Kinetix Physio

Be athletic, even if you’re not an athlete.

What do you do if your hop test says 94% symmetry, but your isometric quad strength says you’re 22% under target?

It’s common to pass hop tests but still have weakness — and only one of them is built to detect the deficits that drive re-injury.

Most return-to-sport decisions still rest on three tools designed for a clinic visit: hop tests, 5RM/strength lifts, and “how does it feel?”

The data on those tools isn’t great:

→ ~30% re-injury rate after standard discharge criteria, ie hop testing battery (Wellsandt 2017)

→ Hop LSI overestimates true knee function by 10–15% — the healthy side compensates (Wellsandt 2017)

→ A 95% hop LSI can hide a 25% deficit in peak vertical force (Kotsifaki 2022, BJSM)

→ ~67% of ACL athletes fail biomechanical RTS criteria (Welling 2018)

→ Bilateral 5RM squats let the uninjured side carry 60–70% of the load — you’ll PR with a quad still 30% behind

→ Pain is a lagging indicator. Tendon and joint capacity return to a symptomatic threshold weeks before structural capacity does

Six numbers actually decide if you’re ready:

01 Peak force (isolated joint MVIC) vs a population norm
02 Limb symmetry across force — not distance
03 Rate of force development (RFD)
04 Reactive Strength Index (RSI) on drop jumps
05 Asymmetry under fatigue
06 Force-trace shape (landing, deceleration, compensation)

Example athlete — 38 y/o male recreational runner, 12 months post-meniscus repair, 80 kg:

• Single-leg hop LSI: 94% (passes)
• Knee extensor MVIC: 2.4 Nm/kg — 32nd percentile, RTS threshold is ≥3.0
• Force-plate impulse LSI (peak): 78%
• Drop jump RSI: 1.62 (target ≥2.0)
• Post-fatigue force drop: −18% (target