Assignment: Compare and Contrast Exercise with Writing

I started the "I Really Mean It This Time Healthy Food and Exercise Plan" yesterday.  Again.  The good news is that I have been doing great (if you'll forgive the rest of my daughter's french fries yesterday afternoon).  I even went to the gym today. 

Here's the deal with me and exercise:  I KNOW I feel better if I exercise regularly.  But the gym is ALL THE WAY ACROSS THE STREET. I mean, it's like half a block away on the other side of the street.  So I drank enough Diet Coke to get a Nike gift card with my rewards points, and I ordered new sneakers.  Then our department business manager and I decided that we would be exercise buddies and go to Tone and Torture class on Mondays.  I have to say, I think I deserve another round of french fries today because
1) I remembered my stuff, and
2) I went, even though Teresa bailed on me. 

The class was taught by a 22 year old Exercise Physiology major.  I am used to taking classes from 30-something  yoga ladies, who appreciate that jogging in place is NOT a good idea for the majority of women over forty.  I had on a decent bra, so that wasn't an issue, but there were other things doing the wave, and it wasn't pretty.  The instructor kept looking at me.  I suspect she is suitably horrified and will now refuse to grow older or have children. 

Anyway. Afterwards, with endorphins singing through my bloodstream, I had a lovely sugar-free Muscle Milk for lunch and came back to work, refreshed and feeling pretty darn good about myself.  I thought, gee, this is kind of like writing.  I have a hard time getting started sometimes, and sometimes in the middle, I hurt and wonder what the hell I am doing, but when I am finished, I feel a sense of accomplishment. 

So.  What do you compare writing with?  Is it something like exercise, that you know is good for you, but you kind of don't want to do, or is it like a bubble bath, something that you GET to do?