I've got my treadmill workout down to a science. Hop on, warm-up, get up to speed, do a couple of hills, and....I'm done (after a cool down, of course). But falling into an exercise rut, like the one I seem to be stuck in, isn't the best way to build fitness. Your body can adapt to your regular exercise routine, causing you to plateau and make your workouts ineffective.

One way to make sure you're challenging yourself at the gym is to keep an eye on the display on your exercise machine. Whether you're on a bike, treadmill, or elliptical, you have your own little electronic personal trainer of sorts right in front of you. By making best use of the little device, you can tweak your workout to challenge you to do your best. Women's Health has broken the code of those little display boxes, and tell us here what to look for while we're working out.