Now that I'm fully in the swing of things - going to the gym nearly every day and recommitting myself to TKD, I've found that I built new muscles. My core is much stronger than it has been in the past, so much so that I can actually do a headstand again.
Yes, you read that right - a headstand.
I hadn't been able to do one of these since I was 7. I don't know if it's because I gave up gymnastics then or if I couldn't get over the fear of trying, but I just never did them again past that age. But today, my technically oriented yoga instructor taught us how to do headstands properly and lo and behold, I did it! I enjoyed the experience so much that I did several of them and was amazed at the accomplishment.
The next challenge is keeping the practice up. I'm going to keep up my yoga practice to make sure I maintain this and other abilities.