In my younger days I waaayyyyy overexercised....
Did my 40hrs in three days, and did nothing but excercise all day into the nights for four days straight every week for nearly three years.
Various types, but the top two hardest things were the heavy bag and jump rope.
First time I heavy bagged (75lb bag) I only lasted five minutes.... And I had been exercising seriously for a long time already! It gave me a whhhooollleee new respect for boxers.
Eventually worked up to half a day split between arms and legs.
One day I took a break from it and never went back.