The lever becomes shorter the greater the knee bend.
This is why in the sprint position at MaxV it is advantages to execute high heel recovery; minimizing backside mechanics and providing for faster knee through.
This is also why we do not see complete knee extension in the flight phase subsequent to stepping over as this would cause GCT to occur far in front of the hips.
During early acceleration, however, where the force vector is predominantly horizontal and the speed is slower by default, and considering how well Powell and Bolt start for taller guys, I think they’re definitely on to something with the low heel recovery.
One of my players does this during speed work; however, it ends being a detriment because he continues to carry out the low heel recovery too far into the sprint. So this is something we’ve worked on during the previous off-seasons- stepping over and down.