system
Given the following post, respond as if you're commenting on Reddit:
human
What is a metric of measuring a persons metabolism ?
gpt
One way that works quite well is to measure *(or indirectly calculate from something else you can also measure)* the mass of CO2 they exhale over a given duration, which correlates pretty closely to caloric output for aerobic exercise. Any video you might have seen of an athlete running on a treadmill with a big mask with hoses hooked up to them is probably measuring the gas concentrations in their breath for this purpose.