[wisty]

Not many people's spouses are in medical residency, and have children who are too young to be left unsupervised for 20 minutes.

Even if you broaden it a bit (single parents, spouse in the military on deployment, etc) you are not looking at 90+% of the population. And most people looking after small children are pretty active anyway (due to all the lifting, running around, and so on).

[btilly]

http://singleparents.about.com/od/legalissues/p/portrait.htm estimates over 13 million single parents in the USA. Granted, not all of their children are small, but a lot are.

Also in every family with small kids, if one parent wants a piece of freedom, it puts pressure on the other parent. So even if it is theoretically possible, if half of those parents get the freedom to exercise in the morning, the other half do not.

Does it amount to 10% with a legitimate difficulty in scheduling exercise? I'm not sure. But it is more than I would have guessed before I had kids.

[dennisgorelik]

Staying as a single adult in the house is a long-term choice. You can: marry, invite your friend to live together, invite your parents, rent our a room or two in your house and ask for occasional babysitting help from them.

You can move into somebody else's house too.