Anthropometry of Wheeled Mobility Project: Final Report

2.2.3 Functional Reach

One-handed reach and lift capability data made at different heights, angles and object weights were collected in 3-D. Determining an individual’s 3-D reach envelope required that the reach envelope be measured relative to certain environmental, wheelchair and personal features (e.g. 3-D envelopes measured relative to a point on the floor, forward most portion of a person or wheelchair and/or from a reference point on wheelchair’s arm support surfaces). Data can be presented in 3-D, in the form of 2-D charts along key planes (e.g. sagittal plane to represent forward reach abilities), or described for a standard reach (e.g. maximum forward reach from a reference point).

The one-handed lifting tasks required individuals to move weighted cylinders that were empty or weighted with filler. Cylinders of 75 mm (3 in.) diameter were chosen because they required participants to use one-handed power or lateral pinch grasps, which are commonly used to hold and manipulate products. The size of the cylinders was held constant across conditions and participants. The four weight conditions were no weight, 1 lb, 3 lb and 5 lb.

Those individuals unable to grasp and/or lift any of the cylinders above shoulder height did not complete the reaches. Further, if a particular weighted canister could not be lifted above shoulder height then reaches involving that particular weight were avoided for reasons of participant safety.

Reaches and lifts were completed in 15 different directions (3 different angles of asymmetry from the orientation of the WhMD at 5 different heights). The angles of asymmetry included 0, 45 and 90-degrees from the sagittal plane that passes through the acromion process on the individual’s dominant side (i.e. forward, asymmetric and side reaches, respectively). The five heights were normalized to the individual's vertical reach capabilities so that reaches were performed at, above and below shoulder height.

Three-dimensional reach data were collected with the electromechanical probe (FaroArm, Faro Technologies). Use of the electromechanical probe required manually digitizing the 3-D location of the maximum reach point after the cylinder was positioned (Figure 2‒3). The point data were used to measure reach distances from reference points (e.g. maximum forward reach from the front of the WhMD, or maximum side reach from the lateral-most point of the WhMD), and construct reach envelopes that illustrate the reaching capabilities of the sample in 2-D and 3-D space.

A computation procedure was developed for performing analyses on reaches that involved combining 3-D reach information from the measured WhMD users in relation to a common reference plane. For instance, a vertical plane at the anterior-most point was used a reference to analyze forward reaches. This is similar to a wheelchair occupant facing a wall such that the forward-most aspect of their foot and/or wheelchair was touching the wall. Likewise, a vertical plane at the lateral-most point was used as a reference for analyzing lateral reaches, similar to a situation where a wheelchair occupant were right alongside a wall.

The percentage of WhMD users able to reach to or beyond a particular reference plane (either forward or lateral) was then computed. The data were analyzed in 100 mm (4 in.) increments from the floor. The reference planes could also be moved away or towards the occupant to simulate different obstruction depths to estimate the relative increase or decrease in reach capability. It should be emphasized that our data depict, in percentages, the reaching capabilities of only those individuals who could grasp and lift a particular cylinder above shoulder height.

Figure 2‒3. Participants moved cylinders in 3 different directions at 5 different heights. Shown are forward reaches for two different heights. The electromechanical probe is used to record the 3-D location of the maximum reach distances from body and wheelchair reference points.