Reactive Strength Quadrant: Part One

RSQ: A Visual Tool for RSI Evaluation

by Richard Burnett, MS, SCCC, CSCS, APCC, CAFS

In modern sports science, one of the most practical ways to understand explosive athletic capability is through the Reactive Strength Index (RSI)—a metric designed to quantify how efficiently an athlete uses the stretch-shortening cycle (SSC). While RSI has long been a staple in field-based assessments, visualizing its components in a two-dimensional quadrant model—the Reactive Strength Quadrant (RSQ)—offers a more nuanced interpretation.

This model, especially when paired with technology like the Plyomat switch mat, allows coaches to evaluate how well and how quickly an athlete produces force, giving context to individual test results and guiding more targeted training decisions.

What Is Reactive Strength?

Reactive strength is best understood as a blend of skill (software) and capacity (hardware)—two interconnected systems that allow the body to rapidly and efficiently utilize the stretch-shortening cycle.

🧠 Skill (Software)

This is the athlete’s neuromuscular coordination and timing ability—their capacity to fine-tune stiffness, anticipate ground contact, and reflexively manage transition speed. It includes: - Proprioception & Anticipation: Recognizing timing and preparing tissues for impact - Pre-activation: Stiffening muscles before landing - Stretch Reflex & Neural Drive: Enhancing concentric output via rapid reflex loops - Motor Control: The brain’s ability to regulate when and how force is applied

💪 Capacity (Hardware)

This refers to the mechanical and structural qualities of the muscle-tendon system that support fast and forceful movement: - Tendon Stiffness & Elastic Recoil: Ability to store and return elastic energy with minimal hysteresis - Muscle-Tendon Interaction: Quasi-isometric muscle action while tendons lengthen and recoil - Rate of Force Development: Speed at which force can be applied concentrically after landing

Together, these components determine how well the athlete can load, store, and release elastic energy during a plyometric task.

When both software and hardware are trained appropriately, the athlete can minimize ground contact time and maximize flight time—hallmarks of high reactive strength.

Reactive strength is the neuromuscular capacity to dynamically and efficiently exploit the stretch-shortening cycle—via optimal pre-activation, controlled stiffness, rapid eccentric-to-concentric transitions, and minimal energy loss—to maximize force output in a short time frame.

It relies on: - Tendon elasticity for energy storage and recoil - Pre-activation and stiffness modulation to minimize energy leakage - Fast eccentric-to-concentric transition to recapture elastic potential - Reflexive and coordinated timing to support quick responses

What Is the Reactive Strength Index (RSI)?

First introduced by Flanagan & Comyns (2008), RSI is calculated as:

RSI = Flight Time / Ground Contact Time

It serves as a practical field measure of reactive strength by assessing how much vertical force (via jump height) is generated in how little time (contact time). A high RSI indicates both fast and forceful movement, often reflecting strong tendon recoil, efficient neural drive, and stiffness control in fast SSC (stretch-shortening cycle) activities.

However, RSI is a proxy, not a direct measurement of tendon mechanics or neuromuscular function. Two athletes may have the same RSI but with very different contact times or jump heights, implying different reactive strategies:

·      Athlete A: 25” jump, 225ms contact (RSI = 3.2)

·      Athlete B: 20” jump, 200ms contact (RSI = 3.2)

These athletes share the same RSI score but reflect different strengths: one favoring elastic return, the other favoring speed of transition.

Introducing the Reactive Strength Quadrant (RSQ)

To bring clarity to RSI outputs, we can plot Ground Contact Time (X-axis) against Jump Height (Y-axis), placing athletes into one of four quadrants:

🔵 HIGH REACTIVITY (Top-Left Quadrant)

·      Low GCT, High Jump Height

·      Examples: Drop jumps <250ms, tuck jumps, max-velocity sprints

·      Indicates: Elite tendon-driven rebound and rapid force application

🔴 STRENGTH-DOMINANT (Top-Right Quadrant)

·      High GCT, High Jump Height

·      Examples: Depth jumps with long amortization, loaded vertical jumps

·      Indicates: Strong force output but slower SSC transition

🟢 SPEED-COORDINATION / ELASTIC (Bottom-Left Quadrant)

·      Low GCT, Low Jump Height

·      Examples: Pogos, rhythm hops, sprint drills

·      Indicates: Efficient stiffness and rhythm, but limited vertical force

🟡 LOW REACTIVITY / GENERAL (Bottom-Right Quadrant)

·      High GCT, Low Jump Height

·      Examples: Marching, rope skipping, low-intensity landings

·      Indicates: Foundational work or diminished reactivity (e.g., youth, rehab)

Why the Quadrant Matters

RSQ gives context to RSI results by showing not just how reactive an athlete is, but how they express that reactivity. It allows coaches to:

·      Differentiate between explosive force and elastic timing

·      Identify whether the athlete needs to get stronger, faster, or more coordinated

·      Program drills that shift the athlete’s profile across quadrants over time

Example Training Prescriptions:

Quadrant	What to Train	Example 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
🟡 Low Reactivity	Build stiffness, motor control, foundational posture	Marching drills, rope skipping
🟢 Speed-Coordination	Enhance vertical force and concentric impulse	Loaded verticals, sprint drills

Research and Technical Context

Recent studies provide physiological backing for RSI and RSQ models:

·      Tendon Efficiency: Kubo et al. showed improved energy return and reduced hysteresis with plyometric training, confirming the tendon’s role in reactivity.

·      Neuromuscular Timing: Pre-activation and stiffness modulation—especially in fast SSC tasks—are critical for optimizing RSI.

·      Context-Specificity: RSI varies based on surface, drop height, fatigue, and athlete maturity. It’s most valid in fast SSC conditions (<250ms).

·      Performance Correlations: Meta-analyses show strong links between RSI and sprinting, jumping, and change-of-direction ability.

Final Thoughts: From Metric to Map

Reactive Strength Index is not just a number—it’s a gateway to understanding how athletes produce force in time-constrained settings. The Reactive Strength Quadrant adds an additional layer by showing how that output is generated.

When interpreted correctly, RSI + RSQ: - Help refine plyometric programming - Support load management strategies - Guide athletic profiling and rehab timelines

Every athlete is reactive. The real value lies in identifying where they are reactive, and designing the pathway toward where they need to be.

References

·      Flanagan, E. P., & Comyns, T. M. (2008). The use of reactive strength index in training and testing. Journal of Strength and Conditioning Research.

·      Kubo, K. et al. (2007). Tendon properties and functional performance before and after plyometric training. Journal of Applied Physiology.

·      Jarvis, P. et al. (2022). Reactive Strength Index and athletic performance: A systematic review.

·      Verkhoshansky, Y. V. (1998). Shock Method and Depth Jumping: Fundamentals of Special Strength-Training.