How does heat generated by metabolism differ compared with heat generated through exercise?

Question

I am from a mathematical background so I don't have much knowledge on biology. I'm building a mathematical model to predict heat generation with parameters of metabolic heat generation and exercise heat generation.

Metabolic heat generation as far as I understand is the heat produced through body's chemical processes, digestion of food, and elimination of waste.

In this article here, the value for metabolic heat generation is given as 33800$W/m^3$. But the exercise intensities as given here only has values of around $582 W/m^2$.

I think we produce more heat when we exercise than through metabolic activities alone. Is this correct?

If so, why does this huge difference in values of 33800 and 582? Why would the heat generated via exercise be such a low value? (Of course they are not measured in same units.)

Is there any other unit other than $W/m^2$ that measures the heat generated through exercises so that it gives a resonably at least closer value to metabolic heat generation?

Answer 1

First, you have to convert your numbers to the same units for any comparison to make sense. Consider that the average human body has a surface area of about 1.8m$^2$ and a volume of about 66L = 0.066m$^3$. Then your numbers are equivalent to 2230W metabolic heat and 1050W exercise heat for an average person.

The value 2230W for basal metabolic rate (from Table 1 of the Bagum et al paper) is nowhere near what's measured in practise. Basal metabolic rate ("metabolic equivalent", 1 MET) would be 105W for an average person according to the wikipedia page you cited, which equals 2150 kcal / day. That's about the recommended daily calorie intake, so it makes sense. I don't know where their value of 33,800 W/m$^3$ for "metabolic heat generation" comes from, perhaps it's meant represent something else (can't say I understand the article) but it's not the metabolic rate for an average human tissue.