There was a story in yesterdays (Sun.'s) Missoulian about this guy who helps NFL hopefuls lower their 40 times for the combine. So, in some ways, speed can be taught. Of course, this is outright speed only. But apparently he does help a lot of guys succeed in the 40.
I overheard, years ago, a Griz coach say something like, "You need speed, skill, and endurance." There might have been a 4th quality in there. But, "endurance" has to be a big part of a player's tools. :twocents: