I did core workouts , yoga based, and it is my arms that actually hurt.

I always had strong abdominal muscles without even training them. I think it is genetic. But darn my arms are screaming. And it is hilarious considering how I use them all day at work. But also I think that's a part of it. I am not resting them enough. That's why I couldn't reach my goals when it came to farmwork. How very obvious and stupid.