Used for conditioning in football, wrestling, and other high-school sports. A single up-down is basically a push-up, with one main catch: One has to fall into the up-down from running in place, get up, and start running in place again. You start out "up," you go "down," and then get up again, hence: "up-down." They are usually done in sets, but the number of up-downs per set is fairly random. Mostly it depends upon the temperament of your coach.