What Causes Weakness In The Legs When Diagnosed With Idiopathic Myopathy?

i have been diagnosed with idiopathic myopathy i have a history of lupus which is well controlled with palquenal . my symptoms include difficulty standing from a sitting position, inability to run or jump, difficulty climbing stairs, and occasional numbness ,tingling in feet, difficulty gettng up from a crouching position. i am awaiting further testing from a neuologist. my concern is my legs seem to be gettng weaker but i am very active walking and working out at gym 4 times a week. what can i expect as time progresses nd numbness in my feet and lightheadednessto jump or run,