Just wondering if any of you can do the calculation that well approximates the amount of joules expended by a push up.
Sure. Determine the centre of mass of the body ( which might be around your belly button or a bit higher ) and then calculate the amount of work needed to raise the centre of mass by doing a pushup. By the way, this will be lower than the energy the body is using internally. Other muscles, for example the stomach muscles, are contracting to keep the body straight.
I'm around 80kg and I go about 0.5m high. So the change in potential energy is 80*9.8*0.5 = 392 J Is that a reasonable estimate of the total minimum possible expended energy? Can you believe a few years ago I was on the second year of an undergraduate Physics degree!? It has completely fallen out of my head -_-
That would mean a few hundred pushups would be expending the same energy as a half-marathon (according to a running app of mine) ... that can't be true maybe i'm confusing calories with kcal or something. hmmfph.
That's probably it. You're calculation of 400 J looks reasonable. Keep in mind that a joule is a pretty miniscule amount of energy. There is a reason electric companies charge by the kW-hr (millions of joules), rather than by the joule.
I think 0.5m is a bit on the high side. There is a large difference between the raw power output (here: used to lift the body) and the amount of chemical energy the body needs. I don't know how the running app calculates its values.
Push up and food Hi guys, i came up with this relations between food and physical exercise,here my calculations: Weight=70kg, Distance for push up=0.5m, Distance for squad=0.5m, distance for abs=0.5m. 70kg(9.81m/s2)=686.7N, so in exercise minimum i have to move my center of mass 0.5m: 1 push up=1squad=1abs: 343.35J=82.06cal Lets say that i eat one can of tuna fish=94.9kcal To waste the energy from tuna fish i would have to do 385 push ups, squads and abs!!! hahahaha to much!!! Be aware that these are very simple calculations
Your body is not 100% efficient, so this number gets reduced significantly. In addition, you need energy even if you are resting (of the order of 100W thermal, ~2000kcal/day, but with significant variation in the population).