That's why I said my knee tendons suck haaaard. If I were to load my knees up like that I would immediately shut down. There is no way of "loading up" like he does in the above video. In the above video, he subjects his knees to tremendous pressures and the CNS isn't coming in and saying "let me shut this down" - no, he gets back the tension that he put into them in the amortization phase.
I have no idea if this is a CNS thing but my hunch is that it's not 100% "strength" related, meaning directly related to his squat to bodyweight ratio. It is to a certain extent, but there must be something more than that. His CNS basically allows that kind of load without shutting down his muscles, his quad tendon can "accept" a tremendous amount of tension and release it quickly.
I'm saying this because I remember when Toddday said that it's all in the "hip tendons" and "nobody has reactive quad tendons anyway". Well, look at the above video and tell me how that is true. Heck, in that plant he has his hips and torso vertical, if anything, the glute contribution is towards the late phases of his takeoff, near the toe-off. But as the initial drivers of the jump, in the deep bend, it's the quads that are doing the work, hence his plant position, and the ability of "his body" to accept that tremendous amount of knee pressure and "not give up".
If you think about the implications of the bent knee, in that it puts the calves in active insufficiency, it's even "worse". It's even more "quad dominant". It means the calves are de-activated because the knees are bent and therefore even MORE pressure is passed into the quads to stabilize, since the calves aren't active (the soleus is when the knees are bent, and the soleus isn't exactly the strongest muscle in the world).
So in any way you turn it, it comes back to quad strength and quad tendon reactivity, off two legs. Maybe the rest of the muscles contribute in the initial touch down in the plant and then move the tension into the quads as the plant is being loaded, but when you break it down, it's the quads.
