Reliability of Ultrasound Measures for Skeletal Muscle Thickness

Abstract

PURPOSE: Ultrasound imaging (US) is an affordable and practical alternative to the current gold-standard measures (MRI, CT) of assessing skeletal muscle architecture in-vivo. The current literature indicates that two predominant US-based strategies are employed to measure skeletal muscle thickness; US captured while the subject stands (STAND) and US captured while the subject is supine (SUP). The purpose of this study was to assess test-retest reliability of these US strategies for measuring muscle thickness and determine the influence of posture and anatomical location. METHODS: B-mode ultrasound was used to attain muscle thickness measurements of the quadriceps in a within subject, repeated measures design. These data were obtained from four recreationally active individuals (2 female, 2 male; age: 39.7±21.8yr; BMI: 23.5±4.3kg/m2) over two visits. During each visit, repeated measures were made by one examiner, during two subject positions (STAND, SUP), from five anatomical sites along the anterior (A) and lateral (L) plane of each leg corresponding to 59% leg length (A1, L1), 39% leg length (A2, L2), and 22% leg length (L3). Data are from 480 independent muscle thickness measures of the rectus femoris (RF), anterior portion of vastus intermedius (AVI), lateral portion of vastus intermedius (LVI), vastus lateralis (VL), and total muscle thickness (TOTAL). RESULTS: SUP and STAND resulted in subtle differences in the measurement of RF (mean diff= 0.877cm, 95% CI: 0.547 to 1.206, p<0.05), AVI (0.9606cm, 0.6756 to 1.246, p<0.05), and VL (-0.2486cm, -0.4205 to -0.0767, p<0.05). Compared to STAND, SUP appeared to demonstrate the highest test-retest reliability [intra-class coefficient (ICC): 0.852 to 0.973] for all muscles, except LVI (ICC: 0.897, 0.714; STAND vs SUP). Posture affected the test-retest reliability in a site-specific capacity. During SUP, test-retest reliability was greatest for RF at A1 (ICC: 0.873), AVI at A2 (ICC: 0.973), and LVI, VL, and TOTAL at L1 (ICC: 0.714, 0.852, 0.907, respectively). CONCLUSIONS: Posture and anatomical site may independently induce subtle differences in the reliability of US measured muscle thickness of the quadriceps. These preliminary data provide highly reliable posture- and site-specific parameters for muscle-specific measures of skeletal muscle thickness.