Measurement of the CSA of the RF
A high-frequency linear US probe was placed perpendicular to the long axis of the RF muscle to achieve an optimal imaging quality. The probe was moved along the length of the muscle to identify the widest portion of the belly. Once the widest portion was identified, the boundaries of the RF muscle were manually traced using the US software. The software calculated the CSA of the RF muscle based on the traced boundaries (ICC > 80).