I enjoyed running when I was doing it, between my 8th and 9th babies. (Never really got going again after the last two kids, especially since my husband broke the treadmill I could use in the house.)
I think one clue to the “rage” is in a subject’s quote, “She interrupted an important training run.” He believes running/racing is important. That attitude about any activity naturally leads to a sense of entitlement and then anger at impediments, no matter how small.
“That attitude about any activity naturally leads to a sense of entitlement and then anger at impediments, no matter how small.”
I think you’ve hit the nail on the head.