Using the tabata interval (20 sec on, 10 sec. rest X8), push either a prowler sled or your car (in a parking lot, put it in neutral). Repeat 3 times, resting 4 minutes between each set of tabata intervals. If pushing a car, feel free to do this in teams of two. I also recommend having someone in the driver's seat to stop the car during rest/avoid running into things.