Technique of the exercise:
On the side of the bench. You settle down by resting your knee and hand (on the same side). Make sure you keep your back straight. With the other hand in a neutral grip on a dumbbell, bring your arm parallel to the floor, so that the arm is level with your torso.
Fix the arm position then perform an elbow extension, keeping it tight close to the body.
Note that there is hardly any negative phase on this movement. To keep more resistance on the muscle, take care not to exceed 90 ° elbow flexion.
Main: triceps brachii
Secondary: anconeus, shoulders (posterior bundles)
With the long portion in the shortened position at the shoulder level, the exercise should focus more on the work on the vasts.
Interest of kick back:
The lack of resistance that would pull the forearm forward makes the exercise compared to other exercises less intensive. But it will allow you to work without putting an excessively heavy load to feel the strain.
Kick back variants:
The pulley kickback.
Danger / contraindication to kick back
No real danger. You just have to pay attention to the physical integrity of your back, and not to put on heavy loads.