I agree RB. The hammering is most effective in the drive phase but most advanced sprinters have learned to do this very efficiently. If you watch a 100m dash at normal video speed you wouldn’t notice the hammering. Slow mo reveals just how much force sprinters (Jeter, MoGreene, Powell, Gay, etc.) are exerting with the downward swing but it takes a conscious effort and training to lift the arms up and pull down mid race. I think many sprinters are trying to produce too much force either up or down with their arms and forgetting to 1. relax, 2. lift and pull down rather than hammering back (which influences longer back side recovery) mid race.
In short, Hammering forcefully downward is essential to the drive phase; lift and pull down (while stepping down, not back) is appropriate for the MaxV phase of race.