....the shorter the race, the less important efficiency becomes. i am not saying geb wasn't hugely efficient when he ran his world records, just that he can get away with minor innefficiencies at those shorter distances far more than he can at longer distances like the half marathon and above.
a change in footstrike is probably a result of geb's body's natural adaptation to racing longer distances, doing longer intervals etc. the body tends to naturally work out even minor inefficiencies that someone like geb has. i think that adaptation plays a part in the reduction of footspeed that we normally associate just with age.
all speculation of course but i find it hard to believe that he just knocked 20 seconds off of an already smoking fast world record running alone more than half the way after having become LESS efficient
Actually, efficiency is a product of VO2 max. Elites with the lower VO2's learn to become more efficient to compensate, runners with the high VO2s don't need to. The 2 extremes are Clyaton with his "shuffle", and Craig Virgin who was known for his ineffecient form. I suspect Geb's is pretty damn high.
Also, I am having trouble believing this record. For a 32 yo. guy this is... well, unbelievable.