Damn, what are the back up shoes?
What I ran in yesterday was a pair of Salewa MS Drop Line trail runners. They’re old enough that I’d taken them out of the regular rotation, but I’d loved them enough to not be ready to toss them. There’s still lugs remaining on the tread but it’s almost down to the sole in the primary strike areas.
The issue I had yesterday was probably more due to my using (relatively new) shoe inserts in them. I’ve been using these inserts in most of my shoes for about 5 months, but this is really the first time I’d combined these inserts with these shoes. The inserts add a bit of rise, in this case probably just moving my foot/heel too high and resulting in the rub/pain.
Once the pain started, even walking in them (with inserts) continued to hurt. I removed the insert for the walk back to the trailhead.
Added the inserts originally to mitigate a sore heel (likely planar fasciitis or similar) and they have worked very well in every pair of shoes - up until yesterday.
Why back-up shoes? In a ~24 hour race with 9 loops I’m fully expecting to get tired of my shoes at least once and will want to plan to switch out a time or two at some point during the day. Luckily I love love love my primary shoes (Salewa MS Ultra Train 2) and have had great runs in them (with the inserts) in this training cycle -including my longest one-day run so far.