Edward R. Laskowski, M.D.: The triceps extension is an exercise you can do with dumbbells to work the triceps muscle. As the name implies, the triceps extension helps strengthen and tone the triceps muscle, which is located in the back of your upper arm.
Nicole L. Campbell: To do a triceps extension, lie on your back with a dumbbell in your hand. Point your upper arm toward the ceiling, with your elbow bent to 90 degrees. Slowly straighten the elbow, moving the weight upward. Then slowly lower the weight to the starting position. You'll feel tension in the muscles in the back of your upper arm.
When you're doing triceps extensions, move your arm smoothly and slowly. Don't jerk your arm as you're extending it.
If it's tough to stabilize your arm during the exercise, use the opposite hand to help keep your arm in a 90-degree position during each extension. Hold your head, spine and lower body stable but relaxed during the exercise. You can do triceps extensions lying on a weight bench or on the floor.
For most people, one set of 12 to 15 repetitions is adequate.
Remember, for best results, move your arm smoothly and slowly during the exercise.