Sorry, the main reason you’re doing this exercise is that you’re looking for magical spot reduction of the fat in your upper arms.
The truth is that spot reduction does not work. You have no more control over where you lose fat than you do over where you gain it.
There’s no other “reason” (again, spot reduction does not and cannot work) for the average person to spend so much time trying to isolate such a relatively small muscle.
What’s even worse is that so many women take this already ineffective exercise and perform it even less effectively.
There are basically two poor options for choosing a weight for triceps kickbacks:
1- If you use a weight that’s challenging at the top of the movement, it’s not challenging at all thoughout the rest of the movement – so you’re wasting your time.
2- If you use a weight that’s challenging at the bottom of the movement where you’re the strongest, there’s no way you can get through an effective range of motion while maintaining even halfway decent form.
In Biomechanics we call this a Backwards Exercise. The resistance is greatest where your body is weakest, and the resistance is lowest where your body is strongest.
Seriously … Ask yourself, “Why is my knee on this bench?”
Look at it this way … your biceps and your triceps move the same joint – your elbow. There’s no logical reason that a triceps technique (like this 2 hands/one dumbbell exercise) or triceps gizmo should be any different from a biceps technique or gizmo.
Don’t waste your time doing ineffective exercises like triceps kickbacks. Focus on big muscle groups with challenging resistance to get the best results in the shortest amount of time.