zacster

My bolt always reads higher on calories. I guess this was my post and I stated that at the beginning now that I've looked!

DrIsotope

Sigh. Upside is (I guess) I'm the most efficient human being alive. 13kcal/mi @ 15mph. AMAZING.

SethAZ 

If I do a ride at 15mph, then ride the same distance at 19mph, the kcal/mile shouldn't be the same at all. The difference in time for those two rides grows linearly, but the effort grows quadratically thanks to wind resistance. I'm unconvinced that the formulas using only HR factor this in properly. As others have already said a bunch of times: use the figures from the power meter. It's the only thing you've got that's actually measuring (not guesstimating) the actual amount of energy that was used to push those pedals. I just got a power meter last week, and one of things about that that pleases me the most is that I finally have some calorie burn figures I can trust. I'm using Garmin head units, and in my rides so far with the PM they seem to be using the kjoule figures appropriately.

DrIsotope

Yeah, literally EVERYONE else uses power data if it's available. I don't know what Wahoo's thinking is, but it's ridiculous.

This morning was 21 miles, 600kj, average HR 105 (47% intensity,) and Wahoo gave me 280kcal.
Thursday was 20 miles, 740kj, average HR 128 (66% intensity) and Wahoo figured 813kcal, which is almost exactly kJ x 1.1, which is what Garmin, etc all use.
Tuesday was 28 miles, 977kj, average HR 135 (68% intensity) and Wahoo figured 1,232kcal, which might as well be a made up number.

So apparently, If I ride with an average HR 125-130bpm, Wahoo will get at the least reasonably close. But drop below 120 or go above 130 and might as well just guess. Efforts above 70% are like 800-900kcal per hour.

Now I do have power, so I know what's what-- but I'm also a slave to the damn Activity Rings on my Apple Watch, and end up doing a lot to close them when Wahoo is giving me half on calorie burn.

SethAZ 

I have to say I'm actually impressed by Strava's calorie estimate, at least so far as I just compared. There's a 32-mile route I've ridden dozens of times in the past, and I just did it today again for the first time since I got back from my deployment, and the first time ever with actual power data. I chose a few rides from that historical data, and especially one particular time with very close moving time and average heart rate to today's ride, and Strava's calorie estimate was within around 10% of what I measured today. That's not actually half bad. I haven't compared other rides, or rides with very high heart rate or whatever. I was actually expecting it to be worse than it actually was.

Iride01 

I never understand the arguments about what's more accurate or this device give one thing when another device gives something else. As long as you take your number from the same source, then you'll be able to see the relative differences in your performance from one to the next with reasonable accuracy. Especially if you are looking at the data of multiple rides.

None is going to be what the real number is. Calories in particular as we don't have sensors to measure the things that will more accurately tell us Calories burned. Even power has some guesstimations in it's numbers.

JohnJ80

Sure they are. Power is a direct measure of the energy used which is what calories are. The power integrated over time is the energy you burned.

Iride01 

You can believe that if you want. But calories, watts or any measure will have some fudge depending on where they are measured on the bike. And if you want to talk Calories, instead of the calories you mentioned, then your body will burn more Calories in order to produce the calories we measure with a power meter. So there lies a fudge factor for that too which is not exactly the same for every person.

While I will agree that power meters are more accurate, they aren't perfect either. It's just they are able to show data that bean counters can balance more often than not. And the difference from whatever that real number is, is a lot closer to the truth.

JohnJ80

So, I can “believe” what? Power isn’t directly related to energy over time? That’s pretty much the actual definition of power.

a power meter measures accurately (within a few percent) of the power put into your cranks which is going to be within a few percent (worst case) of the calories you burn by turning those cranks. The other measurement methods are all over the map and sometimes like +/- 50% based on the 4 different computers/algorithms I’ve tried.

so, I think you’re wrong. Sorry.

Seattle Forrest

According to dozens of dozens of research studies by many independent third parties, the number of kilo joules measured by your PM is within 5% of god's honest truth in terms of calories burned on a bike.

Iride01 

5% is still a difference from the real number.

Most of my argument concerns Calories, which is a dietary thing. When we get in conversations it is hard to know whether someone is talking about the work needed to move a bike and rider a certain distance or whether they are talking about how much energy their body burned while doing that particular amount of work.

If you want to believe that it's such a small number and doesn't matter. I'm actually in agreement with you. It's not big enough to matter. And that goes for either power meter or Calories derived from a cyclometer with HR.

Power meters are more accurate. There is less to argue about with their data for any one particular ride. But they aren't perfect.

So most of my argument falls apart because you and I aren't talking about the same thing or application of how it's used.

JohnJ80

The variance between bike computers and methods used with HRM for caloric measurements are a LOT more than 5% to the point where they are largely useless.

I looked at Garmin, Garmin with HRM, Garmin with PM, and then between the same for Wahoo and for an iPhone App called Cyclemeter. The variance was about 100% - literally twice as much between methods. And around 40% with HRM to PM on a given brand. Repeatability was not good either because heart rate is influenced by a lot more than just exercise. However, the correlation is super tight between a PM because it’s a direct measurement of the effort or energy put into the cranks.

5% is a pretty good tolerance for most things engineering and I think that applies here. I agree, that is small. But the HRM methods to measure calories are not much better than a guess.

I had many of the same arguments until I finally bought a PM and tested it. I’ve been riding with them now for about 5 years and it’s been consistent. Go verify this yourself. You’ll get the same results.

J.

Seattle Forrest

Let's start with the assumption that calories are a real thing. 🙂 A calorie is the amount of energy it takes to raise the temperature of 1 gram of water by 1 degree C. Your body uses energy (normally measured in calories) to do work (here measured in joules; 1 watt = 1 joule per second). You can nail this down in a metabolic ward where you can measure everything, otherwise it's a hidden variables problem.

​​​​​​There's a pretty stable relationship between work and the energy needed to do it. It's just hard to measure how much work was actually done - bikes can coast, for example. Hidden variables problem.

A power meter itself has a maximum error of 2% or better. Human metabolic efficiency ranges from 21 to 25 %. If you just cross out kilo-Joules and write kilo-cals in its place, that assumes you're right in the middle of the range. There's 5% total uncertainty, but it's closer to 2.5% in either direction.

You can get a pretty good estimate for calories burned from walking, too, on the mass over distance principal. Nobody walks fast enough for air resistance to be an important variable, and you can't coast. Running has more uncertainty because of running economy, are you wasting to much energy bouncing up and down for the amount of forward progress you're making? Cycling doesn't have that. Your feet are bolted to pedals that can only move in a fixed circle. You can waste energy with an upright posture, or brakes that drag, but the power meter knows how much energy you're using, just not why specifically.

You can guess without a PM, based on HR or on physics, but those have a maximum error of, well, infinity. I did a little bit of testing a Garmin based on HR vs my PM. It was always within 40% in practice. Sometimes very close, like a broken clock twice a day. You didn't have any idea whether the HR estimate was close or not for any given ride.

It's true that what your PM says isn't the 100% truth but it's the best thing by far outside of an expensive lab, and basically considered a gold standard. For good reason. Do a century ride, and the uncertainty converting for measured kJ to kCal is about one Oreo cookie.

And this is why it's baffling that they would ignore the power meter and guess by any other means.

JohnJ80

great answer.

Bottom line: if you want to know an accurate and repeatable calorie measurement on a bike, you need a power meter.

Seattle Forrest

I know indoor rowing machines can measure power, too. Really don't know much about how that works. I don't think the translation to calories is as close to 1:1 in a boat, I know that what we've been talking about is specific to cycling. Most rowers seem to ignore power.

I want a power meter for Nordic skiing, which probably isn't possible in principal without significant guess work. No idea how those joules would translate to calories. But it would be great for pacing, and it would help me understand where I'm using the most energy, what I get for it, and if a different approach would yield very different results.

There are starting to be running power meters, for people who run hills. As a pacing tool.

Anyway, the calories thing is just a side effect of how a PM works and of how humans behave on bikes. Almost no one buys them for that, that's just icing on the cake. Most common reasons people use them on bikes are for training (targets for intervals, how you actually did in intervals), for overall pacing, for long term fitness vs freshness, and to a lesser extent for aerodynamic testing.