Assessment of Isometric Knee Flexor Strength Using Hand-Held Dynamometry in High-Level Rugby Players Is Intertester Reliable

OBJECTIVE: To assess intertester reliability of isometric knee flexor strength testing in high-level rugby players with testers of different physical capacity and different methods of dynamometer fixation. DESIGN: Reliability study. PATIENTS: Thirty noninjured high-level (Tegner Activity Score ≥9) rugby players, free from hamstring injury in the previous 2 months. ASSESSMENT: Isometric knee flexor strength (in N) in prone 0/15 degrees (hip/knee flexion) and supine 90/90 degrees position. Tests were performed by 1 female and 2 male testers whose upper-body strength was measured with a 6-repetition maximum bench press test. The prone 0/15 degrees measurement was performed with manual and external belt fixation of the dynamometer. MAIN OUTCOME MEASURES: Absolute and relative intertester reliability were calculated using intraclass correlation coefficient (ICC) and minimal detectable change. Paired t-tests were used to identify systematic measurement error between testers and to test for a difference in recorded knee flexor strength between methods of dynamometer fixation. METHODS: Isometric knee flexor strength was measured in prone 0/15 degrees (hip/knee flexion) and supine 90/90 degrees position. RESULTS: Good intertester reliability was found for all pairwise comparisons (ICC 0.80-0.87). MDCs (as percentage of mean strength) ranged from 15.2% to 25.4%. For tester couples where systematic error was identified, Bland-Altman plots and Pearson correlation coefficients demonstrated no statistically significant correlation between mean knee flexor strength and between-tester difference. There was no significant difference in isometric knee flexor strength between manual and belt fixation of the dynamometer. CONCLUSIONS: In strong high-level rugby players, hand-held dynamometry for isometric knee flexor strength assessment in prone 0/15 degrees and supine 90/90 degrees position is intertester reliable.