Here is a good, brief article describing some isometric exercises that can be done with resistance bands. On these exercises, stretch the band as far as you can and hold the contraction for as long as you can, until you're muscles begin to quiver and you have to release the tension. Slowly release the resistance band back to the starting position. These "tension-flex" exercises will leave your muscles with a feeling of a lot of "pep" rather than tiring them out as traditional weight lifting exercises do. This is because the contraction involved is primarily concentric, rather than the eccentric contraction that tears down muscle fibers and causes the fatigued and heavy feeling often felt after doing traditional weight training.
RESISTANCE BAND ISOMETRICS