Intra-rater and Inter-rater Reliability of the KangaTech (KT360) Fixed Frame Dynamometry System During Maximal Isometric Strength Measurements of the Knee Flexors.

Background: Fixed-frame dynamometry systems are used worldwide to assess isometric strength in both general and athletic populations. There is currently a paucity of published work where reliability estimates for fixed-frame dynamometry systems have been estimated. The aim of this study was to determine the inter-and intra-rater reliability of the KangaTech (KT360) fixed frame dynamometry system when measuring maximal isometric strength of the knee flexor muscles.

Study design: Inter and intra-rater reliability single cohort study.

Methods: Twenty healthy university-level athletes (age= 21.65 ± 3 years, weight= 74.465 ± 30kg, height= 170.1 ± 7.0cm) took part in two testing sessions where two raters collected data during a 90° hip and knee flexion protocol. Participants performed each test twice, building to a maximal isometric contraction holding over a 5 second period with 30 second rest between sets. Data were checked for normality using a Shapiro-Wilk test. Intraclass correlation coefficient (ICC), standard error of measurement (SEM) and minimal detectable change (MDC) were calculated. Finally, a Bland-Altman analysis was used to determine the levels of agreement for intra-and inter-rater measurements.

Results: High levels of agreement were demonstrated between left and right knee flexion as 95% of the differences were less than two standard deviations away from the mean. 'Almost perfect' intraclass correlation coefficient (ICC) values were demonstrated (Knee flexion: Inter-rater: Left, 0.99; Right, 0.99; Intra-rater: Left, 0.99; Right:0.99). Standard error of measurement (SEM) for inter-and intra-rater strength ranged from 0.26-0.69 kg, SEM% ranged from 1.34-2.71% and minimal detectable change (MDC) ranged from 1.14-2.31kg.

Conclusion: Overall, high level of inter-and intra-rater reliability were demonstrated when testing maximal isometric knee flexion. Therefore, the KT360 fixed frame dynamometry system may be considered a viable tool for measuring maximal isometric contraction of the knee flexors when repeat measures are required in clinical settings.

Level of evidence: 3b.