How To Strengthen Your Dog's Hind Legs. Preventing dog hind leg weakness Hydrotherapy is an excellent way to strengthen your dog's hind leg muscles without putting stress on their joints!
One of the good ways is to put your dog on some higher ground, like a chair, while hind legs are still on the floor, so the lower body would carry all the weight. I recommend you find a veterinarian trained in physical therapy and rehabilitation for the best outcome (link to find one), but you can get started on your own. Only vibrate for a few seconds until you know he is enjoying it.
How to massage a dog with weak rear legs set your dog on its side in a lying down position.
Exercises to strengthen your dog’s hind end the following are exercises and games to help strengthen your dog’s hind end. Vibration is a good way to end a massage. Extend the front leg forward and the rear leg back. Use a soft, but firm, grip to slowly slide your hands over your dog's rear legs down to its paw.