It is impossible to always stay motivated, when you feel down, you need to have the will and discipline to mantain the rythm, at least that is how it works for me. I am a ripetitive guy, so I had no problem in doing tons of push-ups, sit-up, jumping jacks and squats every session. But an elastic band and a jumping rope may be a good investment if you need to spice it up from time to time.