For try Fartlek runs there are no pre-planned intervals so analysis needs to be performed retrospectively.
At the start of a high pace interval cadence & speed will suddenly increase. The same is true of a finish.
My understanding of Fartlek intervals is that they vary in how quick they are, the duration and the rest period. Because they vary I think there will be variation in the metrics picked up by runscribe. Ideally you would include GPS, but that would require a way to mix your data with a .FIT file so maybe speed is not so easy to incorporate.
With the data you have already the sudden changes in cadence should make it easy to see the start and end of intervals (retrospectively). We can manually see it, but why not automate the finding of the intervals and tell us if our foot strike metrics change?
I think we can probably guess what happens, but are there threshold paces above which our foot strike type changes etc?