Pushing through the wall

I need physical excerise. When I'm not physically exerting myself for any significant period of time...as in maybe 3 days?.....I start to feel really BLAH. I don't excerise for physical appearance. I'm motivated by the challenge and the elation, albeit often accompanied by exhaustion, of conquering that goal. When pushing yourself, however, you often come across that WALL. The point where you can easily convince yourself to stop, that you've done enough, you really don't need to put yourself through this much pain. This is where the mind has to overrule the body. I'm sure everyone has a different method. When I'm rowing and there are other rowers in the boat, it doesn't matter when I reach that point. Although I may feel like dying towards the end of the race, I know that if I let up even a little, then I really could die by catching a crab, screwing up the boat, etc. The sense of responsibility to the rest of the boat far outweighs anything else. But when running I often reach that point of excuses. Yet when I feel like I can't get enough air, that my muscles ache, my tongue is dry and heavy in my mouth, that point where we would say, "I was dying!" I can push through because I know I'm not dying. In fact, I am nowhere near dying which is why I can physically do what I am doing that very moment. I have seen death. I watched my little brother battle cancer and at the lowest point, look like death. I saw him lay in a hospital bed for a month, clinging to life, on the edge, as his body strained to produce white blood cells, and in essence, life. I hated watching death hover and not being able to do anything about it. So I ran. A lot. I run when I'm angry, frustrated, depresssed, etc. It's a coping mechanism. And when I reach the physical "dying" point, I push through because I know I am not dying.