Treadmill run distance not calculated with manual Stride Length

[SunsetRunner]

I have manually entered a run stride length of 100cm in to the Android App. The stride length shows as 100cm in the Fitbit.com Dashboard as well. In the last week I've done several treadmill runs using the Treadmill Activity on my Fitbit Inspire HR, and the run distance has not been been estimated using the stride length I have specified. Today I ran on the treadmill for a distance of 3.4km at a consistent 11km/hr speed. My Fitbit recorded 3,385 steps, which with a 100cm stride length is pretty much bang on 3.4km. But the Fitbit and the App both report a run distance of only 3.13km, which corresponds to a stride length of 92.5cm. The stride length used in distance calculations for other treadmill runs has varied between 85cm and 110cm. So not only is the Fitbit not estimating distance using the stride length I have entered, it is not consistent with the stride length it uses from run to run.

I've searched through the forums for posts about treadmill run distance discrepancies, and most of the posts I found seem to be related to issues with step count being inaccurate for whatever reason. In this case, the step count seems to be accurate. But the math to translate step count into distance based on a manually set stride length seems to be off.

The troubleshooting steps I've already taken include restarting both the Fitbit and/or phone between activities. Neither resulted in improved accuracy for reported distance after treadmill runs.

Moderator Edit: Clarified subject

[JohnnyRow]

There are separate stride length settings for 'Walking' and 'Running'.  I don't know which one 'Treadmill' uses.  If didn't set both, might give that a try.

[SunsetRunner]

Thanks for responding JohnnyRow. My walking stride length is slightly shorter at 90cm. I thought the Fitbit App might be doing something "smart" by averaging the walking and running stride lengths for treadmill runs. But I discounted that (to myself anyway) when I determined that a different stride length was used on each run. I only recently added treadmill runs back in to my fitness regiment after gyms in my area reopened. So I have limited data. But here are back calculated stride lengths from recent runs I tracked using the Fitbit Treadmill Activity:

• Run 1: 96cm
• Run 2 & 3: 105cm (both these runs were on the same day within twenty minutes of one another)
• Run 4: 100cm (This one gave me hope that the issue had been resolved after a phone restart)
• Run 5: 85cm
• Run 6: 92cm

The distance ran for each activity varied between 3.4km and 15km. In all cases the run speed was consistent at 11km/hr over the entire duration of the run, and my arms moved freely. Distance calculated using 100cm stride length and steps recorded by Fitbit matched actual distance reported by the treadmill within 1-2percent. But for whatever reason Fitbit decided to use a stride length it came up with on its own to calculate distance. 

[Rich_Laue]

Fotbit looks at the motion of the arm to determine if the user is walking or running.

The problem with the treadmill is the body does not physically move

So which does the treadmill use? Have you tries serring the stride to a ridiculous number to see the affect?

[SunsetRunner]

Thanks Rich. My arm motion when running on the treadmill is identical to my arm motion when I run outside. The Fitbit auto detects my exercise as running when I run outside. So I would think it would do the same when I'm on the treadmill.

I haven't changed stride length to something ridiculous yet. But I was going to do so later today to see how (or if) that impacts the treadmill run distance. I was going to set both walking and running stride lengths the same so there is no question as to which it is using. I'll post back after doing so.

[Rich_Laue]

@SunsetRunner your arm motion is the same in relation to you, but not the same with the earth.

On the treadmill the body doesnt move, the arm swings forward and backward.

When running the body is moving, the arm swings forward at about twice the runners speed.

Then the arm stays relative to the earth, stationary as the runner runs past the arm.

[SunsetRunner]

@Rich_Laue I understand what you're saying in theory. But if GPS isn't available for the Fitbit Inspire HR to access (i.e. I didn't have my phone with me), is motion relative to earth going to factor in to how it perceives arm movement? It has registered activities as runs that have had similar arm movements but are stationary. The best example I have is that I spent an afternoon sawing 2x4's to build a deck. The arm movement was similar to my arm movement during a run. And the Fitbit auto registered the activity as a run. Based on that, I didn't think the Fitbit would be "smart" enough to figure out if I was running on a treadmill or running outside if GPS wasn't active. Learn something new everyday.

Anyway, after a couple of test runs I can confirm that the Fitbit is using the manually specified running stride length to approximate distance based on the step count for treadmill activities. I tripled both the Running and Walking stride lengths for a 1km run, and the distance of the run estimated by Fitbit was approximately 3x actual. I then dropped the Running stride length back to the actual 100cm stride length, and left the walking stride length at 300cm. The treadmill run distance after doing so was within 5% of actual, which means the running stride length was used. In all scenarios, the run distance estimated by the Fitbit was not exactly equal to Steps Taken x Manually Entered Running Stride Length. Although it was in the ballpark, it was off by 5% on average.

So yes, that Fitbit is using the manually entered running stride length to come up with an approximate distance run on a treadmill. But why isn't it able to do an "exact" calculation to come up with the distance? The stride length it uses in the calculation shouldn't vary from run to run.

[JohnnyRow]

As @Rich_Laue   suggested, it could be that it is sensing that you are running,  rather than walking, so uses running stride length.  Not expecting you to want to do more experimenting, but wonder if "Treadmill' would use walking, instead of running, stride length if were actually walking instead of running, as I would guess, though not sure, more Fitbit users walk on treadmill than run.

If you were really into (over) analyzing it, you could look at it as % error in step count, rather than in distance, to see if distance would come out right if Fitbit were missing some of your steps, say if not swinging arms enough at beginning or end when using controls to start or end run.

[SunsetRunner · Accepted solution]

I'm posting this only because Fitbit is harassing me to choose a right answer. The answer to my question was not provided in this thread. I wanted to know why the Manually entered stride length is not used in Treadmill distance calculations. Steps on treadmill runs are accurate. Stride length has been manually entered and is an exact number. But treadmill run distance does not equal steps x stride length according to Fitbit. This is a programming / coding bug. 10 x 10 = 100. But in Fitbit's world it doesn't. 

[hartley95uk]

I'm having the same issue. I bought the fitbit sense on release day. My running stride length is 1.24 Meters as confirmed with my Garmin venu. I've put this as my running stride length, but on my last run which was 11km. My sense shows 9.78km, 9001 steps which equates to around 1.08 Meters. It did work once after I set it, but seems to ignore since. Would be good if you had the option to calibrate it after a run  like the garmin and huawei watches do.

[Rich_Laue]

Is the step count correct?