The cable pressdown is an isolation exercise that strengthens the triceps. The exercise also improves shoulder stability.
Facing the pulley station, grab the V-handle attachment set to a high pulley with an overhand grip. Bring your elbows to your sides so your forearms are parallel to the floor. This is the starting position and from here your elbows shouldn't move.
Extend your forearms straight down by contracting your triceps. Hold at lockout for one second before returning to the starting position.
Do not move your elbows. Keep your elbows stationary throughout the movement.
Be sure to return to the starting position and achieve a full stretch.
Be sure to pause and hold the contraction at the bottom of the movement.