Depth jump (drop jump): which prerequisites you need, how to choose drop height relative to your own jump, and why build-up comes before height.
The depth jump is a drop jump: you step off a box, land with a short ground contact and immediately jump as high as possible. It trains reactive strength, meaning how quickly you can push off from the landing.
The honest answer to "How high should the box be?": lower than you think. A study with 20 Division I volleyball players tested drop heights from 50 to 150 % of their own jump height. Landing load rose clearly when the drop height exceeded 100 % of own jump height; at 125 and 150 % the negative work of knee and ankle increased. Jump height and reactive strength index (jump height divided by ground contact time) did not differ between drop heights [1]. Anchor: a higher box does not give you a higher jump, but more impact. The authors recommend 50 to 100 % of own jump height.
A review of 22 studies reaches the same conclusion: drop height should not be seen as a measure of intensity. What matters are ground reaction forces, power and jump height [2].
Drop from a low step (10 to 20 cm) and land softly with both feet together. Knees over feet, hips back, chest open. Hold the landing.
Milestone: 5 landings in a row, stable, knees do not fall inward.
Do the box jump (from the floor onto the box) with a soft landing on the box. This is the prerequisite from our skill tree.
Milestone: 3 × 5 box jumps clean, soft landing.
Measure your jump height in the countermovement jump (CMJ): stand at a wall, mark your reach, jump as high as you can and mark. The difference is your jump height.
Milestone: you know your CMJ height.
Drop from a box whose height is about 50 % of your CMJ height and land softly without jumping again [1]. This is called a depth drop.
Milestone: 3 × 5 stable landings from this height.
Drop from the box (50 % to 100 % of your CMJ height [1]), land briefly and jump immediately back up. Think "the floor is hot". Do only a few contacts per session, for example 3 × 3 (practice value).
Milestone: 3 × 3 clean, short ground contact, soft landing, no knee collapse.
How to track progress: Progress here is not box height but quality: shorter ground contact at the same or higher jump height. That is the idea behind the reactive strength index. Film the contact and compare over weeks. Because drop height alone does not describe intensity [2], you do not progress through height but through clean contacts. That is a rule of practice.
Where does it fit in training? The depth jump belongs at the start of the session when you are fresh, after a thorough warm-up, never at the end. Few contacts, full recovery between them. 3 × 3 is a practice value; the studies I read give no number for this.
Warm-up: Without a thorough warm-up you do not start at all: ease in, do squats and hip mobility, then several squat and box jumps with rising intensity. Only then follow the first depth drops and finally the reactive jumps. If you feel tired or heavy, skip the depth jump that day. This is practical advice, not a study statement.
The depth jump is safety-critical: large forces act on knee, ankle and back at impact. It is not an entry exercise. A clinical overview of plyometrics describes guidelines and contraindications for such programmes [3]. I give no fixed strength values as a prerequisite here, because the sources I read provide none.
No maximal heights, no tired jumps, no jumps on slippery ground. Stop immediately with pain in the knee or foot. This guide explains and motivates, it does not replace supervised training or a coach.
Measure quality, not height: film the ground contact and count how long you are on the floor. If contact is clearly longer than in the box jump, the box is too high. That is a practice trick. The studies show that drop height alone does not describe intensity [2].
Calculate relative to your jump height: 50 to 100 % of CMJ height was sufficient in one study, above that landing load rose without jump height rising [1].
Plyometric training improves jump height on average: in a meta-analysis by 4.7 % for the drop jump [4]. That applies to plyometrics overall, not to every individual.
Only with a strength base and secure landing technique. That is a rule of practice; do not rely on a single number but on verified technique.
Few contacts, once or twice a week (practice value). The studies give no fixed number for this [2].
For learning yes: the depth drop (landing only) is the prerequisite.
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