Lower extremity rehab realities
More than 200,000 ACL tears occur every year in the United States, and the re-injury numbers are sobering. Depending on the study, anywhere from 6% to over 30% of athletes will tear the same ACL again after returning to sport.
What makes this even more concerning is that many athletes are "passing" the strength tests we traditionally rely on, yet are still returning with large deficits in reactive ability.
What we're doing isn't enough
The uncomfortable truth at the center of this: restoring strength does not guarantee restoring reactive ability. Three findings from the literature keep this front of mind in my clinic.
Strength symmetry does not equal reactive readiness
A 2024 paper showed that roughly 65 percent of patients who passed their isometric quadriceps strength test still failed reactive strength testing. (Girdwood et al., 2024)
Traditional hop tests don't capture what we need
A study evaluating the relationship between single-leg hop performance and knee extension strength found the relationship to be moderate but imprecise, and the prediction error was clinically meaningful. (Turk, 2025)
Time alone is not protection
Other research highlights that athletes returning before nine months face dramatically higher re-injury rates. (Grindem, 2016) Calendar time doesn't heal the stretch-shortening cycle.
"We cannot rely on strength tests alone. We cannot assume hop distance equals readiness. We need objective measures of reactive strength, symmetry, rhythm, and multi-planar control.
Return to reactivity
These three Plyomat tests help me establish reactivity. They are simple, fast, and repeatable. Most importantly, they give athletes the confidence that their body is ready, not just strong, but responsive, coordinated, and prepared for the instability of sport.
- Single-leg vertical jump, baseline single-leg jumping ability
- Single-leg 5-hop RSI, reactive strength and limb symmetry
- Lateral-to-vertical RSI, multi-planar load tolerance
1. Single-leg vertical jump
This gives you a clean look at three things. I collect three maximal attempts per side, film from the front, and compare both legs for mechanics.
Single-Leg Vertical Jump
- DisplacementHow much height the athlete can produce on each leg.
- ControlLanding mechanics, trunk positioning, how the knee organizes under load.
- ConfidenceYou can see exactly when an athlete is hesitant, cautious, or fearful during propulsion or landing.
Under 10 percent asymmetry in height is passing, but I'm evaluating all aspects, not just the number, to assess the overall grade here.
2. Single-leg 5-hop RSI
This is the reactive strength test I rely on most, but it can also be the most intensive.
- The athlete performs five consecutive maximal hops on one leg, staying tall and minimizing ground contact time.
- They then repeat on the other leg. The Plyomat calculates RSI from each hop, and I plot both legs on the RSQ (Reactive Strength Quadrant).
I hold the line at 10 percent symmetry, but that is paired with video to confirm clean, efficient movement.
The RSQ turns the data into an immediate visual story. You see which leg has shorter contact times, which one produces better flight times, and whether both limbs fall into similar zones of reactivity. Hop distance alone does not provide the level of detail that I seek in clinical practice.
3. Lateral-to-vertical RSI
This is the test that often determines whether I feel comfortable clearing an athlete for true sport activity.
Most ACL injuries don't happen in a straight vertical pattern. They happen when an athlete loads laterally, accepts force, and then tries to redirect it. The lateral-to-vertical RSI captures this exact sequence, and thus has high carryover in the discussion for return to sport.
How the test runs
The athlete starts beside the Plyomat, performs a controlled lateral bound (skater jump) over an 8″ mini hurdle onto the mat, and immediately transitions into a maximal vertical jump, where RSI is taken.
The distance the hurdle sits from the center of the Plyomat is equal to leg length ÷ 2.
A limb-to-limb difference under 10 percent, paired with stable movement, is my threshold for true readiness. We are actively validating this test in a clinical trial with excellent reliability and reproducibility between test sites.
Putting it all together
Each test earns its place by answering a different question, at a different point in the progression.
| Test | When to use it | What it measures | Passing / key criteria |
|---|---|---|---|
| Single-Leg Vertical Jump | Mid to late rehab | Displacement, landing control, competency, and confidence | Symmetry within ~10 percent and stable mechanics on video |
| 5-Hop RSI (plotted on RSQ) | Late rehab through final progression | Reactive strength, timing, and limb-to-limb symmetry | Symmetry within ~10 percent on RSI and clustering in similar RSQ zones |
| Lateral-to-Vertical RSI | Final clearance before return to sport | Multi-planar load tolerance, transition timing, force redirection | Symmetry within ~10 percent plus confident, controlled mechanics |
Practicality of Plyomat
Force plates are phenomenal tools. They give depth and detail that no clinician would deny. But they are not required to evaluate whether an athlete is reactive, symmetric, and mechanically sound.
With a high-quality switch mat and slow-motion video, you can get everything you need for return-to-play decision-making:
- Ground contact times
- Flight times
- RSI
- Multi-planar loading behavior
- Visual confirmation of movement pattern quality
The key is consistency and fast testing. The Plyomat sets up in under three minutes, and in some clinics can be installed directly into the flooring so there is no setup time at all. In a high-volume environment, this matters.