Ridiculously high calorie burn figures from walking (Strava)

Bella_Figura
Bella_Figura Posts: 4,351 Member
in Fitness and Exercise
Can anyone explain why Strava assigns so many calories to gentle walking?

I know you have to take the calorie burn figures from sites such as Strava with a huge pinch of salt (the main reason I set my calorie intake from TDEE and don't eat back exercise calories), but I'm curious why Strava considers walking so energy burning comparative to other activity.

I do 2 main forms of exercise - walking and cycling. Cycling outdoors is an efficient activity - the bike, momentum. gravity, drafting, tailwinds etc do a lot of the work for you. So I can understand why walking might burn more calories than outdoor cycling. Indoor cycling, though, is a different beast. No freewheeling. No drafting from other riders. No tailwind. No momentum. And a 7.25kg flywheel doing it's best to stop you in your tracks.

When I do a session on the turbo trainer, it feels like hard work. I get sweaty. My heart rate is elevated. My legs sometimes tremble with exhaustion when I stop pedalling.

When I walk, I don't feel tired in the slightest. My heart rate is barely elevated. I'm never sweaty or out of breath.

So why does Strava think the walking burns more calories?

Here's today's activity, and the calories assigned by Strava:

Walk -
  • Duration: 49:46
  • Distance covered: 4.34 km
  • Pace: 11.27 mins per km
  • Elevation: 17m
  • Calories burned: 410

Walk -
  • Duration: 57:23
  • Distance covered: 4.95 km
  • Pace: 11.36 mins per km
  • Elevation: 18m
  • Calories burned: 467

Virtual ride -
  • Duration: 46:11
  • Distance covered: 22.08 km
  • Km/hr: 26.7
  • Elevation: 109m
  • Calories burned: 315

I use a power meter and a heart rate monitor for the cycling. According to my HRM, on today's ride I spent 6% in the easy zone (under 100 bpm), 7% in the fat burn zone (101 - 116 bpm), 11% in the cardio zone (117-128 bpm) and 76% in the hard zone (129-146 bpm).

I'd've expected the calorie burn from the indoor cycling to be higher than from my two gentle walks, which didn't feel like exercise at all.

Can anyone explain the rationale behind the calorie burn algorithms?

Replies

  • robertw486
    robertw486 Posts: 2,473 Member
    I haven't used Strava for walking or running in quite a while, but looking back the running numbers are a bit on the inflated side as well. But that is the case with a lot of fitness trackers, not just Strava. I found plenty of others even worse, and that's how I ended up using Strava.

    BUT... your comparison leaves out one major factor. Walking is weight bearing, cycling is not. Since we carry our body weight every day we really don't notice it much unless we go on a power walk of sorts, or a longer walk. WIth bikes all that energy is used towards spinning, so it's used differently, but really just standing up takes energy.


    As for walking, a popular study used for testing prediction equations is often cited, and walking calories are roughly body weight x .3 x miles walked = net calories burned. Running was roughly twice as much for net calorie burns.

    For the bike, assuming you have modern meters of some sort, numbers are numbers. Watts are an efficient measurement of power.
  • sijomial
    sijomial Posts: 19,809 Member
    Strava will be a gross calorie estimate for walking but even when I've adjusted for that it's still seemed high.
    I use the net calorie option from this calculator - https://exrx.net/Calculators/WalkRunMETs

    Are you using your power data for your indoor and outdoor cycling (it will most likely be a lot more accurate than using HR)?
    It's also a net calorie estimate.

    PS - don't put too much significance on sweating as regards calorie burns, getting hot doesn't really mean much as regards actual calorie burns. My gym took away the cooling fans around the indoor bikes and I get horrendously hot and sweaty at lower effort levels.



  • Bella_Figura
    Bella_Figura Posts: 4,351 Member
    edited September 2021
    sijomial wrote: »
    Strava will be a gross calorie estimate for walking but even when I've adjusted for that it's still seemed high.
    I use the net calorie option from this calculator - https://exrx.net/Calculators/WalkRunMETs

    Are you using your power data for your indoor and outdoor cycling (it will most likely be a lot more accurate than using HR)?
    It's also a net calorie estimate.

    PS - don't put too much significance on sweating as regards calorie burns, getting hot doesn't really mean much as regards actual calorie burns. My gym took away the cooling fans around the indoor bikes and I get horrendously hot and sweaty at lower effort levels.

    Thanks for the input @robertw486 and @sijomial. Yes, I have a smart trainer (A Wahoo Kickr) so the power data from that, and the HR data from my Wahoo Tickr, feeds directly into Strava. I'm following a training plan, so I target different power zones and heart rate zones in each session on the trainer. Strava estimates my calorie burn from the virtual rides from that power data. I think it does a much better job of estimating the burn from the cycling than from the walking.

    I didn't realise the virtual cycling estimate was a net calorie estimate - I thought Strava was always gross estimate. That's good to know.

    Road cycling, I don't have a power meter, so Strava estimates the burn from my kph data (and possibly my HR data?)

    Indoor cycling is an innately sweaty sport - even with two fans I miss the cooling effect of being outside on my bike in moving air.

  • sijomial
    sijomial Posts: 19,809 Member
    edited September 2021
    Power (whether virtual or outdoor rides) can give you a net calorie estimate but it depends what Strava does with that data.

    If you were using a Garmin to capture your indoor ride then Strava takes across the net calorie estimate from your power and populates the calorie field.
    But I'm pretty sure it doesn't do that for Wahoo, it doesn't seem to operate in the same way as a trusted data source.
    If you look at your workout record on Strava the "total work" value in KJ should be very close to the number in the calories field. If it's not then Strava is doing some poor maths with the data and using less reliable data.

    Strava for outdoor rides also takes the geography of your ride into account. But it can't know whether you are riding in a peleton, battling into a headwind, aero, quality of your bike etc.
    Personally before I got a power meter I found Strava outdoor ride estimates in the "reasonable for purpose" category for my road bikes if a bit on the high side and far too low for my hybrids.
    I ride solo and have the aero of a brick outhouse though......


  • sijomial
    sijomial Posts: 19,809 Member
    If you like manual maths then.....
    Average watts X 3.6 per hour gives a good net cal estimate (e.g. 150w for an hour = 540cals)

    Per minute average watts X 0.06
  • Bella_Figura
    Bella_Figura Posts: 4,351 Member
    edited September 2021
    sijomial wrote: »
    If you like manual maths then.....
    Average watts X 3.6 per hour gives a good net cal estimate (e.g. 150w for an hour = 540cals)

    Per minute average watts X 0.06

    I love manual maths! (I'm a retired NHS accountant). That's definitely something I can work with.

    I've just checked my last 10 virtual rides on Strava and the variance between the figure for total work (kJ) and the figure for calorie burn ranges between 4.58% and 5.68% (with 70% of the entries being under 5%). In all 10 cases, the figure for total work was the higher figure. Is 5% an acceptable margin of error? Depends on the context. In my day job I'd not have been happy if my budget holders had consistently overshot their budgets by 5%...

    EDITED TO ADD:
    I've just worked out the calorie burn of my last 10 virtual rides on Strava using the 0.06 x average watts x mins formula, and compared the result against the calorie burn assigned by Strava - the variance ranged from 10 calories to 16 calories per ride (with Strava assigning a lower calorie burn in 100% of cases). So that gives me reassurance that Strava isn't over-estimating the calorie burn.

    That's really helpful to know. Thanks @sijomial!

    All of this is just to satisfy my interest and curiosity as I use TDEE to calculate my calorie budget anyway - but I just like to know how things are calculated!
  • sijomial
    sijomial Posts: 19,809 Member
    You're welcome.
    I do think that a reasonable variance for exercise is perfectly OK as it would take ages for that variance to show up on our bathroom scales.
    Lets face it - we don't worry if a ripe and sweeter apple has a few more calories than an unripe one. :smiley:

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