The principle and benefits of High Intensity Interval Training (HIIT) can be applied to almost any physical activity, including the lifting of weights. Provided you have a couple of dumbbells that challenge you and a little time, you can make your body feel the need to change to meet the fresh demands being made upon it. This one not only gives you muscles that know the meaning of endurance but it also works on building strength.
Extra Credit: Hit the same number of push-ups at every round.