To get the full effect from these workouts, you need to stick to the four-digit tempo code for each exercise. The first digit indicates how long in seconds you take to lower the weight, the second how long you pause at the bottom of the move, the third how long you take to lift the weight, and the final digit how long you pause at the top. X means that part of the move should be done explosively. The accumulated time under tension increases your heart rate to burn fat and break down muscle tissue so it’s rebuilt bigger and stronger. Keep each rep smooth and controlled so your muscles – not momentum – do the work.