An 8- 10 week old puppy's bones have not yet fused together.
Their joints are made up of muscle tendon and skin covering.
Nothing joining together and not having a true socket. At this point
If you over run, over train or allow them to be jumping off furniture/stairs or play too much, then it won't give them the chance to grow and form properly.
Stick with reasonable amounts of play
And restrict jumping. My rule of thumb has been. If a puppy falls asleep during play then this is too much. The puppy should stop playing and have some quiet time before he is tired enough to fall asleep.
A well built well structured body is something that comes not only from good breeding but from good care and attention.
Many consider a puppy to be a grown adult at 1 year old, But puppies will continue to grow in height and size, so developing bones can take anything between 6 and 24 months. Skeletal growth will determine how tall they become as an adult
Once your pup has grown you have the chance to play for the rest of the dog's life.