@jfitmisc, I didn't know it too before i tried it out! If you're practicing headstand every single day, in first 2 days you will start to feel every part of your body (legs not so much, almost not at all), especially core/abs, arms (for women it's normal to feel every part of arms :D) and back, because all secret hides (till now i think so) in your core strenght, mostly.
This is about second week (this was my first/previous post about my headstand: https://steemit.com/headstand/@be-healthy/headstand-challange-accepted) i'm doing a headstand and now i feel really comfortable, i think it's because i'm practicing every day. But need to remember - patience, patience, patience - it's not easy to start something new and every new exercise requires a regular work and endurance :)