Sia Cooper, an NASM-certified personal trainer in northern Florida, recommends warming up with two to three minutes of walking or jogging on the treadmill, with a slight incline of 0.5 to 1 percent. "I suggest a slight incline because there really is no flat surface that you would consistently run or walk on in a real world situation," she told POPSUGAR. "Walk or run for 15 minutes and then cool down."