Earlier quoted context omitted.
nitpick: 800m world record is 1:40.91 ... the 800 is also not a race where the WR time is challenged on a regular basis. Championship 800m racing is a wait and kick affair which never lends itself to ultrafast times because the first 400 is loafed. The scary thing about David Rudisha's WR set at the 2012 Oly was that it was a solo wire-to-wire: https://www.youtube.com/watch?v=YKEOjWEzVGs That DOES NOT HAPPEN in champ…
> At 500m, Rudisha accelerates and leaves these other runners In his 2012 Olympic 1:40.91 win (and WR) his splits were 49.28, 51.63, so he didn't accelerate. He slowed down less than the rest of the field. In his prior 2010 WR of 1:41.01 his splits were 48.9, 52.1. So in 2012 he went out slightly slower and then faded less in the second lap. Which is interesting because it's typical of the 800M to run positive splits…
The 800 begins as a race at 150-200m. There anaerobic debt starts to rise in the next 100m, and by 400m we are officially in substantial anaerobic debt.
By "acceleration" I suppose I mean a more nebulous "increase in effort / selling out". At 500m in Rudisha's race, you can see the change in the leaders as everyone begins to try to exert effort above and beyond what their mounting anaerobic debt would sanely allow. I think what happens is that racers try to use the last mental and physical reserves at this point to gain momentum and transition to a sprinters stride in order to gain more RELATIVE speed over the last 300m.
The massive amounts of anaerobic debt in the last 300m, relative to the phosphate and no-debt first 300m of the race, will invariably be slow by the clock. But the speed produced relative to pain and physiological debt, it is much more stark.
Every runner will perceive "kicking" at the end in this manner. The sense of acceleration, real or otherwise, is in relation to an inability many runners don't have in these moments. Physiologically middle distance "kickers" have some sort of hybrid fast twitch muscles they can employ in situations like this that produce higher speeds under extremely high anaerobic debt than other runners. Whether this is also related to higher pain tolerance or other physiological aspects (reduced "lactic acid" release like they claimed Armstrong and Phelps had, etc).
Dave Wottle's victory, which I recall vividly described by Jeff Galloway in one of his books, was a fluke. Wottle was injured, and basically was limited to that speed for the first 400. It was almost as big a fluke as Rudisha's race. He was trying to simply not embarrass himself in the race. So he ran a careful first lap just to try to finish.
The 800m is such a painful event that relies so much on anaerobic tolerance and anaerobic energy stores, that essentially it is a crapshoot under most circumstances. You can't know whether or not that moment of truth: whether you still have kick/speed at 500-600m when everyone else starts also goes "all in" to try to win, whether you'll have the speed that day.
Wottle that day got lucky: all the people in front of him didn't have the stuff, Wottle was able to survive the first 400m and then adrenaline the last 400m. And perhaps the wind that day was particularly graceful towards someone running through the pack, since wind resistance is a factor where you are running 17-20 mph.