Anthropometry of Wheeled Mobility Project: Final Report

4.3.6 Reach Limits

Accommodation models were developed from the research findings for forward and side (lateral) reach in an empty 56 grams (2 oz.) cylinder (figure 4‒8) and a heavier 2.27 kg. (5 lb.) cylinder (see Appendix 3). In our research, only a subset of the individuals in the study sample who could lift a no-weight (56 grams or 2 oz.) cylinder above their shoulder were measured for reach limits. This insures that the accommodation models are not biased by individuals who have limited functional reaching abilities. Using these models, a designer can determine the percentage of wheeled mobility users with functional reaching ability that might be expected to reach (without a weight) to a 100 mm x 100 mm (3.9 in. x 3.9 in.) target location in space at a given height from the floor. The distance in each case can be measured from the location of the hands at the end of the reach to any number of reference points on the WhMD user’s body or chair. The corresponding percentages are color coded to differentiate regions of reach performance. Percentages of reaching ability drop significantly when the object mass is increased from 56 grams (2 oz.) to 2.27 kg. (5 lb.). With weights that weigh more than 56 grams (2 oz.), we found that 20‒25% of all three WhMD users could not reach to the same heights as to the no-weight condition. The dashed lines in the figures show the current ADA-ABA requirement which specifies a threshold value of 1220 mm (48 in.) when reaching to a target located in front of an individual at the plane of the toes or front of footrests, or “anterior most point” (for details on the development of the models, see D’Souza et al. (2009a).

The design and standards implications of the research findings are as follows:

1. Side reach access is far more preferable to forward reach access, which is quite restricted among the wheelchair user population. Targets at locations along the plane of the anterior most point will not be within the reach of a majority of wheeled mobility users, even if the maximum reach height limit were reduced to shoulder height.

2. When forward reach is the only alternative, knee clearance should be provided that allows an individual to extend their legs and front part of their wheelchair beyond the plane on which the target is located. This will allow many more individuals to reach to targets in a forward approach. For the accommodation model of forward reach, the depth of knee clearance needed to accommodate different proportions of the sample can be determined by the columns with negative offset distances and can be interpreted as the increase in ‘percent capable’ (e.g. 74% or 88% of the sample) for every 100 mm (3.9 in.) increase in available toe or knee clearance.

3. The upper height limit in the current ADA-ABA standard for unobstructed side reach, 1220 mm (48 in.) will accommodate the 99th, 95th and 96th percentile of manual wheelchair, power chair and scooter users in our sample. Thus, there is no need to change that dimension. However, a large percentage of the sub-sample of individuals who had functional reach could not safely reach to the lower limit of 380 mm (15 in.). Our results also indicate that the upper limit of reach could be increased for wheeled mobility users but this may result in limitations for people of small stature.

4. Standards developers should consider requiring either side reach access to all targets within the scope of standards or limiting front reach to locations where knee clearance is provided beyond the plane on which the target is located. The lower limit of side reach should be increased to 700 mm (28 in.). We recommend that the lower limit only be applied to controls and devices that are needed for business services (e.g. recharging station for mobile phones or wheelchairs). For long term use in work sites, power strips should be used to provide access to outlets.

5. When designing environments for tasks that require lifting objects, avoid designs that require people to reach to objects above counter height. Adjustable storage units that building occupants can customize to their own needs can improve usability. Devices like sliding shelves that reduce the length of reach tasks are another beneficial strategy.

6. Standards developers should give some consideration to the task in relationship to reach. Reach limits for storage units where lifting objects are inherent in their use, could be different than for other tasks. We believe that this issue requires discussion since there are other approaches to accommodating limited reach as noted above.

Figure 4-8: An accommodation model showing the abilities of the manual wheelchair users to complete a forward reach without lifting weight

Long Description: These data depict the reaching abilities of manual chair users represented as the percentage of users expected to reach to a target location in the forward reach direction for a given (a) height from the floor (shown the vertical axis) and (b) offset distance (shown on the horizontal axis) from the forward-most point of the person or wheelchair (e.g., toe, footrest). Horizontal distances in the positive range represent offset distance away from the body (or barrier depth) when reaching over an obstruction in relation to the forward-most point, and the negative range implying that the reach target is brought closer to the person (such as on a table with knee clearance). The percentages are color coded to differentiate regions in reach performance. The dashed lines indicate the current ADA-ABA requirement.