As urgency dictates and funds permit, future anthropometric surveys should be undertaken to:
- expand the working-adult database created during the pilot study.
- expand the over-65 population whose members may well be the most common users of wheelchairs, and who certainly represent the fastest growing demographic sector of US society.
- survey an appropriate children’s population to keep up with design needs stemming from the trend toward mainstreaming in our schools.
Two other considerations for future study warrant mention: linkage and range-of- joint motion (ROJM) studies useful for the creation of dynamic human modeling software, and compilation of a three-dimensional database of individuals with disabilities obtained by use of scanning equipment.
Digital Human Models
Studies involving the biophysical aspects of wheelchair propulsion involve the anthropometric description of body links . lengths, breadths, and depths of body segments . that are important to the construction of dynamic computer models. Based upon concepts usually credited to Dempster (1955), the body is divided into segments defined by the major joint centers of the body. Although the true center of rotation remains unknown for most joints, especially for the more complex joints such as the hip and shoulder, anthropologists measure the length of various links by palpation of bony landmarks surrounding a given joint. For example, the segment called the lower leg link would extend between the center of the lateral malleolus at the ankle and the center of the lateral femoral epicondyle at the knee. While neither of these two points is located precisely at the center of rotation projected to the lateral surfaces of the respective joints, they can be reliably palpated and landmarked. Proceeding similarly, the linkage lengths for an entire body may be marked and measured. Such data can be treated statistically much like any other body size descriptor and when combined with ROJM data can be used to construct a scaled, dynamic computer model. Such models can represent an individual of specific dimension, or can represent whole groups of individuals. Motion around the linkage center is based upon ROJM data incorporated in the model’s database. A number of such models are currently available for non- disabled analogues (e.g. JACK, CREWCHIEF, SAFEWORK, and RAMSIS) and some, reportedly, reflect elements of true 3-D motion.
Other physical properties of the whole body and of body segment can also be included in these models. Currently available non-disabled data include the center of gravity of the whole body, as well as its segments. Moments of inertia also are known. This class of measurements is used to estimate body dynamics in response to impact or instability, for example, and have the potential of contributing a great deal to the simulation of auto accidents or other events which would be unethical to investigate with human subjects.
Modeling individuals and their disabilities presents particular problems because the very data which make the models appear realistic (e.g., the range of joint motion, the centers of gravity and moments of inertia for body segments, etc.) are potentially different, and largely unknown, for this population. It is for this reason that collecting such data on this population is of critical importance.
3-D Shape Digitization
Currently in the forefront of measuring methodology for anthropometric studies is 3-D shape digitization. The first such instrument used by the Air Force was a small low- density laser scanner which rapidly passed over the head and face and, in combination with computer graphics software, produced a 3-D digital image on a computer screen. The Air Force, the Army, and NIOSH now all use larger scanners capable of producing 3-D images of the whole body and could digitize volumes large enough to include a positioned wheelchair user (in many, but not all, wheelchair models). Among the advantages of 3-D measurement is that resulting images record not only the size of objects (including the human body) but also their shape. Three-dimensional data from these scanners will also be extremely useful in providing shape to the digital human models. Large quantities of 3-D scan data have not yet been collected on any population (with disabilities or without) so the potential usefulness of the data is largely unexplored.