Intrarater Reliability of Assessing Strength of the Shoulder and Scapular Muscles

Abstract

Context: Handheld dynamometry (HHD) is considered an objective method of measuring strength, but the reliability of the procedure can be compromised by inadequate tester strength and insufficient stabilization of the dynamometer especially, for the scapular muscles. Objective: Primarily, to determine the intrarater reliability of HHD when testing shoulder and scapular muscle strength, and secondarily, to report reliability when corrected for body-mass index (BMI). Design: Technical report. Setting: University physiotherapy department. Participants: 57 adults (17 men, 40 women; mean age = 35.05 ± 13.5 y), both healthy individuals and patients with shoulder impingement. Intervention: HHD. Main Outcome Variables: Muscle strength of the upper, middle, and lower trapezius; anterior deltoid; serratus anterior; supraspinatus; and latissimus dorsi determined by HHD. Each muscle was assessed 3 times, and the mean value was calculated. The subjects were divided into 3 groups according to BMI. Group 1: BMI ≤ 20 kg/m2 (n = 22); Group 2: BMI ≤ 24.9 kg/m2 (n = 54); and Group 3: BMI ≤ 29.9 kg/m2 (n = 38). Results: Correlations were calculated for each pair of strength scores. Intraclass correlation coefficients (ICCs) ranged from .77 to .99 in healthy subjects and from .75 to .99 in patients, for all muscle groups except the upper trapezius (P < .05). Reliability values ranged from good to high in healthy subjects but were less consistent for the upper trapezius (ICC .45-.65). The relationship with BMI and muscle strength illustrates that as BMI increases, there is a decrease in reliability values of the lower trapezius (ICC = .35-.65). Conclusion: The study demonstrates that evaluating the strength of scapular and shoulder muscles using HHD presents reliable results for both patients with impingement syndrome and healthy subjects. Reliability values were compressed when testing the trapezius in subjects with higher BMI. This is likely a result of the examiner's difficulty in overcoming the patients with this maneuver.