The last workout I did was easy. This one was not. There were five 20 second intervals in the warm up, the first of which I hit hard without regard to what I should have been doing. I did 375 watts for 20 seconds. The next four were at the required effort. The main set is what nailed me. It called for five two minute intervals at or near my critical power. My heart rate climbed into the 160 beats per minute range. These worked me hard but I did them all.