Here's what happens when you move large muscles fast, time and again: The body's temperature goes up (you sweat), ATP and glycogen stores run out fast (you burn fat), your VO2 Max gets maxed out fast (you get out of breath). Trial By Fire is a workout that delivers on all of these fronts from the very first set. Pump your arms when you do High Knees and bring your knees to waist height. Remember to land on the ball of your foot each time. Add EC, we dare you!