All described in detail at HI.
In a similar fashion, Miyahira identified the need for scrunch including lumbar lordosis (arch lower back) and side bend (tilt) and scap dig (scap retraction/lateralABduction, not truly scap "loading" because you do not want to unload/protract or laterally ABduct until after contact in hitting - in overhand throw the scap does unload to whip the arm before release) to permit "spine engine"-type recruitment of elastic soft tissue properties to improve the swing.
Unlike golf, the high level BB swing is adjusted to be rear hip focussed to permit early batspeed for late adjustability.
In a similar fashion, Miyahira identified the need for scrunch including lumbar lordosis (arch lower back) and side bend (tilt) and scap dig (scap retraction/lateralABduction, not truly scap "loading" because you do not want to unload/protract or laterally ABduct until after contact in hitting - in overhand throw the scap does unload to whip the arm before release) to permit "spine engine"-type recruitment of elastic soft tissue properties to improve the swing.
Unlike golf, the high level BB swing is adjusted to be rear hip focussed to permit early batspeed for late adjustability.