For the past couple of days I get an extremely tight feeling in my achilles when I run. It feels like my ankles are locking up and I cannot provide any power when i run from my ankles. I don't think it is tendonities, because it doesn't hurt in the mornings or walking up or down stairs or hills. It only hurts after about 5 minutes of running. A throbbing kind of pain that feels like it completely locks up my ankle. I have new shoes, thought it is the same model I always wear (Asics 2120). Has anyone had this before? What is it? What can I do to make it stop so I can run and what can I do to prevent this from happening again?