Selecting Drop Height with the Reactive Strength Ratio

Walk into most weight rooms running depth jumps and you will see the same box every session, at the same height, chosen months ago because it looked about right. Nobody retested it. Nobody asked whether a 175 cm sprinter with a 1.8x-bodyweight squat should be dropping from the same 40 cm platform as a 160 cm gymnast working knee stability. The result is a plyometric session that trains whatever height happens to be sitting against the wall rather than the quality the athlete actually needs.

The reactive strength ratio (jump height or flight time divided by ground contact time) gives you a way to test this properly instead of guessing. By running an athlete through a short ladder of increasing box heights and tracking how the ratio responds, you find the point where they stop rebounding and start absorbing — and that point is where your programming decisions should actually start.

The reactive strength ratio (commonly shortened to RSI) is calculated as jump height divided by ground contact time, or equivalently as flight time divided by contact time. Both versions describe the same underlying quality: how much vertical displacement an athlete produces per second spent on the ground during a fast stretch-shortening cycle (SSC) action. A high ratio means the athlete is converting the eccentric landing force into a rebound quickly and efficiently. A low ratio, even with a respectable jump height, usually means the athlete spent too long absorbing the landing before pushing back off.

Flanagan and Comyns (2008), writing in Strength and Conditioning Journal, formalized the practical framework most coaches still use today: classify ground contact times below roughly 0.25 s as fast SSC actions (sprinting, most depth jumps, change of direction) and contact times above that as slow SSC actions (most squat and countermovement jump patterns). Their central argument was that drop height is not a fixed prescription — it is a variable that should be manipulated systematically, height by height, until you find the point where an individual athlete's ratio peaks, rather than borrowed from a generic plyometric chart.

That individualized peak is often called the optimal drop height, and it is specific to the athlete's relative strength, technique, and eccentric tolerance on that particular testing day — not a fixed number that transfers between athletes of similar height or bodyweight.

Bobbert and colleagues (1987), in a foundational biomechanics study published in Medicine and Science in Sports and Exercise, tracked seven trained jumpers across drop heights from 0.20 m to 0.60 m and found a consistent technique shift as height increased. At lower heights, subjects used a stiff, rebound-style landing with limited knee flexion and short ground contact. Past a certain height — different for each subject — several switched to a countermovement-style strategy: deeper knee flexion, longer contact time, and a slower, more strength-dominant rebound. Jump height sometimes still crept up slightly at these taller heights, but the ratio of output to ground time collapsed, because the athlete was no longer performing a fast SSC action at all.

This is the trap of picking a box height by eye: a taller drop can still produce a bigger jump while the actual stimulus has quietly shifted from fast-SSC reactive work to slow-SSC strength work. If the programming goal was sprint-specific ground contact quality, that box height now works against you even though the athlete is jumping just as high, or higher, than before.

Byrne, Moran, Rankin, and Kinsella (2010), publishing in the Journal of Strength and Conditioning Research, tested this directly in 20 trained male jump-sport athletes across box heights of 0.30 m, 0.45 m, and 0.60 m, comparing three common ways coaches define an optimal height: the height producing the greatest jump, the height producing the highest reactive strength ratio, and the height that keeps contact time under a fixed threshold. For a meaningful share of the athletes tested, these three criteria pointed to three different box heights. The practical takeaway is blunt: there is no single universal optimal height, and the criterion you choose to define optimal changes the number you end up training at.

Finding an individual's ratio-optimal height takes one session and about 20 minutes once warmed up. Use a contact mat, force plate, or an IMU device that splits flight time and ground contact time per rep; a stopwatch cannot resolve contact times frequently under 250 ms.

1. Warm up fully. Include ankle hops, 2 to 3 submaximal countermovement jumps, and one or two drop jumps from a low 20 cm box to prime the stretch reflex before recording begins.
2. Select a starting height based on training background. Athletes with a squat 1RM under roughly 1.5x bodyweight, or anyone new to depth jumping, should start at 20 cm. Athletes with a squat 1RM above 2x bodyweight and prior plyometric exposure can start at 30 cm.
3. Test in 10 to 15 cm increments (a typical ladder is 20, 30, 40, 50, and 60 cm), performing 2 clean reps per height with full rest of 60 to 90 seconds between reps and 2 to 3 minutes between heights.
4. Record ground contact time and flight time (or jump height) for every rep and calculate the reactive strength ratio immediately, discarding any rep with visible technique breakdown (excessive knee valgus, arm-swing compensation, or a stutter step on landing).
5. Stop the ladder once the ratio drops for two consecutive heights, or once contact time exceeds roughly 300 ms for a given individual — whichever comes first.

Keep landing surface, footwear, and box type identical across the session; a softer landing mat or a box with an unstable lip will alter contact time independent of any real change in reactive ability.

These ranges are rough population estimates drawn from the drop-height biomechanics literature; the athlete's own ratio curve from that day's testing is what actually determines their working height, not the table.

Once you have a ratio value for every tested height, plot them in order. Most athletes show a rise-then-fall pattern: the ratio climbs from the lowest height, peaks somewhere in the middle of the tested range, and declines as contact time lengthens faster than jump height compensates for it. The height at the peak is the individualized optimal drop height for that session.

A common misread is treating the tallest height an athlete can physically land from as the best one, simply because it produced the highest jump. Go back to the Bobbert et al. (1987) finding above: jump height can keep rising for a stretch even after technique has shifted to a slower, absorption-dominant strategy. The ratio shows the rebound quality has already broken down, even when the raw jump number still looks fine.

Where the curve is flat rather than sharply peaked — a difference of less than about 5% between two adjacent heights — treat both as usable and choose based on the training goal, since ratio differences this small are within an athlete's normal session-to-session variability and are not worth chasing precisely.

Once you know an athlete's ratio-optimal height, you still have a choice about whether to train exactly at that peak or deliberately away from it, depending on what the block is targeting.

For sprint-specific ground contact work, train at or slightly below the peak height, in the range that keeps contact time under the roughly 250 ms fast-SSC threshold described by Flanagan and Comyns (2008). Ground contact times at top sprint speed are typically well under 150 ms, so anything resembling a slow countermovement is not specific to that demand.

For general reactive strength and jump-sport conditioning (basketball, volleyball closing steps, change of direction), training at the peak height itself is usually appropriate, since the goal is maximizing the ratio rather than strictly capping contact time.

For eccentric overload and tendon-stiffness work in more advanced athletes, a height 10 to 15 cm above the ratio peak can be used deliberately, accepting a lower ratio for greater eccentric loading — but only after clean technique at the peak height across multiple sessions, and only for short blocks of 2 to 3 weeks given the added joint stress.

Retest the full ladder every 4 to 6 weeks, after any meaningful strength or bodyweight change, and at the start of a new phase. An athlete's optimal drop height moves as eccentric strength and technique improve, and a height appropriately challenging in week 1 is often sub-maximal by week 8.

A short list of errors accounts for most poorly chosen drop heights in practice:

• Copying a height from a teammate or a chart. Per Byrne et al. (2010), even athletes with similar training backgrounds can have meaningfully different optimal heights, so a shared team height will be wrong for a good portion of the group.
• Testing while already fatigued. Ground contact time lengthens under fatigue independent of true reactive ability, making the optimal height look artificially lower than it is. Run the ladder early in a session, before heavy lower-body work.
• Chasing jump height instead of the ratio. Per Bobbert et al. (1987), jump height alone keeps climbing after the movement has already stopped being a fast SSC action. Track contact time on every rep, not just displacement.
• Never retesting. A height selected in preseason stops matching an athlete's capacity within a few weeks of consistent training, especially for athletes making rapid strength gains.
• Ignoring landing mechanics as a disqualifier. A rep with visible knee valgus or a stutter-step landing should be discarded entirely, since it reflects a technique failure rather than a true measure of reactive capacity at that height.

Treated as a short, repeatable test rather than a one-time setup step, drop height selection turns a generic plyometric session into one that trains the specific quality each athlete actually needs.