I finally made it to fifteen minutes on the exercise bike!!
I'm pleased about this because in the past it seemed like once I got to a point where my heart was pumping at a good rate and I had been going for several minutes, the time passed much quicker.
Although it took some effort and persistence to get to this point, I have a feeling that I'll be able to maintain and increase the amount of vigorous exercise I get. That's really my goal - the get a good aerobic exercise so that I can exercise my heart and lungs.
UPDATE: Today (two days after I originally wrote this post) I spent another fifteen minutes on the bike. This bodes well for a habit!
