Spinning.

As in on  a bicycle at 5:45am.  I was there.   I went to the "training" last Saturday.  I thought I was ready.  How long could 45 minutes be?
Surprise #1
"These early morning rides are an hour."
O.k.  What's 15 more minutes right?  Right.
Surprise #2
I really, really liked most of the music.  Queen, Bryan Adams, a little metal, lots of fun.  That will probably vary by instructor though.
Surprise #3
I made it through the entire hour, not that I didn't think about quitting about 20 minutes in.  I did.  Then I remembered what I learned from yoga. Breathe.  When it's hard, just focus on your breath and be present.  That got me through the next 20 minutes.  The encouragement of the instructor, a fuzzy mind, and some adrenaline pushed me through the rest.
Right now, my first thought is ow.
My second thought is two times a week is enough for this, for now, but it's definitely time. 
I could not have made it through this class when I started about 6.5 weeks ago.  So I am moving forward.  Now the goal is to keep moving forward.