Calorie Counting - Apple Watch Vs. Power Meters
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05-07-20, 12:34 PM
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A power meter measures work done. (1 watt = 1 Joule per second.)
This active/total breakdown doesn't exist for power meters. If you stayed on the couch, it would read zero. You're still burning your BMR on top of what the PM says.
A power meter doesn't "see" effort like keeping the bike upright, but there's very little effort involved there, the bike "wants" to remain in balance. Thousands of independent studies have demonstrated that a PM is the most reliable way to "measure" calorie use outside a metabolic ward. When you run there's a lot of opportunity to waste energy, it's called "running economy." But we don't have that. You spend 99% of a ride seated. Your feet are clipped to pedals turning the exact same circle every time. There's no vertical oscillation with each step, there's no tradeoff between flight time and stride length, etc. You can waste energy by sitting upright or using brakes that rub, but a PM will see the result of things like that because it measures work done overcoming all opposing forces.
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05-07-20, 12:59 PM
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I don't have an outdoor PM, but I just got a Tacx Neo 2T which has a built in PM.
These are my numbers from my 20 mile, 1hr 15min ride yesterday:
AW Total Calories - 873 (workout + calories I would have burned if I didn't workout)
AW Active Calories - 743 (workout only)
PM Calories - 501 (I'm not sure who's algorithm this is... i.e. Zwift, Strava, or the Tacx?).
So yeah... quite a difference.
On the other hand, I've tested the AW HR against my Garmin HRM and they are pretty spot on. I've even tested it against a HRM at a gym and the AW is always the same as others.
These are my numbers from my 20 mile, 1hr 15min ride yesterday:
AW Total Calories - 873 (workout + calories I would have burned if I didn't workout)
AW Active Calories - 743 (workout only)
PM Calories - 501 (I'm not sure who's algorithm this is... i.e. Zwift, Strava, or the Tacx?).
So yeah... quite a difference.
On the other hand, I've tested the AW HR against my Garmin HRM and they are pretty spot on. I've even tested it against a HRM at a gym and the AW is always the same as others.
Last edited by justonwo; 05-07-20 at 01:07 PM.
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05-07-20, 01:03 PM
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For the sake of clarity, someone needs to point this out. I'm not about to say anything anyone doesn't know, just maybe solidify the concept.
A power meter measures work done. (1 watt = 1 Joule per second.)
This active/total breakdown doesn't exist for power meters. If you stayed on the couch, it would read zero. You're still burning your BMR on top of what the PM says.
A power meter doesn't "see" effort like keeping the bike upright, but there's very little effort involved there, the bike "wants" to remain in balance. Thousands of independent studies have demonstrated that a PM is the most reliable way to "measure" calorie use outside a metabolic ward. When you run there's a lot of opportunity to waste energy, it's called "running economy." But we don't have that. You spend 99% of a ride seated. Your feet are clipped to pedals turning the exact same circle every time. There's no vertical oscillation with each step, there's no tradeoff between flight time and stride length, etc. You can waste energy by sitting upright or using brakes that rub, but a PM will see the result of things like that because it measures work done overcoming all opposing forces.
A power meter measures work done. (1 watt = 1 Joule per second.)
This active/total breakdown doesn't exist for power meters. If you stayed on the couch, it would read zero. You're still burning your BMR on top of what the PM says.
A power meter doesn't "see" effort like keeping the bike upright, but there's very little effort involved there, the bike "wants" to remain in balance. Thousands of independent studies have demonstrated that a PM is the most reliable way to "measure" calorie use outside a metabolic ward. When you run there's a lot of opportunity to waste energy, it's called "running economy." But we don't have that. You spend 99% of a ride seated. Your feet are clipped to pedals turning the exact same circle every time. There's no vertical oscillation with each step, there's no tradeoff between flight time and stride length, etc. You can waste energy by sitting upright or using brakes that rub, but a PM will see the result of things like that because it measures work done overcoming all opposing forces.
1:15:39 hh:mm:ss @ 116 W is 526,524 Joules delivered to the power meter. Strava estimates 501 kcal consumed by your body, or 2,143,000 Joules. This yields an efficiency of 24.5%, which is right in the normal wheelhouse. I think Strava is giving you a very active number for calories burned, within the limits of what is reasonable/feasible.
I was actually looking for a better way to keep track of my progress (I used to use miles ridden when I was riding the same route outside without a PM). Now I think I'll use total Joules.
05-07-20, 01:50 PM
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I use a lot of things to judge how I'm doing. Quick and easy is how much power I put out over various time frames. I can make big numbers for 10 seconds, that's what my genetics gave me, so I want to improve my 60+ minute power. Most of the riding I do is in the city, so I can't go as hard as I can for an hour, but I have routes that let me go all out for 20 minutes. So my best 20 minutes power winds up being a pretty good way to make a graph of my bike fitness.
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