Concurrent Validity of Isokinetic Hip and Knee Strength Measurements Using the UGO Exoskeleton in Healthy Young Adults: Cross-Sectional Validation Study

Background The UGO lower limb exoskeleton rehabilitation robot is designed for patients with lower limb motor dysfunction, and it can be used to assess the peak torque of hip and knee flexors and extensors. Objective The primary aim of this study was to establish the concurrent validity of peak isokinetic torque using the UGO exoskeleton and Humac Norm dynamometers in healthy young adults. Methods Twenty healthy young adults were enrolled in this study. All participants underwent isokinetic muscle strength tests using both the UGO exoskeleton and the Humac Norm dynamometers. Peak torque (Nm) of the hip and knee flexors and extensors was measured. The Pearson correlation coefficient was used to determine concurrent validity. Bland-Altman analysis was used to assess the agreement between the 2 devices. Results At the knee, peak torque of the extensors measured by the UGO exoskeleton correlated strongly with that measured by the Humac Norm dynamometer (right: r=0.662; P=.001; left: r=0.768; P<.001), with 95% limits of agreement (LoA) ranging from −22.89 to 82.21 Nm and from −24.60 to 75.65 Nm, respectively; the right knee flexors showed a moderate correlation (r=0.547; P=.01), with 95% LoA ranging from −26.27 to 36.01 Nm, whereas the left knee flexors showed no significant association (r=0.347; P=.12), with 95% LoA ranging from −2.40 to 75.02 Nm. At the hip, peak torque of the flexors correlated strongly on the right (r=0.615; P=.003) and moderately on the left (r=0.443; P=.04), with 95% LoA ranging from −15.52 to 86.57 Nm and from −12.53 to 98.50 Nm, respectively, whereas the bilateral hip extensors showed no significant association (right: r=0.337; P=.14; left: r=0.391; P=.20), with 95% LoA ranging from −51.57 to 76.80 Nm and from −28.19 to 79.59 Nm, respectively. Conclusions In healthy young adults, the UGO exoskeleton demonstrated moderate to strong concurrent validity for peak torque of the bilateral knee extensors and hip flexors, but not for the nondominant knee flexors or bilateral hip extensors. The device may serve as a convenient torque assessment tool for selected muscle actions, but systematic overestimation and posture-related differences must be considered, and validation in the intended clinical population of patients with neurological conditions is required in further studies.