Validation of force production during quadriceps set exercise using a hand-held dynamometer: A comparative study with isokinetic dynamometry in healthy individuals

The study aim was to compare lower extremity muscle strength measurements obtained during the quadriceps set exercise in healthy individuals. Twenty-four healthy individuals (23.1±2.1 years, 13 females) were recruited. Lower extremity muscle strength measurements were obtained using a hand-held dynamometer during the quadriceps set exercise and using an isokinetic dynamometer with isometric testing at 30° of knee flexion and at 60°/s concentrically. Validity was assessed using Pearson correlation and Bland and Altman analyses, while within-session reliability was assessed using the Intraclass Correlation Coefficient (ICC). Also, standard error of measurement (SEM%), minimal detectable change (MDC95) and minimal important change (MIC95) at the 95% confidence interval were assessed. Hand-held dynamometer measurements during the quadriceps set exercise were strongly correlated with isometric measurements at 30° of knee flexion (r=0.598, p=0.002) and concentric measurements at 60°/s (r=0.535, p=0.007) on the isokinetic dynamometer. The hand-held dynamometer demonstrated a good within-session reliability (ICC=0.88, 95%CI:0.80–0.94), while the isometric measurements at 30° of knee flexion (ICC=0.91, 95%CI:0.85–0.95) and the isokinetic measurements at 60°/s (ICC=0.92, 95%CI:0.86–0.96) demonstrated an excellent within-session reliability. Across all measurements, SEM% values ranged between 9–11%. The MDC95 was calculated as 5.97 (95%CI:3.5–8.5) for the hand-held dynamometer, 34.25 (95%CI:16.9–51.8) for the isometric measurements at 30° of knee flexion, and 40.0 (95%CI:20.8–59.3) for the isokinetic measurements at 60°/s. The MIC95 values corresponded to an approximate change of 14% for the hand-held dynamometer and 19% for the isokinetic dynamometer relative to the mean muscle strength values of healthy participants. These findings indicate that the use of the hand-held dynamometer as a measurement method in the quadriceps set exercise position is valid and reliable, and it may serve as a viable alternative to isokinetic testing, particularly in the early postoperative phase when isokinetic strength assessment is often considered unsafe.