The Functional Continuum® represents the broad spectrum across which individuals "function". Contrary to the common misuse of the word "function" in the exercise world, function is best thought of as how well someone or something is "functioning". Something is "functional" if it is "operational".... working as it should. It is with this understanding that the extremes of the Functional Continuum are defined.
Someone's physical ability to perform an activity should be considered "External Function" or "External Performance". This is measured outwardly and often with numbers (seconds, minutes, points, inches, yards, weight, stats, even the precision or gracefulness of movement, etc.). But just as a house, a car, .... truly anything... is often valued for its curb appeal or its speed (respectively), how well it functions as a house or a car is ENTIRELY determined by how well its components... its parts... function!
The performance of a race car at the track is inescapably determined in part by how well the engine and countless other components function. The quality of the materials composing the walls and electrical system of the house, and certainly the foundation, are all ultimately the key to the overall long term ability to provide its expected "gross function". Homeowners and car drivers simply "use" these things with varying degrees of respect, care, concern, and/or skill level.
These internal components and the manner in which they function... the quality of their performance during their individual jobs, the integrity of their materials... should be recognized as the Internal Function or Internal Performance of the house, car.... or individual! And while one component may be functioning exceptionally well, one or more others may not, and the collective outcome may be currently or eventually affected.
Somehow the exercise world came to believe that improving the parts can't or won't influence the whole. Yet, while they dismiss and demonize the practice of improving the contractile ability or "output" of the knee flexors independent of the total body activity in which they are vital, they hypocritically sit or stand still and "stretch out the hamstrings" in attempts to influence virtually any and every total body activity.
Ultimately, understanding that there is a continuum that represents not only ones ability to perform a skill or daily activity, but also the current operational or functional status of the components that are "used or required" to build that total body external outcome, is vital to a true Exercise Professional's perspective!