At last I got out for some exercise today with a ride on the bike after work. It didn’t rain, but the road surface was quite wet, which I always find a little intimidating with my skinny little road tyres and all those white lines painted on the road – they can be very slippery if you’re not careful. I stayed around the local area because of the threatening skys, just over 29kms in 1:06.

On her blog today Scarlett referenced my 4,000 kCals per week / 6 hours of exercise goal and marvelled at this being 666 kCals/hour. Scarlett, I use the kCal calculation from SportsTracks from my Garmin data. I was finding that the native calculation from my Garmin was a bit screwy, especially as it was telling me I was burning more calories cycling than I was running – which I know is not the case – I know how much more screwed I am after a run than a ride. Anyway, when I download the data in SportsTracks and click the little calculator icon next to the Calories field it recalculates down a fair bit, and the cycling goes down below the running on a per hour basis, and it ends up pretty close to where it was when I was using my Polar watch. So, I think it is reasonably accurate.

For a run it ends up being in the 820-850 kCal/hour range and for a ride it is about 720-750 kCal/hour range. I only occassionally wear my heart strap during home exercise and so estimate these at about 260 kCal/hour. Similarly when I swim it is an estimate, based on wearing my Polar strap during a few swims a while back – my swim estimate is 500 kCal/hour. Overall my average for the year to date, for all exercise types is 648 kCal/hour.

Now, if there was any doubt about my Nerdy McNerd-ness, let me rid you of it. I often forget to put my heart strap on when I ride my bike, and was therefore constantly going back looking for rides of similar length and speed to make an estimate when I put the ride in my training journal spreadsheet. So, I decided to extract about a years worth of bike data and come up with a formula I could use to estimate my kCals when I ride without my heart strap. After a few iterations, here’s what I came up with;

kCals = (32.3+(AvgSpeed-25.6)*0.525)*(24*Duration)*AvgSpeed

where AvgSpeed is in km/hour and Duration is in Excel time format (ie fraction of a day, eg 12 hours would be 0.5).

For me, this seems extremely accurate, it seems to be within 4-5 kCals for every ride where I’ve checked it against the Garmin/SportsTracks number. Recently I’ve actually stopped wearing the strap because I’ve got a bit of eczema underneath where it goes and have just been using my formula.


5 Responses to “kCals”

  1. katsmumblings Says:

    wow. I think I will just stick to wearing my strap and looking at the watch to tell me what I’ve done. I am just way too lazy.

  2. Cilla Says:

    The general consensus is that we over-estimate calories burned during exercise – whether it be ourselves or a computer doing for us.
    We think we can eat what we like after we have been for a run. This is not true.
    I don’t worry so much about calories burned during exercise – I am now trying to be a little more mindful of what I put down the cake-hole.

  3. Cilla Says:

    nerdy mcnerd? hahahaha is that what your kids call you??

  4. morseyruns Says:

    All hail King Nerdy McNerd- seriously, that is a very nerdy thing to do- and I am only massively jealous that you had the ability and inclination to do it! Nice.

  5. Scarlett Says:

    Mmmmmmmm statistics… Once I get back to my Cert 4 I can imagine myself as a numbers obsessed personal trainer, figuring out the sort of calculations that you just demonstrated. Thanks for the explanation 🙂

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