Adopting an adult dog skips the puppy chaos but not the physics. A big dog on a lead is a moving load your arm, shoulder and lower back have to manage, and the first weeks decide whether the arrangement suits a fragile spine.
How much does a pulling dog load your back?
More than most people expect, because the load arrives suddenly. A lunge is a sideways jolt while you are twisted to look at something else, which is close to the worst combination a lumbar spine knows. The answer is not grip strength but set-up: a front-clip harness, a lead length you can actually manage, and training time before the long walks.
What do the first weeks with a rescue dog look like?
Slower than the adverts suggest. A magazine on adopting an adult rottweiler in North Carolina lays out the first thirty days plainly: decompression, routine, short calm walks, and the health checks worth asking a rescue about, including hips, elbows and the cancers the breed is prone to.
Whatever the breed, the pattern transfers: quiet first week, predictable routes, and no marathon walks while the dog is still learning the house rules.
How do you protect your back on walks?
Shorten the lead before excitement, not after. Keep the dog on the side away from the road and the hand that takes the load near your centre of gravity. If a lunge is likely, plant both feet and let the harness take it rather than catching the pull with one shoulder.
Lead skills are trainable at any age, and a dog that walks on a slack lead is a different animal for your back from day one.
When should you walk away from a match?
If the dog is too strong for you today, the honest answer is a different dog, not a braver grip. Rescues would rather hear that at the meeting stage than after an injury.
Before any of that, the choice of dog itself is weighed up in choosing a dog when your back complains.
Sources
For the breed's size, temperament and exercise profile, see the American Kennel Club's rottweiler page.