Academic journal article Human Factors

Stature, Age, and Gender Effects on Reach Motion Postures

Academic journal article Human Factors

Stature, Age, and Gender Effects on Reach Motion Postures

Article excerpt

The rapid adoption of software to simulate human reach motions in the design of vehicle interiors and manufacturing and office workstations has required a sophisticated understanding of human motions. This paper describes how more than 3000 right-arm reaching motions of a diverse group of participants were captured and statistically modeled. The results demonstrate that stature and age have a larger effect than does gender on reach motion postures for motions chosen by the participants while reaching to targets placed throughout a typical automobile interior. We propose that these methods, models, and results can assist the further development of human motion simulation software for ergonomic purposes, such as for the design or evaluation of vehicle interiors or industrial workplaces, to ensure that various population groups are physically accommodated.


Many common tasks require that a person coordinate the movement of multiple segments of the body to reach successfully to a designated location in space. The task of interest in this paper is reaching to a variety of locations within the interior of an automobile (e.g., moving the right hand from the steering wheel to the center console, overhead console, radio, or passenger side door). Some of these motions can require one not only to extend the upper extremity toward the designated target location but also to rotate the shoulder and torso to assist in the motion. As described in a recent study by Zhang and Chaffin (1997), these types of motions can be modeled based on a four-segment linkage system consisting of torso, shoulder, arm, and forearm-hand segments. Various empirical and kinematic modeling approaches have been used to predict these types of complex motions (see Badler, Phillips, & Webber, 1993, for further information on these models).

The purpose of this paper is to empirically describe and analyze the effects of size, age, and gender on the postures chosen while performing these types of reaching motions. If these three demographic effects can be satisfactorily quantified, the understanding of human motion will be enhanced and future human motion simulation software will more accurately reflect these population attributes in the resulting motion predictions.

There is little debate that the size of an individual often has an important effect on postures when the reach target is located away from the body. In a static sense, when the upper extremity is extended so that the hand-forearm-arm segments are nearly aligned, the reach boundary is defined by the length of these body segments unless the shoulder and torso are also allowed to move toward the target. Computerized human reach simulations, such as those performed by SAMMIE[TM], Crewchief[TM], SAFEWORK[TM], and JACK[TM], often predict reach boundary conditions without shoulder and torso assistance, unless the user specifically modifies the initial torso and shoulder postures (Karwowski, Genaidy, & Asfour, 1990). This strategy, though rendering useful approximations of extreme reach postures, does nothing to assist a workplace or vehicle designer in understanding how differentsize people actually choose to move and position themselves when performing a variety of reach tasks in their particular reach boundar y conditions. This latter type of information is valuable in designing a workspace in which a person can reach to various areas in an unobstructed fashion.

A reason to believe that age could affect complex reaching motions is derived from the following studies. The most general evidence is from the 1987 National Health Interview Survey (Supplement on Aging), in which selfreports of performance declines by older individuals were greater in motor tasks requiring multisegmental coordination (e.g., reaching overhead, crouching, lifting objects, and bathing) than in simpler motions (e.g., shaking hands or eating; Lawton, 1990). Also, one laboratory study of 61 participants 20 to 80 years of age by Potvin, Syndulko, Toutellotte, Lemmon, and Potvin (1980) disclosed that decreases in performance time were greater with age when the tasks required multisegmental motions (e. …

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