Ouch! I just did this work out and boy can I feel it! I feel it a lot in my abs (150 crunches does that to ya!) and then also in my arms from the pushups and planks! I skipped the second bridge because I didn't find it very worthwhile (didn't really feel it, my head felt funny from being upside down) but everything else was soooo worthwhile! I'm glad I did it!