It’s long been believed that, if you over pronate, you’re more likely to suffer a running injury. That’s why we have so many motion control shoes with so many types of plastic, dual density foam and other materials to control our pronation.
In the spring of 1996, I lowered my 5K PR from 17:06 to 16:08 in two races. Afterward, I could consistently run in the low 16s. However, lowering that PR just wasn’t happening for the remainder of that track season or the 1997 season.
Then, after a year away from track for reasons that had nothing to do with running, I returned in the spring of 1999 and progressively worked my PR down to 15:43. Sub-16 became routine. I took my 10K PR from 34:12 to 32:57 in a single race. A mid-33, a short time earlier over 30 seconds faster than my PR, would now be a bad race.