Being outdoors for prolonged periods is very beneficial to the brain and body. Maybe that idea (link below) is sufficient motivation. But I would also compare your enthusiasm issue to what I used to feel when I ran every day. There were often days when I didn't look forward to the run. The deal I made with myself was to get dressed for the run every day and go out allowing myself to plan on a very short run --like a half mile or maybe just around the block. Every single time I started out with the intention of a shortie --I always ended up doing the whole route --and loving it. I may not have looked forward to it, but I ended up loving doing it --and loving having done it.

http://www.outsideonline.com/fitness...e-Morning.html