it was worded that way in the Pettit +1 workout and in a handful of other workouts that I did not write down. I decided instead of skipping the workouts because I didnt understand them that I better ask or Ill never workout! LOL
Work outs are generally consist of a warm up, a main set of intervals, then a cool down.
Looking at Pettit +1 you have
a 5 min warm up
a main set which consists of first 40mins at X-Y, then a 20sec sprint, then 5min40s at X, then 20sec sprint again, then another 5 min 40s at X (a main set of 52mins in total)