The Gym Styles used to be the backbone of my strength training, back in the day! They are amazing. I'm not surprised your chest & triceps were trembling! Mine used to tremble just thinking about that workout LOL! The Shock Cardio series with the MMAs and the Circuits are hidden gems in Cathe's collection, IMO. Those roll-around cores are not the nicest of things, are they?? I like the idea of substituting stand core!