STANDARDIZATION OF MUSCLE ARCHITECTURE MEASUREMENTS OF THE VASTUS LATERALIS AND RECTUS FEMORIS FROM IN VIVO ULTRASOUND IMAGES IN HEALTHY ADULTS

Abstract

Background: Muscle thickness, pennation angle, and fascicle length describe the architecture of a muscle. These properties can be observed alongside subcutaneous fat thickness using ultrasonography; however, measurement is sensitive to the angle of the transducer against the skin. Typically, the transducer is held perpendicular to skin for imaging. Nonetheless, a convenient, reliable method to ensure transducer angle consistency has not been reported. Objectives: The purpose of this study was to determine the influence of transducer angle on muscle architecture and subcutaneous fat measurements of quadriceps muscles (vastus lateralis and rectus femoris) in healthy young adults. A secondary objective was to determine intra- and inter-rater reliability. Methods: Thirty men and women were recruited (25±2.5 years; BMI: 22.6±3.0 kg/m2). Ultrasound images were acquired from two muscles. An image was taken at an estimated perpendicular angle to the skin. Then, using a 3D-printed device with a protractor that attached to the ultrasound transducer, images were taken at measured angles 5-10˚ medial and lateral to perpendicular. Agreement and error were determined using intraclass correlation coefficients (ICCs) and standard error measurements (SEMs). Results: Good to excellent agreement was demonstrated for muscle and fat thicknesses regardless of transducer angle (ICC >0.66). Intra-rater reliability was excellent for all outcomes within both muscles (ICC >0.89). Inter-rater reliability for the rectus femoris was good to excellent for all transducer angles except for measurements of fascicle lengths at 85° (ICC: 0.33–0.99). Inter-rater reliability improved >20% for the vastus lateralis with the device. Conclusion: Measurements of muscle pennation angle and fascicle lengths, but not muscle or subcutaneous fat thicknesses, were sensitive to transducer angle. Reliability of pennation angle and fascicle lengths improved with the use of our device. Using our device, reliable muscle architecture measures can be made for the rectus femoris and the vastus lateralis in healthy young adults.