My husband usually bicycles home from giving blood, and doesn’t notice any recovery needed, beyond what they make him do there. When I used to give blood I always felt tired for a couple days. I also used it as an excuse to make chicken livers wrapped in bacon (which I love) since liver is very high in the easiest-to-absorb type of iron.
It does take some time to refresh your red blood cells. If you have more than you need, you won’t notice anything. But it doesn’t take a lot of time to refresh them. When I visited Utah I found it significantly easier to hike at high altitude on day 5 than on day 1. Pretty sure that was because my body reacted to spending time in thin air.
Given that some athletes “dope” by getting an infusion of their own red blood cells, it seems plausible that a runner would compete less effectively right after donating blood. But red blood cells only live 120 days, and I’ve felt my red cells boost from being “low” for high altitude, and i also recovered in a couple of weeks after i lost a lot of blood to a breach delivery. i bet they regenerate after donation, as well.
Bouncing back in a day? Probably not, at least for top aerobic performance. In a couple of weeks? Yeah, I’d expect that.
I was kind of nervous since the person doing the pre donation screen seemed to be doing a half-assed job but it ended up being a easy jab when she stuck me for the actual donation.
By the way, they significantly changed the travel restrictions since the last time I checked. In the recent past you weren’t allowed to donate blood for a year if you had been to a malaria endemic area. Pretty sure I checked sometime in 2022 and that was still the case. That has knocked me off the allowed list many times. They’ve cut that to 3 months if you just traveled there (still long restriction if you lived in a malaria endemic region.