Intra-tester and inter-tester reliability of maximum isokinetic hip and knee strength measurements with the exoskeleton in healthy young adults

TL;DR

This study shows that the UGO exoskeleton can reliably measure hip and knee strength in healthy young adults during walking-like movements.

Contribution

The study establishes the intra- and inter-tester reliability of the UGO exoskeleton for measuring isokinetic hip and knee torque in a near-natural posture.

Findings

Inter-tester reliability for hip and knee torque was good to excellent (ICC 0.791–0.975).

Intra-tester reliability was excellent (ICC 0.834–0.955) with low measurement variability.

Bland–Altman plots confirmed reliability with minimal mean differences and acceptable agreement limits.

Abstract

The UGO exoskeleton enables gait training and simultaneous, in-situ assessment of peak isokinetic torque at the hip and knee joints while participants maintain an upright, near-natural walking posture. The primary aim of this study was to establish the inter- and intra-tester reliability of peak isokinetic torque using the UGO exoskeleton in healthy young adults.

Two independent cohorts were enrolled to determine the inter- and intra-tester reliability of the UGO exoskeleton. Each cohort consisted of 20 fourth-year undergraduate students (10 male, 10 female), with mean ages of 22.55 ± 1.05 and 21.40 ± 1.00 years, respectively. Testing was conducted by two experienced therapists. Peak isokinetic torque (Nm) in hip and knee flexors and extensors was collected. Relative and absolute reliability of peak torques were estimated using the intra-class correlation coefficient (ICC) and standard error of measurement (SEM), respectively. Bland–Altman plot was utilized to further elucidate the differences between tests obtained by different testers or by the same tester at different times.

Inter-tester reliability was good-to-excellent, as evidenced by ICCs of 0.791–0.906 for the hip and 0.859–0.975 for the knee (all P ≤ 0.001). Intra-tester reliability was excellent, with ICCs of 0.834–0.905 for the hip and 0.917–0.955 for the knee (all P < 0.001). The SEM values further indicated moderate to high reliability, spanning 13.1–16.1 Nm (11.9–15.6%) at the hip and 8.5–10.2 Nm (8.8–16.0%) at the knee for inter-tester assessment, and 11.5–13.1 Nm (10.2–13.1%) at the hip and 6.4–8.0 Nm (8.2%–9.2%) at the knee for intra-tester assessment. Bland-Altman plots confirmed this, showing mean differences from −3.3 to −26.5 Nm (inter-tester) and −1.4 to −15.7 Nm (intra-tester), and 95% limits of agreement ranging from −71.2 to 31.2 Nm and from −51.8 to 26.2 Nm, respectively.

The UGO exoskeleton provides a reliable, time-efficient, and functionally relevant means of quantifying hip- and knee-flexor and -extensor torque in healthy young adults while maintaining a posture that closely replicates natural gait.

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