Intra-Rater Reliability and Concurrent Validity of Quantified Muscle Testing for Maximal Knee Extensors Strength in Men with Myotonic Dystrophy Type 1.

Abstract

Myotonic dystrophy type 1 (DM1) is the most prevalent degenerative neuromuscular disease in adults. Knee extensor (KE) maximal strength loss is a strong indicator of physical limitations in DM1. A reliable, precise and accessible maximal strength evaluation method needs to be validated for this slowly progressive disease. This paper aims to assess the intra-rater reliability, the standard error of measurement (SEM), the minimal detectable change (MDC), and the concurrent validity of quantified muscle testing (QMT) using a handheld dynamometer with a gold standard: the Biodex isokinetic device. Nineteen men with the adult form of DM1 participated in this study by attending 2 visits spaced by one week. The evaluation of KE muscle strength with QMT was completed on the first visit and the same QMT evaluation in addition to the maximal muscle strength evaluation using an isokinetic device were performed on the second visit. The intra-rater reliability was excellent with an intraclass correlation coefficient (ICC) of 0.98 (0.96-0.99 : 95% confidence interval). SEM and MDC values were 1.05 Nm and 2.92 Nm, respectively. Concurrent validity of QMT of KE muscle group with the Biodex was also excellent with a Spearman's correlation of ρ= 0.98. The excellent concurrent validity and intra-rater reliability, and the small SEM and MDC of the QMT make this test a method of choice, in either a clinical or research setting, to precisely evaluate muscle strength impairments of the KE in men with DM1.