Converting between Power, VO2, and METs
 

Putting this here to make it searchable, so when anyone (I) needs to do a conversion, they (I) can find it. Please comment if you think I got something wrong, and I'll update.

These conversions are based on a leg ergometry equation from ACSM's Guidelines for Exercise Testing and Prescription, (a paper book that I am too cheap to buy).

Definitions:

• MET: Metabolic Equivalent of Task. A common measure used by scientists. One MET unit is roughly the energy expended when sitting quietly, set by convention at an oxygen consumption (VO2) of 3.5 ml/kg/min.
• VO2: A person's rate of oxygen consumption, typically in units of milliliters per kilogram body mass per minute (ml/kg/min).
• PWR: Power to Weight Ratio. Power produced at the cranks divided by body mass (watts/kg).

Conversions from PWR (W/kg):

• VO2 (ml/kg/min) = (10.8 * PWR) + 7
• METs = 0.286 * VO2 = (3.09 * PWR) + 2

Limitations:

• steady state sub-maximal aerobic exercise
• power range 50-200 watts

ACSM Leg Ergometry Equation:


https://cimg0.ibsrv.net/gimg/bikefor...51b917c4f7.png

Source: PowerPoint from immagic.com


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UPDATE:

What About Power At VO2max?

Since the ACSM formula is limited to "sub-maximal aerobic effort", it doesn't apply to VO2max.

However, this paper:

Hawley, J. A., & Noakes, T. D. (1992). Peak power output predicts maximal oxygen uptake and performance time in trained cyclists. European journal of applied physiology and occupational physiology, 65(1), 79–83. https://doi.org/10.1007/BF01466278

has a formula for VO2max and peak power, based on a ramped power test, starting at 100 watts and increasing by 25 watts every 150 seconds.

Definitions:

• Peak Power Output (PPO): highest power achieved (Watts)
• Body Mass (BM): body mass of cyclist (kg)
• Peak Power to Weight Ratio (PPWR): PPO divided by BM (W/kg)
• VO2max: maximum oxygen consumption (ml/min/kg)

Formulas:

• Calculate VO2max from PPO: VO2max = (1000 / BM) * (0.01141 * PPO + 0.435)
• Calculate VO2max from PPWR: VO2max = 11.41 * PPWR + (435 / BM)
• Calculate PPWR from VO2max: PPWR = 0.0876 * VO2max - (38.12 / BM)

Thanks.

Whenever I see the ACSM guidelines, I always wonder what the goodness-of-fit is on these equations, and what happens above 200 watts.

a (probably) dumb question that doesn’t seem to be readily explained or answered.

if using the formula above to calculate VO2 MAX, what duration does the power output need to be sustained for? is the watt value intended to be FTP, a power output level the can be sustained indefinitely, peak for 5 min, etc?

I don't think the formula is valid for calculating VO2max. It's limited to "steady state sub-maximal aerobic exercise".

makes sense. especially given the watt range limitation.

Seems like pretty good rules of thumb. Thumbs up.

FTP and VO2 max relationship does vary especially older athletes. Maybe they get more efficient as some have proposed to explain the high capacity utilization or maybe oldtimers just more stupid

A third and, to my mind, more likely, possibility is that VO2max falls faster than FTP with age. Certainly true in my case. Longitudinal studies are needed to answer the question.

I started doing rando when I started getting dropped on the hills in competitive group rides, and did very well with rando. I also see that trend in various event rides. We lose the high end first. Experience in pacing might have something to do with it, too.

There was a saying going around in the clubs, I don't know if it's still around:

When you no longer can go fast, go long.

This was the inspiration for some of the "death march" rides in California. We olds may no longer contest the city limit sign, but we tend to do okay on the longer stuff.

Yes, that's the symptom. We may not even care about the cause. :)

I added an update, above, for a formula to relate power and VO2max.

I plugged in some numbers to the formula, and the results don't seem crazy.

Comments welcome.