Loop an exercise band under your left foot and step through it with your right foot so that the side of the band in your right hand is behind your right leg. You may need to experiment to see how much length you need to have on each side of your foot.
Bring the band up and around your back as you extend your right upper arm straight up from your shoulder with your elbow bent as much as is comfortable with your right hand behind your head/back.
Contract your triceps to extend your right arm; keep your upper arm stationary and end with your arm fully extended above your shoulder but not locked.
Slowly lower your forearm back down as you bend your elbow, bringing the right hand down on your back as much as is comfortable. Repeat the motion for a set number of repetitions or a set time period before switching arm and leg positions to repeat the motion on the left arm.
The Overhead Tricep Extension, whether done with a band or a dumbbell, is an extremely effective exercise for toning, strengthening, and/or increasing definition in the upper arms. Unlike other exercises that target this muscle (such as kick backs, or dips), the Overhead Tricep Extension gets more muscle activation by elongating the tricep and forcing the muscle to work through a range of motion that other exercises can not hit. This is a great exercise to add to a toning or strength training routine to target the muscles on the back of the upper arms.