If it weren't for rowing and hiking, and dogs onboard(which make it mandatory), the type of coastal sailing we do would be quite sedentary.
Rowing for exercise can be a fun easy workout, especially good for keeping your back in shape. Rowing dinghys are popular in our area.
If you're cruising, you can get a lot of exercise just taking care of daily needs, with no car. Sailors as a group up and down the east coast look pretty fit to me.