Test-retest reliability of hand-held dynamometry and functional tests in systemic lupus erythematosus

The aim of this study was to evaluate the test-retest reliability and determine the degree of measurement error of tests of isometric muscle strength and upper and lower limb function in women with systemic lupus erythematosus (SLE). Twelve women with SLE (age 39.8 ± 10 years) were assessed on two occasions separated by a 7-10-day interval. Strength of six muscle groups was measured using a hand-held dynamometer; function was measured by the 30-s sit to stand test and the 30-s 1 kg arm lift. Relative reliability was estimated using the intraclass correlation coefficient (ICC), model 2,1 (ICC2,1). Absolute reliability was estimated using standard error measurement and the minimal detectable difference was calculated. All ICCs were greater than 0.87. Muscle strength would need to increase by between 18% and 39% in women with SLE to be 95% confident of detecting real changes. The functional tests demonstrated a systematic bias between trials. This study demonstrates that hand-held dynamometry in SLE can be performed with excellent reliability. Further work needs to be completed to determine the number of trials necessary for both the 30-s sit to stand and 30-s 1 kg arm lift to decrease the systematic bias.