I am making an exercise for physics students about the first law of thermodynamics, burning heat and evaporation heat. So my idea is to use cycler which runs on fats and sugars where proportion determined by respiration quotient. The amount of evaporated sweats would be determined from inefficiency of using the fuel. Unfortunately I am unable to find efficiency data to form the exercise.

So what are typical efficiencies to run skeletal muscles on either fat or sugar molecules?


Assuming respiratory quotient measured at the time of cycling is 0.7 so all energy is obtained from oxidizing fats: $$ C_{16}H_{32}O_2 + 23 O_2 -> 16CO_2 + 16 H_2O + \Delta G$$ what part of the $\Delta G$ can do mechanical work $A$ or simply what is typical value of efficiency coefficient: $$\mu = \frac{A}{\Delta G}$$

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    $\begingroup$ A quick google on "muscle efficiency" turns up a number of articles. Wikipedia gives an estimate of 18--26% efficiency, en.wikipedia.org/wiki/Muscle $\endgroup$ – Roland Oct 19 '15 at 6:04
  • $\begingroup$ Muscles first transform those compounds to ATP. $\endgroup$ – inf3rno Oct 19 '15 at 14:54

This is a very complicated question. You need to rephrase your question to be more specific.

Efficiencies of energy utilization from glucose in the presence of O2 (aerobic respiration) are considered to be in the 40% range. Quite good when you consider that an automobile combustion engine is in the 20-25% range.

There is some evidence that betahydroxybutarate (B-OHB) actually provides more available energy for work than does glucose. See Paper Here.

However, what is often overlooked is the energy needed to generate B-OHB from fat during ketosis, which results in a net loss in efficiency compared to glucose.

One of my favorite blogs is Peter Attia's "The Eating Academy." He has a Post that goes into this subject somewhat.

I know this isn't a complete answer to your question, but again, you need to be more specific.

Respiration with or without O2. Efficiencies in generating ATP from source material or only net efficiencies after the ATP -> ADP.

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  • $\begingroup$ I made second part more specific. In your language I want efficiency of energy utilization from fats in the presence of O2. $\endgroup$ – Jānis Erdmanis Oct 19 '15 at 6:39
  • $\begingroup$ If its needed you can also assume that fats are taken only from tissues $\endgroup$ – Jānis Erdmanis Oct 19 '15 at 6:54
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    $\begingroup$ Ok I got right source ncbi.nlm.nih.gov/pmc/articles/PMC543577/pdf/1743-7075-1-15.pdf the lipids have the same efficiency of generating ATP specificly 40% $\endgroup$ – Jānis Erdmanis Oct 19 '15 at 15:53
  • $\begingroup$ Excellent. If my answer was useful, please do indicate so. $\endgroup$ – akaDrHouse Oct 19 '15 at 16:28

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