How much do you know about the disease called, 'Myopathies'?
Myopathies are diseases that affect muscles connected to bones (called skeletal muscles), such as the biceps in the upper arm and the quadriceps in the thigh. Myopathies can be caused by inherited genetic defects (e.g., muscular dystrophies), and endocrine, inflammatory (e.g., polymyositis), and metabolic disorders.
Nearly all of the myopathies produce weakening and atrophy of skeletal muscles, especially those closest to the center of the body (called the proximal muscles), such as the thigh and shoulder muscles. Muscles furthest from the center of the body (called the distal muscles), such as those in the hands and feet, are generally less affected.
Ref. https://www.neurologychannel.com/myopathies/
All of the myopathies definitions do nothing to describe the actual diseases. I encourage you to look up the different myopathies listed on the web page and see what each does. Almost all myopathies are extremely painful and take many years to work a person down. People with myopathies often live many years after diagnosis, though usually there last years are very painful. There are no cures for most myopathies.