Lean Forward on the Treadmill
You already: Jog at the gym (259 calories for 6 mph, 0 percent grade, 20 minutes).
You should also: Increase the incline (351 calories for 6 mph, 1 percent grade, 25 minutes). "Never walk or run on a completely flat treadmill," says Bob, "because you need to compensate for the moving belt, which is doing some of the work for you, as well as the lack of wind resistance you'd encounter outside."
Bonus tip: Crank up the grade to be even steeper—and don't even think of using the handrails for support (365 calories for 6 mph, 5 percent grade, 20 minutes).