A pregnant bitch may walk as normal in the first 3 weeks of pregnancy, but thereafter, walking should be enough, and light jogging(?). You need to keep the dam fit so that she is able to whelp the puppies. when the puppies are 4 weeks old you can take the dam for a ten minute walk daily as well as the regular bathroom breakes. When the pups are 6 weeks old you can take your dam for longer walks and at 8 weeks you should be able to walk her as normal.
It important that a dam gets regular exercise during prenancy so that she is able to whelp and care for the pups properly.