Is there an easy way to measure the power production of living beings? For example, Wikipedia says that humans can sustain about 75 watts of output.
How did they measure that? I’m envisioning some sort of enclosed dome where some hapless guy just keeps doing jumping jacks while scientists measure the increase in temperature, or something like that. But I haven’t got a clue.
Well, a horse can manage 745 watts - one Horsepower.
Generally, you measure this using a dynometer - moving a known mass a measured distance. However, a treadmill or cycle hooked up to a generator is common - you just measure the electrical output.
You can also just do some basic math - if you know a cyclists weight, the mass of his bike, the height of the col and the time he took, you can make a good estimate of their power output. Same for animals, but working animals are generally easier to generate numbers for.
There might have been an upgrade or two in the past 100 years.
Well, I guess that measures their capacity for work, but not their resting metabolism, for example. Or for some species that you can’t easily control (sharks, fish, primates, whatever) and you can’t get them to pull a weight on command, what do you do?
You measure oxygen consumption. This can give an inaccurate measure of output in the short term since some work can be done anaerobically. However, performing work without sufficient oxygen results in oxygen debt. This debt will be repaid in the form of higher baseline oxygen consumption after the work ceases.
No, this measurement is not the heat produced in the body, the measurement includes NONE of the heat produced in the body.
This measured power is the mechanical power delivered externally. Watt’s specification was to say that that a horsepower was the force (F ) ,eg on a rope, that a work horse can pull when walking at ordinary work horse gait, velocity v… and power =F * v. In fact this is the net power the horse makes, what power the horse contributes to a load only.
The horsepower unit of 700 odd Watts is a nominal figure, and is certainly far from the peak result off the best horses… its probably measuring a weak horse or a horse working in poor circumstances (eg slipperly floor.)
How do we measure the runners power ? We aren’t measuring the ability to drag a load … what load ? So they look at the power put into the bulk movement of the person… Do we just estimate the drag of the air ? or do we measure the temperature of the sole of the shoe and work out what power it takes to warm the shoe like that ? Do we include the power it takes for the runner to flap his arms ? Thats part of the reason for the wide rangers quoted in the wikipedia entry - who knows what each author is including or excluding ?
You can calculate Metabolic activity by monitoring heart rate, oxygen consumption and carbon dioxide production both resting and under defined load. Such experiments are used to calculate human efficiency rates, and provide the basis for exercise monitors that use defined load and/or heart rate to estimate energy use. They are all just approximations, but some are claiming high levels of accuracy.
For animals, it is harder. But we have good stats for some working animals (horses, dogs, oxen, elephants) that can be used to inform us about other animals. We also have good models of drag/resistance for aquatic animals, so can make estimates for some fish/ sharks/mammals. But you are correct - it is very difficult to measure directly or accurately.
I worked at a Department of Energy facility in the 1990s where we built calorimeters for measuring heat produced by plutonium samples. To demonstrate the sensitivity of our most precise calorimeter, we stuck an ant inside and recorded differential the temperature. According to the data we collected, the ant ran around inside the calorimeter for three days, and then died. I don’t recall how many watts the ant produced, but it wasn’t much.