Monday, August 4, 2008
Muscle mechanics: part 1 of 2
I must apologize for the visual pun--I usually try to avoid having a photograph that is tangentially related to the topic, but in this case, I don't exactly have any photographs of hulking bodybuilders or pieces of muscle tissue--I take or have taken all of the photographs myself, and as of this moment my life is lacking in muscle-bound semi-naked men.
So a turkey will have to do: this particular turkey and its chick (what my sister and I like to call "gibblet") happened to land in the backyard of my parents' house last spring. Turkeys have a lot of muscle, most of it in their breast, which is where the prime cut is.
Muscle tissue is basically long strings of protein that slide past one another. The full biochemical story can be found here, and I recommend that you look at the figures (links on the right) in conjunction with the text to get the whole picture.
The human musculoskeletal system is really a very elaborate system of pulleys, where a contraction of one muscle gets transmitted into a movement across a particular joint. Bones, in this case, are more than merely the support structure for the rest of us--they provide the foundation upon which these pulleys are anchored. Nowhere is this more evident than in the hands:
The muscles that control the flexion and extension of our fingers are actually located in our forearms. There are two sets, one to bend the first knuckle, and one to bend the second. Another two sets are on the backside of the hand, to provide extension of the fingers. The tendons must be threaded through a very narrow gap in the wrist (and we wonder why carpal tunnel is such a problem) before they can attach to the their assigned bone, but when you are typing, it is the muscles in your forearm that are doing the work (even if it feels like the muscles in your wrist--which there aren't any).
The hands also serve to illustrate the principle of opposing pairs. Just like Newton's Third Law, muscles work in opposing pairs. The usual example is that of the biceps vs triceps, where one relaxes while the other contracts. While it's a useful illustration of the concept, it's not the whole story, as muscles can also "contract" even while they lengthen. The best example of this is to bend over and pick something up--if the muscles in your back were to go loose as you started to bend, you'd have a very hard time reaching the floor without injury.
Next: Dara Torres...