Jeffrey E. Fernandez

The effect of upper-extremity posture on maximum grip strength

Abstract The objective of this study was to determine and document the position of peak grip strength in different shoulder, elbow, and wrist posture combinations. Fifteen (15) male subjects performed maximal exertions with their dominant hands in nine wrist postures, three elbow postures, and two shoulder postures. Analysis of the data revealed that shoulder and elbow angles had significant effect upon the grip strength. Similarly, it was seen that grip strength at elbow at 135 degrees flexion was significantly different from those with elbow at 90 and 180 degrees. Further, the results revealed that peak grip strength occurred at a combined posture of shoulder abducted 0 degrees, elbow flexed 135 degrees, and the wrist in the neutral posture. Decrements of up to 42% in grip strength could be seen as elbow and wrist angles deviated. This means that use of handtools at deviated postures of shoulder, elbow, and wrist would decrease the percent of MVC at which a worker operated. Hence, the implementation of the finding of this study might be a reduction in the risk of injury, increase in productivity, and well-being of the workers.

Psychophysical frequency for a drilling task

Abstract A laboratory experiment was conducted to determine the maximum acceptable frequency (MAF) for a simulated gripping task at different gripping forces and gripping durations using a psychophysical protocol. A modified Lafayette handgrip dynamometer was used to simulate the gripping task for twelve female subjects. Results show that MAF was significantly reduced as gripping force and gripping duration increased. Also, the various physiological responses, EMG analyses, and ratings of perceived exertion supported the MAF values obtained using the psychophysical approach. MAF values for gripping task can be applied in many industrial tasks for the reduction of risk factors for cumulative trauma disorders of the upper extremities.

Range of motion of the wrist: implications for designing computer input devices for the elderly

Purpose : The purpose of this study was to report normative values of the amplitude of joint wrist motions and grip strength for older age groups. Method : Volunteers, (N = 147) were divided into four age groups, 60-69, 70-79, 80-89 and 90+ years, with a total of 62 men and 85 women. Maximum range motion values were obtained for wrist flexion, extension and ulnar deviation. In addition, grip strength measures were obtained for each participant. Results : In general, the strength and ROM values for the oldest participants in this study were lower than those of the younger age group (age 60 to 69) and significantly lower than those published for subjects between 25 and 54 years of age. Furthermore, across all age groups males were significantly stronger than females. However, females tended to have greater ROM than males, particularly for wrist extension and ulnar deviations. Joint ROM and grip strength declined significantly with age for both males and females. Comparisons with published data for younger subjects (age 25-35) indicate that a 60-69 year old male, will on average experience a decline in wrist flexion, extension and ulnar deviation of 12%, 41%, and 22% respectively. By age 90, an individual may be expected to have ROM values that are only ¨ 60% of an average 30 year old individual. Conclusion : The results suggest that the ageing population (particularly men) may face greater difficulty using an input device such as a mouse that relies on motions of the wrist. In addition, the reduced ROM of the wrist may put the elderly at greater risk of developing cumulative trauma disorders. The implications of these findings for the design of input devices are discussed.

The need for worker training in advanced manufacturing technology (AMT) environments: A white paper

The international globalization of the World markets for manufactured goods, particularly consumer goods, has placed an emphasis on nations to improve manufacturing productivity. This need to improve productivity is further prompted by a potential loss of competitive edge in the global marketplace. The market competitiveness and e

Accessibility and ergonomic analysis of assembly product and jig designs

ciency of any nation is primarily dependent upon the economy, reliability, quality, quickness, and ease of its manufacturing processes and the resulting quality of outcomes (products). To a major extent, the skills of the workforce determine the e!ectiveness and the e

Predicting peak pinch strength: Artificial neural networks vs. regression

ciency of the process of manufacturing and the quality of goods produced. And yet, there is a severe lack of standardized and consistent worker training programs for skills needed by workers in modern manufacturing organizations. This review paper shows that there is a dire need to train workers in manufacturing organizations and thereby improve the overall e!ectiveness and e

Normative data on joint ranges of motion of 25- to 54-year-old males

ciency of such organizations. Relevance to industry As technology changes, so do the skills workers need. In order to compete successfully in the global market, manufacturing organizations must aim at training workers in skills necessary to produce quality goods. ( 1999 Elsevier Science B.V. All rights reserved.

Physiological capacities of individuals with cerebral palsy.

Abstract In the aircraft industry, the design of floor assembly jigs (FAJs) is an important activity that directly affects productivity. It involves tool frame generation and locator and clamp placement to ensure that the assembly components are held properly with respect to each other to meet the required tolerances. The tool designer also has to analyze the design to ensure that the assembly process does not pose accessibility and ergonomics related problems. The current approach is dependent on the experience of the tool designer and the limited visualization possible on commercial CAD systems. This leads to extensive redesign when accessibility and ergonomic related problems are detected on the physical prototype. In this research, an integrated Virtual Reality-based environment is being developed for the analysis of assembly product and jig designs. CAD models of the assembly product and jig are imported into a Virtual Reality (VR)-based visualization system for accessibility analysis. A motion tracking system is integrated to allow ergonomic posture analysis. The combined VR and motion tracking system allows evaluation of alternate assembly sequences and the jig design. In this paper, the theoretical basis for the analysis environment is presented along with details of the prototype implementation of this system. Relevance to industry Floor assembly jigs are used extensively by the aircraft industry. Improvement of their design process will lead to savings in better design and reduced development time and cost. Better designs will require fewer changes after the jigs have been fabricated. The overall result will be a reduction in product realization time and cost and improved product quality.

The effects of posture, duration, and force on pinching frequency

Abstract Cumulative trauma disorders (CTDs) of the upper extremities are one of the major ergonomics areas of research. Pinching is a common risk factor associated with the development of hand/wrist CTDs. The capacity standards of peak pinch strength for various postures are needed to design the tasks in harmony with the workers. This paper describes the formulation, building and comparison of pinch strength prediction models that were obtained using two approaches: Statistical and artificial neural networks (ANN). Statistical and ANN models were developed to predict the peak chuck pinch strength as a function of different combinations of five elbow and seven shoulder flexion angles, and several anthropometric and physiological variables. The two modeling approaches were compared. The results indicate ANN models to provide more accurate predictions over the standard statistical models.

Ergonomics in the workplace

The purpose of this study was to determine age-related changes of joint range of motion (ROM). Twenty-three joint ROM measurements based on descriptions given in the handbook of the American Academy of Orthopaedic Surgeons (1965) were performed bilaterally (where appropriate) on fifty-five Caucasian males. The group was divided into three age subgroups. The subgroups consisted of twenty-five to thirty-four years, thirty-five to forty-four years, and forty-five years to fifty-years old males. Motion was measured to the nearest one degree. Measurements were repeated until two readings within 4 degrees were obtained. Results indicated a decrease in joint ROM with age, with decreases from 4% to 30%. Right versus left side ROM were different for the wrist and glenohumeral joints. This implies that the aging population with reduced ROM may be at a higher risk of injury for manual material handling and cumulative trauma disorders.