I started a kickboxing class 3 months ago. It's really tough. Like, really hard workouts, think you might pass out tough. I love it, I really do. It pushes me. It burns a lot of calories.
I'm happy to say that now, in my third month, I've noticed that I have a new line on my arm. My arms have never had definition, NEVER. So with this new line, I now have two: one at the base of my bicep, running from my armpit to my elbow, and this new one, running in the opposite direction between my bicep and my shoulder.