I met with a new client the other night and we were discussing motivation and inspiration. She was relieved to hear that even for me, a personal trainer, 90% of my workouts are relatively uninspired "just get it done" workouts. Occasionally I am really inspired and jacked up for my workout, but it is not the norm.
Considering this, remember CONSISTENCY is key, and the cumulative effects of the "just get 'er done" workouts are just as tangible as if every workout were mentally inspired! So today, JUST GET 'ER DONE, and tomorrow, and the workout after that. Cherish the truly inspired workouts and the rest of the time just do it. Results are results and they will come regardless of the enthusiasm for the work :)
Remember it is the results we are after, and workout after cumulative workout, they will come.