I'm still trying to understand it and organize the information in my brain. But my take right now is that I think it could be a tool to get kids to a better drive off of their toe and feel more bounce than push. Drive mechanics talk about the ankle being a rigid level but I think this HA goes into further detail on how to make that happen. Some kids after doing 2 step, putting them in sprinter poses, creating better overlap, were still having trouble getting that "push" to transfer all the weight into the front leg on stride and the drive foot would stick or drag heavy. I was thinking it was a lack of core strength or muscle deficiencies. I was working with a national team (non US) player once who threw 67 but lacked control. She had a very strong core and everything else and she was very explosive but her drag foot ankle was on the ground IMO causing the lack of control. We worked on her just trying to transfer more weight to her front leg and it helped. She had excellent sprinter poses, overlap, all that mentioned in the drive mechanics but something wasn't connecting. She also had really bad ankles (sprains ect.). I think that even though she was strong she wasn't activating the right muscles on the drive. I'm going to go back to my videos of her and see if I see anything.
One thing thing Chong talks about in regards to basketball is that you don't need knee bend. So this confuses me with the sprinter poses in pitching and sprinters. My thought is pitchers and sprinters need it in the beginning to catapult them forward. Where as a jump shot is up and down. Sprinter pose gets you the angle then extend the hips HA gets you the bounce off of your drive toe. Thoughts?
A couple things to keep in mind. If you are quad dominant, you can't really "lock your ankle" and push off. Quad dominant means your glutes won't fire and without a push off via quads and via ankle plantarflextion, your not going to get far off the mound. It really comes down to the fact that a locked ankle is a result of an active foot, it is not something that you can just do. A strong athlete with no glute issues will just naturally have a mechanically locked ankle during the push off phase. If you were manually locking your ankle via shin muscles and then your glutes fired with full force, your shin muscle would collapse. The rigid locked ankle is a resulting action that happens naturally when you have a good active posterior drive chain.
Another thing that is true but very hard to conceptualize is that quad dom vs glute dom people have slightly different centers of gravity. A quad dominant person will tend to have a posture with slightly forward bent upper torso. This will put the COG further out than for a glute dominant person. As a result, a quad dominant person just can't hardly achieve a good forward tilt posture. They will get close and will fall on their face if they try and go just a little bit more. I know it's weird, but we've experienced the difference.
Regarding knee bend. When a quad dom person gets down and ready in the infield, they tend to have knee bend with an upright posture. When a glute dom person does the same, they too have knee bend, but also hip hinge. The knee bend during hip hinge is very different than knee bending with an upright posture. I know that is strange and I wish I had the full anatomical knowledge to explain why, but I can only explain what I feel. When a quad dom person changes levels via bending knees, the knee bend is supported via quads. When a glute dom person changes levels, they do it via hip hinge, but as they hip hinge, the knees naturally bend in a way that is not as noticeable in the quads... Somehow the glutes still carry the load. I do think that there are some mechanical linkages that are affected differently between the two, but I have no anatomy knowledge or data to support this.
Sorry for the wordy posts, but I hope that it helps .