Leg tension leading to relapse.

I don't actually have such a strong urge; I just open pornography on impulse. I show enough willpower to close it immediately, but even if I've only looked for a minute, it doesn't leave my mind, and I feel a tension in my legs. It's not like blue balls; my legs ache, and I inexplicably become angry. I've experienced this repeatedly, and I don't know the reason. How can I prevent this if it happens? I just do it because of pyhsical pain not for fun. I do it to walk properly. I know best thing to do is prevent to look at it. But If I do it again, what should I do not to relapse?