Incorrect pool swim interval data

[thibaultfq]

Actually, i noticed the swim pace being off for my garmin FR 245 swims.
Connect file: Garmin Connect
main set laps as being clocked and shown in Garmin Connect:

lap time(m:s)
12	1:29,8
13	1:25,4
14	1:29,4
15	1:25,1
16	1:25,3
17	1:26,6
18	1:28,9
19	1:24,3
20	1:23,9
21	1:24,8
22	1:25,7
23	1:26,2

compare this to the same file synced to ICU: Intervals.icu
using the ‘Use Laps’ function, you would expect the same times but ICU gives

lap duration (s)
12	91
13	88
14	92
15	87
16	88
17	89
18	92
19	86
20	86
21	87
22	89
23	88

all laps in ICU are about 2-3 seconds longer.

If i can help by providing any further details of data please let me know.

[david]

I am going to look at this some more on the weekend. I might be able to “stack” the lengths one after the other to keep the recorded durations instead of adjusting the start time to avoid starting during the previous length.

[Errolleesw]

Bringing this one back to life again after reading this. Tried uploading the .fit file directly, but still getting discrepancies between Strava / HealthFit and intervals.icu. A bit more context:

• This workout was recorded from my Apple Watch Ultra.
• Data was extracted using HealthFit and synced to Strava and Intervals.icu.
• I tried deleting the strava and intervals.icu activity entry and uploaded the fit file directly. Same Intervals.icu result.

Link to fit file here.

Intervals.icu screenshot:

Strava activity link here.

Healthfit screenshot:

• notice the difference in avg pace. 1:56 autoset pace to 1:38 pace on intervals.

Is there any way to bring in the Auto Set data into Intervals?

Thank you in advance.

[Howie]

@david, I’m noticing that ICU and Garmin swim interval times and paces don’t match. I discovered this when doing a TT test (500m WU, 5x 100m tempo, 1000m TT, CD)

Pool Swimming

Intervals.icu

[Jpwoodi]

@david Was hoping to bring this topic back to life - I’m experiecing the same problem using the native Apple watch workout feature to record a swim, then importing into healthfit before exporting to intervals.icu. Did you find a ‘fix’?

@Errolleesw Did you find a work around for the healthfit / intervals.icu set discrepancies?

I’ve also noticed that total distance is correct - 1.6km, however sum of intervals is off?

Intervals.icu workout

Iphone auto sets - i.e. the ‘correct’ view of my session, aligning with stopwatch for 400 and 200 time trials.

Any help would be appreciated!

J

[jorge_cabra]

Hi David, any progress on this matter. The average pace is still off and I just noticed a weird thing in the Pace graph. The laps info shows a 36seconds duration, but the pace/100mts shows a 1:25 time, which is 13seconds off.

For the whole session strava and coros shows a 1:34 average pace/100mts while intervals gives me a 1:22 which I wish I could do.

Is there anything I could do to fix this?
Thanks in advance

[Matthew_Greer]

Sorry to bring up a zombie thread, but this was the first link when searching.

My swims have always been 2-3 seconds longer in intervals than other platforms.

After looking into the contents of a .fit file, I think I understand where the Garmin vs Intervals.icu discrepancies are coming from.

It appears that intervals is using the “start time” field from the lengths portion of the .fit file which has a resolution of 1s. It then creates a time based data stream at 1hz frequency to locate intervals in. This results rounding errors that that add up to 1-2 seconds. Then, for whatever reason, the the interval finding algorithm seems to add 1 second on top of that (possibly it includes the preceding or trailing data point where speed is 0).

Garmin shows lap data using the sum of the individual length “total elapsed timed” field, which are stored at 0.001s resolution.

Below is 1 example.

Intervals.icu identifies the first interval as starting at 11:03:34 and ending at 11:04:58. That’s or 84s/1:24. Add 1 more second and it matches. The same is true for every interval I looked at in this particular .fit file.

[jorge_cabra]

This is great work from you. thank you for your interest.The same thing is happening to me. Most intervals are 1-2 seconds longer. Sometimes the average for the session is wrong also, I do not know why.

[Ashley_Rolleston]

@david The above post by @Matthew_Greer should be reported as a bug

[david]

I know. I need to do a bunch of work for pool swims. People want to be able to edit the lap data to fix missed laps, fill in the stroke etc etc…

[ErikvdB]

Swimming watch tools does this. I use it often

[Delando1]

Im having the same issue
Uploading Apple health > Strava > Intervals → Pace is ok
Uploading Apple Health > Healthfit > Intervals/Strava → Pace is completely off

[Delando1]

Im having exact the same issue. Did you found a solution?

[app4g]

did you check the source FIT file diff between what was sent via strava vs what was sent via Healthfit?

@Delando1

ploading Apple Health > Healthfit > Intervals/Strava → Pace is completely off

Is pace on Strava ok? or only off on intervals?

[Delando1]

Hi

Apple > Strava > Intervals - Pace / Moving time is ok on Strava also on Intervals (26min - 2:40/100)
Apple > Health fit > Strava/Intervals - Pace / Moving time is not ok on Strava and intervals (On healthfit it is) (15min - 1:33/100m)

I could keep using “Apple > Strava > Intervals” but for removing complexity / Strava API I want to use healthfit because I can import all my different sports in there, gather them in Apple health and exporting everything to dropbox and than to Intervals. Everything is okay except the swim data. I already contacted Healthfit but he says that the fit file is correct.

I actually have the same issue as @Jpwoodi and @Errolleesw mentioned in this thread earlier on

[app4g]

@Delando1

Everything is okay except the swim data. I already contacted Healthfit but he says that the fit file is correct

If you import the HealthFit → Strava/Intervals is OFF but
AppleWatch → Strava is OK, doesn’t that make HealthFit as the odd one out?

[Delando1]

@app4g Agree, problem is that I don’t get the original .fit file because Strava is syncing to Intervals… Also strava is removing a lot of data…

Ill add another topic to show/discuss my data flow

[Piet_van_Vliet]

Is it just me, or has there been a substantial improvement in the accuracy for individual workout & recovery interval durations as well as average session pace? Seems like work vs recovery is always correct and the split time differences versus my Coros data are just rounding errors, instead of the +/- 10s per 100 from a couple years ago.

(also really nice to see how my swimming has improved over the last 2-3 years… OMG)

[MTreys]

@david, I know there’s a lot on your list, but do you plan to work on some improvements for swim activities anytime soon?
I’d be glad to help/remote experiment stuff to make it easier for you if needed.
Thanks in advance!

[david]

Yes I will be doing that soon. Busy with what has turned out to be a big chunk of work:

Configurable activity summary fields

I am halfway done with a new premium feature: Making the fields and layout of the activity summary panel configurable (including custom fields) and shareable. [Screenshot 2025-03-25 at 13.09.24] You will also be able to add multiple panels with different configurations to all of the activity pages. This will help a lot with Intervals.icu on small screens. Also the columns now line up a lot better, especially for non-English languages.