Isokinetic Quadriceps Strength at Slower Speeds Following ACLR More Strongly Influences Hop Test Performance in Adolescent Athletes.
Zac Blaydes, Gabrielle Griffin, Taha Saifullah and 3 others
Quadriceps strength at 60°/sec was the only isokinetic speed linked to hop test performance in adolescents about 6 months after ACL reconstruction.
But it explained only 23–57% of hop performance, so strength alone is far from the whole picture.
Key findings
1Quadriceps strength measured at 60°/sec was the only isokinetic speed significantly associated with hop test performance; 180°/sec and 300°/sec showed no significant association with any hop test.
2ISKT results explained a modest portion of hop performance: R² ranged from 23% to 33% in the LSI analysis and 49% to 57% in the normalized analysis, meaning most of the variance in hop performance came from factors other than isolated strength.
3No isokinetic speed showed a significant association with the 6-meter timed hop when calculated as LSI.
Still to come
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Single center, single surgeon, retrospective design — results may not generalize to other surgical or rehabilitation approaches. The 180°/sec normalized value was removed from the regression model because of multicollinearity, so its independent contribution could not be assessed. The timed hop could not be normalized, leaving a gap in whether 60°/sec strength relates to speed-based hop performance. All patients were assessed at roughly 6 months post-op; findings may not hold at earlier or later recovery stages. Multiple graft types (bone-patellar tendon-bone, hamstring, quadriceps tendon) and meniscal involvement were included without subgroup analysis. The study is correlational: it shows that 60°/sec strength and hop performance move together, not that improving 60°/sec strength will improve hop performance.
Declared interests
Funded by St. Louis Children's Hospital. No industry sponsor, device manufacturer, or commercial conflict of interest is declared.
The easy way to misread this
Do not read the significant 60°/sec association as proof that fixing quadriceps strength at that speed will fix a patient's hop performance. The R² values (23–33% for LSI, 49–57% for normalized) mean that most of the variance in how far or fast a patient hops comes from something other than isolated knee-extensor strength — coordination, confidence, movement strategy, or psychological readiness. A patient who passes the 60°/sec strength test but still hops poorly needs a different intervention than more quad strengthening.
Summarised by AI from the full paper, without a clinician reviewing it. Check it against the source before it changes what you do. Read it on PubMed →