These are a valuable exercise for targeting and strengthening the triceps, the muscles at the back of your upper arms. It is typically performed using a cable machine found in most gyms. It's an effective exercise to strengthen and tone the triceps while offering the benefit of constant tension on the muscle throughout the entire range of motion.
First, place both cable pulleys as low as possible, then grab the handles in each hand and position yourself facing away from and in the middle of the pulleys. Move slightly forwards, then have your elbows pointing up and your hands pointing down.
This is the starting position.
From here extend your hands up and above your head, by extending at the elbows until the arms are fully extended or as far as you can. After this, slowly return the arms down to the starting position. This is one repetition, now repeat this for the desired amount.
If you have limited gripping ability try using the Active Hands Gripping aids or D-Ring Aids clipped straight into the carabiner to make this exercise as safe as possible.