WC Seating & Mobility

Objective Measures of Hand and Finger Strength

Chronic Trauma Disorder Prevention


Chronic Trauma Disorders (CTDs) are now a major cause of disability. CTDs occur when the forces acting on the body repeatedly exceed its functional capacity resulting in musculoskeletal, vascular or neural abnormalities. Traditionally, CTD prevention and treatment has focused on decreasing limb use which limits functional independence, particularly among wheelchair users.

The goal of this research is to investigate the benefits of increasing the functional capacity of the limb to maintain use within the limb\'s functional capacity. Strength training, which improves movement efficiency, increases bone density and strengthens muscles, tendons and ligaments, would increase the limb\'s functional capacity and allow the limb to meet increased demands without inducing microtrauma to the tissues.

Current assessments of hand strength use hand grip and pinch dynamometers which measure limited hand movements, are unable to measure the forces specific to a variety of hand functions, provide gross measures of strength rather than isolated forces for each digit or joint and cannot assess the extension musculature. As such, they are unable to provide a comprehensive strength assessment of the fingers, hand, wrist and forearm.

Research Objectives

The purpose of this project was to develop devices to provide quantitative measures of isometric wrist, hand and finger strength as well as the grip strength on a wheelchair pushrim. Measures of individual joints or digits, gross measures of pinch and hand grip, assessment of opposing joint motions, and suitability for clinical rehabilitation were incorporated into the designs.

Four prototype devices were proposed to complete the required measurements:

Hand strength assessment device (HSAD): flexion and extension of isolated MCP and PIP joints;

Image of HSAD

Pushrim grip assessment device (PGAD): grip strength on wheelchair pushrim;
Image of PGAD

Multi-finger assessment device (MFAD): flexion and extension of all fingers at MCP or PIP joints; and
Image of MFAD

Wrist strength assessment device (WSAD): flexion/extension, pronation/supination, radial/ulnar deviation of wrist.
Image of WSAD flexion/extension

Image of WSAD radial/ulnar deviation

Image of WSAD pronation/supination

The designs were evaluated using models and simple prototypes, and then working prototypes were evaluated for safety (static strength, fatigue).


Twenty-seven subjects (4 female, 23 male) completed the validity and/or reliability testing. Subjects without disabilities were selected as age (+/- 5 yrs) and gender matched controls for the subjects with disabilities. Subjects, recruited through clinics and the community, were primarily male, white, independent in activities of daily living and relatively fit and active.

Device validity was evaluated through comparisons to existing measures of hand strength (handgrip and pinch dynamometry). Repeat assessments were used to determine reliability and the potential influence of subject characteristics (e.g. gender, age) was considered.

Results & Discussion

The results indicated that the PGAD, MFAD, and WSAD devices provide valid and reliable measures of isometric strength for diverse subject groups (e.g. males and females, with and without CTDs). The HSAD did not provide sufficiently reliable and valid results, probably due to insufficient standardization of joint positioning.

The PGAD, MFAD and WSAD devices provide objective measures of agonist and antagonist musculature of the hand, wrist and forearm. The devices are ready for commercialization, are suitable for use in a clinical rehabilitation setting, and are acceptable to subjects in terms of comfort, time required and ease of use.

Further refinement of the devices will enhance their suitability for use in clinical rehabilitation programs. Use of these devices in future research will enable evaluations of the relationship between joint strength and overuse injury and/or the impact of training/rehabilitation programs.


This work was funded by the National Center for Medical Rehabilitation Research in the National Institute of Child Health and Human Development at the National Institutes of Health through Small Business Innovation Research Phase I Grant #1 R43 HD33940-01.

Applying the Balans Seating System to Wheelchair Design

Need for Alternative Wheelchair Seating Systems

Wheelchairs have had the same basic design configuration for over fifty years. Though wheelchair frames are now made from lightweight materials such as composites, modern wheelchair seating still consists of the same sling-back upholstery used in older models. As most wheelchairs serve more as seating than mobility devices, a wheelchair used primarily as a chair could take advantage of principles employed in state of the art seating systems for office personnel.

Applying the Balans Seating System to Wheelchair Design

The Balans seating system uses knee pads and a sharply tilted seat to promote good back posture. Curved knee pads and a seat cushion with significant pelvic support were added to a Balans chair to accommodate people with spinal cord injuries. Testing determined that people without feeling in their legs could sit in such a system comfortably for up to six hours.

The prototype wheelchair constructed from the Balans design has three sitting postures: a forward or desk work posture, a neutral balanced posture, and a semi-reclined seating posture. The semi-reclined posture allows a rider to climb curbs up to four inches high. Casters located below the knee pads and behind the seat stabilize the chair\'s position. The innovations of the Balans wheelchair represent significant departures from traditional wheelchair designs.

Current Project Status

The Balans wheelchair prototype is currently located at the University of Virginia. Plans are being made to fabricate a standard four wheel configuration Balans wheelchair platform.

Image of a balans chair.


This project was sponsored by Beneficial Designs, Inc. and the University of Virginia Rehabilitation Engineering Center.

Back Support Shaping System

Need for a Better Back Support

The upholstery on most sling-back wheelchairs sags after a few months of use. Sitting in a wheelchair with sagging upholstery causes poor posture that, over time, can lead to back pain, neck pain, and spinal and pelvic deformities.

Project Goal

The goal of this project was to develop an affordable, lightweight, comfortable, orthopedically correct, and easily adjustable back support designed to work with existing sling-back upholstery. Unlike commercially available back supports, which must be removed to fold the wheelchair, cannot be added to existing sling upholstery, and are unable to conform to the contours of different individuals, the back support shaping system was designed to adjust to the different activities of the wheelchair user.

Phase I Prototype Development and Clinical Testing

In January 1993, Beneficial Designs developed a back support system that consists of support pads that hook onto the upright frame members of a wheelchair behind the sling-back upholstery. One support pad is contoured to fit the lower back, while the other, consisting of two smaller pads connected by a tension strap, is designed to provide support for the upper back. The horizontal tension straps on each support can be adjusted to customize the amount of support the pad provides.

Sixty-nine subjects participated in a short term clinical evaluation of back support prototypes and provided feedback to optimize the design specifications. The Back Support Shaping System improved comfort, spinal posture and wheelchair mobility in the majority of subjects, and 70% reported it was more effective than any back support they had used before.

Phase II Long Term Clinical Testing

In June 1994, 40 subjects wore the back supports for a year and evaluated them for durability, posture, comfort, and function. Their comments were used to develop the back support shaping system into a design suitable for commercial marketing. The back support shaping system was shown to improve posture, comfort, and function.

The low back support is now being manufactured by PinDot Products by Invacare Corporation as the PaxBac, and was introduced at the March 1996 International Seating Symposium held in Vancouver.

PaxBac by PinDot Products


This project was funded by the National Center for Medical Rehabilitation in the National Institute of Child Health and Human Development at the National Institutes of Health through Small Business Innovation Research Phase I Grant #1 R43 HD29983-01 and Phase II Grant #2 R44 HD29983-02.

Hip Grip Pelvic Stabilization Device 

Need for Better Pelvic Support

Project Goal

The goal of this research project is to develop an innovative, dynamic pelvic stabilization device. The Hip Grip will consist of contoured pads that "grip" the pelvis and allow anterior/posterior tilting of the pelvis. Mounted to a wheelchair, it will offer firm support around the pelvis, while allowing the user to actively extend the lumbar spine without losing pelvic position within the wheelchair. The Hip Grip will be comfortable, adjustable, and will improve posture. The Hip Grip will link the user with the wheelchair to provide a stable base of support from which to perform functional tasks, such as reaching and bending, without risk of falling out of the wheelchair. This will potentially increase wheelchair propulsion efficiency and user independence.

Need for Better Pelvic Support

Many people who rely on specialized seating in their wheelchairs have difficulties achieving and maintaining good sitting posture. Maintaining appropriate pelvic positioning and stability are critical to achieving proper sitting posture. Commercially available positioning devices do not provide firm support for the pelvis while allowing functional movement, and often result in misalignment and areas of high pressure.

Phase I Hip Grip Prototype

In Phase I, a prototype was developed and evaluated by 20 wheelchair users during a brief clinical evaluation. The Hip Grip prototype incorporated rear, front, and side support of the pelvis in an adjustable unit which allowed the pelvis to pivot forward about the hip joint within a specified range. The Hip Grip reduced undesired pelvic movement and provided variable resistance to bring the pelvis back into its neutral posture after allowing movement. The device improved posture, comfort, and upper body function in the majority of the subjects.

Phase II Proposed R&D

The objectives of Phase II of the research project were to:

  • refine the Hip Grip based upon Phase I results;
  • perform safety and durability testing; and
  • conduct a 3-6 month clinical evaluation with 20 wheelchair users to determine the postural and functional benefits and to optimize the design to better control pelvic movement and enhance upper body function.


This work was funded by the National Center for Medical Rehabilitation in the National Institute of Child Health and Human Development at the National Institutes of Health through Small Business Innovation Research Phase I Grant #1 R43 HD36156-01
Phase II Grant # 2 R44 HD36156-02A2

FlexRim Low Impact Wheelchair Pushrim 

Final Report PDF

Project Goal

The goal of this research project is to develop and evaluate a FlexRim low impact wheelchair pushrim. This innovative pushrim is designed to lower the impact forces experienced by wheelchair users during propulsion. The FlexRim reduces impact forces by replacing the rigid interface normally found between the wheelchair wheel and the pushrim with a flexible interface. When an impact load is delivered to the FlexRim during propulsion, the FlexRim is able to displace relative to the wheel and reduce the impact stresses related to upper extremity injuries.

Need for Low-Impact Pushrims

Approximately 65% of manual wheelchair users experience upper extremity pain or injury, which can significantly impact their mobility and independence. Research has demonstrated a relationship between impact stresses on the upper extremities during wheelchair propulsion and upper extremity injury. Impact stresses occur when the hand contacts the pushrim, transmitting the stresses to the wrist, elbow, and shoulder. Current pushrim technologies do not effectively reduce these impact stresses.

Phase I FlexRim Concepts

In Phase I, three FlexRim concepts were developed and evaluated to determine their effect on propulsion kinetics, wheelchair maneuverability, and mechanical efficiency. The concepts allowed the pushrim to translate relative to the wheel, thus lowering the impact forces. FlexRim prototypes that allowed translational displacement resulted in reduced impact forces and mechanical efficiencies greater than 96%. Wheelchair users preferred FlexRim prototypes with conservative force-displacement characteristics.

FlexRim Shock Mount Concept

Phase II Proposed R&D

A proposal was submitted to the National Institutes of Health in April of 1999 for Phase II funding. In Phase II, new FlexRim concepts will be developed and evaluated based upon Phase I results. Biomechanical evaluations of impact loading and mechanical efficiency will be conducted at the Pittsburgh Human Engineering Research Laboratories with 15 subjects. In addition, 30 wheelchair users will evaluate the FlexRim over a three to six month period of use. Because the FlexRim reduces impact stresses related to upper extremity injuries, it serves to prevent injury, and preserve function and mobility.


This research was co-funded by the National Institute of Child Health and Human Development and the National Center for Injury Prevention & Control (NCIPC), Centers for Disease Control and Prevention (CDC) through Small Business Innovation Research Phase I Grant # 1 R43 HD36533-01.