To restrict the activity or free movement of
Hence a favourable posture of the limb for eliciting the jerk is one ensuring relaxation of the hamstring muscles, as when the leg has been crossed upon the other.
Extend your front knee and lean your torso forward until you feel a good stretch in the hamstring of your extended knee; you'll probably also feel a stretch in your lower back.
So a machine and a workout that gives you the most effective glute and hamstring workout available, while also allowing you to target your lower back and your core is a big plus.
Even team sports like volleyball, softball, and basketball benefit from the hip, back, and hamstring flexibility that you gain from the skill.