Trust your Garmin??

21 September, 2014

I always thought it was weird when Jess and I would do the same ride and our Garmin/Polar gizmos would say that I burned significantly more calories than she did. Jess said it was probably because I was bigger, male, and had a larger muscle mass. I was happy with that since it meant that I was burning an extra 50% of calories without putting in any extra effort. More cake for Rusty 🙂

Then I decided to graduate from the wrist-mounted HRMs (I’ve got a Garmin Forerunner 405 GPS/HRM and a Garmin FR70 HRM) to a handlebar mounted one (Garmin Edge 500). This is a fun new toy that makes ongoing monitoring of my HR and speed really easy. Digging under my sleeve and glove to see the readout on the wrist-mounted version was really annoying.

I knew I’d got fat over autumn/winter and am keen to shed a few kilos so I’ve been keenly watching the calorie counter on the new Edge 500. Unfortunately, I’ve been horribly disappointed. I thought I was doing rides at efforts that used to  burn way more calories than I was seeing. We’ve all done Lake George a million times – it’s not hard to know when something isn’t right.

So I ran a little experiment this morning. I set my three Garmins to exactly the same settings (age, weight, sport etc) and paired them all to the same chest strap. I did a little check and it was working well – I had the exact same HR on all three devices. Then I went for a reasonably easy ride to Lake George this morning. The picture says it all…….

The only issues is that I don’t know which one to believe. Am I allowed cake or not!?!?!

Three garmins with all the same settings and paired to the same chest strap for exactly the same time. Dodgy!!
Three garmins with all the same settings and paired to the same chest strap for exactly the same time. Dodgy!! (nb: the HR on the Forerunner405 on the right is the average HR for the whole ride, the other two are showing current HR. I checked all three and the average HR for the whole ride was 118 on all devices. This means they all paired to the chest strap and recorded HR the same. IT was in the calculation of calories burned that they stuffed up)
General

3 thoughts on “Trust your Garmin??”

  1. I think you’re barking up the wrong true. I think the calorie number comes from some formula that is based on your kms covered, speed, accelerations in speed, and height climbed that calculates work done (no heart rate input). The different numbers reflect different formulas? (and maybe inputs?). A power meter would give you a more accurate calculation of work done which, I suppose, approximates calories burnt.

    Keep on geeking brothers!

  2. The Garmin on the right is showing 118 bpm, and the left pair are showing 68 bpm
    .
    I am not sure it is valid to pair more than one device with one HRM.

    Perhaps use three chest straps to do this more reliably.

    1. The one on the right is showing the AVERAGE HR for the whole ride. To see the calories on the Forerunner 405 you first need to end the recording and look at the stats for the whole ride in the history. The other two have stopped recording but are still showing CURRENT HR.

      Using three straps would introduce a whole new variable that would, in turn, introduce a whole new error factor. Using the same strap for all three ensures the signal is consistent. It is only the interpretation of the signal that varies. Reductionist science is the most effective.

      I checked it more carefully than that. You can trust me (but not garmin)

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