So in every workout you are supposed to warm up with (fill in the blank cardio). Cardio, CaRdIo, CARDIO! Thats all you hear when it comes to workouts, and to be blunt cardio sucks. I found this cute little workout that you could do on the days that you just don't feel like going out and running.
Now remember I'm not saying this works as well as good mile or so run, but do this a few time through and you will feel as tired as if you did!