The Science of Decline Sit-ups

As I am a moderately well-read person, my poor understanding of science is a source of embarrassment. It’s possible I know as much science as the average American. Still, I haven’t studied it as much as I would like, nor does my brain seem particularly well-suited for it. I’m good with words and pretty good with numbers, but thinking spatially or mechanically is a challenge.

Because I spend a lot of time in the gym, I have decided to improve my understanding of certain scientific principles by studying different exercises and equipment. My hope is that in actually using my own body to do various movements, the principles will sink in better than they have before.

Shortly after choosing decline sit-ups for my first investigation, I explained my plan to a science-minded friend. “What forces do you think are involved?” he asked. “Fulcrums, levers, gravity?” I hazarded. “And torque,” he replied. Torque. The word calls to mind cars.

My next step was some online searches. The Wikipedia “Torque” entry was potentially informative. On one site, I found the following: “However, to avoid a lesson in physics we can summate the concept [of arm placement during decline sit-ups] as follows.” Not helpful, except that with a quick side investigation I learned that “summate” is a legitimate word, though it sounds off to my ear. Back at Wikipedia, I clicked links on the “Torque” page.

Source: http://en.wikipedia.org/wiki/Torque

I admit I breezed through these and several other websites. Part of the problem is that I am not really all that interested in learning more science. It’s something I think I should do, and I kind of wish I could automatically deposit the knowledge in my brain. Still, perhaps if I can get a few footholds through this gym/science scheme, I’ll begin to find it more interesting.

Eventually I wound up on a website that looks to be quite informative and reputable, ExRx.net. It contains a page about levers, as well as a page on the weighted decline sit-up (and hundreds of other exercises). On the decline sit-up page, I read, “Lower decline to increase resistance.” I then set about to answer the simple question “Why does lowering the decline increase resistance?” If this is the physics equivalent of “Who wrote Adventures of Huckleberry Finn?”, so be it.

My first thought was that gravity might be involved. Something along the lines of slightly more air offering resistance as one is moving up. But that didn’t seem right—that air would only weigh minimally more, wouldn’t it, not enough to produce the effect that I know from experience is more significant. Then I remembered that as distance increases from the point of the fulcrum, or something like that, it requires more effort to move.

Returning to the lever page on ExRx.net, I saw I had the idea right, if not the terminology. What I thought of as the point of the fulcrum is in fact called a fulcrum, while the whole thing is a lever. Decline sit-ups seem to be either second– or third-class levers, the latter only if you hold a weight behind your head. As the page states, a third-class lever “requires relatively great force to move even small resistances.” I was able to empirically verify this statement during my last weight training session, when I held a 10-lb. weight behind my head instead of on my chest like I usually do. It was not easy.

A Third-class Lever

Source: ExRx.net

I have only scratched the surface of levers here, and I haven’t yet figured out what torque is or followed up on whether my gravity instinct has any truth to it. Yet I’ll be damned if I don’t feel a bit more eager to continue learning more science. And as far as I’m concerned, that makes this first inquiry a success.