Diagnostic Accuracy of Handheld Dynamometry and 1-Repetition-Maximum Tests for Identifying Meaningful Quadriceps Strength Asymmetries

STUDY DESIGN: Clinical measurement, cross-sectional. BACKGROUND: Quadriceps deficits are common in individuals with knee joint impairments and impact functional and quality-of-life outcomes. Quadriceps strength symmetry influences clinical decisions after knee injury. Isometric electromechanical dynamometry (ISO-ED) is the gold standard for measuring symmetry, but is not available in all clinical settings. OBJECTIVES: To compare concurrent validity of handheld dynamometry and 1-repetition-maximum leg press, knee extension from 90 degrees to 0 degrees, and knee extension from 90 degrees to 45 degrees to that of ISO-ED in identifying meaningful quadriceps strength deficits. METHODS: Fifty-six participants with knee joint impairments completed ISO-ED and 4 alternative measures of quadriceps strength symmetry in a single session. Absolute agreement of alternative measures with ISO-ED was calculated with intraclass correlation coefficients (ICCs). Clinical agreement values at thresholds of 80% and 90% symmetry were compared between the alternatives and ISO-ED. RESULTS: Knee extension from 90 degrees to 45 degrees (ICC = 0.67) and handheld dynamometry (ICC = 0.70) had the greatest ICCs. Clinical agreement was also best for these measures for 80% symmetry (kappa = 0.56 and 0.55, respectively) and 90% symmetry (kappa = 0.19 and 0.33, respectively). CONCLUSION: Handheld dynamometry and 1-repetition-maximum testing of knee extension from 90 to 45 are fair alternatives, although symmetry is typically overestimated. Receiver operating characteristic analysis identified alternative measure thresholds that correlated with the 80% and 90% symmetry thresholds on the ISO-ED. Clinicians should use more stringent symmetry values for these alternative tests to increase the probability that individuals have a minimum ISO-ED symmetry of 80% or 90%.