I am a runner and occassionally when I move my leg at rest a cettain way or when walking down stairs I get a twing that causes a sharp pian below the knee cap. IT can last for a few minutes to a few hours and only happens when I move my leg a certain way after being at rest. It may be sitting at a desk and when I stand uop the discomfort starts or walking down a staircase and one step triggers the pain. I am very active and jog four or five days a week and that does not cause any problem.