dumbbell seated reverse grip one arm overhead tricep extension

Sit on a bench with your back straight and feet flat on the ground.

Hold a dumbbell with an underhand grip and extend your arm straight up overhead.

Lower the dumbbell behind your head by bending your elbow, keeping your upper arm stationary.

Pause for a moment, then extend your arm back up to the starting position.

Repeat for the desired number of repetitions, then switch arms.