This time I look at the effects of WEIGHT and HEIGHT on the Garmin Running Power numbers. Does it take weight into account as it claims?

In an attempt to partly fill my own curiosity I have looked at some of the inputs to Garmin’s Running power algorithm over the last week or so.  These links show what I anecdotally found.

• VO & GTC (link here)
• Pace from different sources (link here)
• Wind  (link here)

So what else can I look at? Well, the table below is directly from Garmin.com and nicely summarises the inputs to their running power model.

As a note to that table, Garmin point out the following, (complete with typos):

*The running power app uses the same speed that is displayed on the watch and logged in the activity file.  If you have the footpod selected as your speed source, then that is what is used by the running power app.

Note: The equations to compute these components of running power also require some constants (sic) values such as your weight, acceleration due to gravity, and the density of air.

When you run, you will notice that running power responds quickly when you speed up or slow down. You’ll also find that running power is higher when you are running up hills than when you are running at the same pace on flat ground.  Wind also effects (sic) running power.

So that leaves me two things to have a play with:

1. Weight – let’s adjust the weight of ‘me’ on the watch and see how the Garmin Power numbers change. Christmas will come early on Today’s run as I miraculously consume several pre-run turkeys all by myself ie I will double my weight,
2. Height – I’m going to go from mini-me to mighty-me with a doubling in my height. Garmin do NOT say above that height is a factor although I would have thought in reality it might have some CdA effect. Even if it did have an effect at that speed, I’m guessing it would be 0.1% or something of that kind of tiny magnitude.
3. I’ll look at all 4 combinations of those 2 factors over about a mile; running at 5:00/km in a tiny bit of wind over a slightly down and up route around my block.
4. I have STRYD and RunScribe as control devices (although I won’t show their data below)

Here is what I found:

Clickable

In time order, from top to bottom they are: blue (2x height and 2x weight); red (normal weight and 2x height); green (2x weight and normal height); yellow (normal).

Observations

1. Clearly weight is factored into the algorithm. I can’t say if that is done correctly.
2. Doubling the weight seems to just about double the power. Someone can say below if that makes sense in the overall scheme of running with power.
3. There is no indication that height is included as a factor. As Gamin didn’t mention it (earlier) I would assume they have not included it (as they say)
4. The only thing that looks strange to me is that there appears to be a disproportionate increase in the variability of power with the higher weight setting. The yellow and red lines are much flatter – doubling the yellow/red lines would not produce variation of the same magnitude as the other two lines.

Disclaimer: I’m clearly not a scientist. I just found this interesting to do.

If you wnat to play with Garmin’s ‘freebie’ Running Power then you will need one of these…. 😉