Hellfire is a fast-moving, muscle-loading workout that revolves around burpees and utilizes a host of eccentric and concentric muscle movements to make the workout more challenging in a shorter space of time. Each time you do High Knees bring your knee up to waist height so that you load three times your body weight on each step as you land and when you do burpees work your legs fast to get in as many reps as possible. Add EC and you will feel the burn in your lungs.