Knee isokinetic test-retest: a multicentre knee isokinetic test-retest study of a fatigue protocol

The aim of this study was to establish the test-retest reliability of a knee extensor and flexor muscle fatigue protocol using a biodex system 3 isokinetic dynamometer.

Three-outpatient Rehabilitation Departments undertook the study. Fatigue was evaluated in the dominant knee of 90 healthy female volunteers, non-sportswomen, aged between 20 and 40. They performed 40 consecutive concentric knee flexions and extensions, at 120 degrees /s, on a Biodex 3 isokinetic dynamometer. Two evaluations were done over a period of seven days. Analysed variables were: maximal repetition of total work, maximal work repetition number, work to body weight ratio, total work, work during first and last third of the protocol, fatigue ratio, work fatigue. Statistical analysis determined mean values, medians and box-plots. Intraclass Correlation Coefficients (ICC) (confidence interval 95 %), t-test and one-way analysis of variance (ANOVA) evaluated reliability. Difference of means (di), standard error of measurement (SEM) and 95% of interval confidence (IC di) were also calculated (P<0.05).

All participants completed the study. Reliability data were excellent (ICC>0.75) for total work (0.85), work during first third (0.80) and last third (0.80) in extension, and for total work in flexion. Reliability data were fair to good (ICC 0.4-0.75) for the rest of the variables. Median varied less than 20% in all cases during test-retest.

This knee fatigue protocol is reliable for flexion and extension, above all when using the total work as a variable. The desirability of multicentre studies in rehabilitation and standardisation of protocols is emphasised.