The act of doing various leg workouts in a hot shower. This is usually done by jumpers who want to gain leg strength. Typically, you wash your face, do a series of calf raises, wash your hair, do a series of calf raises, wash your body, do a series of calf raises, and so on. The heat from the shower relaxes the muscles and works them out better than outside of a shower.
"You going to jump 6' 4" this year, man?"
"Hopefully, I've been taking jumper showers every night for a month now."