Running Cadence Training Hypothesis

I think about it the other way around. Cadence is a metric of reaction time. If you're stepping 180bpm, then you're moving multiple muscle groups at sub-thirds-of-a-seconds, tactically to maintain/correct the cadence. This is completely a neurological exercise, and neurology is upstream from muscle activation so it should get fixed first.

I train with a 180bpm metronome because 180 just happens to be the popular number among top athletes. When I am done training at 180bpm, I might decide that a difference cadence works better for me. 

In order to maintain cadence, I simply reduce stride length. It's easy. Think of it as a marching drill. Over training cycles, as you get less fatigued at a particular ( variable-length-per-step * constant-steps-per-minute = variable-length-per-minute = pace ) you can increase step length bit by bit, and thereby cover the distance faster.