Here we have the magnificent Michelle Trapp demonstrating the classic exercise, the dumbbell kickback. She gives a good demo, going over the main points of the exercise.
The problem with this exercise is that a muscle only works when working against gravity and with the standard tricep kickback set up – on a flat bench with a flat back – the range of movement where the tricep is actually working is quite small. If you concentrate when doing this exercise, you will feel the muscle begin to pull only after the elbow angle is greater than 90°.
A short search on Youtube will dig up Scooby doing this exercise, which he calls a camel kickback. In his version, he drops his supporting arm down from the hand to his forearm, so his bottom is higher than his shoulders and sticking up in the air. Then, starting with the elbow above the body line, slightly behind the shoulder, the active range of motion is greater, and so achieving a better workout.
The weight can only be fairly light or swinging and General Cheating happens.
Advantages of the exercise: if you go to a fully straight arm, you should really feel the triceps contract, which is quite satisfying. Ignore any bollocks about not locking out the arm. Tell an Olympic lifter to not lock his arms when some ginormous weight is above his or her head. That would be daft since they’d never hold the weight up there. And if your arms bend the wrong way when fully locked out, where Olympic lifting is concerned, this is considered a major advantage. So lock out that elbow at the end of the relatively puny tricep kickback.
If you keep the weight you use down, you can achieve good form fairly easily, especially if you squeeze your armpit to remove any movement at the shoulder joint.
Instead of a serious tricep builder, this could be viewed more as a finisher offerer at the end of a good arms workout.