Triceps extensions are another great way to work the back of the arms. This version is a bit more challenging, since you're lying down and have to work against gravity to control the weight during the downward motion. For this reason, you may want to start with light dumbbells to get your form down before attempting to go heavier.
- Lie on the floor or a bench/ball and extend the arms straight up over the chest, palms face in. Use light-medium weights.
- Bend the elbows and lower the hands until they're next to the ears, elbows at about 90-degree angles.
- Squeeze the triceps to straighten the arms without locking the joints.
- Keep the elbows steady throughout the movement, only moving the forearms.
- Repeat for 1-3 sets of 10-16 reps.