Typically 400m training and jumps training are not synonmous to achieving maximum potential in the jumps. although many athletes can have success if the do the explosive work before the tempo, speed endurance or special I/II. With my multi’s, we will have a speed endurance/tempo session every so often after a jumps session in season to keep the stimulus and produce some lactate. Both of my athletes came from heavy volume backgrounds, so dropping it off completely for a while tends to have a negative effect.
A lot can be learned from multi-eventers as far as training. A wise man once told me (well more than once) to “train everyone like a multi.” The challenge of many biomotor abilities makes for a better overall athlete.