Would people please read the actual posts and pay attention? Michael Johnson commented on it (and it is what I was responding to in the quotes, obviously) and he was pointing out an observation that any layperson can see from the race. It is distinctly different from all of his best races and, in fact, something that his coach said was a problem when he was a junior athlete an d fixing it is one of the reasons he has improved. Bobbing your head, while not causing massive changes in your time, could easily contribute to problems (lack of concentration, fatigue, poor race distribution, postural problems, etc.) that would lead to a near miss in a world record/best attempt over 300m.