I love that feeling!
When you work to the point of becoming acutely aware of every major muscle you have, you know you have made yourself better for it.
I can't really work out because I get migraines if I expend too much energy or overheat. But just recently I went on a trip up near a ski resort (no snow, so no skiing) and had to do a lot of uphill walking, and the tops of my thighs are KILLING me. Plus, I pulled one a little bit, so it hurts a bit more. School is going to be murder on me tomorrow.
When you work to the point of becoming acutely aware of every major muscle you have, you know you have made yourself better for it.