Author(s): Canon Bukhari, Luis Gonzalez
Mentor(s): Brent Feland
Institution BYU
Introduction: Shear Wave Elastography (SWE) is a non-invasive technique that measures tissue stiffness, useful for assessing muscle properties. Muscle stiffness varies with muscle length—stiffer when lengthened, more relaxed when shortened. However, how joint angles affect muscle stiffness and variation in measurement with repeated measurements over time has not been well documented. Understanding how joint positions affect stiffness (kPa) of biceps vs brachialis could improve methodology for clinical research applications. Purpose: This study aimed to examine how different joint angles influence the stiffness of the biceps and brachialis using SWE. Additionally, we sought to identify which muscle provides more stable measurements and to establish protocols for consistent SWE use in muscle assessment. Methods: Five healthy volunteers participated in the study over five days (height: 172±11.35 cm, weight: 73±15.78 kg, age: 24±2.56 years). During this period, subjects were instructed to avoid upper body exercises that could affect muscle stiffness. Measurements were taken in a seated position with the left arm resting on an adjustable arm rest. The arm was positioned at 45°, 90°, and 180° using a goniometer, and kPa values were recorded daily. Ten measurements were taken at each angle for both muscles. To ensure accuracy, a surgical skin pen was used to mark the measurement sites, allowing for consistent placement of the SWE probe at the same locations each day. Measurements were taken using a 9L US probe in a long axis view. Results: Data were analyzed using SPSS version 29 and checked for normality. Using a repeated measures ANOVA, we found a significant difference in stiffness between the biceps and brachialis (p<0.003), and angle of measurement (p<0.001). Post hoc Tukey HSD showed significance (p<0.001) for all muscle comparisons at each angle. Brachialis kPa values were greater than bicep for each angle with greater variability in kPa measurement at each angle also. Conclusion/Clinical significance: This study analyzed daily variation in kPa values across different joint angles for the bicep and brachialis to help determine the difference in expected SWE stiffness for further research utilizing damage and intervention strategies. Overall, the bicep appears to be the more stable muscle to measure with the 45-degree angle demonstrating less measurement variation for both muscles. Future studies need to determine the sensitivity to change in both muscles at this angle to determine if small amounts of eccentric damage can be adequately monitored at this angle.