So I went to my Gym today planing on doing the thruster challenge, but my free-weight area was backed up like a truck stop shitter. So I decided to try this out on an eliptical (seeing as this is my cardio day anyway). After a 5 minute warm up, I cranked up the resistance and went for it. I have to say I was a bit skeptical at first, but by the 5th "set" of 20 seconds on I was wondering how I was going to finish. I ended up repeating the whole 4 minute drill 4 times with 1 minute in between. Of course I had to lower the resistance each time in order to keep going, and by the last set I could barely get off the machine, but it took me 20 minutes to fully catch my breath and 45 minutes later I can still feel my lungs burning. I feel like I got a better "burn" than my regular 45 minute interval session. I am officially hooked.....