Hello. Thank you for contacting HCM. Fatty tumors or Lipomas usually are benign growths and do not require any treatment usually....but if they start to grow in size, causes pressure effects or causes pain it may need to be removed. They may cause pain if they are near a passing nerve or have many supplying blood vessels in them. Your muscular stiffness and pain after exercising appears to be due to the fatty tumor. I would recommend you consult your local physician to get that fatty tumor clinically evaluated. In the meantime you can apply local Diclofenac Sodium Gel locally thrice a day to the affected area. I hope this answers your question. Please feel free to contact HCM again if you have any concerns. Wishing you good health.