My dad did this. He would force us (me and my brother) to do exrise (I can't spell the word) that he knew we couldn't do. He would add time each time we dropped to the floor.
Once, he told me to plank because I wouldn't go outside to play with my brother (even tho I have for around a hour) when I couldn't do it and started crying. He grabbed his belt, and spanked me multiple times (it lasted around 5 minutes of spanking), I ended up pissing myself and trying to grab the belt, it didn't matter how much I begged him to stop. My step mom sat to the side and didn't even try to stop him.
After this, it hurt to move, to sit down. My thighs and my butt where bruised, it hurt for around a week.
I was to scared to tell my mom or anyone so I didn't.