What is reactive strength?
Reactive strength is the skill and the capacity of an athlete's neuromuscular and musculo-tendinous system to rapidly convert stored elastic energy into concentric force, minimizing energy loss while maximizing output within a short time window (i.e., minimal ground contact).
That definition has two halves, and they matter for training:
Skill: the software
The athlete's neuromuscular coordination and timing ability, how they fine-tune stiffness, anticipate ground contact, and reflexively manage transition speed. This is what improves with rehearsal, intent, and technical exposure.
Capacity: the hardware
The mechanical and structural qualities of the muscle-tendon system that support fast and forceful movement. This is built over time through tendon loading, eccentric work, and heavy strength.
"Skill is the software. Capacity is the hardware. You need both running, and you need a way to measure where each athlete is sitting.
RSI, the field measure
The Reactive Strength Index (RSI) is the field measure most coaches reach for first. It's a clean, repeatable ratio:
RSI is useful. But the score alone is just a ratio, it doesn't tell the whole story. Two athletes can score identically and look nothing alike on the floor.
Consider these two athletes from a recent 10/5 testing block:
RSI = 3.2
RSI = 3.2
Both athletes score the same. But one is higher-powered with slower contact, and the other is faster with less output. They sit at fundamentally different points on the force-velocity curve, and they need different training inputs to keep developing.
That's why plotting the result on the Reactive Strength Quadrant offers far more diagnostic value than the ratio alone.
Introducing the RSQ
The Reactive Strength Quadrant (RSQ) gives context to RSI results by showing not just how reactive an athlete is, but how they express that reactivity.
To build it, we plot two axes:
- X-axis: Ground Contact Time (.010s to .500s)
- Y-axis: Jump Height (1″ to 24+″)
Every athlete's jump lands in one of four quadrants based on where those two numbers intersect.
The four quadrants
Reactive (top-left)
Short contact, high jump. The athlete who finds elastic snap and turns it into vertical output, the picture-book reactive athlete. Long, springy tendons; well-rehearsed timing; high stretch-shortening cycle quality.
Compliant (top-right)
Long contact, high jump. Big athletes who produce real height but settle into the ground before launching. The output is there, but the reactive timing isn't, usually a power athlete who needs faster force application to fully express what they have.
Stiff (bottom-left)
Short contact, lower jump. Fast turnover, light output. Common in younger athletes, smaller athletes, and athletes who are good at the SSC but need more raw strength behind the spring.
Developing (bottom-right)
Long contact, low jump. Foundational work needed. Could be a deconditioned athlete, an athlete returning from injury, or an athlete who hasn't been taught the mechanics yet.
"RSI tells you the score. The RSQ tells you the strategy. Same RSI, four different programming responses.
Training prescriptions
Based on general RSI testing protocols, 10/5, 4/2, or Drop Jump, the table below is a good starting point for guiding plyometric programming once you know which quadrant the athlete sits in.
| Quadrant | Emphasis | Drills |
|---|---|---|
| Low Reactivity | Build stiffness, motor control, foundational posture | Marching drills, rope skipping |
| Elastic-Dominant | Enhance vertical force and concentric impulse | Loaded verticals, sprint drills |
| Strength-Dominant | Faster force application, reduce amortization | Drop jumps, contrast training |
| High Reactivity | Maintain capacity, fine-tune tissue control | Depth jumps, pogo hops, shock method |
This isn't a rigid prescription, it's a starting frame. Athletes drift between quadrants across a season as fatigue, training emphasis, and competition load shift things around. That's why retesting matters: an RSQ snapshot becomes a real planning tool only when you have two or three data points to compare.
Coach takeaway
RSI is the score on the test. The RSQ is what tells you what to do with it.
If you're already running 10/5s or drop jumps in your testing block, you have everything you need, jump height and ground contact time, to plot every athlete on the RSQ. The Plyomat app does this automatically every time an athlete steps on the mat.
In Part Two of this series, we look at how to take the quadrant placement and turn it into a tier-based plyometric program: Light, Medium, Ping, and Deep tiers tied directly to where each athlete sits on the chart.