A Study on the Nonlinearity Relationship between Quadriceps Thickness and Torque Output during Isometric Knee Extension

The quadriceps femoris is a large muscle group which is crucial in walking, running, jumping and squatting. Therefore, study on quadriceps muscle activity is of realistic significance. As one of architectural parameters, muscle thickness has been investigated in many aspects for various purposes. However, there are few studies on quantitating the relationship between quadriceps muscle thickness and torque output. In this study a coarse-to-fine method based on a compressive tracking algorithm is used for real-time estimation of muscle thickness during isometric contraction on ultrasound images. Ultrasonography is a convenient and widely-used technique to look into the muscle contraction as it is non-invasive and real-time. The relationship between quadriceps muscle thickness and torque output are investigated with data from 13 subjects. The experimental result showed that the change of muscle thickness in cross-sectional plane is similar to its torque during muscle contraction, but the relationship between them is nonlinear.