Hi Graf,
I am not sure I understand what you are asking regarding exercise. It does sound as if he is getting a good amount of it. You should be able to feel the ribs when you press on them, if you don't feel them then the dog is overweight. Also pups go through a gawky stage where they may look thinner for a time but then catch up at around a year old.
dog training consultant
24 years training & behavior,pet first aide, Therapy dog eval., PA Animal Response Team
Thank you Graf for that information. German Shepherds are prone to panosteitis which is inflammation of the layers of bones as the dog grows. There is no way to prevent this but if you should notice lameness, fever or loss of appetite then the dog should be checked as an anti inflammatory drug may be needed along with rest. Here is more on this. http://www.petplace.com/dogs/panosteitis/page1.aspx
Elbow dysplasia is another problem with this breed so again if you notice lameness coming on or stiffness after resting then the dog should be seen.
http://www.petplace.com/dogs/elbow-dysplasia-in-dogs/page1.aspx
Degenerative myelopathy will be something to watch for as the dog enters senior years. This unfortunately does not have a great prognosis at this time.
http://www.petplace.com/dogs/degenerative-myelopathy/page1.aspx
You may want to think about adding cosequin to the daily diet to further help the joints. This can be purchased on line or from your vet. Be sure to talk to your vet about this.
http://www.petplace.com/drug-library/glucosamine-and-chondroitin-cosequin/page1.aspx
Also large breed dogs should be fed a dog for made specifically for large breeds to slow bone growth and help prevent bone problems in the future.
When a pup tires then rest should be given as most young pups can sleep 12 to 18 hours during a 24 hour period. Leash walking and listening to commands would not be the same as a free romp as leash walking is controlled and the pup is less likey to hurt himself.