Let's not confuse terms. In the NLRB's terminology, "work" doesn't just mean "hard" or "challenging" or "demanding." It means labor performed in exchange for financial compensation. It means "a job."
To see what I mean, let's look at the service academies. They have athletes competing to be on the rosters of all the sports, from football to basketball to golf to tennis to boxing to water polo to team handball.
Not a single one of them is paid to do the sport.
Not a single one of them will go pro as anything but a military officer.
They're all on the equivalent of 100% scholarship, whether they join a sports team or not.
Every student feels a duty to the school (or more accurately, to the nation behind that school's identity).
So there is no way on this planet that the sport(s) they pursue are "work." Hard, challenging, demanding ... but not work.
They're doing it for fun. They're busting their butts, getting up before dawn for two-a-days, suffering through ice baths and treatment for injuries, and embracing all the other non-fun aspects of the sport, because they want to, because it's what they think of as fun, satisfying, enriching.
That's not "work," not using the NLRB's definition.