A question for you track and field experts, and I know you're out there.

Every time a sprinter or hurdler slows down before the tape in a heat, I get a vision of Leon Lett in the Super Bowl

Why do sprinters and hurdlers "shut it down" -- that is, stop running fast -- a few feet from the finish line when they're leading in qualifying heats? I get the idea that the top runners, who figure to advance, don't go all out in the heats because they're saving their energy for the final.

But that's different than what I've been seeing time and time again in the heats: A runner runs hard enough to be in first or second place near the finish, then starts slowing down about three steps before the tape.

It looks to me like a recipe for being overtaken by two or three battling also-rans and missing out on the medal race for no good reason. I haven't seen that happen yet, although it's possible I've seen it in previous Olympics and forgotten it. I have no mental "save" key for track and field. But I've seen it almost happen several times.

It just can't be that slowing down in the last few strides is a significant energy saver. Like, what, running hard for 42 steps is OK, but you shoot your bolt if you run hard for 45? No way.

Run just hard enough to qualify, but do it through the tape. Right? What am I missing?