Rectus Femoris Shear Elasticity Varies with Flexio-Extension of Hip and Knee During Gait

Elastography is an acoustic technique that allows measuring the tissue elasticity by assessing its shear modulus in vivo, in real-time, and non-invasively. Particularly, surface wave elastography is a new elastographic method that offers relevant advantages for biomechanical research. Unlike classic shear wave elastography (sampling rate ~ 1–2 Hz), it can be used in dynamic conditions as its sampling rate is ~15 Hz. Thus, this work shows preliminary results of applying this method to measure the shear modulus of the Rectus Femoris (RF) muscle during gait. We measured a single volunteer during three independent gait cycles and measured the hip and knee flexion-extension angles with a 3D motion capture system. The results showed that the muscle shear modulus increases during the first half of the gait cycle (first right heel contact - left heel contact), from typical resting values at the beginning of the cycle to its maximal value reached at the middle of it. On the other hand, during the second half of the cycle (left heel contact - second right heel contact), the muscle shear modulus decreases from maximal to resting values. Thus, these results show the tendency of the RF shear modulus to increase during the support phase, and conversely to decrease during the swing phase, according to the muscular force needed to vary the knee and hip angles during gait. This study shows the first attempt to characterize the muscle shear modulus during walking, whose connotations could be important for both basic and clinical research.