Here’s a great look at the vertical jump and the different joint positions.
In the video, this athlete has great arm action with an explosive descent and ascent. But as you can see there’s a horizontal displacement with the take-off and landing. Ideally, we like a parallel relationship with the shin and trunk throughout the entire movement.
At the beginning of the take-off there’s a shift forward to the toes. This will place more stress on the quads and a disruption with that parallel relationship. The upper half is moving faster vertically than the lower half. This means that the jump will be initiated by the lower back. The lower body will be delayed and therefore causing a limited “push-off” or leg drive. This is an inefficient jumping technique that will negatively affect the athlete’s force production.