I swear, I do not understand how some people have so little energy. Lead them through a simple jitterbug basic, and they already get tired. It's one thing if you have a glandular disorder, but for a lot of people, simple exertion is enough to tax them heavily.
That's why a lot of people are obese. It's not simply that they move sluggishly because they're fat; after all, I know a lot of dancers who are significantly overweight, and who still move with energy. Rather, a lot of people are fat because they've gotten used to moving sluggishly. They don't want to put any effort into everyday motions, and so even simple dance moves are enough to wear them out. Ditto for simple things such as walking up two flights of stairs.