if you can find a hill to walk the dog up and down it really makes a difference . a dog carries most of their weight on the front , a dog with a weak rear will walk with it's head dropped and leaned forward taking even more weight off the rear , leading to a weaker rear , a hill prevents them from doing that .......... i'd also suggest you teach your dog to gait properly when you walk him , you need to find the right speed where his trot is correct , and encourage the proper gait ....... imo , there is less impact on a dogs joints when they have a fluid correct gait ...... at 8 months a dog is carrying 60-100 lbs more weight than they were 6 months ago . if they weren't kept as strong as possible for their whole life they need to catch up , and it needs done safely ......... lots of time on their legs without excessive impact ......