Wirelessly posted (HunnyBunny: Opera/9.80 (iPhone; Opera Mini/5.0.019802/22.401; U; nb) Presto/2.5.25 Version/10.54)
6% climb @ 90% intensity, slow jog down. Lather, rinse, repeat until your insides come out your mouth.
try this for barf variety...
go all out on 3 different activities with no rest in between... the length of each set being like a long sprint.... or a short fast middle-distance race.
treadmill run for (insert distance here)
rowing machine all out for (insert resistance / distance here)
stationary bike (insert resistance / distance here)
repeat once or twice.
you're going from one set of muscles to a different (or used at different positions / functions etc).... whether you crawl to the next station to buy rest like a pansie, or sprint like you're insane is up to you.
my old gym set some standard distances, resistances, and reps and made a 'triathlon' race out of it. it was a lot of fun. i always won. but the majority of the gym's members were a good 20 years older than me