Running Distance Usually Short?

The whole point of the thread is garmin device under report running mileage, which can be verified by using gpx distance rather than fit file calculated distance. And the problem is the mileage in garmin devices can swing around depends on your arm swing. If you are holding a bottle, drinking, tired, then mileage will be off and avg and lap pace number won’t be accurate. Then you cannot use the numbers on your watch to pace your run because the number cannot be trusted, for me max it is11-13 sec different than my true pace. 

I understand the point in the thread but I do not see this shortage. If I export a GPX it may be a few meters longer than the FIT distance - but neither are short vs. a certified course.

I agree pace is awful though.

For my run in the link below, it is 3.14 in actual distance vs 3.08 in garmin’s distance. Yes, it is only 100 meters difference. However, that translate to pace difference of 10:13 min/mile for a 10:00 min/mile pace. Your pace is always somewhere between these 2 so you don’t know to speed up or slow down during running.

For garmin instinct it is most inconsistent, depends on the model or the quality of internal component, some garmin user is not affected.

forums.garmin.com/.../which-activities-doesn-t-use-accelerometer-when-gps-signal-is-weak

5135968 said:

On Sunday I ran a 10 mile race under UK athletics rules which has been measured accurately and certified as such.

My Fenix 6 Sapphire recorded slightly OVER the measured distance and with around 200 runners of which I'd estimate 90% using Garmin I cannot spot any examples of short measurement - everyone is my Strava feed is 10+ miles by a few meters 

It is far complicated than that. In general GPS devices add some distance on straight lines due to wobbling and lose some distance in turns due to cutting corners. So at the end, whether the distance is short or long depends on a number of turns. Furthermore, the effects amplify when GPS reception isn't very strong. We you just use a GPS track without any help of correction from other sensor, and the GPS signal isn't strong, the track would look like a squiggly line and the distance would be quite a bit longer. So some degree of smoothing is definitely needed. That comes mostly from calculating the vector of speed and predicting of where each next position should be, but accelerometer and gyroscope input is used too. But on the other hand the smoothing results in smoothing turns too much, which cuts the distance. So that is a delicate balance.

What I am trying to say, that depending on terrain (open, urban, forest) distance measurement results may be quite different. Personally I think that Garmin distance measurement is OK on open terrain, but way too conservative on forested trails. The more it depends on other sensors the shorter the distance measurement seems to be. But, as I mentioned, if it didn't depend on the sensors, in some cases the distance measurement would be too long. A simple example is stopping during your run. Without input from accelerometer you'd be getting a "GPS flower" around your position as the GPS positions start randomly wonder 3-5 meters from your true position while you are taking a break. I've definitely seen that with some older watches. Fenix avoids that by detecting a break in movement.

Garmin distance have been better lately compared to GPS distance. Im measuring every run. But its still usually around 2% short of real controlled distance for me. Im unsure how Garmin should fix it but i think its about better 3D distance and interpolating curves in the run activities.

I am not sure if I want a fix - since August I have run 3 certified races - a 5k, a half marathon and a 10 mile run.

At the finish line my recorded distance is always over the race distance by a few meters. And this distance is reported to Garmin Connect then to Strava, Runalyze etc. Never ever short. Always a tiny bit long by maybe 40 meters long over 13.1 miles, and even less over 5k.

That sounds awsome! Do you use a foot pod or not?

No - they do end up short by about 3 to 5% depending on pace and shoe stack height. Cant risk it in race.

I have never ever seen anyone use a footpod in real life. I tried one, but its worse than GPS due to cumulative errors... maybe it would be different if running near tall buildings or forests.

6563734 said:

However, that translate to pace difference of 10:13 min/mile for a 10:00 min/mile pace. Your pace is always somewhere between these 2 so you don’t know to speed up or slow down during running.

My suggestion would be to configure your run screen to add average pace and pay attention to that, not the 'instant' pace

So if you want to run a 5k in 20 minutes, then try to keep your average pace around 6:25 /mi - this is much more steady than instant pace, and is actually the most important figure if you want to finish in a particular time anyway.