# Efficiency of muscle

• 04-28-2004, 11:30 AM
Big & Tall
Efficiency of muscle
I was wondering what is the efficiency of human muscle? For example, how many kilocalories does one burn in order to, say, increase the potential energy of a bar while bench pressing. Of course, simple PE calculations wouldn't quite work--you'd really have to look at an integral of acceleration (~force) over a range of motion to calculate the actual work done, but you get the idea.

Similarly, when doing cardio, you are essentially working against a brake dynomometer. Is the number of calories burned reported by the machine a direct representation of the work disipated by the dyno, or is it modified by some average efficiency value?

Yes, I was bored, and yes, I am an engineer.
• 04-28-2004, 11:42 AM
ectx
Here's the catch. BIological systems are very different from mechanical systems. Muscular efficiency is calculated on multiple levels with a high degree of variability. this is not a pure science like physics and chemistry. Think about it...what will govern it's efficiency:
temperature
fuel source
efficiency of metabolic enzymes
cellular permeability
fiber composition
rate of nutrient delivery.

Within each is a series of variables that provide even greater variability...

ie. for each metabolic enzyme or delivery molecule efficiency will vary because of variation in the molecule's structure.

or

ie. The rate of transcription for a particular enzyme or molecule.

Can you see where this starts to get very complicated?

It's not a simple formula answer. And this, my friend, is why drugs cost outrageous amounts of money.
• 04-28-2004, 11:47 AM
Pudgy
ouch my brain
• 04-28-2004, 11:52 AM
GonePostal
mgh*k
where k is the coefficient of efficiency which in reality can only be measured on a case bay case basis but in general they just make an estimation.
• 04-28-2004, 11:59 AM
ElPietro
• 04-28-2004, 12:07 PM
ectx
but what is the question?

*goes and chops up pedrito's brain to figure out the question to the answer the very smart mice requested*
• 04-28-2004, 12:10 PM
ElPietro
I do not have the time to explain things to those who cannot understand.
• 04-28-2004, 08:39 PM
Big & Tall
Yeah, 42 is about what I was thinking :)

Gonepostal: That is what I figured on for a very rough calculation, but how is it even possible to make an estimation of an efficiency coefficient? How can we really get an internal measurement of calories burned? External work is easy enough to measure, but I have no idea how internal work could be measured.

As an example of this, how have we arrived at the old standby of burning 3500 calories to lose a pound? One pound (448g) of animal fat, would contain 4032 calories if eaten (at 9 kcals/g). Does human adipose have a higher water content, or is there some measure of efficiency in there? i.e. by doing 3500 kcal of external work, one can reduce fat mass by 1 pound. This would give 3500/4032 = ~87% efficiency, which seems pretty high. Are existing data based on long term changes in fat mass based on measurements of external work?

Okay, time for me to stop thinking before I hurt myself.
• 04-28-2004, 09:05 PM
VasDeferens
Quote:

Originally Posted by Big & Tall
Yeah, 42 is about what I was thinking :)

6 X 9 = 42