Thank you for contacting HCM, Brief ans - It calls muscle fatigue. Explained answer - It is much different than the feeling you get from a workout where muscles are tired. it feels like there is no energy or ability to will the muscles to react. That s just my description. But it is very frustrating and disheartening. I get confused on whether it s the RA or medication. The main thing is chin up and keep moving forward while taking care of yourself and concern to your nearest doctor once. Take care of your mother. Hope you will fond this tips useful for your mother. Wishing u good luck.