How old is your GSD? Long walks may not be good for younger dogs when they're on concrete or pavement because it is hard on their joints. But I have always taken my puppies on walks on dirt trails and grass. The issue would be if you make them go much further than they can reasonably walk. I wouldn't expect an 8 week old puppy to take a five mile hike. But age appropriate walks can be very good. It allows them to take in the world around them, get in some smells, and bond and train with you.
Circuit training could be good as long as the dog is older and has worked up to a point that she can handle the exercise without overtaxing herself.