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I was wondering if anyone here had done the flash workout? I am interested in trying it alongside the beginners bodyweight workout to increase cardio fitness/burn fat. http://www.nerdfitness.com/blog/2012/04/27/superhumanspeed/ My question is how do you know what percentage of effort you are putting in? In the past I have tried running longer distances, but start too fast and have to stop. I think I am worried that I will not push myself enough or push myself too much, making the workout less effective or flying off the treadmill in the gym. I know it sounds like I am over thinking things, but I have zero intuition with this and would appreciate any tips from those of you with more experience in this.