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Tuesday, August 30, 2011

Bolt's false start and Blake's 'twitch' - the actual start block data explained

The official start data from the 100m final - Blake's twitch doesn't register

This is a final post on the Bolt false start controversy, since as you'll all know, there was some talk that Yohan Blake in Lane 6 (immediately to Bolt's right) might have "twitched" while in the "set" position, and that perhaps he should have received the false start, that he "pushed" Bolt into the false start.

So yesterday, I posted on this question about whether Blake's twitch might have constituted a false start, and wrote the following:
  • If you believe that Bolt was 'triggered' to jump by Blake's movement, then Bolt should NOT have been disqualified, but Blake should have been
  • If you believe that Bolt was unaffected by that movement, then BOTH should have been disqualified
  • And if you believe that Blake's movement was too small and not "irregular", then Bolt is the only athlete who should have been disqualified
So today, I can provide you with the actual data from the starting equipment during the race, courtesy a reader and journalist in Daegu (Thank you so much Remo!).

The image from Lanes 4, 5 and 6 is shown below, for clarity.  You'll recall that Walter Dix is the athlete in Lane 4, while Bolt is in 5 and Blake in 6.  The image should be fairly self-explanatory, but I've explained it briefly below (click to enlarge)

So the vertical grey lines show the firing of the gun, and the green lines immediately to the right of them are the 100ms limit for a false start.  The vertical red line is the point where the actual start of each athlete is registered.  As I wrote yesterday, a start that happens BEFORE this cut-off line shown in green is deemed a false start.

So, each of the sensors in the start blocks is sensitive to the pressure being applied by the athlete.  At some point, as the pressure increases as the athlete pushes off, and the blocks will register enough pressure to signal a start.  I have shown that as a start pressure threshold with the red arrows for all three athletes.  You'll see, for example, that Walter Dix in Lane 4 reaches the threshold soon after the green line, and the start is triggered 139 ms after the firing of the gun (grey line).  

Now look at Blake's graph, in Lane 6.  You'll see a small bump there BEFORE the gun, which I have circled in blue.  This is the twitch that was picked up in the slow motion replays, and which you can see in the video to my previous post on this subject.

If you look over to the right hand side in Blake's pressure graph, you'll see that when he did eventually start (153 ms after the gun), the pressure it took was slightly higher than the pressure registered during his twitch.  I have drawn a dashed green line across from the pressure threshold, and you can see that while the twitch came close to the required level, it was NOT sufficient to trigger the sensors.  Had that twitch been any larger, then Blake would have exceeded the limit, and it would have constituted either a false or faulty start.

This says to me that it would be a pretty tough call to say that Yohan Blake is guilty of a false start, given that the sensitive equipment could not detect it.  It would have been up to the recallers watching the athletes, and it was really a very small movement, only detected later in HD slow motion replays.  Of course, technically, he twitched, and that is, by definition, grounds for at least an aborted start.  But the data say the twitch was tiny, and let's be honest - if Blake was DQd for that, he might have been justifiably upset with the call himself!  So I would conclude that in the end, the right decision was made, even if the technically correct conclusion is that this twitch should have been picked up.  So I'll go with option three in that list above!

Just to add one last though - you can see Bolt's start on the graph above - it comes 104 ms BEFORE the gun even goes off (so it's 204ms before the legal limit), but then you didn't need data to tell you that!  What this graph doesn't say is whether it was Blake's twitch (however small) that caused Bolt to jump, or whether Bolt would have gone anyway.  That remains a point of discussion I guess.  Regardless, it's all just conjecture now, the race is in the books!  


P.S.  Let me take this chance to also correct an error in the post I did earlier today - I said that the bronze medal in the men's 400m was won by Jonathan Borlee.  It was in fact KEVIN Borlee who claimed third, while Jonathan was fifth!  The danger of identical twins!

Enjoy the rest day tomorrow!


Cynical Optimist said...

This is a nice logical analysis.