Calories burned and Strava/Wahoo/Garmin calculation

navrig2

I did a small group ride this morning and afterwards I compared stats between me and a friend who did the same ride.

The basis stats are:

Weight me: 82kg
Weight him: I guess 90-95kg
Device me: Wahoo Elemnt
Device him: Garmin 810

The ride data for both of us is similar enough not to make a significant difference so just taking mine from Strava.

Distance: 75km
Moving time: 183mins
Elevation: 765m

Now the difference:

Calories me: 1527
Calories him: 3527

I checked on the Elemnt app and calories are not shown so I assume that Strava does the calculation. I am not sure in Garmin calculates and provides calories data.

According to this website: https://caloriesburnedhq.com/calories-burned-biking/

My calories should be 3100 which is probably more in line with his 3527 given his extra weight.

Why the difference and is it Wahoo or Strava which is screwing the calcualtion?

navrig2

Neither of us was wearing an HRM.

N0bodyOfTheGoat

Any significant bike weight, other bits added to bike stats like water bottles; tools etc. difference?

pblakeney

navrig2 said:

Neither of us was wearing an HRM.

I was under the impression that Garmin uses HRM to calculate effort and therefore calories. I could be wrong.

navrig2

N0bodyOfTheGoat said:

Any significant bike weight, other bits added to bike stats like water bottles; tools etc. difference?

No but even if there was the calculation would not factor that in unless it was reflected in the personal data in the app or device.

navrig2

pblakeney said:

navrig2 said:

Neither of us was wearing an HRM.

I was under the impression that Garmin uses HRM to calculate effort and therefore calories. I could be wrong.

I can believe that but I should imagine that it only determines the effort rather than the energy expended. Basic physics/maths should determine the calories/energy expended on the basis of moving a defined mass (82kg) over a certain distance and height. The HRM and speed will/should only fine tune the calculation.

I looked back at my Trainer Road sessions and a typical 60 minute session recording HR, cadence, power for me expends just under 500 calories. However that recognises that I am not actually moving my 82kg any distance along or up. A 3 hour ride should, I think, expend more than 3 times the TR 60 minutes session. So 1500 calories plus the difference in energy to shift my 82 kg.

All this makes me thing that Wahoo and/or Strava have got something wrong with my calculation.

pblakeney

I was thinking a fat heavy bloke at 170 bpm would be burning more calories than a fit muscular heavy bloke of the same weight doing the same ride and speed at 130 bpm. Again, I could be wrong.

sungod

without real power data, they simply are using different incorrect methods to guess different incorrect answers (including the website)

if you want a guess, choose one method, stick to it

it'll be wrong, but there may be some useful comparative/trend indication (barring day to day variations in aerodynamic impact, which can be significant)

navrig2

pblakeney said:

I was thinking a fat heavy bloke at 170 bpm would be burning more calories than a fit muscular heavy bloke of the same weight doing the same ride and speed at 130 bpm. Again, I could be wrong.

I think you are right but the higher heart rate would not be the main consumer of energy, it would be the physical effort of shifting the body (I think).

sungod said:

without real power data, they simply are using different incorrect methods to guess different incorrect answers (including the website)

if you want a guess, choose one method, stick to it

it'll be wrong, but there may be some useful comparative/trend indication (barring day to day variations in aerodynamic impact, which can be significant)

I get that but why the discrepancy. Any adopted method which is inherently inaccurate should have some consistency. If it is down to differences between how Wahoo and Garmin calculate calories burned then surely there should be an easy way for one of them to recognise their significant inaccuracy and adopt a different but better method.

N0bodyOfTheGoat

Given that Strava gives a headline average speed based purely on your moving speed, rather than how long it took you to ride "x" miles, plus its weighted average power gives an often lower figure than the Dr Coggan Normalised Power formula etc. ... I know which Calorie estimate I'd be more wary of.

ugo.santalucia

Without a power meter, it is difficult to get a good estimate. With a power meter, just take the total energy output number (or total work) in Kj and roughly that is your energy consumption in KCal. The conversion between Kj and Kcal is about 4 to 1, so 25%, which is also roughly the thermodynamic efficiency of the average athlete… so for every calorie you spend, you produce 1 joule of work

navrig2

The calorie numbers I quoted are taken from the Strava app on my phone. On the desktop website calories are not given, instead Strava shows energy output.

Me - 1,370kJ
Him - 1,631kJ

At least there is some correlation with these numbers.

wavefront

I can’t answer your question about the discrepancies but, as you measure power on your turbo, I assume you know the av watts you’d put out for an easy, moderate, pacy, and race efforts. You could then guess the power you do outside on a ride based on your experience indoors (if you don’t use a PM) , and simply multiply by 3.6 and the length of the ride in hours.

An easy ride for me is around 190-200 watts, so I know in 3 hrs I’d use around 2160kj. On a fast paced tempo same duration I’d be at 2700kj. A 40k tt would be 1000kj.

On your example you’d only be riding at around 140watts …. At 82kg and 25kph I’d think you’d be pushing out more watts than that and hence more calories. But I doubt your mate would be pushing 325w for three hours and only achieving 25kph so his kJ consumption is far too high.

wavefront

navrig2 said:

The calorie numbers I quoted are taken from the Strava app on my phone. On the desktop website calories are not given, instead Strava shows energy output.

Me - 1,370kJ
Him - 1,631kJ

At least there is some correlation with these numbers.

Sorry, just seen this. What power numbers did strava attribute to you and your mates ride? (I assume the Strava derived ones and not actual PM numbers)

navrig2

Power from Strava
Me 125W
Him 141W

wavefront

navrig2 said:

Power from Strava
Me 125W
Him 141W

So that ties up well with the KJ strava is estimating. As Ugo said, 1kj used is pretty much the same as 1 calorie used (only in cycling - there’s many an explanation why on the internet, trainer road has a good explanation). So, IF, the power was accurate on Strava, you’d have used 1370 calories on your ride. Your mate 1631 calories, as calories used are linear to power output and nothing to do with weight. But as you know Strava can be quite inaccurate with power estimates. I’ve been thinking lots about this and still I can’t answer your original question, as to why the you originally got strange calorie values. sorry!

navrig2

Thanks guys that has helped somewhat.