I'm sure that it's all that stuff, Riddick that causes the confusion. Also, I was thinking that since "resting length" is the mid-point between fully shortened and fully stretched that 'contraction' got worked in there and it became 'mid-contraction'. Lots of possibilities but probably you are closer to the mark because it's usually one thing written by an influential person that carries this stuff into infinity.
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Originally Posted by Riddick
speaking of Jones, isnt that what he tried to acheive with his off set cam design? constant tension throughout the ROM? not sure how much efficacy it actually has but it sure was a great marketing tool and helped sell a LOT of machines! he had some kooky (and some downright dangerous) 'theories' on training but he sure was market saavy and had great taste in women too, lol.
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Yes, except it was to make big muscles. It doesn't matter if you build a machine when you actually pick up a free weight the everything changes as the angle changes including tension. The force you are putting on a weight is a momentary thing and changes as you lift. Force, after all is a momentary measurement.
First, there is somethig that must be realized. You cannot directly measure the maximum force one muscle is able to generate in a living person. You'd have to take a muscle fiber from them and shock it to make it contract maximally and measure the force it is able to exert. That is how they learned a lot about muscle workings. From that you get the force-velocity curve or relationship (inversely related) and the length-tension relationship which is really like the force length relationship. But that only tells you in an approximate way how muscles work.
Basically the muscles cause the body segments to rotate about the joints. The turning force is called a 'moment' or a torque. I don't understand the math, it factors in the distance from the muscles attachment point to the axes of rotation and the joint angle ad the tension on the muscle, but if you look at it as a simple lever like a bicep curl it's easy to see how things change as the angle changes if you just know a few things.
Only the part of the muscles force that is directed perpendicular to is effective in causing rotation around the joint (axes).
Maybe I can get some diagrams but imagine a bicep curl from the side. The only time that 100% of the muscles force is perpendicular to the bone is when the elbow is at 90 degrees. Think of a line of force moving up from the forearm. Straight up. Now think of the angle of the upper arm. Only when the upper arm is more or less vertical does that force line up perpendiucular to it, right? At every other place that force is at an angle to it. This is the product of all the forces we're talking about, we are not saying that all the force actually is applied in one direction. It's just an illustration.
But seeing that you see why you seem stronger when you are curling at 90 degrees rather than 120 or 70 degrees. This does NOT mean that the muscles are able to exert more force at midcontraction only that more of the force that the muscle exerts is effective in rotation the bone at that point.
Thinking about it another way, imagine that you were actually able to exert less force at the beginning of the contraction, say at a slightly stretched position. Being that the force is less effective at rotation the bone at that angle then if you are actually weaker you'd never be able lift a damned thing!
Given that there are always points and positions at which the most force can be applied and most movments are intentionally started at those points. That, however, does not mean that we do partials only resistance training because there is more to it.
So, you can invent any number of machines but when you pick up a weight you can't change the laws of physics.
Sorry to get into a bunch of lab talk but there is no other way to counter-act this stuff.
I'm pretty sure that my fellow admin at GUS could correct me on a lot of this but he is 'conspicuously' silent