If 4 miles is a "short run" you have no life outside of running. I'm sorry. I'm all for being healthy, but running is bad for your joints in the long term. There are other ways to work out. Why does everyone think the best workout is running?! I detest running.
I run for the challenge! I run to discover what my body and mind can endure! I run for the exhilaration. I run to be free! I run to turn my weakness into strengths because I can do all things through him (Christ) that strengthen me!