My guess is you are starting to overstride and maybe not leaning enough. Two rules to keep in mind are 1) don’t step past your hips and 2) don’t step in front of your knee. Also, you may need to relax more to allow some pelvic rotation. Let the ground ‘grab’ the back foot, which in turn pulls the leg and then the hip back. This lets you stride behind as opposed to reaching out front.
Hope that helps!
Certified Chi Running and Chi Walking Instructor
I am struggling with this too. I run in fivefingers and trying to get into higher gears or run downhills I find same issues. I believe since I do not have good hip rotation (and not very good flexibility in hips) I can either increase cadence or overstride, since I run with a metronome I think its causing overstriding and a few heel landings (ouch!). Curious dmendo how you progress.