The Influence of Task Frequency and Force Direction on Psychophysically Acceptable Forces in the Context of Biomechanical Weakest Links (original) (raw)
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This research investigated if proportional relationships between psychophysically acceptable and maximum voluntary hand forces are dependent on the underlying biomechanical factor (i.e. whole body balance or joint strength) that limited the maximum voluntary hand force. Eighteen healthy males completed two unilateral maximal exertions followed by a 30 min psychophysical load-adjust protocol in each of nine pre-defined standing scenarios. Center of pressure (whole body balance) and joint moments (joint strength) were calculated to evaluate whether balance or joint strength was most likely limiting maximum voluntary hand force. The ratio of the psychophysically acceptable force to the maximal force was significantly different depending on the underlying biomechanical factor. Psychophysically acceptable hand forces were selected at 86.3 ± 19.7% of the maximum voluntary hand force when limited by balance (pulling exertions), 67.5 ± 15.2% when limited by joint strength (downward pressing) and 78 ± 23% when the limitation was undefined in medial exertions.
Observational Assessment of Forceful Exertion and the Perceived Force Demands of Daily Activities
Journal of Occupational Rehabilitation, 2004
The primary objective of this study was to assess the accuracy and precision with which analysts observe and estimate the force produced as subjects performed exertions on a work simulator. Eight analysts observed 32 subjects and estimated force as a percent of subjects' maximum voluntary contraction (% MVC). Analysts exhibited bias toward the mean, as high force exertions (>67% MVC) were underestimated (mean: 11.6% MVC) and low force exertions (<34% MVC) were overestimated (mean: 6.7% MVC). Average error for medium force exertions (34-67% MVC) was not statistically different from zero (2.1% MVC). For all force levels, precision of the estimate was very poor (standard deviation range: 16.2-20.7% MVC). Experience of the analyst in performing ergonomic analysis did not affect accuracy. A secondary objective of the study was to conduct a survey in which subjects identified activities of daily living they perceived as equivalent to controlled force levels. A total of 59 different activities ranging from minimal force required to near maximum were listed by at least 5% of the participants. This list may be used to assist health care practitioners and patients convey the force demands required of occupational tasks as well as for evaluating the diminished strength of the patient.
Evaluation of perceived and self-reported manual forces exerted in occupational materials handling
Applied Ergonomics, 1996
The main objective of the study was to evaluate the ability of workers to reproduce simulated manual work forces correctly and to quantify these forces in Newtons (N) by means of selfreports. Fourteen male and 14 female workers participated in the study. Three experiments were carried out. In the first experiment, the ability to reproduce the magnitudes of simulated manual forces occurring in daily work and to estimate these forces in Newtons was tested. A specially designed force-measuring device was used for this purpose. In the second experiment, the subjects estimated the weights of five boxes ranging from 1 to 30 kg. In the third experiment, the subjects were asked to produce five predetermined push and pull forces ranging in magnitude from 10 to 300 N on to the handle of the force-measuring device. The ability to reproduce the magnitudes of manual forces when simulating four familiar work tasks was good (the intraclass correlation coefficients ranged from 0.75 to 0.95). The ability to quantify these forces in Newtons was not as good (the product moment correlation coefficients ranged from 0.21 to 0.69). When the subjects estimated the weights of boxes they underestimated the weights. When they produced predetermined push and pull forces they exerted higher forces than expected when low force levels were requested, and lower forces when high force levels were requested. However, the forces were correctly ranked. In summary, simulation of the manual push/pull forces used in familiar work tasks seemed to offer sufftcient reproducibility to be worth testing for validity. Self-reports, used without previous training or without known 'reference forces', seemed to be very rough when the aim was to estimate in kg or Newtons. However, the fact that individuals could rank the forces correctly opens a potential for refinement of self-reports as a method for quantifying manual forces in objective terms, e.g. kg or Newtons.
Ergonomics, 2012
The objective of this study was to investigate potential associations between an individual's psychophysical maximum acceptable force (MAF) during pushing tasks and biomechanical tissue loads within the lumbar spine. Ten subjects (eight males, two females) pushed a cart with an unknown weight at one push every two minute for a distance of 3.9 m. Two independent variables were investigated, cart control and handle orientation while evaluating their association with the MAF. Dependent variables of hand force and tissue loads for each MAF determination and preceding push trial were assessed using a validated, electromyography-assisted biomechanical model that calculated spinal load distribution throughout the lumbar spine. Results showed no association between spinal loads and the MAF. Only hand forces were associated with the MAF. Therefore, MAFs may be dependent upon tactile sensations from the hands, not the loads on the spine and thus may be unrelated to risk of low back injury.
Psychophysical basis for maximum pushing and pulling forces: A review and recommendations
International Journal of Industrial Ergonomics, 2012
The objective of this paper was to perform a comprehensive review of psychophysically determined maximum acceptable pushing and pulling forces. Factors affecting pushing and pulling forces are identified and discussed. Recent studies show a significant decrease (compared to previous studies) in maximum acceptable forces for males but not for females when pushing and pulling on a treadmill. A comparison of pushing and pulling forces measured using a high inertia cart with those measured on a treadmill ...
Proceedings of the Human Factors and Ergonomics Society Annual Meeting
Force and frequency in manual handling tasks are known risk factors for work related upper arm disorders. Three force levels and three frequencies are used to define the external load in a pinching task. The effects of these external loads on subjective and objective responses are studied. Subjective ratings poorly reflect the levels of external load. EMG variables P50 en P10 of the prime mover muscle seem useful variables in evaluating the effects of task frequency above a certain threshold in task frequency. P90 of the prime mover muscle is useful in evaluating the effects of external forces. It can be concluded that the P50 does not reflect the differences in force levels in tasks with low intensities.
International Journal of Industrial Ergonomics, 2014
This paper examines an approach to modeling the relationship between perceived acceptable work exposures and physical stressors in upper-extremity tasks using psychophysical methods. Several years of laboratory-based studies and results from a variety of simulated work tasks and task elements are summarized. The original impetus of these studies was founded in the pioneering work and successful application of psychophysical methods applied to manual materials handling tasks (e.g., lifting) generally beginning in the 1960s and 1970s. This approach provided unique and feasible solutions to work design problems involving exposure to the hazard of cumulative trauma. Presently, these methods were adapted to studying common upper-extremity tasks and task elements. Results provide conclusive evidence of the impact of required posture, force, gender and other variables on acceptable task frequency. These results and the psychophysical method in general, may be particularly helpful in establishing realistic and reasonable work design guidelines when workers are exposed to multiple, simultaneous hazards such as force, frequency, with deviated posture, etc, and in the absence of well-defined biomechanical or physiological-based models. Finally, a review of psychophysical theory and methods which can be applied to a wide range of occupational activities is provided. Relevance to industry: Psychophysical methods have been utilized for realistic work design guidelines for jobs with risk of musculoskeletal disorders, particularly the low back. This paper summarizes psychophysical methods and results developed for upper-extremity tasks. Required task frequencies should be reduced when postural deviation, required force, and other factors such as vibration, are greater than nominal.
Safety and Health at Work, 2016
The purpose of this review is to name and describe the important factors of musculoskeletal strain originating from pushing and pulling tasks such as cart handling that are commonly found in industrial contexts. A literature database search was performed using the research platform Web of Science. For a study to be included in this review differences in measured or calculated strain had to be investigated with regard to: (1) cart weight/ load; (2) handle position and design; (3) exerted forces; (4) handling task (push and pull); or (5) task experience. Thirteen studies met the inclusion criteria and proved to be of adequate methodological quality by the standards of the Alberta Heritage Foundation for Medical Research. External load or cart weight proved to be the most influential factor of strain. The ideal handle positions ranged from hip to shoulder height and were dependent on the strain factor that was focused on as well as the handling task. Furthermore, task experience and subsequently handling technique were also key to reducing strain. Workplace settings that regularly involve pushing and pulling should be checked for potential improvements with regards to lower weight of the loaded handling device, handle design, and good practice guidelines to further reduce musculoskeletal disease prevalence.
Ergonomics, 2018
Though biomechanically determined guidelines exist for lifting, existing recommendations for pushing and pulling were developed using a psychophysical approach. The current study aimed to establish objective hand force limits based on the results of a biomechanical assessment of the forces on the lumbar spine during occupational pushing and pulling activities. Sixty-two subjects performed pushing and pulling tasks in a laboratory setting. An electromyography-assisted biomechanical model estimated spinal loads, while hand force and turning torque were measured via hand transducers. Mixed modelling techniques correlated spinal load with hand force or torque throughout a wide range of exposures in order to develop biomechanically determined hand force and torque limits. Exertion type, exertion direction, handle height and their interactions significantly influenced dependent measures of spinal load, hand force and turning torque. The biomechanically determined guidelines presented here...
International Journal of Industrial Ergonomics, 2007
The purpose of this experiment was to replicate a previous psychophysical experiment . Maximum acceptable forces of dynamic pushing: comparison of two techniques. Ergonomics 42, 32-39] which investigated maximum acceptable initial and sustained forces while performing a 7.6 m pushing task at a frequency of 1 min À1 on a magnetic particle brake treadmill versus pushing on a high-inertia pushcart. Fourteen male industrial workers performed both a 40-min treadmill pushing task and a 2-h pushcart task, with a unique water loading system, in the context of a larger experiment. During pushing, the subjects were asked to select a workload they could sustain for 8 h without ''straining themselves or without becoming unusually tired, weakened, overheated or out of breath.'' The results revealed that similar to the previous study maximum acceptable sustained forces of pushing determined on the high inertia cart were significantly higher (21%) than the forces determined from the magnetic particle brake treadmill. These results were countered by an 18% decrease in maximum acceptable forces for the criterion magnetic particle brake treadmill task, perhaps due to secular changes in the industrial population. Based on the present findings, it is concluded that the existing pushing data [Snook, S.H., Ciriello, V.M., 1991. The design of manual tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34, 1197-1213] still provides an accurate estimate of maximal acceptable forces for this pushing distance and frequency.