Quoting she nan igans:" Exactly. It should be exciting to see if you can run further, lift more. It should be exciting to see ... [snip!] ... changing and appreciate what it can do rather then exercising to punish it because it doesn't fit the mold you think it should."
RIGHT! If you're exercising and you don't enjoy it, find something else. There are so many ways to move your body, so many inventive things out there to test you physically. There's no reason for you to be miserable while you exercise.