Comparison of subjective comfort ratings between anatomically shaped and cylindrical handles

Effect of a Novel Adaptive Handle Design on the Ergonomic Performance of Periodontal Curettes in Dental Hygienists with and without Musculoskeletal Disorders: A Pilot Clinical Study

(1) Background: Musculoskeletal disorders (MSDs), discomfort, fatigue, pain, and other acute and chronic work-related injuries are common among dental clinicians. Hand instruments constitute a primary risk factor for these conditions. The overall goal of this study was to compare in dental hygienists with healthy hands, and in those with MSDs, the effect of three different handle designs on instrumentation-related muscle work, comfort, fatigue, and quality of tactile feedback. (2) Methods: Clinicians tested three periodontal curettes: one with a novel adaptive silicone handle, another with a rigid resin handle, and the third with a rigid silicone handle. Ten hygienists-five with MSDs and five without-each scaled three typodonts using the three different curettes. Statistical analysis was performed using a General Linear Model (GLIM) and Tukey's post hoc test, and a significance level of p < 0.05 was implemented. (3) Results: On average, mean comfort and fatigue across all instruments were significantly worse in testers with MSDs, who also expended significantly more work to complete the same task. In all testers, a novel adaptive handle design was associated with significantly reduced total muscle work and post-instrumentation fatigue, as well as better comfort than conventional rigid handle designs. (4) Conclusions: An adaptive curette handle design demonstrated significantly better ergonomic outcomes than conventional rigid curette handle designs. Hygienists with MSDs expend significantly more muscle work during dental instrumentation.

The effects of umbrella handle shape and grip type on muscle activation and postural variability under windy conditions

This study investigated how different shapes of umbrella handles and grip types influence muscle activation and postural variability under windy conditions. Seventeen adult participants were enrolled in this study, and different handle shapes (cylindrical, ellipsoidal, and triangular prism-shaped), grip types (four- and five-finger grip), and wind strengths were tested. Activation of the forearm and upper arm muscles was recorded using surface electromyography. Postural variability and ratings of (1) perceived difficulty of use and (2) perceived grip-posture variability were measured. The results indicated that activation of the finger flexor muscle increased under windy conditions, whereas postural variability was not affected. Weak wind (3.2-7.5 m/s) conditions caused greater perceived postural variability and activation of the wrist extensor muscle. The ellipsoidal handle shape had lower endpoint postural variability when held with a five-finger grip and also had lower perceived postural variability and difficulty compared to that with the cylindrical shape. Our findings can be used to select appropriate umbrella handle designs based on grip type and wind conditions.

A Novel Ergonomic Curette Design Reduces Dental Prophylaxis-Induced Muscle Work and Fatigue

BACKGROUND

To compare fatigue, comfort, and muscle work associated with the use of two periodontal curettes during scaling: one with a novel adaptive design, the other with a conventional non-adaptive design.

METHODS

Twelve hygienists scaled a typodont using two Universal Barnhart 5/6 curettes: (1) a prototype featuring an adaptive silicone-covered handle (Curette A), and (2) a stainless-steel curette (Curette B). Surface Electromyography (sEMG) traced muscle work. Hand positions, fatigue, comfort, pinch, and grasp strength were recorded. Paired t-tests and a repeated measures ANOVA with covariates were tested for differences. The significance level was set at p < 0.05.

RESULTS

Curette A performed significantly better in all categories. Pinch and grasp strength and fatigue were significantly reduced post-instrumentation for Curette B. Curette A required significantly less (i) total muscle work and (ii) work in individual muscles. Comfort, correct grasp, and blade adaptation were significantly better using Curette A.

CONCLUSIONS

A curette featuring a novel adaptive handle design demonstrated significantly improved ergonomic performance. Additional clinical studies are needed to solidify our understanding of the potential short- and long-term benefits of the novel curette handle design.

PRACTICAL IMPLICATIONS

A novel adaptive curette handle design that enables the clinician to adapt the instrument across the index finger may reduce musculoskeletal burden and fatigue, as well as improve comfort during periodontal instrumentation.

Force Control Strategy of Five-Digit Precision Grasping With Aligned and Unaligned Configurations

OBJECTIVE

To investigate the digit force control during a five-digit precision grasp in aligned (AG) and unaligned grasping (UG) configurations.

BACKGROUND

The effects of various cylindrical handles for tools on power grasp performance have been previously investigated. However, there is little information on force control strategy of precision grasp to fit various grasping configurations.

METHOD

Twenty healthy young adults were recruited to perform a lift-hold-lower task. The AG and UG configurations on a cylindrical simulator with force transducers were adjusted for each individual. The applied force and moment, the force variability during holding, and force correlations between thumb and each finger were measured.

RESULT

No differences in applied force, force correlation, repeatability, and variability were found between configurations. However, the moments applied in UG were significantly larger than those in AG.

CONCLUSION

The force control during precision grasp did not change significantly across AG and UG except for the digit moment. The simulator is controlled efficiently with large moment during UG, which is thus the optimal configuration for precision grasping with a cylindrical handle. Further research should consider the effects of task type and handle design on force control, especially for individuals with hand disorders.

APPLICATION

To design the handle of specific tool, one should consider the appropriate configuration according to the task requirements of precision grasping to reduce the risk of accumulating extra loads on digits with a cylindrical handle.

A novel sensor-embedded holding device for monitoring upper extremity functions

There are several causes that can lead to functional weakness in the hands or upper extremities (UE), such as stroke, trauma, or aging. Therefore, evaluation and monitoring of UE rehabilitation have become essential. However, most traditional evaluation tools (TETs) and assessments require clinicians to assist or are limited to specific clinical settings. Several novel assessments might apply to wearable devices, yet those devices will still need clinicians or caretakers to help with further tests. Thus, a novel UE assessment device that is user-friendly and requires minimal assistance would be needed. The cylindrical grasp is one of the common UE movements performed in daily life. Therefore, a cylindrical sensor-embedded holding device (SEHD) for training and monitoring was developed for a usability test within this research. The SEHD has 14 force sensors with an array designed to fit holding positions and a six-axis inertial measurement unit (IMU) to monitor grip strength, hand dexterity, acceleration, and angular velocity. Six young adults, six healthy elderly participants, and three stroke survivors had participated in this study to see if the SEHD could be used as a reference to TETs. During result analyses, where the correlation coefficient analyses were applied, forearm rotation smoothness and the Purdue Pegboard Test (PPT) showed a moderate negative correlation [r (16) = −0.724, p < 0.01], and the finger independence showed a moderate negative correlation with the PPT [r (10) = −0.615, p < 0.05]. There was also a highly positive correlation between the maximum pressing task and Jamar dynamometer in maximum grip strength [r (16) = 0.821, p < 0.01]. These outcomes suggest that the SEHD with simple movements could be applied as a reference for users to monitor their UE ability.

Evaluation of the bio-dynamic response of the hand-arm system and hand-tool designs - A brief review

Hand-operated tools transmit a high magnitude of vibration exposure to the hand-arm system that causes occupational diseases. The health effects caused in various countries for the past years due to usage of hand tools are necessary to identify the occupational disorders. Researchers have conducted various studies on biological effects, hand-transmitted vibration exposure and biodynamic responses throughout the years. This article goes over each of these studies in detail, as well as identifying areas where more research is needed. The majority of studies deal with the following topics: general guidelines for hand-transmitted vibrations; assessment techniques of vibration exposure; hand-tool evaluation methods; influence of hand-tool design to overcome the biomechanical effects; and finite element modelling for quantifying vibration exposure. In response to this, understanding the biodynamic behaviour of the hand-arm system is useful for better ergonomic intervention in hand tools to reduce fatigue and increase comfort.

The contact length parameter as a geometric factor for user-centered design of pistol grip geometries of power tools

In this study the geometric parameter of the contact length is introduced, which intends to combine force exertion and perceived handle comfort in an anthropometric length in order to determine an optimal handle circumference. To prove suitability of the approach, 31 subjects were determined and correlations to handle circumferences with the highest finger forces and highest rated comfort were investigated. For all fingers, medium correlations were found among the contact lengths and the circumferences determined with maximum force (p < 0.001, r_index = 0.348, r_middle = 0.419, r_ring = 0.374 and r_little = 0.337) with high accordance of median values. Weak to moderate correlations were found between circumferences with maximum comfort and the contact lengths (p < 0.001, r_index = 0.150, r_middle = 0.265, r_ring = 0.174). Using finger-specific proportionality factors, the contact lengths can be determined directly from the hand lengths, which enables great benefits for user-centered design.

Identify dominant dimensions of 3D hand shapes using statistical shape model and deep neural network

Hand anthropometry is one of the fundamentals of ergonomic research and product design. Many studies have been conducted to analyze the hand dimensions among different populations, however, the definitions and the numbers of those dimensions were usually selected based on the experience of the researchers and the available equipment. Few studies explored the importance of each hand dimension regarding the 3D shape of the hand. In this paper, we aim to identify the dominant dimensions that influence the hand shape variability while considering the stability of the measurements in practice. A novel four-step research method was proposed where in the first step, based on literature study, we defined 58 landmarks and 53 dimensions for the exploration. In the second step, 80,000 virtual hand models, each had the associated 53 dimensions, were augmented by changing the weights of Principle Components (PCs) of a statistical shape model (SSM). Deep neural networks (DNNs) were used to establish the inverse relationships from the dimensions to the weight of each PC of the hand SSM. Using the structured sparsity learning method, we identified 21 dominant dimensions that represent 90% of the variance of the hand shape. In the third step, two different manual measuring methods were used to evaluate the stability of the measurements in practice. Finally, we selected 16 dominant dimensions with lower measurement variance by synthesizing the findings in Step 2 and 3. It was concluded that the recognized 21 dominant dimensions can be treated as the reference dimensions for anthropometric study and using the selected 16 dominant dimensions with lower measurement variance, ergonomists are able to generate a 3D hand model based on simple measurement tools with an accuracy of 5.9 mm. Though the accuracy is limited, the efforts are minimum, and the results can be used as an indicator in the early stage of research/design.

Prevalence and severity of carpal tunnel syndrome symptoms among Iranian butchers and their association with occupational risk factors: Implications for ergonomic interventions

BACKGROUND

Carpal tunnel syndrome (CTS) is a common disorder among occupations where upper extremities are actively involved in. Many occupational and non-occupational risk factors may contribute to this disorder. Knowledge regarding occupational risk factors can guide us to implement interventional programs.

OBJECTIVE

The aim of the present study was to assess the prevalence and severity of CTS symptoms among butchers and their association with several occupational and non-occupational risk factors.

METHODS

In this study, 152 butchers in Hamadan, Iran, were examined. The Boston Carpal Tunnel Syndrome Questionnaire (BCTQ) was used to investigate the severity of CTS symptoms among the individuals. Several risk factors such as body mass index (BMI), wrist ratio, active working hours per day, working experience, and the ergonomic quality of hand tools used by butchers were also investigated. Statistical tests such as the crude and robust regression were used to analyze the data.

RESULTS

The prevalence of moderate and mild symptoms of CTS were 7% and 54%, respectively. Moreover, 39% of the butchers were free of CTS symptoms. Crude regression analyses showed that the severity of CTS symptoms had a significant relationship with age, work experience, active working hours per day, working hours per week, and ergonomic quality of the hand tools (p value <0.05). There was no significant relationship between the severity of CTS symptoms and wrist ratio and BMI. Results of the robust regression analysis showed a significant relationship between the severity of CTS symptoms with experience, active working hours, and quality of the hand tools.

CONCLUSION

Occupational risk factors such as working experience, active working hours per day, and the ergonomic quality of hand tools are significant risk factors of CTS symptoms among butchers. Slippery handle is the main non-ergonomic feature of knives and cleavers used by butchers. There was no association between BMI and wrist ratio with CTS symptoms.

Comparative Study of the Use of Different Sizes of an Ergonomic Instrument Handle for Laparoscopic Surgery

Previous studies have shown that the handle design of laparoscopic instruments is crucial to surgical performance and surgeon’s ergonomics. In this study, four different sizes of an ergonomic laparoscopic handle design were tested in a blind and randomized fashion with twelve surgeons. They performed three laparoscopic tasks in order to analyze the influence of handle size. Execution time, wrist posture, and finger and palm pressure were evaluated during the performance of each task. The results show a significant reduction in the time required to complete the eye-manual coordination task using the appropriate handle. The incorrectly sized handle resulted in a rise in palm pressure and a reduction in the force exerted by the thumb during the transfer task. In the hand-eye coordination task, the use of the right handle size led to an increase in middle finger pressure. In general, surgeons had an ergonomically adequate wrist flexion in all tasks and an acceptable radio-ulnar deviation during the transfer task using the ergonomic instrument handle. Surgeons found it comfortable the use of the ergonomic handle. Therefore, the use of an appropriately sized instrument handle allows surgeons to improve ergonomics and surgical performance during the laparoscopic practice.

Evaluation of two wheelchair hand rim models: contact pressure distribution in straight line and curve trajectories

Manual wheelchairs are essential for people with disabilities or limited mobility. However, manual propulsion causes biomechanical loads, including contact pressures on the palms of the hands. The hand rim design has received little attention over time, remaining almost unchanged since its creation. This study investigated how two different designs of such devices - one standard and another with a contoured design - influence the contact pressure on the surface of the hands. The procedures included a figure-of-eight shape propulsion task on a regular floor, using both models on a wheelchair. A pressure-mapping system coupled with a pair of fabric gloves recorded the data. The results show that the contoured hand rim provides lower pressure in most of the analysed regions. Considering that manual propulsion is performed during a considerable part of the day as a routine activity, improving the hand rim interface may benefit the user's comfort and safety during wheelchair use. Practitioner summary: The design of the hand rim used in wheelchair propulsion influences the contact pressure on the hands. Conventional round tube rims tend to concentrate high levels of pressure on the distal phalanges and metacarpal regions. A contoured design generally provides better stability and promotes the distribution of pressure. Abbreviations: AT: assistive technology; kPa: kilopascal.

A novel anatomical woodworking chisel handle

A novel anatomically shaped ("anatomical") woodworking chisel handle was developed for wood scraping operation. 18 students participated in an evaluation study to compare the new handle against seven readymade handles of ¾-inch bench chisels in the context of a standard wood scraping task. A comfort questionnaire for hand tools (CQH) and a hand-based pain map were used for evaluating and comparing the handles. 'Functionality' and 'sweating' were found to be the most and least important comfort concerns, respectively. Maximum pain was reported at distal digit 1, and least pain at proximal digit 4. The anatomical handle was rated best for most of the comfort descriptors, least painful for most hand regions and took the least time for a standardized task.

Electromyographic evaluation of different handle shapes of masons' trowels

The effects of five different handle shapes of masons' trowels on muscle activity of the arm and forearm muscles (through electromyographic measurements of the biceps brachii [BB], flexor digitorum superficialis [FDS], pronator teres [PT] and extensor carpi ulnaris [ECU]) were evaluated in a simulated masonry task. The results showed a significant effect of handle shape on the muscle activity of the BB, PT and ECU. The muscle activity of the extensor (ECU) and flexor (FDS) were generally larger than those of the supinator (BB) and pronator (PT). Some improvements were found in terms of muscular exertions with prototype designs C, D and E, which had either handles with variable diameter (designs C and E) or a slightly bent handle (design D). These findings have practical implications for the design of single-handle hand tools but may need further validation for specific contexts of use.

An Ergonomic Customized-Tool Handle Design for Precision Tools using Additive Manufacturing: A Case Study

A study was carried out with 135 surgeons to obtain a surgical laparoscopic grasper handle design that adapts to the size of each surgeon’s hand, in a functionally appropriate way, and has the sufficient ergonomics to avoid generating the problems detected nowadays. The main conclusion of the work is the practical 3D parametric design obtained for a laparoscopic surgical graspers handle that is scalable to fit each particular surgeon's hand size. In addition, it has been possible to determine that the anthropometric measure of the surgeon's hand defined as Palm Length Measured (PLM) allows the design of the 3D parametric model of the surgical handle to be conveniently scaled. The results show that both additive manufacturing and the application of ergonomics criterion provide an efficient method for the custom design and manufacture of this type of specialised tool, with potential application in other sectors.

Effects of the center of mass of a stick vacuum cleaner on the muscle activities of the upper extremity during floor vacuuming

Cordless stick vacuum cleaners on the market have two distinctive styles. One with the center of mass (CoM) near user's hand and the other with the CoM near the brush. The main objective of this study was to determine whether the CoM would affect the muscle activities of upper extremity during floor vacuuming. Twenty-four participants conducted floor vacuuming strokes on carpeted floor and tiled floor at two different speeds with a 2.57 kg stick cleaner model with the CoM near its handle and near its brush. The 50^th %-ile muscle activities ranged from 5.4% to 16.3% of the maximum activity level (mild to moderate intensity), with significantly greater activities (p < 0.05) when vacuuming with the high CoM model. Study results suggest that conventional low CoM stick cleaners are preferable to high CoM stick cleaners to lower physical loads to user's upper extremity muscles for floor vacuuming.

Ergonomics investigation for orientation of the handles of wood routers

OBJECTIVES

Improperly designed hand tools not only expose workers to potential health risks but also hamper their productivity. This study tries to improve the ergonomics of wood routing tasks, suggesting better handle orientations for hand-held wood routers.

METHODS

Seven different handle combinations were tested over two routing tasks (beading and dado) with regard to perceived discomfort, electromyography (EMG) of biceps brachii and extensor carpi radialis brevis and hand-arm vibrations (HAV).

RESULTS

Handles with 30° and 60° inclinations were found more comfortable than previous 90° handle inclinations for routing tasks. Perceived discomfort in the dado task was found to be significantly higher than in the beading task (p < 0.001); EMG activity also supported this observation. However, EMG data showed no significant difference for the different handles used in the study. No worthwhile reduction was obtained in HAV levels for the modified wooden handles compared to initial plastic handles. Relevance to industry. The ergonomic intervention in wood routers described in this article will contribute to the existing knowledge of ergonomics of handle design and will aid the designers/engineers to design such tool handles that may reduce the risk of work-related musculoskeletal disorders/hand-arm vibration syndrome in workers using wood routers.

Effects of tool handle dimension and workpiece orientation and size on wrist ulnar/radial torque strength, usability and discomfort in a wrench task

The effects of tool handle dimension (three modified designs of wrenches with 30-50 mm diameter cylindrical handles and traditional design with rectangular cross-sectional (5 mm × 25 mm) handle), workpiece orientation (vertical/horizontal) and workpiece size (small/large) as well as user's hand size on wrist ulnar/radial (U/R) torque strength, usability and discomfort, and also the relationship between these variables were evaluated in a maximum torque task using wrenches. The highest and lowest levels of maximal wrist U/R torque strength were recorded for the 30 mm diameter handle and traditional wrench design, respectively. The prototype handle with 30 mm diameter, together with 40 mm diameter handle, was also better than other designs as they received higher usability ratings and caused less discomfort. The mean wrist torque strength exerted on a vertically oriented workpiece (in the sagittal plane) was 23.8% higher than that exerted on a horizontally oriented one (in the transverse plane). The user's hand size had no effect on torque exertions. The wrist torque strength and usability were negatively correlated with hand and finger discomfort ratings. The results are also discussed in terms of their implications for hand tool and workstation configuration in torque tasks involving wrenches.

Using subject-specific three-dimensional (3D) anthropometry data in digital human modelling: case study in hand motion simulation

Digital human modelling enables ergonomists and designers to consider ergonomic concerns and design alternatives in a timely and cost-efficient manner in the early stages of design. However, the reliability of the simulation could be limited due to the percentile-based approach used in constructing the digital human model. To enhance the accuracy of the size and shape of the models, we proposed a framework to generate digital human models using three-dimensional (3D) anthropometric data. The 3D scan data from specific subjects' hands were segmented based on the estimated centres of rotation. The segments were then driven in forward kinematics to perform several functional postures. The constructed hand models were then verified, thereby validating the feasibility of the framework. The proposed framework helps generate accurate subject-specific digital human models, which can be utilised to guide product design and workspace arrangement. Practitioner Summary: Subject-specific digital human models can be constructed under the proposed framework based on three-dimensional (3D) anthropometry. This approach enables more reliable digital human simulation to guide product design and workspace arrangement.

Can Prior Experience Influence Seating Comfort Ratings?

Most research on product comfort focuses exclusively on the use of the evaluated product (e.g., Kyung, Nussbaum, & Babski-Reeves, 2008; Harih & Dolšak (2013). We sought to investigate the influence of a sitting precondition on ratings for first impression of comfort, short-term comfort, and discomfort of a product. The aim was to assess if and how sensations experienced prior to product use affected product evaluation. Therefore, a vehicle seat was evaluated with two preconditions in a within-subjects design. The comfort model of Vink and Hallbeck was extended according to the findings of this study.

A better way of fitting clips? A comparative study with respect to physical workload

The clip fitting task is a frequently encountered assembly operation in the car industry. It can cause upper limb pain. During task laboratory simulations, upper limb muscular activity and external force were compared for 4 clip fitting methods: with the bare hand, with an unpowered tool commonly used at a company and with unpowered and powered prototype tools. None of the 4 fitting methods studied induced a lower overall workload than the other three. Muscle activity was lower at the dominant limb when using the unpowered tools and at the non-dominant limb with the bare hand or with the powered tool. Fitting clips with the bare hand required a higher external force than fitting with the three tools. Evaluation of physical workload was different depending on whether external force or muscle activity results were considered. Measuring external force only, as recommended in several standards, is insufficient for evaluating physical workload.

Finite element evaluation of the effect of fingertip geometry on contact pressure during flat contact

Several studies investigated the mechanical loads developing in the hands during the use of various products in order to enhance user's performance, increase satisfaction and lower the risk of acute and cumulative trauma disorders. Values of pressure discomfort (PDT) and pressure-pain threshold (PPT) were, hence, provided. PDT and PPT may differ significantly for each subject and area of the hand because of psychological and physiological factors. A finite element study of the effect of fingertip anthropometry and anatomy geometry on mechanical loads developed during grasping is carried out in this research in order to assess physiological aspects behind variations of PDT and PPT existing between different subjects. It is found that the underlying anatomical structure and geometry (especially of the bone) significantly affect contact pressure distributions and pressure peak values. The largest difference in peak contact pressure between two different fingertips was in fact 27% for the same applied force. Furthermore, contact pressure distributions varied significantly between different subjects. The findings of this research provide novel insight into the phenomena of human grasping and the variation of contact pressure from subject to subject.