Lauren - I am amazed at how just five simple exercises (the PB ones) work my entire body, which means the core has tone working a lot in all of them. I have never really lifted weights or anything and sporadically did cardio. My main exercise has always been playing golf while walking and carrying my bag. For those that don't know a golf course is about a five mile walk and a golf bag weighs anywhere from 20-40 pounds. (i have done trips where I play 11 rounds of golf in 6 days.) Weather permitting I do this twice a week on a very hilly golf course. What surprised me about the PB exercises, especially the side planks is how much stronger the core muscles on my left side are. As a right handed golfer I pull through the swing with my left hip.