Standards and Anthropometry for Wheeled Mobility

4.3 Reach Ranges

Figures 14-15 and Table 4 show the standards from the four countries related to reach from a wheeled mobility device. Figures 16-19 show key findings from the research.

Figures 14-15.  Forward and Lateral Reach

Table 4

*R.E. = Reach Envelope

The U.S., Canadian and Australian standards are similar, although the latter use a reach envelope to provide guidance for obstructed forward reach and both the Australian and the Canadian standards are less restrictive for low side reach. On the whole, the U.K. standards proscribe much more restrictive reach ranges although they do include different limits for different types of applications.

Figure 16. High Forward Reach

Figure 17. Low Forward Reach

* Three outliers removed from IDEA Center data due to data translation errors in software

Figure 18. Upper Side Reach

Figure 19. Low Side Reach

Note:  3 outliers removed from IDEA Center – Protocol data due to translation errors in software

For the IDEA results, the forward reach graph represents reach over the anterior most (forward) point of the wheelchair or body for trials with no weight lifted (as in Fig. 14-15). We do not know how forward reach was measured in the UDI study. In the BS8300 study, trials were conducted over a counter and it is not known whether the results reported represent highest reach for each person in general or over the anterior most point. It is also not clear who was excluded or included in the UDI and BS8300 results.

The 5^th percentile values for high forward reach in both the IDEA and UDI studies are well below the current U.S., Australian and Canadian standard of 1220 mm (48 in.). The reason for the very low 5^th percentile and minimum values in the IDEA study is that several individuals’ reach envelope only intersected the anterior most plane at the extended part of their reach envelope (near the bottom of the arch). They could reach higher but only behind the anterior most plane, e.g. if they had knee space in which to pull their device. This may be true of other studies as well but information is not available to understand what is meant by highest reach. 

The UDI and IDEA results are remarkably similar given that there are so many ways that reach can be measured. The results indicate that there are some people at the lower tail end of the distributions who have very restrictive reaching ability. The minimum value for the BS8300 research (the only one reported) was close to the current standards. We believe that this is due to either a different measurement technique (highest reach regardless of whether it was behind the anterior most point) or exclusion of individuals in the sample who could not reach to the anterior most point.

High side reach results have a similar pattern although the BS8300 study results were lower than the standards of the other countries. The BS8300 and the UDI results for low side reach were within 100 mm (4 in.) of each other at the minimum end of the range. The participants in the IDEA sample with the most restricted reach ranges were not allowed to reach lower, however, due to the safety considerations imposed.

The reach results for the different studies demonstrate great differences, even though some consistent trends are evident. More information is needed to clarify exactly how the UDI and BS8300 reach studies were completed, how the data in each was analyzed, and who the people with extreme values were. The UDI data may include some outliers that need to be identified and eliminated. The BS8300 study may have excluded people whose reaching ability may be more restricted than those included by the UDI and IDEA center.

The reach results for the different studies demonstrate great differences even though some consistent findings emerged. More information is needed to clarify exactly how the UDI and BS8300 reach studies were completed and how the data in each was analyzed. More detailed information is needed about the people at the extremes in reaching in both studies. The UDI data may include some outliers that need to be identified and eliminated. The BS8300 study may have excluded people whose reaching ability may be more restricted than those included by the UDI and IDEA center. The IDEA Center results demonstrate that some individuals can only reach the anterior or lateral most plane at the extreme of their reach range. Additional analyses, removing individuals whose forward or side reach range is restricted in this way may result in more comparable findings.

Thus, standards should reflect the most functional reaching approach. Besides free reaching ability, there are additional exclusion criteria that could be imposed for the purpose of establishing standards, for example, the ability to lift an object or perform a grasping task. The IDEA Center studied the impact of grasping and lifting a weight during a task. The standards make no mention of the task so those results are not presented here. These data may perhaps be more relevant for developing standards since they are more realistic tasks. Our preliminary analyses of the weighted reach trial data indicate that many of the participants with marginal reaching abilities would be eliminated from an analysis of these trials because they could not perform the task at all (even with the aid of an assistive device called a “cuff” that eliminates the need to grasp the object). The remaining participants are likely to have more extensive reach envelopes and thus the low end of the range could actually be higher than with free reach simply due to exclusion of people with marginal reaching abilities. Our preliminary analysis also indicates that many participants could reach higher at a 45 degree angle than forward or to the side. Thus, this set of trials may provide information for changing the approach used in the standards. Individuals are likely to use the approach that is most functional for them, if there is enough room.

Currently the U.S., Canadian and Australian standards address reach over an obstruction in a very simplistic manner. They specify maximum and minimum heights but do not take into consideration the fact that the depth and height of the obstruction can vary with a corresponding impact on the reach envelope. Reaching over an obstruction was studied in the BS8300 study, and, the limits of obstructed reach can be derived from the IDEA data. But, since there are so many variables that have an effect on reach over obstructions, e.g. knee space depth, armrest height, depth of obstruction, height of obstruction, etc. it is not easy to devise a means to represent it in a way that is useful for designers. The BS8300 approach included different requirements for different scenarios. This seems to offer a promising direction for improving this aspect of accessibility standards.

Recommendations

• Develop revised criteria for reaching from a wheeled mobility device that are more realistic and comparable to everyday tasks.
• Base reach limits on a sample of individuals that excludes those with marginal abilities.
• Advisory information should be used either in the standards themselves or in a companion document to help designers address the variety of reaching conditions not specifically addressed in the requirements. That is the approach that the U.K. has taken in BS8300.
• Examine the implications of knee clearance on reach envelopes.
• Develop a method to represent reaching over obstructions.