My favourite body part to work is the abdominals. I work In a job the requires a lot of lifting so in order To protect my back I make sure to have a strong core In working on my abs I make sure to do a lot of excersices That force me to work on all the stabilizer muscles while Performing the exercise. I use the bosu and physio ball a lot. My favorite ab excersice is the high plank onto the Physio ball & then rolling the ball forward and trying to hold That pose as long as I can. I move the ball far ward/backward. The core Doesn't get rest. Try it out