You do not run faster by moving your legs faster

Turnover is a symptom of the force a sprinter puts into the ground, and training it directly gets the causation exactly backwards.

Somewhere in every sprint squad there is an athlete being told to get his feet down quicker. He duly shortens everything, cycles his legs at a frantic rate, and runs slower, because the instruction inverted the mechanism it was aiming at.

A runner's speed is stride length multiplied by stride rate, which is true and unhelpful, because the two are not independent inputs you can dial. Both are outputs of one thing: how much force goes into the track during a contact that lasts about a tenth of a second at top speed. Push hard into the ground and you are thrown further, which lengthens the stride. You are also thrown higher, which gives the recovering leg time to come through, which is what allows the next contact to arrive without the athlete having to hurry it.

So the elite sprinter is not moving his legs faster in the way a spectator imagines. His contacts are shorter, his flight times are longer, and his hip is doing an enormous amount of work in a very brief window. Trying to raise turnover directly means cutting the flight time, which means reducing the force, which means going slower while feeling busier. It is one of the few situations in sport where effort and outcome point in opposite directions.

The part I think is genuinely arguable is what to do about it. One school says get stronger in ways that transfer, which mostly means heavy hip extension and stiff, fast bounding, and let the mechanics organise themselves. Another says the coordination is the limiter and no amount of strength helps an athlete who cannot arrange his limbs in time. I lean towards the first for young athletes and the second for mature ones, because you cannot coordinate force you have not got, and because I have watched too many well drilled sprinters with beautiful positions and nothing to put into the ground.

What both camps agree on, and what the get your feet down instruction violates, is that the ground contact is where the race is won. Everything in the air is consequence.

Stop coaching the legs. Coach what happens in the tenth of a second when the foot is down.