Notice how they always turn their head or eyes to either spot where they will land or towards the ball. Notice the balance of tension and relaxation (open palm/hand). Amazing!
I am just finishing up Z Health I Phase (yes once again) and it has been great! Excellent reminders and more practice for me on the I Phase drills with some feedback which is always helpful.
I Phase works to integrate eye muscle movements and also vestibular (inner ear balance) into your practice. Remember that the body primarily gets information your joints (proprioception), eyes (visual and proprioception from eye muscle movements) and vestibular (inner ear-balance); so it makes sense for optimal athletic performance that you will need some work on each one of these systems AND a way to know that they are working correctly.
All of them feed into the brain via the nervous system and some times they can become "rewired." For an example, see the link HERE so I Phase provides some cool tools to retrain the nervous system and gets you on the fast track to amazing movement!