When the arms are hanging relaxed at the sides, nothing looks more impressive than a thick, shapely pair of triceps. The popular standing rope pulldown is a good movement, but by nature of the leverage involved, this exercise allows for too many other muscle groups to assist in the “pulling down” – namely the rectus abdominus. If you’re going to train with weights, learn this lesson to start: “Yanking” a weight from point A to point B is not the goal. Working the muscle through the full range of motion is.

To effectively circumvent any assistance while isolating all three heads of the triceps, try the kneeling triceps extension. You need a bench approximately 16″ high and a rope pulley attached to the upper section of a cable station.
Facing away from pulley with the bench in front of you, grasp the rope behind your head.
Kneel down on the floor. (You may want to brace your feet against the frame of the station.)

Place your elbows on the bench in front of you, shoulder width apart.
Keeping your head down, push the rope forward in a smooth, controlled motion. Contract hard at the full extension point.
When returning the rope to the original position, be sure the hands go back as far as possible. Your hands should almost touch the back of your neck and your elbows should stay on the bench.
Make this your sole exercise for your next triceps workout. Shoot for 8 to 10 reps per set, do 6 sets and go heavy! This is a great mass-building exercise, but it’s imperative to use substantial resistance to derive the maximum benefit.

I believe the best time to work triceps is after working the chest or shoulders. The pressing movements involved in chest and shoulder workouts also utilize the triceps, so you’ll get them nice and warm and ready to work at full intensity.
The kneeling triceps extension requires intense concentration. It’s all triceps! So stick with this exercise and you’ll soon develop that coveted “horseshoe” shape on the backs of your arms. Then just make sure you’ve stocked up on short-sleeved shirts!