Day 3. Triometrics. P90X3.
Mostly consists of one-legged squats while positioning the arms and other leg in different positions. Plus some two-legged squats that evolve into jumps. Very tough. My thighs were already sore. 1/2 way through, I just shook my head. Sore is good. Injured is bad. I'm gonna feel this burn tomorrow. I hope to be able to do a full workout by 30 days,... but, I'll be happy just to stick with it. It could take me 180 days to be able to do these workouts, not gonna sweat it.
Incidentally, my lower abs are sore, and we haven't even focused on abs yet. Everything engages the core.