Michener LA; Pidcoe PE; Frith AM; Dept of Physical Therapy; Virginia Commonwealth University-Medical College of VA; Richmond, VA. lmichene@hsc.vcu.edu.

PURPOSE: Muscle strength testing is commonly used outcome measure for patients with shoulder dysfunctions. The purpose of this study was to determine the test-retest reliability and validity of measurements of isometric scapular muscle strength. SUBJECTS: Patients (n=25) with shoulder pain and functional loss. MATERIAL AND METHODS: A hand-held dynamometer (HHD) was used to measure the kilograms applied during four scapular manual muscle tests (MMT) for the lower trapezius, upper trapezius, middle trapezius, and serratus anterior. Simultaneously, surface electromyography (EMG) was collected on the same muscles. The subjects returned 24-72 hours after the initial testing, for repeat of day 1 testing procedure, performed by the same tester. Each test was completed 3 times on both occasions, and the average used for data analysis. ANALYSIS: Test-retest reliability was determined for HHD measures by calculating an ICC (two-way random)] for each muscle test. To determine error of the HHD measures, standard error of the measure was calculated for each muscle test to assess measurement error. Concurrent criterion validity was determined using the amount of EMG as the criterion measure. The amount of EMG muscle activity for each of the four muscles for during each of the four muscle tests was calculated. Validity was determined by comparing the amount of EMG muscle activity of the designated muscle of the test to the other non-designated muscles during the test. RESULTS: Test-retest reliability coefficients [ICC (two-way random)] for HHD measures were 0.91 for the lower trapezius test, 0.93 for the serratus anterior, 0.94 for the upper trapezius test, 0.94 for the middle trapezius test and; the standard error of measurement (90% CI) was 2.0 kg, 2.6 kg, 2.8 kg, and 1.3 kg, respectively. The highest muscle activity during the lower trapezius test was the lower trapezius muscle, during the middle trapezius test was the middle and lower trapezius muscles, during the serratus anterior test was the serratus anterior muscle, during the upper trapezius test was the upper trapezius and serratus muscles. CONCLUSIONS: The MMTs for scapular muscles using HHD have excellent levels of test-retest reliability and error in patients with shoulder pain and functional loss. However, criterion validity results indicate that these four muscle tests do not isolate the muscle indicated in the description of the tests. FUNDING SOURCE: Dept of Physical Therapy, VCU, Richmond, VA.

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