12onny:
Didn't you post about
getting your two puppies at 5 weeks old?
If so, it's almost certain you got your puppies from a BYB.
BYBs, by definition, do not breed for temperament and they don't breed for health or soundness. You have a huge unknown with your puppies. Your breeder likely didn't provide you with verifiable info on the soundness of dam or sire in terms of hips and elbows. You have no idea how good your puppies' hips and elbows will be.
All the more to let them grow up before you use that treadmill.