Carbonfiberboy 

I made a mistake in my post 43 up there. I said that TP had calculated the calories for those two 154 miles rides. However Strava shows those same numbers, i.e. they were calculated in my Garmin 800 and therefore the PM made zero difference to their calculation - way, way off. I use an HRM whether a PM is present or not, so that's probably what the Garmin used for the calc. So if one doesn't use a PM or HRM, where would Strava get calorie numbers? It's a little bizarre that Strava does a nice kJ calculation from the terrain, no PM, but then doesn't use that figure for calories.

Or are you saying that Strava does use the PM for calories calculations if there's no HRM, but with an HRM it defaults to deriving calories from HR?

WhyFi

I think that Strava is going to prioritize device/app data. In lieu of that, power data x efficiency. If power data isn't available, duration x HR and other bio factors (age, gender, weight, etc, I would think). If there's no other data available, they probably estimate power (speed, terrain, weight, bike type, etc) and then estimate calories based upon that estimate.

Maybe.

Carbonfiberboy 

Interesting that calculations based on HR or power come out that different and that using a PM did not produce a better calorie estimate. I always wear a HR transmitter, so I don't have any no-HRM data. My inputs are accurate, though my Gear weight was a little low for that ride, carrying 3 liters + .~1.5 lbs. of carbs.

WhyFi

I'm not sure what you're referring to. In which instance did using a PM result in a poor caloric estimate? In your two 154 mile rides? If so, what makes you believe that the estimate is poor? What was your total kj via the PM? My ~100 mile rides are typically in the region of 4k cal, so those estimates for 150 miles, even at a slower pace, don't seem far-fetched at all.

If you're talking about the rides that I'd posted, there was no PM present, I was just changing parameters of the bike with Strava.

Carbonfiberboy 

I didn't say that the PM gave a bad calorie estimate, rather that its presence made no difference to the calorie number one way or the other, while you said upthread that it should have. The info you request in in my post 43 which you probably didn't notice. I believe that the calorie estimate is poor because it conflicts with both the PM data and Strava's own estimated kJ figure without the PM.

It's a trifle amazing to me that Strava would use a device's calorie estimate in place of hard data from a PM. It shouldn't be that hard to get that right.

And yes, "at a slower pace." Those two rides were at a 14.9 average, down from 16 in my early 60's. It does have over 9000' of climbing. It was interesting to me that Strava's estimate of my climbing power worked perfectly with the PM on the long climbs.

GhostRider62

Using heart rate is bogus.

Output varies tremendously. Some have a stroke volume of 70 ml per beat and others have 140 or even 200 ml. Moreover, stroke volume of top athletes increases nonlinearly with increasing heart rate.

Any calorie estimate w/o a measure of power is a crapshoot.

ussprinceton

I just bought a Garmin Edge Explore, which I will use this coming weekend. The weather is sunny Saturday, and I will post how many calories I burned, with distance.

WhyFi

Oh, okay, now I see what you're saying. You think that, since calorie estimate was the same on TP and Strava, the calorie data originated with your Garmin 800 and was simply passed on to both TP and Strava.

A quick search yields an old DC Rainmaker post about the various methods that Garmins of that vintage will calculate calories. Seems like a bit of a mess and I can't say that I've ever seen a disparity like that between kj and cal when using a power meter. DCR mentions something about different settings yielding different results, but I don't see mention of whether or not the method used is selectable by the user... but it might be worth poking around the menu.

Regardless, I can't fault Strava with prioritizing data that it's given. I guess it'd be nice if they would provide a "correction" option, like they do with Distance and Elevation, but I still think that your gripe should be with Garmin.

Carbonfiberboy 

Yes, exactly. It's not really a big gripe, it just seems to me that the presence of a PM should default the Strava calories number to the PM data. Shouldn't be that complicated to program.

In any case, MinMan's restart question was "why I'm getting such wildly different numbers on Strava for energy (kJ) and calories here?" I'm pointing out a different source of this type of discrepancy which involves Garmin, along with showing how bad Garmin's calories estimate can be, like a little over half the of the true expenditure. Seems like this PM forward programming should apply to any device, rather than accepting the device's calorie estimate.

Seattle Forrest

I googled and it looks like the average man burns around 2,400 kCals a day, so this probably isn't what's going on.

burnthesheep

For the 1000th time.........HR calories and kj's over count usually because you get credit during recovery when you're not producing any output. Anytime you coast down, aren't pedalling, and the thing is recording.......that's not work you need to get credit for. This is amplified even more for the folks who die on the cross of not using autopause. That in combo with using HR will get you a lot of "fake" work you didn't do.

DaveLeeNC

I assume when you say "KJ's overcount usually because you get credit during recovery ..." you are referring to KJ's derived from a power meter. If so the statement makes no sense. So what kind of KJ calculation are you referring to?

Thanks.

dave

Seattle Forrest

If you've ever seen a graph of heart rate against power, you know this can't possibly be true.

burnthesheep

I typed that on my phone. It copied KJ twice when it shouldn't have. I'm referring to how if someone doesn't use autopause, your HR is recording. However sitting idle no work is being done. So HR calories would accumulate, but not kj's.

Although I would hope the software smart enough to see zero speed and not give credit for the HR while stopped.

So, while stopped your HR might go from sweetspot down to z2 and sit in lower z2 for a couple minutes before you pull off again. There should be no credit for that.

That's what I was trying to say.

DaveLeeNC

burnthesheep Got it - makes sense now. dave

Seattle Forrest

Your heart rate is still elevated after a hard effort finished, because HR lags. But that lag affects the start of an effort too. It takes 30-45 seconds for your HR to start to elevate after you start working. You can see this in your own intervals.

The reason HR is so bad for calories is that there relationship between HR and energy use is weak and tenuous. If the problem was timing, programmers would have solved it, the problem is HR just doesn't have enough information about calories in it.

OBoile

In the absence of power, Wahoo uses HR to calculate calories. Previously, they used HR no matter what, but changed that (I submitted a ticket, but likely so did a bunch of other people). Their HR based value was always greatly overestimated. Strava takes the value from Wahoo (or any other computer that calculates it) rather than calculating calories itself.
Similarly, in my experience anyway, Strava significantly underestimates power in many cases.

sfrider 

Looks like they base it on the old trope of age-related max HR.
Which as we all know is complete garbage.
A lot of genetic variation, but HR also falls off faster when someone is fat than fit.
According to the formula above someone with the same weight, same HR, at a higher age will consume more calories. This is complete nonsense; two people performing the same work will consume exactly the same energy. Age, HR, and weight are all irrelevant.

Better would be to look at the weight, estimated bike rolling resistance, terrain, wind, speed, temperature and humidity, then estimate power and integrate the power estimate over the course slope.

MinnMan

I have noticed that my Strava average power numbers are always lower than that given by my Wahoo, even when I'm using a PM. I've not dug in at all to figure out why. As the PM is giving power at each time step, I figure that Strava is counting increments of time (i.e., below 3 mph or something), that the Wahoo is not counting as "moving time". But I don't really know.

WhyFi

The discrepancy is usually whether or not they're counting zeros in to the average, though an auto-stop threshold might do it, too.

OBoile

I think it's just lower. Strava pauses counting for things like time and average speed, so I don't see why estimated power would be different. Strava's estimates can't know about things like wind speed and direction (often my hardest rides would show the lowest estimated power because it was into the wind), how aero you are, rolling resistance of a given tire/surface combo etc. so they are bound to be inaccurate.
IIRC, I'd average about 170-180 watts on my commute when using a PM and Strava would estimate ~120-130 when I didn't (both done on a road bike). I don't think the relatively few stops (about 80% of my ride is on a bike path) I made would account for such a large difference.

MinnMan

You are talking about Strava's estimated power, which comes into play when there isn't a power meter. I notice a difference when the power is measured with a pm. wind speed and the like shouldn't enter into it.

OBoile

Okay, I was commenting with respect to your OP. As I said above, when there is no power meter, Wahoo uses HR which, for me at least, wildly overestimates calories burned. Strava uses this for calories, but uses it's own algorithm for calculating power and Kj.
With a PM, Wahoo now uses power instead of HR for calorie burn calculations.

With a PM, between Strava and Wahoo, I find they are quite close. Strava actually reads a bit higher for me. This is, as you and others have said, likely due to minor differences in when the unit is paused vs when Strava considers you paused. If it is way off, then yeah, one likely isn't pausing at all.

WhyFi

Just pop in to you Wahoo settings and check to see if it's including zeros (coasting) in the average power calculations - if you're seeing a significant difference, this is probably the culprit. Strava definitely includes zeros in to the average.