• Journal of the Korea Safety Management & Science
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• v.15 no.4
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• pp.123-129
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• 2013

Among various manual materials handling tasks, pushing/pulling was known to be one of the risk factors for the low back and shoulder musculoskeletal disorders (MSDs). This study was conducted to find out an optimal solution set of the handle height and distance for 4-wheel cart with two vertical handles. Ten male college students participated in the pushing force measurement experiment. The face-centered cube design, one of the central composite designs, was applied for the experiment, and the isometric voluntary pushing force was measured in 9 treatment conditions. The second order response surface model was predicted by using the pushing strength as a response variable, and the handle height and distance as independent factors. According to the 2nd order response model, the handle height and distance showed nonlinear relationship with the isometric pushing strength. To maximize the 2nd order response model (pushing force), the handle height and distance were optimized. The optimal handle height was 'xyphoid process height - stature', and the optimal handle distance was '$1.25{\times}shoulder$ width'. When calculated using the anthropometric data of the subjects of this study, the optimal handle height was $115.4{\pm}3.4$ cm, slightly higher than the elbow height, and the handle distance was $52.9{\pm}2.3$ cm.

• Journal of the Korea Safety Management & Science
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• v.16 no.4
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• pp.371-378
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• 2014

Manual materials handling tasks are the main risk factors for the work-related musculoskeletal disorders. Many assistant tools for manual materials handling are being used in various kind of industries. One of them is a 4-wheeled cart which is widely used in manufacturing factories, hospitals, etc. The major force required to control the 4-wheeled cart is pushing and pulling. There are two types of handles being used for the 4-wheeled cart : vertical type (two vertical handles), and horizontal type (one horizontal handle). This study tried to investigate the pushing forces and subjective discomforts (hand/writst, shoulder, low back, and overall) of the two handle types with different handle height and distance conditions. Twelve healthy male students (mean age = 23.4 years) participated in the experiment. The independent variables were handle angle (horizontal, vertical), handle height (low, medium, high), and handle distance (narrow, medium, wide). The full factorial design was used for the experiment and the maximum pushing forces were measured in 18 different conditions ($2{\times}3{\times}3$). Analysis of variance (ANOVA) procedure was conducted to test the effects of the independent variables on the pushing force and discomfort levels. Handle height and angle were found to be the critical design factors that affect the maximal pushing forces and subjective discomfort. In the middle height, subjects exerted higher pushing forces, and experience lower discomfort levels compared to the high, and low height. There was no statistical influence of the handle distance to the pushing forces and subjective discomfort levels. It was found out that the effects of the handle angle (horizontal and vertical) on both pushing force and subjective discomfort were statistically significant (p < 0.05). The vertical handle revealed higher pushing force and lower discomfort level than the horizontal handle. The reason for that was thought to be the different postures of the hand when grasping the handles. The horizontal handle induced pronaton of the hand and made hand posture more deviated from the neutral position.

• Safety and Health at Work
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• v.8 no.1
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• pp.11-18
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• 2017

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.

• Journal of the Ergonomics Society of Korea
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• v.32 no.4
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• pp.405-411
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• 2013

Objective: Product design process without considering the strength of the user can cause the excessive burden on musculoskeletal system of human body. Since the muscle strength will vary depending on the body posture, the design of product should consider the characteristics of body posture. This study was performed to investigate the effects of forearm postures on the push and pull strength. Background: Overexerted force has been identified to cause musculoskeletal disorders. It is important to know the push and pull strength exerted by human when designing so that exerted force does not exceed the safety limits. Method: Maximum isometric push and pull strength of left, right and both hands were measured according to forearm postures with pronation, neutral and supination. For the study, 66 male and 30 female undergraduate students were participated as subjects. All subjects were normal and healthy with no clinical history. Results: The results showed that the push strength of male and female were 93.3% and 85.4% of pull strength. It showed that the strength of one-hand was 72.1~81.0% of the strength of two-hands, and the strength of left hand was 93.1~95.8% of the strength of right hand. The strength of female was 62% of the one of male. It was found that the strength with pronation $90^{\circ}$ was reduced up to 20% compared to the strength with neutral posture. Conclusion: Push and pull strength of male and female were reduced when forearm was rotated extremely. Application: The results of this study will be used for the prevention of work related musculoskeletal disorders and design of industrial equipment.