A diagnostic surgical procedure in which a small sample of skeletal muscle tissue (usually from the thigh or arm) is removed under local anesthesia. The sample is prepared and analyzed using immunohistochemical, enzyme-linked histochemical, and sometimes electron microscopy and molecular analyses. The aim is to assess the muscle's histological structure, detect cellular abnormalities, abnormal protein deposits, and enzyme activity, thus contributing to the diagnosis of a wide range of primary and secondary muscle disorders.