Feeling Like a Wimp

Today I did a pretty serious strength training session (about 45 minutes) for the first time in too long, and man, I feel like a wimp.  I hate doing core exercises because my core is weak and the exercises are hard, which is all the reason I should be doing them.  About 15 minutes after I finished, I had this weird achiness that was like a stomach ache only not; it took me a moment to realize that what I was feeling was sore abdominal muscles.  Well, I guess the upside of this is that when you start at a wimpy point, it's easy and quick to start seeing improvement.