Abstract

Manual muscle testing (MMT) and hand-held dynamometry (HHD) are commonly used in people with inflammatory myopathy (IM), but their clinimetric properties have not yet been sufficiently studied. To evaluate the reliability and validity of MMT and HHD, maximum isometric strength was measured in eight muscle groups across three measurement events.

To evaluate reliability of HHD, intra-class correlation coefficients (ICC), the standard error of measurements (SEM) and smallest detectable changes (SDC) were calculated. To measure reliability of MMT linear Cohen‘s Kappa was computed for single muscle groups and ICC for total score.

Introduction

Inflammatory myopathies (IMs), including dermatomyositis (DM), polymyositis (PM) and associated myopathies, are systemic rheumatic muscle diseases characterized by chronic muscle inflammation . With a worldwide average annual incidence rate ranging from 0.2 to 8 in 100‘0000, IMs are relatively rare.

However, the burden of the disease for affected patients is considerable. The most prominent clinical features in IM are muscle weakness and low muscle endurance, which progresses over a period of weeks or months . Most commonly, the weakness is symmetrical, proximal extremity muscles appear to be more affected, and neck flexors are weaker than extensors .

As a consequence of muscle weakness, people with myositis often report difficulties with activities of daily living, e.g., getting up from a chair, going up- or down the stairs, getting into a car, stepping onto a curb, lifting objects, washing hair, brushing teeth, and gripping objects

Manual muscle testing (MMT)

Manual muscle testing (MMT), which is scored using a 0–5 point Medical Research Council muscle strength scale or a 0–10 point Kendall grading scale and hand-held dynamometry (HHD)

which measures the peak isometric force generated from a muscle group, are two common methods to assess muscle strength in therapeutic IM trials .( MMT is less time consuming and, therefore, less stressful for people with myositis but has decreased sensitivity and specificity in detecting mild weakness and exhibits ceiling effects ).

Furthermore, the grading system of MMT is subjective and varies with the strength of the examiner . Despite this deficiency, the MMT, a myositis specific subset of MMT, is the most frequently used assessment in myositis trials . HHD is used less commonly than MMT, but being an objective measure of muscle strength, it has the potential to overcome some of the limitations of the latter. HHD may detect mild deteriorations or improvements during the course of IM or after a resistive strength training program

The first aim of the present study was, therefore, to evaluate intra– and interrater reliability of the MMT8 and HHD in adults with myositis. Secondly, this study aimed to determine concordance between MMT8 and HHD.

It was hypothesised that HHD would demonstrate excellent reliability (ICC>0.75), that MMT8 would demonstrate substantial reliability (Kappa values between 0.61 and 0.8) and that the concordance between HHD and MMT8 would be good (Spearman correlation between 0.7 and 0.9) for all tested muscle groups.

Manual muscle testing (MMT

Manual muscle testing (MMT). The dominant side of the following eight muscle groups was tested in a standardised order: shoulder abduction, elbow flexion, ankle extension, hip abduction, hip extension, knee extension, wrist extension and neck flexion. The dominant side was based on the self-declared hand preference. Detailed description of the therapist‘s position and the precise test instructions for each muscle group is described in the“manual muscle testing procedure for MMT8 Testing”. Each muscle group was scored according the Kendall 10-point Scale. Scores between 0–3, 4–6, and 7–9 indicate severe, moderate and mild weakness, respectively and a score of 10 means that there is no detectable
weakness . The single scores were added to receive a total score varying from 0 to 80 (0 = no muscle contraction, 80 = normal strength).

Hand-held dynamometry. Muscle strength of the same muscle groups that were included in the MMT8 was assessed using the MicroFET2 hand-held dynamometer. The MicroFET2 is a battery operated hand-held device which measures peak force in Newtons (N), up to a value of 890N (Force Evaluating and Testing, Hoggan Health Industries Inc. West Draper, UT,
USA). Each muscle action was measured in a gravity-neutralized position. Testing procedure and test position were performed according to standardised protocols . After at least one familiarization trial, each muscle group was assessed twice. Isometric “make” tests were used . Peak force values were recorded for each trial. Participant position, placement of the dynamometer, verbal instruction and location of stabilisation provided for each tested muscle group are described in the “Manual Quantitative Muscle Testing”. The individual in this manuscript demonstrating a measurement set-up has given written informed consent (as outlined in PLOS consent form) to publish these case details.participants’ and