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How many joules expended for a push up?

by wannab
Tags: energy, press up, pressup, push up, pushup
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wannab
#1
May18-13, 09:53 AM
P: 32
Just wondering if any of you can do the calculation that well approximates the amount of joules expended by a push up.
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256bits
#2
May18-13, 10:15 AM
P: 1,484
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.
wannab
#3
May20-13, 06:01 PM
P: 32
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 -_-

wannab
#4
May20-13, 06:03 PM
P: 32
How many joules expended for a push up?

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.
Redbelly98
#5
May20-13, 06:28 PM
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Quote Quote by wannab View Post
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.
mfb
#6
May20-13, 06:31 PM
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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.
antlhem
#7
Jul17-13, 05:13 PM
P: 1
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
mfb
#8
Jul17-13, 06:13 PM
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P: 11,928
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).


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