Dumbbell Triceps Kickback
Place your left knee and left hand on a flat bench with your back straight, and hold a dumbbell in your right hand with your arm extended, palm facing inward. Bend your elbow and lift your arm close to your side, and hold your upper arm here as you extend your elbow and press the weight toward the sky. Squeeze hard, then bend your elbow to return to 90 degrees. Complete all reps on one side, then switch.