Dear Doctor, I am 49, 5'6", 125 lbs and I am having muscle weakness mostly in my thighs and upper arms. I experienced this same problem 5 yrs ago. It was very pronounced for about six months (could barely go up or down a flight of stairs, or do simple chores). I had many blood tests and neurology work up with nothing found. Recently I had a physical and was vitamin D deficient so I am taking vitamin D supplements (50K units a week). Besides chronic headaches and a heart arrhythmia I have been in good health. The only other meds I take is Ibuprofen for the headaches. I really hope you have some suggestions more me. Thanks, Jane