Mobility assistance dog
A mobility assistance dog is a service dog trained to assist a physically disabled person who has mobility issues, such as wheelchair dependency or poor balance. Roles include "providing balance and stability" picking up and carrying objects, and (controversially) pulling wheelchairs. A mobility assistance dog can also be trained to open and close doors, and operate light switches, and can "have a major positive impact on the lives of recipients". These dogs usually wear a special vest so that the owner can attach a cane-like handle. This allows the dog to guide the owner and assist with their balance.
Some larger-statured dogs with sound joints are trained to pull individuals in wheelchairs, and wear a type of harness specifically designed for pulling. However, wheelchair pulling remains controversial, and is illegal in England. Many US programs limit "wheelchair pulling" to short straight distances, most commonly for assistance getting in and out of a crosswalk. One study has found that using the traction provided by the service dog has physical benefits because manual wheelchair users can operate their chairs with less effort
Another type of mobility assistance dog task is that of a "walker dog". They are used for Parkinson's disease and multiple sclerosis patients, along with other disorders and conditions. These dogs are not canes, and the handler does not put full weight on them. However, the dog can greatly assist a person with their gait and balance while walking. This technique is usually called "counterbalance". It can also be helpful for those with symptoms of proprioceptive sensory loss, such as an inability to walk in a straight line.
As with other types of assistance dogs, in many countries disabled individuals have the right to bring their mobility assistance dogs with them into places where animals are generally not allowed, such as public transportation, restaurants, and hotels. In the United States, the Americans with Disabilities Act guarantees this opportunity to disabled individuals for public access situations. If access is denied to a disabled individual, Federal and some State laws have penalties that may be brought against the business denying access.
Service dogs are often trained and supported by charitable organizations. In the UK, the dogs are called disability assistance dogs. 
Assistance Dogs International (ADI) "is a coalition of not for profit organizations that train and place assistance dogs." They publish a Guide to Assistance Dog Laws which summarizes the federal and state-by-state laws pertaining to service dogs.
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- "Effect of Service Dogs on Manual Wheelchair Users with Spinal Cord Injury: A Pilot Study", Journal of Rehabilitation Research & Development".
- "Assistance Dogs Transform Lives of Veteran Partners", U.S. Department of Veterans Affairs.
- Thomson, Philip D (2004). "Gait Disorders". In Bradley, Walter George et al. Neurology in Clinical Practice: Principles of Diagnosis and Management, Volume 1. Philadelphia: Butterworth Heinemann. pp. 324-326.
- "Revised ADA Requirements: Service Animals", U.S. Department of Justice, Civil Rights Division.
- "Assistance and Guide Dogs" Archived 2012-04-22 at the Wayback Machine, NIDirect.
- Assistance Dogs International website
- "Guide to Assistance Dog Laws", Assistance Dogs International.