Standards and Anthropometry for Wheeled Mobility

IDEA Center

The IDEA study (Steinfeld, Paquet, Feathers, 2004; 2005; Feathers, Paquet, Steinfeld, 2004; Paquet and Feathers, 2004) included static anthropometry of occupied wheeled mobility devices, reach measurements and measurements of maneuvering clearances. At the date of the analyses conducted for this report, 275 participants with a wide range of chronic conditions had been recruited through outreach efforts with several organizations in Western New York and mass media. Fifty-three percent of the sample was male and 47% female. The mean age of the sample was 51.5 with a range of 18-94 years of age. Fifty-five percent used manual wheelchairs, 36% used power wheelchairs and 9% used scooters. Three-dimensional locations of body and wheelchair landmarks were collected with an electromechanical probe (Feathers, Paquet and Steinfeld, 2004). A reliability study was completed before data collection (Feathers, Paquet and Drury, 2004).

Participants were recruited through presentations at organizational meetings, television news, mailers, posters, flyers, brochures and cooperative outreach efforts with several organizations in Western New York that serve people who use wheeled mobility devices. Organizations that helped to recruit participants included the Western New York Independent Living Center, the United Cerebral Palsy Association of Western New York, the Western New York Veterans Administration Medical Center, Eastern Paralyzed Veterans of America and DeGraff Skilled Nursing Facility. Some employees of the University at Buffalo were also recruited. Only those who relied on a wheeled mobility device for their primary means of mobility were eligible for participation. Participants had to be at least 18 years of age. All participants were paid $50 plus travel expenses.

Participants were asked to bring in the chair that they use on a regular basis. Most of the individuals in this study had more than one chair (60%), and many of these people had another type of chair as their alternate (52%). Most of the individuals brought the chair that they would normally use when out in public. Informally, most respondents reported that they had smaller and more maneuverable chairs for use at home. Some individuals did not bring in their footrests (4%) because they prefer not to travel with them.

Analysis of individual participants with very large measurements for length identified two clear “outliers” who were excluded from the sample. One of these individuals needed to have one of his legs extended fully during the measurements. The second had spastic tendencies that made it impossible for him to remain still long enough to take the length measurement accurately. Uncorrectable data conversion problems with software caused additional outliers for several analyses.

The measurement protocol included the collection of wheelchair specifications, demographic information, structural anthropometric information and functional anthropometric information for each participant. Three-dimensional locations of body and wheelchair landmarks were collected with an electromechanical probe. A single origin point on the floor was used to identify the location of all landmarks. Thousands of dimensions can be computed from a limited set of landmarks. This reduced the amount of trials and measurements needed significantly. Photographs were taken of each participant in a variety of positions and video recordings were made of all maneuvering trials.

Body and device landmarks were defined in detail in a manual (Feathers, Paquet and Steinfeld, 2004), which also described how the definitions relate to generally accepted anthropometric landmarks and how they differed for this population. The probe used to record body and device landmark locations with respect to one another and to reference planes (e.g., floor, seat, arm support) was an articulating arm with six degrees of freedom that had a precision of 0.3 mm. The three-dimensional coordinates of each landmark point were recorded by pressing the probe’s activation button three times in rapid sequence.

For the reference planes, a minimum of five points on different locations of the physical plane such as on the floor or on the top of a footrest were recorded to define the plane. Distances between points or reference planes were used to derive estimated widths, heights, and depths of key device characteristics and body dimensions. A reliability study showed that this method of obtaining anthropometric dimensions is reliable but measurements may differ from those obtained with conventional anthropometric measuring devices (Feathers, Paquet and Drury, 2004). This occurs mostly with dimensions near the hands and other body parts that may move slightly during data collection.

Occupied length of devices was calculated by computing the dimension from the extreme rear and forward points on the body or chair. This was usually a toe in the front and the trailing edge of the wheel, backpack or edge of the power base in the rear for manual and power wheelchairs. For scooters, the extreme front point was usually a basket that hung off the handlebars or part of the scooter housing and the extreme rear point was usually the rear edge of the housing. Occupied width of devices was calculated by computing the dimension from the extreme left and right points on the body or the chair with hands in resting position. For manual wheelchairs, including attendant propelled models, this could be the outside edge of the wheel guide, the elbow or the hand. For power chairs it could be the outside edge of the control box, an elbow or other body part extended over the side. For scooters, it could be the outside edge of the device housing, the elbows or the outside surface of the hips or shoulders, if they hung over the housing.

The reach protocol utilized a standardized procedure in which participants utilized an apparatus with a series of five shelves that could be moved in and out from the main part of the device and positioned at 100 mm (4 in.) increments while lifting .46, 1.4 and 2.3 kg (0, 1, 3 and 5 lb.) weights. Reach limits were digitized with the mechanical probe, and, from the data, a reach envelope for each individual was constructed. Standard cylindrical canisters 75 mm (3.5 in.) in diameter were used to assess reaching ability. These weights were empirically derived through a study of common bathroom products. If an individual could not grip the canister, a cuff around the palm and attached to the canister was used. If the cuff could not be used, the individual did not complete the reach protocol except for free reach. If a person was unable to reach above the shoulder, they were excluded from all reaching tasks. This eliminated bias in results due to the inclusion of individuals who could not perform a functional reaching task. In all reaching trials except free reach, individuals were asked to reach as far as they could without endangering their safety or causing pain. Free reach trials were completed without bending or stretching.

An envelope of reaching ability was measured with the individual’s preferred hand. To determine maximum reach, the individual held the canister in their preferred hand and placed it on a shelf at the extreme of reach. Reach was recorded using the probe at the “MCP5”, a bony protuberance at the outside of the hand below the pinky finger. This landmark was used because functional reach involves grasping and manipulating objects and the tip of the fingers does not give a measure of reach that reflects grasping tasks. In calculating the actual reach, we computed the location of the target on the shelf itself using the known dimensions of the target and the reach dimension to the MCP5. Similar trials were completed for high reach, mid range reach and low reach. A shelf location closest to the highest vertical free reach was used to measure high reach; mid level was set at or near the shoulder and the shelf for the lower reach was set at the MCP5 height while an individual was asked to reach as low as they possibly could at the side (lateral). The lowest possible shelf was 390 mm (15.3 in). This limit was set for safety reasons.

Three sets of reach trials were completed at three different positions – forward, laterally and at a 45 degree angle. There were no obstructions under the shelves because they projected out from the main part of the apparatus. The order of the trials was counterbalanced to control for fatigue but participants were told to stop and rest whenever they felt tired. Data is not reported here for the 45 degree reach.

Three-dimensional digital data has many advantages in reach studies. The distance between any pair of three-dimensional landmarks or reach coordinates can be computed. Moreover, projections of the coordinates to virtual planes at any orientation provide additional flexibility. As an example, reach limits can be computed from precise landmarks on the shoulder, parts of the mobility device, like the most leading edge (anterior most) or trailing edge (posterior most) of the person or device. Reaching abilities can also be projected onto planes inserted at any location in the reach envelope.

The uniform variables for forward reach in the standards assume that an individual is reaching to a plane that is at the anterior (forward) most point on the device or the body (e.g. toes) or set back from a counter edge (reach over obstruction). For side reach, the uniform variables assume that an individual is reaching to a plane at the extreme lateral (side) most point of the body or device or set back from a similar counter edge. A computational procedure was used to identify the locations where forward and side reaching abilities, as measured by the three dimensional reach envelope, intersect virtual planes at the anterior most point and the lateral most point. For lateral reach we also calculated reach to a second plane set 254 -610 mm (10 - 24 in.) back from the lateral most point (not reported here). For the purpose of this report, all reach limits were calculated to the acromion, a bony protuberance on the shoulder. 

Maneuvering clearances were measured while participants conducted standardized maneuvers inside a set of lightweight movable walls. The walls were gradually moved further apart until the maneuver could be completed without the participants moving the walls. Clearances were pre-measured on the floor of the test site using tape and marker and the locations of walls were recorded after each trial. Maneuvering trials included an L or 90 degree turn and a 360-degree turn within a confined space. The latter could be completed as a “K”-turn or a “U”-turn or any other maneuver as long as the participant wound up facing in the same direction as their starting position. Clearances were pre-measured on the floor of the test site using tape and marker.

In the L turn, the starting width of the clearance was the closest pre-measured clearance to the occupied width of the individual’s device (leaving no more than 50 mm of clearance to either side). In the 360 degree turn in a confined space, the starting clearance was an 1100 mm (43 in.) wide square space. Each participant was asked to complete the trial and, if a wall was moved in the course of the trial, the clearance was increased 50 mm and another trial completed until the participant was able to complete a trial without moving a section of wall. In the 360-degree turn in a confined space, two adjoining sections of wall were moved out as one unit along the diagonal so that the space stayed square in proportion. All trials were videotaped for later observation although the minimum clearance required was noted during the trials.