Vertical jump training and assisted vertical jump training (essentially with a negative load) can each increase vertical jump height through increases in countermovement depth, even while actually reducing peak force produced in the jump. This seems to happen because the tendon becomes more compliant after these types of training, which means they elongate more during the countermovement phase of the jump.
Each time you land, spring immediately back up. Don’t hesitate. The single beat that typically happens after we hit the ground is a natural reflex, and we may not even realize we’re doing it. But that extra pause has to go if we’re looking for a way to jump higher. Check the mirror or watch videos of yourself as you hit the ground. The momentary pause you may see between one vertical jump and the next may be holding you back. For more detail on how this works, visit the plyometrics section of our website.
A second, more efficient and correct method is to use an infrared laser placed at ground level. When an athlete jumps and breaks the plane of the laser with his/her hand, the height at which this occurs is measured. Devices based on United States Patent 5031903, "A vertical jump testing device comprising a plurality of vertically arranged measuring elements each pivotally mounted..." are also common. These devices are used at the highest levels of collegiate and professional performance testing. They are composed of several (roughly 70) 14-inch prongs placed 0.5 inches apart vertically. An athlete will then leap vertically (no running start or step) and make contact with the retractable prongs to mark their leaping ability. This device is used each year at the NFL scouting combine.