I am a 49 yr old male, in good shape and used to physical activities. Last four weeks I’ve had a soreness in both my thighs and knees, but only when I flex the muscles. Standing or sitting I feel nothing, but sitting down is very painful, from the knees and halfway up the front of the thighs. It is very similar to the soreness you get the day after a hard workout in the gym. No swelling, no fever, no rash, no hot areas. No medication and no activities for weeks, but the pain still remains.