A number of measures are required to describe the capacity of an individual (or population) to achieve task performance (e.g., reach, lift, pull). Joint range-of-motion (ROM, also called mobility or flexibility) and joint (or muscle) strength begin to describe capacity and are especially relevant for tasks performed briefly or infrequently. Additional information will be required for highly demanding, prolonged, or frequent tasks, as well as additional types of measures (e.g., fatigue and environmental stress as described below).
Range of Motion
Joint ROM refers to the limits of joint motion and is represented as rotations about a given joint or of body segments (e.g., torso flexion). Two different forms of ROM are commonly measured. The first, passive (or assisted), involves external sources of force or moment to achieve joint motion. Examples include the use of gravity during a squat, to assess knee flexion, or forces /moments applied by an experimenter or device. The second, active ROM, requires muscle contraction to achieve joint motion and is associated with narrower motion limits than passive. In practice, the relevant type of ROM is determined by task requirements.
Measuring ROM from individuals is possible using a variety of equipment, from lowcost goniometers (for measuring included angles) to high-cost and sophisticated marker tracking systems. More often, population ROM data are obtained from a number of accessible sources (often in conjunction with anthropometric data). A number of factors can be expected to have an influence on ROM. Although ROM decreases with age, the changes are usually minimal in healthy individuals until the end of typical working life (i.e., 65). Women generally have higher ROM ranges, although gender differences are typically 10%. Little association has been found between anthropometry and ROM, although ROM does decrease with obesity. In simple cases, such as those involving one joint, application of ROM data is straightforward and follows similar methods described in anthropometry (e.g., using percentiles). When multiple joints are involved, it is common to use human modeling software to assess the potential limitations due to ROM.
Maury A. Nussbaum
Industrial and Systems Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia
Jaap H. van Diee¨n
Faculty of Human Movement Sciences
Vrije Universiteit
Amsterdam, The Netherlands
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