Handle grip span for optimising finger-specific force capability as a function of hand size

Lee, Soo-Jin,Kong, Yong-Ku,Lowe, Brian D.,Song, Seongho Taylor Francis 2009 Ergonomics Vol.52 No.5

<P> Five grip spans (45 to 65 mm) were tested to evaluate the effects of handle grip span and user's hand size on maximum grip strength, individual finger force and subjective ratings of comfort using a computerised digital dynamometer with independent finger force sensors. Forty-six males participated and were assigned into three hand size groups (small, medium, large) according to their hands' length. In general, results showed the 55- and 50-mm grip spans were rated as the most comfortable sizes and showed the largest grip strength (433.6 N and 430.8 N, respectively), whereas the 65-mm grip span handle was rated as the least comfortable size and the least grip strength. With regard to the interaction effect of grip span and hand size, small and medium-hand participants rated the best preference for the 50- to 55-mm grip spans and the least for the 65-mm grip span, whereas large-hand participants rated the 55- to 60-mm grip spans as the most preferred and the 45-mm grip span as the least preferred. Normalised grip span (NGS) ratios (29% and 27%) are the ratios of user's hand length to handle grip span. The NGS ratios were obtained and applied for suggesting handle grip spans in order to maximise subjective comfort as well as gripping force according to the users' hand sizes. In the analysis of individual finger force, the middle finger force showed the highest contribution (37.5%) to the total finger force, followed by the ring (28.7%), index (20.2%) and little (13.6%) finger. In addition, each finger was observed to have a different optimal grip span for exerting the maximum force, resulting in a bow-contoured shaped handle (the grip span of the handle at the centre is larger than the handle at the end) for two-handle hand tools. Thus, the grip spans for two-handle hand tools may be designed according to the users' hand/finger anthropometrics to maximise subjective ratings and performance based on this study. Results obtained in this study will provide guidelines for hand tool designers and manufacturers for designing grip spans of two-handle tools, which can maximise handle comfort and performance.</P>

Evaluation of Gender Effect in Various Pliers' Grip Spans for Maximum Isometric Grasping Tasks

Yong-Ku Kong,Dae-Min Kim,Ji-Soo Park,Sung-Yong Lee,Kyeong-Hee Choi,Kyung Ran Kim 대한인간공학회 2014 大韓人間工學會誌 Vol.33 No.6

Objective: The purpose of this study was to evaluate the effect of gender (male, female) and grip spans (45, 50, 60, 70, 80mm) on total grip strength, resultant force, finger force and subjective discomfort ratingI. Background: In order to prevent musculoskeletal disorders, studies of hand tools need to be preceded based on grip strength, finger force, and subjective discomfort rating. However, experimental apparatus using tools such as pliers that reflect the actual work place was almost non-existent. Method: Fifty-Two (26 males and 26 females) participants were recruited from the student population. In this study, a pair of revised pliers, which can change grip span from 45 to 80mm was applied to estimate total grip strength, resultant force and individual finger forces. All participants were asked to exert a maximum grip force with three repetitions, and to report the subjective discomfort rating for five grip spans of pliers (45, 50, 60, 70, 80mm). Results: There were significant differences of total grip strength, resultant force, individual finger forces and subjective discomfort rating according to grip span. The lowest total grip strength was obtained from the grip span of 80mm for both genders. For resultant force, the highest resultant force was exerted at grip spans of 50, 60 and 70mm for females and 50 and 60mm for males. The lowest subjective discomfort rating was observed in the 50mm for both genders. Conclusion: Based on the result, 50mm and 60mm grip spans which provide the highest force and lowest discomfort rating might be recommendable for the male and female pliers users. Application: The findings of this study can provide guidelines on designing a hand tool to help to reduce hand-related musculoskeletal disorders and obtain better performance.

MFFM System을 이용한 손가락 별 파지 폭들의 변화에 따른 악력 및 개인 선호도에 대한 연구

김대민(Dae Min Kim),공용구(Yong?Ku Kong) 대한인간공학회 2008 大韓人間工學會誌 Vol.27 No.3

Individual finger/total grip forces, and subjective preferences for various individual finger grip spans (i.e., four fingers had identical grip spans or different grip spans) were evaluated by using an "Adjustable Multi-Finger Force Measurement (MFFM) System". In this study, three grip spans were defined as follows: a 'favorite grip span' which is the span with the highest subjective preference; a 'maximum grip span' which is the span with the highest total grip force; a 'maximum finger grip span' which is a set of four grip spans that had maximum finger grip forces associated with the index, middle, ring, and little fingers, respectively. Ten males were recruited from university population for this study. In experiment I, each participant tested the maximum grip force with five grip spans (45 to 65㎜) to investigate grip forces and subjective preferences for three types of grip spans. Results showed that subjective preferences for grip spans were not coincidence with the performance of total grip forces. It was noted that the 'favorite grip span' represented the lowest total grip force, whereas the 'maximum finger grip span' showed the lowest subjective preferences. The individual finger forces and the average percentage contribution to the total finger force were also investigated in this study. The findings of this study might be valuable information for designing ergonomics hand-tools to reduce finger/hand stress as well as to improve tool users' preferences and performance.

Optimal Grip Span of A-type Pliers in a Maximum Gripping Task

Yong-Ku Kong,Jin Woo Jung,Sangmin Kim,Heewoong Jung,Hakje Yoo,Dae-Min Kim,Hyun-Sung Kang 대한인간공학회 2013 大韓人間工學會誌 Vol.32 No.6

Objective: The objective of this study is designing an optimal hand tool through maximum grip force study accordance to the hand grip span. Background: In order to prevent musculoskeletal diseases, studies on hand tool design are proceeding based on grip strength, finger force, and contribution of individual finger force on total grip strength. However, experimental apparatus using a tool that is actually used in work place was almost non-existent. Method: 19 males were participated in an experiment. Using the load cell inserted real plier, finger force, grip strength, and subjective discomfort rate of both hands (dominant and non-dominant) were measured in 5 different hand grip span(45mm, 50mm, 60mm, 70mm, and 80mm). Results: There was significant difference(p<0.001) of total grip strength, individual finger force and subjective discomfort rating according to various hand grip span(45, 50, 60, 70, and 80mm). Also, statistically significant different(p<0.001) was shown between the dominant hand and non-dominant hand. In addition, individual finger force in maximum grip was in order of middle finger, ring finger, index finger, and little finger. Conclusion: Optimal grip span of pliers that exerting maximum grip strength is 50~60mm. Application: This finding is expected to be used for designing proper pliers.

Biomechanical analysis of grip span and tendon force ratio to grip strength in cadaver-arm experiment

Dae-Min Kim,Hyun-Sung Kang,Ji-Soo Kim,Yong-Ku Kong 대한인간공학회 2013 대한인간공학회 학술대회논문집 Vol.2013 No.10

Objective: The purpose of this study was to biomechanically analyze the effect of different force ratios(1:1, 1:1.5, 1:2, 1:3) of tendons and grip spans(45, 50, 55, 60mm) on the total grip strength in target forces(70, 105, 140N) using cadaver arms. Background: Researches on cadaver have been under way in various areas, there are many obstacles in researches from supply of cadaver to establishment of environment, and there has been lack of researches on hand which performs the most complex and diverse movements of humans. Method: For this study, a system to fix the cadaver-arm, to control muscle force and to measure total grip strength was constructed. First, the cadaver-arm was fixed using the T-slotted profile. Second, for measuring muscle force, muscles were connected to a power cylinder by wires, and load cell was hanged in front of power cylinder. The last, the MFFM(Multi-Finger Force Measurement system) system was developed to evaluate individual and total finger forces when all fingers have identical grip spans as well as varying grip spans. Results: Statistical analysis showed that the effect of target force and grip span on total grip strength was statistically significant. Total grip strength had a tendency of increase as the increase of tendon force which was statistically significant. In particular, target force of 70N led to the lowest level(15.1N) of total grip strength, where as target force of 140N led to the highest (37.3N) level. The target force was to 2.75 times from 5.15 times higher than the total grip strength. Total grip strength of each specimen was different, according to grip span, and thus showed statistically significant differences, as well. Conclusion: As a study on the process of building and applying a system for a cadaver experiment, this was conducted to develop and use a biomechanical model mathematically and simulative. In conclusion, for this objective, the limits of this research will be corrected and supplemented continuously.

Evaluation of pliers in a maximum gripping task

Yong-Ku Kong,Min-Tae Seo,Ji-Soo Kim,Hyun-Sung Kang 대한인간공학회 2013 대한인간공학회 학술대회논문집 Vol.2013 No.5

Objective: The objective of this study is to derive the optimal grip span of pliers in a maximum gripping task. Background: Although many previous studies have been performed for I-Type and cylinder-type handles and evaluated their various grip span size, there are only few studies regarding on A-Type handles such as pliers. Methods: A total of 25 males participated in this experiment and conducted maximum gripping task using custom-made pliers with three grip spans (50, 70, and 90㎜). The effects of grip spans on grip strength, muscle activity, and subjective discomfort were analyzed. Results: The experimental results showed that total grip strength of 50㎜ grip span had significantly higher than another grip spans. Subjective discomfort showed that the discomfort rating of radius side of the palm was higher than most other parts, significantly. The %MVC of the muscle has no significant difference in three grip span. Conclusion: It was recommended to use the 50mm grip span to exert the maximum grip strength with similar muscle activities in uses of pliers. Application: This finding is expected to be used as the basic data for designing proper pliers.

Grip Strength of Pliers on the Maximum Gripping Task for Females

Yong-Ku Kong,Dae-Min Kim,Ji-Soo Park,Sung-Yong Lee,Kyeong-Hee Choi 대한인간공학회 2014 대한인간공학회 학술대회논문집 Vol.2014 No.11

Objective: The primary purpose of this study was to evaluate the effects of various grip spans of pliers on the resultant force and subjective discomfort in female users. Background: Despite the automation of facilities, many workers were still using hand-tools such as wrench, screwdriver, and pliers. Those hand-tool users are having trouble with hand-related musculoskeletal disorders. Especially females tend to have a higher rate of hand-related musculoskeletal disorders than males. Method: A total of 26 females who had no history of upper extremity musculoskeletal disorders (MSDs) were participated in this study. All female participants were asked to exert a maximum grip force with three repetitions, and to report the subjective discomfort rating for five grip spans of pliers (45, 50, 60, 70, 80mm). Results: Results showed that the effects of grip span were statistically significant on the total grip strength, resultant force, and subjective discomfort rating in this study. The lowest total grip strength was obtained from the grip span of 80mm. For resultant force, the 50mm and 60mm grip spans showed also significantly higher resultant force. The lowest subjective discomfort was observed in the 50mm span. Conclusion: Based on the study, the 50mm and 60mm grip spans which provided highest resultant force as well as lowest discomfort rating might be recommendable for the female pliers users. Application: The results of the study might help to reduce hand-related musculoskeletal disorders and perform efficient task in the real-work environment.

Study on the grip spans of combination pliers in a maximum gripping task

Kim, D.M.,Choi, K.H.,Lee, S.Y.,Kong, Y.K. Elsevier 2016 International journal of industrial ergonomics Vol.54 No.-

A newly developed system was applied in this study to evaluate the effects of the grip spans (45-80 mm) of combination pliers on the total grip strength, individual finger force, resultant force, and subjective discomfort. A total of twenty-six males participated and were asked to exert their maximum grip strength with two repetitions. The highest and the lowest total grip strength and resultant force (311.8 N and 737.9 N vs. 210.1 N and 501.7 N) were obtained at a 60 mm and 80 mm grip spans, respectively. In general, the participants considered the 50 and 60 mm grip spans as being the least discomfort, whereas the 80 mm grip span was considered as the most discomfort grip span in a maximum grasping task. The results can be utilized as basic data for the manufacturing and design industries of two-handle hand tools, such as pliers and wrenches. Practitioners summary: Custom-made combination pliers were applied in this study to evaluate grip strength, resultant force, and subjective discomfort, relative to five grip spans. The authors expect that the results of the present study will provide valuable information for the designers and users of pliers.

Development of DFM(Double-Handle Force Measurement) System For Measuring Individual Finger Forces

Yong Ku Kong,Dae Min Kim,Cheol Min Lim,Min Tae Seo 대한인간공학회 2011 대한인간공학회 학술대회논문집 Vol.2011 No.10

Objective: The purpose of this study was to develop DFM(Double-handle Force Measurement) System for measuring grip strength and individual finger force. Background: A handle shape has not been considered in man previous studies of grip strengths. Accordingly, Design of double-handle tools on ergonomic aspect have many limitations. Methods: In this study, five grip span of A-type was used for measuring total grip force, individual finger force, and finger force distributions. Ten males were recruited from University population for this study. Each participants were asked to exert their maximum grip strength with 3 repetitions for five grip spans(45, 50, 55, 60, 50mm). Results: The highest grip strength was performed on 45mm and 50mm grip spans. On the other hand, among the entire finger, middle and ring fingers showed the highest force as well as distribution to the total finger force. Discussions: The findings of this study might be important information, basically, for designing ergonomic doublehandle tool type.

파지 폭과 손 크기에 따른 각 손가락이 총 악력에 미치는 영향 분석

정명철,김대민,공용구,Jung, Myung-Chul,Kim, Dae-Min,Kong, Yong-Ku 대한인간공학회 2007 大韓人間工學會誌 Vol.26 No.3

In this study, six grip spans (45mm-65mm) were tested to evaluate the effects of handle grip span and user's hand size on maximum grip strength, individual finger force, and subjective ratings of comfort using a digital dynamometer with individual force sensors. Forty-six males were assigned into three hand size groups according to their hand lengths. Results showed that overall 55mm and 50mm grip spans were the most comfortable sizes and associated with the highest grip strength in the maximum grip force exertions, whereas 65mm grip span was rated as the least comfortable size as well as the lowest grip strength. In the interaction effect of grip span and hand size, small and middle hand sized participants rated the best preference and the least preference grip spans differently with large hand sized participants. With respect to the analysis of individual finger force, the middle finger force was the strongest and the highest contribution to the total finger force, followed by ring, index and little fingers. In addition, it was noted that each finger had a different optimal grip span for exerting maximum force resulting in a bowed contoured shaped handle for two-handle hand tools. Thus, the grip spans for two-handle hand tools might be designed according to the users' hand and finger anthropometrics to maximize performance and subjective perception of comfort.