<s>[INST] Hello doctor, My 12-year-old son has been complaining about pain on his front thigh (quadriceps) on both legs since he was 3 years old. It happens to him after playing and doing activities like sports and after school. It happens to him at least once a week and it lasts between 12 - 72 hours. Sometimes he feels clicking on front quadriceps and he feels relieved after clicking. Sometimes he says it is burning and stinging. Sometimes he needs rest to get rid of the pain. Sometimes he cannot walk even for a day and need pain killers. I could say it is always with him. This isssue had affected his running, sports and activities. He is always the last person in all sports activities, which means he is too slow. We visited many doctors and took different x-rays and blood tests and gave many physiotherapies. But nothing has been diagnosed. I need help to know what to do and what is his problem. His health and life has been affected because of this issue and he has lost his self-confidence as he is always a loser in all games. [/INST] Hello. The symptoms you are describing are signs of malnutrition. There is probably some deficit in protein intake for this child. I would suggest a high protein diet along with some iron supplements for this child.  Another rarest of rare possibility can be myasthenia gravis, which can be diagnosed by doing tests for nerve conduction and velocity and results on electrical stimulation of the muscle and its response to the stimulus. Please visit a pediatric neurologist for going through the above tests. First, give him a high protein diet along with iron supplements and see. If there is no relief, then approach a pediatric neurologist. </s>