Women: 101 finishers, 66 PBs.
Men: 117 finishers, 71 PBs.
That means almost 2 runners out of 3 did their PB yesterday, sometimes increasing it of several minutes.
How do you explain it?
Is it the shoes effect now that Adidas can product the same kind of shoes than Nike?
tail wind along the open segments and not headwind once they turned back. Worth 1-2 min?
Most athletes are not over raced this year because of the lack of events. This also creates an incentive to really go for it since you don't have any other races/paydays that you can count on going forward. A great performance was needed to keep your contract or federation financial support.
Let's also be frank that WADA hasn't been making the rounds this year and that could also be having an effect on performances. Sorry to be cynical but, this was a great year to pull shenanigans if you wanted to.
Deep fields mean many runners had packs to run with or people to pace off of.
Part of it can be explained by the fact that many of the runners had little or no experience at the half-marathon distance. Looking at the entry list, there were 29 runners (16 men; 13 women) who had no mark for the half-marathon coming in. So they all automatically PB'd if they finished. Included in those numbers were the men's winner (Kiplimo) as well as Cheptegei.
So it's not like the field was composed of 100% half-marathon specialists by any means. Many of the runners were running their first or second half-marathon.