Don't do bicep-curls if your quads or calves are sore. If you have sore stomachs after a ride, work on the abs. If you've got sore lower-back, do back-exercises. You want them to be equally sore after a ride.

You also need to have the back in roughly the position you'd be in on the bike when doing exercises. So you need to be bent over; go from about 90-degrees bent over up to a straight back. Roman chair back-extensionss are great. Work up to holding 30-50lb weight and your lower-back should be able to deal with any loads imposed by biking.


Also squats and dead-lifts are good for lower back as well: http://www.bodybuilding.com/fun/catback.htm