Losing Endurance

You know what endurance is; that thing that keeps you going, even though you are ready to quit. The technical definition is the ability for a human or animal to exert itself and remain active for long periods of time. Such things as running, biking, swimming, volleyball, I'd even say homework takes endurance.

Of course, the endurance that I'm talking about right now has to do with running. I am officially seven weeks into my half-marathon training program, and it gets harder every day. I feel like I'm taking one step forward, two steps back. For example, I ran four miles today and I felt like I wasn't going to be able to make it. Last weekend, I ran eight pretty-easy miles. Maybe it's just the heat?

There's nothing I hate worse than feeling like I can't do something. It's just so depressing to realize that you're not strong enough. My "running verse," Isaiah 40:31, says this: "But those who hope in the Lord will renew their strength. They will soar on wings like eagles; they will run and not grow weary, they will walk and not be faint."

If I follow God and trust Him with all my heart, I can do anything, as long as it's His Will. That's supposed to make me feel better, and it does, but I'm not sure how much I can keep up my "endurance." Help me out here? Any cross-country, track, marathon runners know what I'm doing wrong?