Ugh we hate doing up-down planks so very much, but that’s probably why they work. The good news is you can do them anywhere; the bad news is that they are really difficult. Start in plank position with your arms straight and make sure your abs are engaged. Then lower one arm down to your forearm, then the other. Then lift back up so your arms are outstretched, one arm at a time. Repeat this motion for 45 seconds, or as long as you can handle. It might seem innocent; after all, you’re on the floor. How bad could it be? We promise, you’ll work up a sweat and will love/hate the up-down plank in no time.