When I step onto a treadmill at the gym, some days I'm just not feeling very motivated to push myself. I'm sure this happens to you too, so you should give this little game a try.
Find someone on a treadmill that looks like they're working hard and pretend you're running with them. It's great inspiration to feed off their fire, and you'll be surprised at how suddenly you have a burst of energy. I find that I can run longer or faster when I'm mock running with someone else.
This of course works for any cardio machine, so the next time you're feeling sluggish, use someone else's drive and passion to pep you up.