This weekend I went bicycling and skateboarding, and worked in the garden. Yesterday I carpooled part of the way to work and skateboarded the rest of the way. Today I took the bus to work, carpooled home, then mowed the lawn with a manual push mower, worked in the garden some more, and turned the compost pile. There's plenty of exercise to be had in a world without oil.
I forget where I heard this, but someone said that Americans are people who pay others to do their yard work so they have free time to drive to the gym and work out. It's kind of true, but maybe not for much longer.