Stuff like that is real cool to watch because it shows how much physics rules. When we perform a task at speed, we do whatever it takes (compensations and funky movements) to complete the task at hand (and in sprinting...who gets the rock down the track fastest wins).
After looking at the video as an armchair observer, I wondered if Bolt's turning his knee inwards was a learned compensation for his extraordinary leg length - kinda like folding his legs under him (allowing him to stay low in the early part of the race and still turn over his feet quickly). It is also quite possible that all that side-side movement could be a source of his recent back issues (and not Swedish models as our esteemed forumites might want to believe
)
I have another one for you. When Ato used to run,his right leg often landed splayed way off to the side (and me in my armchair would be like "Ato! Straighten yuh right foot nah man!") Now I wonder if that quirk was due to a leg length difference (ie turning foot outward functionally shortens the leg...or it could have been something as simple as hip flexor weakness.)
http://www.youtube.com/watch?v=PwvtPJB9Ff4<![CDATA[<a href="http://www.youtube.com/v/PwvtPJB9Ff4" target="_blank" rel="noopener noreferrer" class="bbc_link bbc_flash_disabled new_win">http://www.youtube.com/v/PwvtPJB9Ff4</a>]]>It's a great discussion though, and that's where good coaching comes in by knowing what fine adjustments to make when, without compromising performance.
