Eating back calories earnt on a bike - kJ or Calories?

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ConicalFern
ConicalFern Posts: 121 Member
edited January 2017 in Fitness and Exercise
I recently got a PowerTap hub for my bike and have been looking forward to getting accurate calorie reading with this. Looking online, everyone seems to says that, for cycling, 1 kJ = 1 calorie. However, when I upload to Strava, these two figures seem rather different, for example, on a recent 61 mile ride the calories were 2753 but the total work 2469 (12% difference), or a Mars bars' worth.

I always eat back my exercise calories - which one should I chose?

Thanks

George

Replies

  • waynetimmins
    waynetimmins Posts: 3 Member
    edited January 2017
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    I also use a power meter for training(stages) the measurement of kj derived from watts is very accurate as it a quantifiable measurement, however it does not take into account the actual energy needed by the body to convert fuel into energy i.e thermal effects etc. Software carries out some sort of wizzardry black magic stuff to calculate this but this is the part where there is a slight bit of guess work that is why you will always see a variation between the two readings. It's still way more accurate than using heart rate alone and I always use kj as a metric.
  • NorthCascades
    NorthCascades Posts: 10,970 Member
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    Studies show that all humans fall into a very narrow range of metabolic efficiency on a bike. It's not like running or skiing, you're turning pedals in a circle.

    Calories = Joules * 1.1 to 1.3, you're somewhere in the middle. In the grand scheme of things it's such a small difference it really doesn't matter.

    My Garmin (Fenix 3) just changes the label from kJ to kCal. I guess that's erring on the side of safety. I'm using Vector pedals.

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