Jump height tells you almost nothing about a runner's plyometric progress

The thing that makes running cheap is how quickly the leg leaves the ground, and a tape measure on a vertical jump cannot see it.

Plyometric work has become standard in distance programmes, which is progress. What has not caught up is the way it gets assessed. Somebody jumps, you measure how high, the number goes up over eight weeks, everybody is pleased. The problem is that a higher jump does not necessarily mean a better runner.

Running economically is largely a question of elastic return. Each step lands, the Achilles and the arch and the surrounding tissue stretch and store energy, then give a large fraction of it back on the way out. The tissue is a spring. Springs work best when they are stiff enough to return energy quickly rather than absorbing it and slowly bleeding it away as heat.

The signature of a good spring is short contact time. Not big amplitude. A vertical jump from a standstill mostly measures how much force you can produce over a long push, which is a strength quality and a legitimately different thing. An athlete can add several centimetres to a countermovement jump by getting better at a slow deep push and change nothing at all about how the leg behaves during a two tenths of a second ground contact at race pace.

The measurement that would actually tell you something is a repeated hop with a short contact. The useful output is not how high but the ratio of flight time to ground time, and whether the athlete can hold that ratio across a set instead of drifting into deeper, slower contacts as they tire. That drift is the interesting bit, because that is precisely what happens to a marathon runner in the last hour.

Which changes how you write the session. Sets of long, deep, maximal jumps train something. Sets of short sharp bounces with an instruction to spend as little time on the ground as possible train something else, and the second is closer to what running asks for. Volume should be low, quality should be strict, and the moment the contacts get sloppy the set is over. Not two more for the count.

Coaches want a number that improves, and jump height obliges by improving under almost any training.

Contact time is harder to measure and more honest, which is a reasonable summary of most useful things in this sport.