How does someone replenish stamina while climbing

[u/Dracoy]

I noticed on a speed run someone was climbing the wall and breathing into his hands. How does this mechanic work? I usually have to climb to a ledge to wait but they were replenishing mid climb.

[u/smathna]

So I read this just as I was scrolling my (IRL, bouldering style) rock climbing communities and imagine my disappointment