Just like in ourselves, we have to build stamina and muscle slowly in our dogs. We need to
increase the amount of weight the dog will carry slowly over time as muscle
develops. Think of it this way….you wouldn’t go to the gym and lift 50 pounds
would you? You’d start out a three or five pounds. The stronger your muscles
became the more you’d be able to lift.
I usually start out with an empty back pack simply because most dogs are
unfamiliar with wearing them. Then I add one magazine to each side of the pack.
They’re lightweight and can roll up. As the dog is building up his
muscles/stamina etc you’d increase the weight by adding a small amount (another
magazine maybe) to each side of the pack.
Now it doesn’t have to be magazines you can use an “empty” water bottle. As you’re
building the dogs muscles add a water. A quarter to each side. Increase as you go
along. Half a bottle, three quarters bottle, full bottle. Once you reach one
bottle add an empty bottle and increase the amount just as you did the first few
bottles.
Get the picture? For proper dog training, just add weight slowly over time.
I never put weight on pups. As someone mentioned earlier their bones and joints
etc are still growing/fusing. So take it easy when training dogs.

Using Weights To Train Your Dog