Isokinetic Quadriceps and Hamstring Peak Torque in Athletes Aged 10-50+: Preoperative Uninvolved Limb Reference Values for ACL Reconstruction.

Retrospective records review at UW Health (two hospital-based sites) of athletes who had a planned ACL reconstruction and underwent pre-operative isokinetic testing between July 2021 and January 2026. Inclusion required a documented sport to return to and pre-operative testing on the uninvolved limb; exclusions were non-primary ACL injuries and any prior knee surgery. Testing consisted of five maximum-effort concentric extensions and flexions at 60°/sec on a Biodex System 4 Pro dynamometer, with the uninvolved limb tested first. Peak torque was normalised to body mass (Nm/kg) and the H:Q ratio calculated. Linear regression models examined age, sex, and their interaction as predictors of quadriceps strength, hamstring strength, and H:Q ratio. The study was IRB-exempt with a waiver of consent; testing was part of standard clinical care. No external funding was received.

Age was the only significant predictor. Quadriceps peak torque decreased by 0.016 Nm/kg per year (95% CI –0.022 to –0.009, p < 0.001) and hamstring peak torque by 0.009 Nm/kg per year (95% CI –0.013 to –0.005, p < 0.001), each with a moderate standardised effect size (–0.30 and –0.32). The models explained about 25% and 24% of the variance, respectively. Males showed numerically higher values than females, but the sex effect was not significant (quadriceps p = 0.085; hamstring p = 0.151). The H:Q ratio was not significantly associated with age, sex, or their interaction (all p > 0.30), and the model explained less than 1% of the variance. The cohort's average H:Q ratio was below the 60% benchmark commonly cited for post-ACLR rehabilitation.

This gives you age-stratified reference values for isokinetic strength at 60°/sec in a sport-rehabilitation population. A 45-year-old's 'normal' uninvolved-limb torque will be lower than a 20-year-old's, so a fixed Nm/kg target (such as the 3.0–3.1 Nm/kg figure often quoted) may set an unrealistic expectation for older or younger patients. The paper notes that target was derived from isometric testing in people in their 20s and cautions against applying it to isokinetic testing or other age groups. The H:Q ratio did not shift with age, so the 60% target does not need age adjustment — but the cohort's average was already below 60%, meaning many patients enter surgery with relatively weak hamstrings and may need targeted hamstring work early in rehab. Sex-based strength targets are not supported by this data: the difference did not reach significance.

Single institution, sport-rehabilitation–skewed cohort; findings may not generalise to non-athletic or sedentary populations. The uninvolved limb was tested after an ACL injury, so it may have been subtly affected (e.g., altered gait, compensatory loading), potentially lowering the reference values. Time from injury to testing varied across participants, and activity levels, sport positions, and training exposure were not captured or adjusted for. Fewer participants in the youngest (10–14) and oldest (50+) age bands, reducing precision of estimates in those groups. No inter-rater or inter-site reliability data were available despite testing at two locations. The 3.0–3.1 Nm/kg target the paper discusses was derived from isometric testing in 20-somethings; the current data are isokinetic at 60°/sec, so direct comparison is not valid.

No external funding. Testing was performed as part of standard clinical care at UW Health. No conflicts of interest are declared in the supplied text.

Do not apply the 3.0–3.1 Nm/kg quadriceps target to a 14-year-old or a 50-year-old, or carry it over from isometric to isokinetic testing. The paper states that target came from isometric data in 20-somethings and explicitly cautions against extrapolation. Also do not set different strength expectations for male and female patients on the basis of this study: the sex difference did not reach significance (p = 0.085 for quadriceps, p = 0.151 for hamstrings).