[smilebot]

Find a sport/activity that you can enjoy where fitness is a byproduct.

I get bored at the gym lifting weights/running on the treadmill etc. I've always enjoyed tennis and swimming so I forced myself to signup for lessons. I now swim and play tennis regularly. It is something that I look forward to.

Another tip that worked for me is to start identifying yourself with an activity. I guess you could call it brainwashing yourself. Like: "I'm a swimmer", or in your case, "I'm a runner".