, etc) often becomes necessary. If you have questions, please ask.

i Homeostasis: the maintenance of relatively stable internal physiological conditions (as body temperature or the pH of blood) in higher animals under fluctuating environmental conditions Definition from MerriamWebster.com