I don’t think anything other than sagital plane vertical oscillation of the head is desirable. The head is about 16 lbs (essentially a bowling ball). Excessive movement with respect to the spine can have serious (bad) outcomes on posture. This is especially true in someone as tall as Bolt where the lever arm that is his legs, trunk and neck create an even more exaggerated effect when deviations of head position with respect to the spin occur.
ELITETRACK Founder