They mix up the movements and there is a rest day every fourth day. If I do deadlifts one day, box jumps and pullups the next, and running/situps/back extension

They mix up the movements and there is a rest day every fourth day. If I do deadlifts one day, box jumps and pullups the next, and running/situps/back extensions on day 3, my body can handle it just fine. It beats running or biking every day, and I know plenty of people who do that, putting the same stresses on the same muscles day in and day out. You have to listen to your body of course. When I first started, sometimes I would take extra days off when I knew I needed recovery time. As with any activity, you have to be smart about what you're doing.