Service Dog: Brace/Mobility Support Dogs (BMSD)
Job: A Brace/Mobility Support Dog works to provide bracing or counterbalancing to a partner who has balance issues due to a disability. Many BMSDs also retrieve, open/close doors or do other tasks to assist in day-to-day life or in an emergency.
Handler: Will vary in presentation depending on disability. Could be any age.
Gear: Most Brace/Mobility Support Dogs wear a specially-fitted and designed harness to help them safely assist their partner. However, just because a dog isn’t wearing a brace harness doesn’t mean he may not be a brace dog
Notes: Brace/Mobility Support Dogs must be large enough to safely support their human partner. In general, BMSD must be at least 23″ tall and 55 pounds to perform brace/counterbalance work safely, and must be proportionally larger if their human is larger than average.
excerpt taken from http://www.anythingpawsable.com/types-of-service-dogs