We all know sitting at a desk all day doesn't burn up the calories. There are simple ways to exercise at work, like disappearing into a restroom stall to do some squats, but what about getting some cardio? To work out while on the job, you might have contemplated a treadmill desk, but the size of both the price tag and the desk itself prevents you from asking your boss to spring for one. Here's another, much cheaper option — an under your desk, wheel-less, mini exercise bike. You can stow this model, made by Stamina ($49), under your desk and pedal with your feet without your co-workers knowing. Or you can place it on top of your desk to conspicuously work your upper body. You can adjust the tension to make it easier or more difficult, and it also comes with an electronic monitor to time your workouts. There are even protectors on the legs to prevent it from slipping on the floor. What a great way to burn some calories while working or watching TV. To see some more photos, click the images below.