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Thread: Pec Dec

  1. #1
    Quester's Avatar
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    Pec Dec

    Put pin in at 200lb.
    If one uses both arms at 200lbs, its 100lb/arm. But, If one uses only one arm, is it 200lbs on that arm?

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    I don't think it would work that way, the machine takes a lot of the actual weight away so its probably not really 200lb. Maybe it is but i dont think so..
    The machine is supporting the weight so how are you moving 200lb exactly on the pec dec?
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    Pulleys?
    -I get the argument of free weights vs everything else. However, that is more about angles and compensatory (stabilizing) muscles and the rest than simply: look at machine, subtract lbs from the total it says one is moving.
    -Ok, so it takes away weight, I gotta think that the engineers who designed the machine compensate for that byt doing some engineering shit to it and then meausre the load at what it actually the equivalent of 200lbs of pressure against the squeeze.
    -Just to get back on track before this thread is diverted away from my question. Either way, my question is about the total load being divided by two or not. (I spent a little bit more time explaining in the first post.)

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    Quote Originally Posted by Quester View Post
    Put pin in at 200lb.
    If one uses both arms at 200lbs, its 100lb/arm. But, If one uses only one arm, is it 200lbs on that arm?
    No the stack is pulled by a dual pulley
    Pec Dec-maxresdefault.jpg

    See there is it right above stack.

    If one arm is used the machine through physics anchors off of the other arm pulley, and the stack pulley is allowed to act as a pulley, instead of a stationary point.

    So it's splitting resistance by using one arm.
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    Quote Originally Posted by Couchlockd View Post
    No the stack is pulled by a dual pulley
    Click image for larger version. 

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    See there is it right above stack.

    If one arm is used the machine through physics anchors off of the other arm pulley, and the stack pulley is allowed to act as a pulley, instead of a stationary point.

    So it's splitting resistance by using one arm.
    Good explanation and pic but, just cause I'm slow, "So it's splitting resistance by using one arm," means that the one arm is only doing 1/2 of 200lbs? Or, put another way, that one arm is only getting 100lbs i.e. 1/2 of the 200lb. load due to the use of only one of the dual pulleys?

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    Well there is a pulley on top of the stack with cable running through it and going up over a pulley for each lever.

    So when both levers are being used simultaneously, the only pulleys bring used as pulleys are the ones right behind the arms set on a 90 angle (making the cable take an "L" shape, then going up under the stack pulley.)
    In this mode the stack pulley isn't really a pulley anymore, it's an anchor point.

    So each arm is being used to collectively pull the 200lb stack. With some slight assistance from the pulleys directly behind arms levers.
    .now when one lever is only being used, the cable is basically tethered to that lever and pulley and the stack pulley is now being used for leverage and is actually spinning

    So one arm is getting major assistance from the anchor point (fulcrum) and lever (stack pulley) so it's seeing half the resistance of stack.

    So if you pin whole stack, no matter what, one arm is only seeing half of the resistance.

    One arm - 100lbs
    Two arms - 200lbs, split between each other...

    You can see this effect, by unevenly pinchibg, lifting, levering. Whatever you call it,. Let's call it lifting.

    Use both arms, but force one to lag, you'll see that the lagging side will be shoving done resistance to the non lagging side.

    Any time the stack pulley starts to spin, it's splitting the workload to some percentage.
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    Couch, are you an engineer?

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    Quote Originally Posted by Quester View Post
    Couch, are you an engineer?
    Nope, just watched alot of Wile E. Coyote as a kid.
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    I might not have the exact words or phrases to explain it perfect, but I'm good with angles, and levers.

    It's one of the reasons my Glock has a measured 2lb trigger and all safeties engage

    It's all levers and angles.
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