I have in the past gone looking for wicking fabric hijabs and didn't find any, so it's on my mental list of things to maybe-possibly-someday get around to sewing for myself. As it stands now I just go with cotton or rayons, and like umsami if I'm going to be doing anything where loose fabric could get in the way I make sure to wear an amira. Much though I loathe them fashion-wise, they are really, really practical.
IMO hiking is like the world's most perfect outdoor hijabi activity. But even back in my teens before I really cared about religious modesty I was that person who in the middle of summer would not touch a trail without long sleeves and long pants to help with warding off bugs and brush, and I usually added a bandanna to keep branches and ticks (
) out of my hair and to help keep sweat from running down into my eyes. So oddly enough hiking was when I was my closest to wearing hijab before I wore hijab.
There's a periodically updated book series which gets into a lot of hiking equipment recommendations ... I'm like 99% sure what I'm thinking of is The Complete Walker
. At any rate, they talk a lot about modern materials for keeping cool and dry while covered ... a lot of it is with cool-weather layering in mind so you don't get sweaty and then freeze to death when you stop, but it's just as practical advice for warm weather coverage just by stripping off the over-layers. Anyway, my whole point is that, while the series is oriented to hikers, it could be a really good resource for learning about what options are available for keeping covered while active in a more general way. (And I'm guessing there are probably similar guides oriented towards runners anyway?) Not really a "buy now!" kind of thing, but I know my local library back in PA carried it.
(Also? The trail marathon sounds really cool.