Jeff the Baptist on the importance of being able to run:
It always amazes me when self-proclaimed serious self-defense enthusiasts are fifty or more pounds overweight. Some of them smoke like chimneys. Now I'm no pro athlete, but I try to keep myself somewhat healthy. Why? Because the first skill you want to have down for self defense is running away. Hotfoot your ass out of trouble. I can do that. My knees will be sore the next day, but the alternative is even less appealing.
A couple of weeks ago, my wife burst into the apartment gym where I was running, and told me that the baby was running a 104 temperature. So I ran back to the apartment to get her ready to go to the ER. And later I thought "This is exactly why I run -- so that I can run when I absolutely have to." There's no substitute for the ability to move quickly in an emergency.
This is also why I have my rule about shoes: I only wear shoes that I can run in, hence my 'no flip-flops' moratorium. You never know when you're going to have to run, so always be ready to do so.