Don B. Chaffin

Bio: Don B. Chaffin is an academic researcher from University of Michigan. The author has contributed to research in topics: Torso & Population. The author has an hindex of 63, co-authored 251 publications receiving 12420 citations. Previous affiliations of Don B. Chaffin include Northwestern University & University of Oklahoma.

Back disorders and nonneutral trunk postures of automobile assembly workers.

Abstract: A case-referent study was conducted in an automobile assembly plant to evaluate the health effect of trunk postures, such as bending and twisting, that deviate from anatomically neutral. Cases of back disorders were all those of workers who reported back pain to the medical department in a ten-month period and met the severity criteria of an interview. The referents were randomly selected workers free of back pain according to medical department records, an interview, and an examination. For each of the final 95 cases and 124 referents, the job was analyzed for postural and lifting requirements with a video recording and software analysis system by analysts blinded to the case/referent status. Back disorders were associated with mild trunk flexion [odds ratio (OR) 4.9, 95% confidence interval (95% CI) 1.4-17.4], severe trunk flexion (OR 5.7, 95% CI 1.6-20.4), and trunk twist or lateral bend (OR 5.9, 95% CI 1.6-21.4). The risk increased with exposure to multiple postures and increasing duration of exposure.

A longitudinal study of low-back pain as associated with occupational weight lifting factors.

Abstract: A review of the biomechanics of weight lifting as it relates to low-back stresses is presented first. This serves as the basis for the development of a Lifting Strength Rating (LSR) methodology. Then a study is reported wherein the LSR methodology is used to evaluate 103 jobs having various amounts of required two-handed load lifting. The 411 people populating these jobs were also evaluated. For a period of one year following their evaluation, any low-back pain problems in the group were noted. The primary result of the field study is that the incidence rate of low-back pain is correlated with higher lifting strength requirements as determined by assessment of both the location and magnitude of the load lifted. It is, therefore, recommended that load lifting be considered potentially hazardous, and that the LSR methodology be used to guide corrective actions.

A Proposed Standard Procedure for Static Muscle Strength Testing

Abstract: (1974) A Proposed Standard Procedure for Static Muscle Strength Testing American Industrial Hygiene Association Journal: Vol 35, No 4, pp 201-206

An investigation of fitts' law using a wide range of movement amplitudes.

Abstract: The relationship between Fitts' Index of Difficulty (ID = log2 2A/W) and movement time was investigated for finger, wrist, and whole arm motions over a wide range of movement distances (0.25 to 30.5 cm). Results supported Fitts' original speculation that various limb segments may show different maximum information processing rates. Short-distance finger and wrist motions showed much higher rates (38 and 23 bits/sec, respectively) than longer-distance arm motions (10 bits/sec). Examination of motion trajectories qualitatively supported a descriptive model whereby a visually mediated discrete-correction control process is used, as proposed by Crossman and Goodeve (Note 1) and Keele (1968). However, evidence of severe nonlinearities in the measured human movement responses did not support the use of linear control models in explaining the empirical validity of Fitts' law in predicting human motor performance.

Revised NIOSH equation for the design and evaluation of manual lifting tasks

Abstract: In 1985, the National Institute for Occupational Safety and Health (NIOSH) convened an ad hoc committee of experts who reviewed the current literature on lifting, recommend criteria for defining lifting capacity, and in 1991 developed a revised lifting equation. Subsequently, NIOSH developed the documentation for the equation and played a prominent role in recommending methods for interpreting the results of the equation. The 1991 equation reflects new findings and provides methods for evaluating asymmetrical lifting tasks, lifts of objects with less than optimal hand-container couplings, and also provides guidelines for a larger range of work durations and lifting frequencies than the 1981 equation. This paper provides the basis for selecting the three criteria (biomechanical, physiological, and psychophysical) that were used to define the 1991 equation, and describes the derivation of the individual components (Putz-Anderson and Waters 1991). The paper also describes the lifting index (LI), an index of relative physical stress, that can be used to identify hazardous lifting tasks. Although the 1991 equation has not been fully validated, the recommended weight limits derived from the revised equation are consistent with or lower than those generally reported in the literature. NIOSH believes that the revised 1991 lifting equation is more likely than the 1981 equation to protect most workers.

Motor-output variability: a theory for the accuracy of rapid motor acts.

Abstract: Theoretical accounts of the speed-accuracy trade-off in rapid movement have usually focused on within-moveme nt error detection and correction, and have consistently ignored the possibility that motor-output variability might be predictably related to movement amplitude and movement time. This article presents a theory of motor-output variability that accounts for the relationship among the movement amplitude, movement time, the mass to be moved, and the resulting movement error. Predictions are derived from physical principles; empirical evidence supporting the principles is presented for three movement paradigms (single-aiming responses, reciprocal movements, and rapid-timing tasks); and the theory and data are discussed in terms of past theoretical accounts and future research directions. Examining the current level of understanding about the production and control of motor responses, many would no doubt be tempted to say that we have not come very far since the early writings of Woodworth (1899) and Hollingworth (1909). These writers were concerned with the basic laws of limb movements (analogous, perhaps to the basic laws of motion that were the cornerstone of physics) that denned the relationship between the simplest aspects of motor

Fitts' law as a research and design tool in human-computer interaction

Abstract: According to Fitts' law, human movement can be modeled by analogy to the transmission of information. Fitts' popular model has been widely adopted in numerous research areas, including kinematics, human factors, and (recently) human-computer interaction (HCI). The present study provides a historical and theoretical context for the model, including an analysis of problems that have emerged through the systematic deviation of observations from predictions. Refinements to the model are described, including a formulation for the index of task difficulty that is claimed to be more theoretically sound than Fitts' original formulation. The model's utility in predicting the time to position a cursor and select a target is explored through a review of six Fitts' law studies employing devices such as the mouse, trackball, joystick, touchpad, helmet-mounted sight, and eye tracker. An analysis of the performance measures reveals tremendous inconsistencies, making across-study comparisons difficult. Sources of experimental variation are identified to reconcile these differences.