Please assist my mental pull up
August 23, 2012 9:38 AM Subscribe
My gym has an assisted pull up machine that provides varying degrees of assistance depending on how much weight is selected. I'm pretty sure it's lying.
The way it works: You select an assistance amount by putting a pin into a stack of weights. A cord attached to the weights wraps around a pulley overhead, and is connected to a padded platform on the other side. You kneel on the platform and hoist yourself up. In theory, if you weigh 150 and 50 pounds of assistance is selected, each pull up would require as much effort as if you weighed 100. Makes sense, right? BUT! If I set the machine to 50 (it's minimum assistance amount), and I put a 20 pound weight on the platform, the platform goes down, lifting the "50" pounds. Putting 17.5 pounds on the platform seems to bring the two sides into equilibrium. So, aren't I really only getting 17.5 pounds of assistance? Is the minimum weight mislabelled, or are some crazy pulley physics messing with my head? Side note: selecting 50 + x pounds of assistance causes the equilibrium amount to change to 17.5 + x, so it's apparently proportionate.