Representation of Joint Patterns in HD SEMG: A Case Study

Investigation of joint patterns is one of many ways to detect soft tissue pathology. Functional blockage of the joint is a common clinical term that expresses one of the most common functional disorders in the musculoskeletal system. In this paper, we focus on HD SEMG signal processing with artificially induced joint blockage using reflective heel pad. Four bipolar electrodes were placed on the muscle vastus medialis and six on the muscle rectus femoris. One proband (male, 46 years) sat on the chair with the knee joint fixed at 70 ∘ flexion and hip at 120 ∘ between the pelvis and the femur, which corresponds to a relaxed sitting position. HD SEMG signals were recorded during three isometric maximum voluntary contractions of the knee extensors. The first data set of three contractions was measured without heel pad and the second and third data set with using pronation and supination heel pad respectively. Results show that stabilization of the knee is eliminated by fixing the leg in the chair and the muscle vastus medialis has only extension function without using heel pad. Thus, the contraction begins with activation of the muscle rectus femoris, which only has an extension function and then the muscle vastus medialis is added to the contraction. If we use the heel pad, the muscle vastus medialis stabilizes the knee and the contraction begins simultaneously with the musle rectus femoris.