Ergonomics
ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20
Hand strength: the influence of grip span and grip type CHARLOTTE FRANSSON & JØRGEN WINKEL To cite this article: CHARLOTTE FRANSSON & JØRGEN WINKEL (1991) Hand strength: the influence of grip span and grip type, Ergonomics, 34:7, 881-892, DOI: 10.1080/00140139108964832 To link to this article: https://doi.org/10.1080/00140139108964832
Published online: 30 May 2007.
Submit your article to this journal
Article views: 288
Citing articles: 85 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=terg20
ERGONOMICS, 199 1, VOL.
34, NO. 7,88 1-892
Hand strength: the influence of grip span and grip type CHARL~ITE FRANSSONand JBRGEN WINKEL National Institute of Occupational Health, Division of Applied Work Physiology, S-171 84 Solna, Sweden
Keywordr: Hand; Finger; Tool; Grip strength; Isometric contraction. The maximal force from each of the fingers II-V (FF) and the resultant force between the jaws of the tool (RF), due to contribution from all fingers, were measured using a pair of modified pliers. The RF was measured at 21 handle separations and the FF was measured at seven handle separations for each finger. A traditional grip type was compared with a 'reversed' grip where the little finger was closest to the head of the tool. Sixteen subjects (8 females and 8 males) participated in the study. Both the RF and FF varied according to the distance between the handles. For both grip types, the highest RF was obtained at a handle separation of 50-60 mm for females and 55-65 mm for males. For wide handle separations, the RF was reduced by 10%(cm increase in handle separation)-'. The force-producing ability of the hand was influenced by the grip type and the highest R F was obtained when using the traditional grip. An interaction was found between the fingers, i.e., the maximal force of one finger depended not only on its own grip span, but also on the grip spans of the other fingers. About 35% of the sex difference in hand strength was due to hand size differences.
1. introduction The present study is part of a Swedish interdisciplinary project entitled 'Hand-held tools-design with regard to optimal hand-arm function and performance'. The aim of the project is to develop ergonomic design criteria for hand-held tools, especially cross-action tools, such as pliers, nippers and tongs. Injuries to the hand, lower arm and shoulder are often claimed to be due to poor design and/or inappropriate use of hand tools. Also, work requiring high force has been identified as a risk factor for hand-wrist cumulative trauma disorders (Silverstein et al. 1986). Work with cross-action tools often requires a substantial amount of force, and one important factor, directly influencing the grip strength for this type of tools, is the distance between the handles. An isometric grip, performed with parallel handles, has been investigated by numerous authors, e.g., Bechtol (1954), Hertzberg (1955), Montoye and Faulkner (1965), Cotten and Bonnell (1969), Cotten and Johnson (1971), Petrofsky el al. (1 980), Pheasant and Scriven (1 983) and the Ergonomics Group at Eastman Kodak Company (1986). Most of the studies describe an optimal handle separation, giving maximal force output. This varies between 38 mm and 64 mm depending on gender, equipment and experimental design. A dynamic grip, performed with angulated handles, was studied by Fitzhugh (1973). At a closing speed of 29 mmls, the highest force was developed when using an initial handle separation of 83-89 mm. Still, the optimal handle separation, where the highest force was obtained, was approximately 52 mm. An isometric grip, performed with angulated handles, is of great interest to cross-action tool work, because many tasks are performed with such a grip. To our knowledge, optimal handle separation for this grip has not yet been studied. 0014-0139191 $3.00 0 1991 Taylor & Francis Ltd.
C.Fransson and J. Winkel
882
The fingers differ in strength, the middle finger being the strongest and the Iittle finger the weakest. Hence, the force output from fingers II+III (index-plus middle finger) is larger than that from fingers I V f V (ring-plus little finger) (Hazelton et al. 1975, Ohtsuki 198 1). Usually, a cross-action tool is held in a power grip with the index finger closest to the head of the tool (figure 1). With this grip, the weakest fingers obtain the longest lever arms. A 'reversed grip' (figure 1) offers the longest lever arms to the strongest part of the hand, and may thus increase the total torque produced by the hand. Spontaneous use of the reversed grip has been observed among workers who are accustomed to the use of various hand tools within their daily work (Kadefors ei al. 1989).
Traditional grip
Reversed grip
Figure 1 . The two investigated grip types: traditional and reversed grip.
The aim of the present investigation was to study the force contribution of each finger (FF) and the resultant force between the jaws of the tool (RF) using an isometric grip with angulated handles. The FF and the RF were studied according to: (1) grip type (traditional and reversed grip); and (2) handle separation, using acrossaction tool.
2. Material and methods 2.1. Subjects Eight females and eight males (table 1) volunteered for the study, which was approved by the local ethical committee of the Karolinska Institute, Stockholm. The subjects, who all claimed to be right-handed, were healthy members of staff. For the right hand, palmar hand length (hl) (DIN 33 402, measure 3 . 1 3 , metacarpal breadth (hb) (DIN 33402, measure 3.19) and finger length (fl) (DIN 33402, measure 3-9-3.12) were measured and the mean length of fingers 11-V was calculated (table 2). Table 1. Characteristics of subjects (n= 16). Mean
Age (years) SD Range
Mean
Stature (rn) SD Range
Body weight (kg) SD Range
Mean
Women (n-8)
36
14
18-60
1.66
0.05
1.60-1.74
61
8
56-78
37
10
22-57
1.76
0.06
1.69-1.85
71
10
60-89
Men (n==8)
Grip and hand strength
883
Figure 2. The experimental set-up: the 'reversed grip'.
2.2. Equipment A pair of modified multiple slip joint pliers (model Gedore No 145110-250) was used in the set-up, keeping the slip joint at a constant position throughout the study. The jaws of the tool, which were extended in order to obtain a suitable force output, were fixed to a strain-gauge dynamometer (figure 2). Figure 3 shows the device for measuring the FF. A fixture was designed to apply a small commercial load-cell (Sensotec; Subminiature Load Cell, model 13) to the lower leg of the pliers. In
C. Fransson and J. Winkel
884
Table 2. H a n d size measurements used in the study. Finger length refers to mean length of fingers 11-V. Finger length (mm) Mean SD Range -
-
Women (n-8) Men (n = 8) Total (n- 16)
-
Hand breadth (mm) Mean SD Range
-
66 72 69
-
9 9 9
48-80 55-90 48-90
79 90 84
-
7
5 8
Hand length (mm) Mean SD Range
-
72-92 83-99 72-99
171 186 178
7 8 11
159-183 175-197 159-197
addition, three dummy fixtures were used to provide a similar grip surface for all fingers. The four fixtures were freely movable along the handle of the pliers. Only the perpendicular composant of the FF could be measured by the load cell. The actual FF was calculated as shown in figures 3(a)-(c). The finger grip span was defined as the shortest distance between the handles of the tool directly under the finger; the hand grip span was defined as the shortest distance between the handles at the position between middle and ring finger (figure 4(a)). The RF and the FF from one finger at a time were measured simultaneously (figure 4(b)). The RE- and FF-signals were amplified (time-constant 1 s) and .monitored on pen recorder and oscilloscope. A screen separated the subject from the recording devices to avoid visual feedback (figure 2).
2.3. Procedure The subject stood in a standardized position (figure 2). Using the right hand, maximal force was exerted steadily without jerking. Each test session comprised seven measurements, separated by a 2min rest. The resting time between test sessions was at least 4 h. All fingers were engaged in the grip although the FF was measured for only one finger at a time. The investigated finger grip spans were 41, 50, 60, 70, 80, 90 and 100mm. 41 mm was the narrowest handle separation possible for our equipment. This finger grip span was studied 6 months later, since the optimal hand and finger grip span appeared to be narrower than 50 mm for some of the subjects. Each subject performed 1 12 exertions: 4 fingers x 2 grip types x 7 finger grip spans x 2 (the measurements were repeated after 2-3 weeks).
2.4. Statisrical methodr Mean values and standard deviations were calculated by standard methods. Linear correlation analysis was applied to study the relationship between RF and hand size as well as between the RF and hand grip spans over 60mm. Analysis of variance (ANOVA) was used to study the effects of finger, finger grip span, grip type, sex and subject on the FF as well as the effects of hand grip span, grip type, sex and subject on the RF. An unpaired t-test was used to test for differences in hand size between males and females and a paired t-test was used to test for effects of training. Multiple regression analysis was used to study the influence of hand size parameters on the RF.
885
Grip and hand strength
a
=distance between finger and the centre line of tool when the pliers are closed x =opening distance 1 =distance between finger and rotation axis of the tool, measured along the handle s =distance between finger and rotation axis of the tool, measured along the centre line d =distance between finger and the intercept between (centre line+a) and its perpendicular line at the level of the rotation axis a! =angle of inclination p, =angle between finger and the centre line of tool when the pliers are closed 8 =angle between finger and the centre line of tool when the pliers are open 8, r, p, c: are introduced variables, used for description and calculation only sinyl =all sin8 = (a+x)ll /9 =180D-8 y =xitan8 s =(P-a2)l r =(x2-t$)i
d
a
p =I--r c =@2-a2)i d =($+$-2cr s i n d r = sinpld
cosp)h
a =amin(rsu@/d)
Figure 3. (a) The device used for measuring finger force. F (finger force), Fcosa! (finger force composant recorded by the Load cell). All fixtures were movable along the handle. (b) Symmetrically opened pliers: designation of angles and distances. (c) Calculation of the angle of inclination (a).
886 Finger grip span
C. Fransson and J. Winkel Hand grip span
Finger force
Resultant force, RF
Figure 4. (a) The arrows show how finger and hand grip spans were measured. (b) Illustration of how finger force (FF) and resultant force between the jaws of the tool (RF) were measured.
3. Results 3.1 Finger force (FF) Data concerning the FF are shown in figure 5. The FF differed from finger to finger (p
ISSN: 0014-0139 (Print) 1366-5847 (Online) Journal homepage: http://www.tandfonline.com/loi/terg20
Hand strength: the influence of grip span and grip type CHARLOTTE FRANSSON & JØRGEN WINKEL To cite this article: CHARLOTTE FRANSSON & JØRGEN WINKEL (1991) Hand strength: the influence of grip span and grip type, Ergonomics, 34:7, 881-892, DOI: 10.1080/00140139108964832 To link to this article: https://doi.org/10.1080/00140139108964832
Published online: 30 May 2007.
Submit your article to this journal
Article views: 288
Citing articles: 85 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=terg20
ERGONOMICS, 199 1, VOL.
34, NO. 7,88 1-892
Hand strength: the influence of grip span and grip type CHARL~ITE FRANSSONand JBRGEN WINKEL National Institute of Occupational Health, Division of Applied Work Physiology, S-171 84 Solna, Sweden
Keywordr: Hand; Finger; Tool; Grip strength; Isometric contraction. The maximal force from each of the fingers II-V (FF) and the resultant force between the jaws of the tool (RF), due to contribution from all fingers, were measured using a pair of modified pliers. The RF was measured at 21 handle separations and the FF was measured at seven handle separations for each finger. A traditional grip type was compared with a 'reversed' grip where the little finger was closest to the head of the tool. Sixteen subjects (8 females and 8 males) participated in the study. Both the RF and FF varied according to the distance between the handles. For both grip types, the highest RF was obtained at a handle separation of 50-60 mm for females and 55-65 mm for males. For wide handle separations, the RF was reduced by 10%(cm increase in handle separation)-'. The force-producing ability of the hand was influenced by the grip type and the highest R F was obtained when using the traditional grip. An interaction was found between the fingers, i.e., the maximal force of one finger depended not only on its own grip span, but also on the grip spans of the other fingers. About 35% of the sex difference in hand strength was due to hand size differences.
1. introduction The present study is part of a Swedish interdisciplinary project entitled 'Hand-held tools-design with regard to optimal hand-arm function and performance'. The aim of the project is to develop ergonomic design criteria for hand-held tools, especially cross-action tools, such as pliers, nippers and tongs. Injuries to the hand, lower arm and shoulder are often claimed to be due to poor design and/or inappropriate use of hand tools. Also, work requiring high force has been identified as a risk factor for hand-wrist cumulative trauma disorders (Silverstein et al. 1986). Work with cross-action tools often requires a substantial amount of force, and one important factor, directly influencing the grip strength for this type of tools, is the distance between the handles. An isometric grip, performed with parallel handles, has been investigated by numerous authors, e.g., Bechtol (1954), Hertzberg (1955), Montoye and Faulkner (1965), Cotten and Bonnell (1969), Cotten and Johnson (1971), Petrofsky el al. (1 980), Pheasant and Scriven (1 983) and the Ergonomics Group at Eastman Kodak Company (1986). Most of the studies describe an optimal handle separation, giving maximal force output. This varies between 38 mm and 64 mm depending on gender, equipment and experimental design. A dynamic grip, performed with angulated handles, was studied by Fitzhugh (1973). At a closing speed of 29 mmls, the highest force was developed when using an initial handle separation of 83-89 mm. Still, the optimal handle separation, where the highest force was obtained, was approximately 52 mm. An isometric grip, performed with angulated handles, is of great interest to cross-action tool work, because many tasks are performed with such a grip. To our knowledge, optimal handle separation for this grip has not yet been studied. 0014-0139191 $3.00 0 1991 Taylor & Francis Ltd.
C.Fransson and J. Winkel
882
The fingers differ in strength, the middle finger being the strongest and the Iittle finger the weakest. Hence, the force output from fingers II+III (index-plus middle finger) is larger than that from fingers I V f V (ring-plus little finger) (Hazelton et al. 1975, Ohtsuki 198 1). Usually, a cross-action tool is held in a power grip with the index finger closest to the head of the tool (figure 1). With this grip, the weakest fingers obtain the longest lever arms. A 'reversed grip' (figure 1) offers the longest lever arms to the strongest part of the hand, and may thus increase the total torque produced by the hand. Spontaneous use of the reversed grip has been observed among workers who are accustomed to the use of various hand tools within their daily work (Kadefors ei al. 1989).
Traditional grip
Reversed grip
Figure 1 . The two investigated grip types: traditional and reversed grip.
The aim of the present investigation was to study the force contribution of each finger (FF) and the resultant force between the jaws of the tool (RF) using an isometric grip with angulated handles. The FF and the RF were studied according to: (1) grip type (traditional and reversed grip); and (2) handle separation, using acrossaction tool.
2. Material and methods 2.1. Subjects Eight females and eight males (table 1) volunteered for the study, which was approved by the local ethical committee of the Karolinska Institute, Stockholm. The subjects, who all claimed to be right-handed, were healthy members of staff. For the right hand, palmar hand length (hl) (DIN 33 402, measure 3 . 1 3 , metacarpal breadth (hb) (DIN 33402, measure 3.19) and finger length (fl) (DIN 33402, measure 3-9-3.12) were measured and the mean length of fingers 11-V was calculated (table 2). Table 1. Characteristics of subjects (n= 16). Mean
Age (years) SD Range
Mean
Stature (rn) SD Range
Body weight (kg) SD Range
Mean
Women (n-8)
36
14
18-60
1.66
0.05
1.60-1.74
61
8
56-78
37
10
22-57
1.76
0.06
1.69-1.85
71
10
60-89
Men (n==8)
Grip and hand strength
883
Figure 2. The experimental set-up: the 'reversed grip'.
2.2. Equipment A pair of modified multiple slip joint pliers (model Gedore No 145110-250) was used in the set-up, keeping the slip joint at a constant position throughout the study. The jaws of the tool, which were extended in order to obtain a suitable force output, were fixed to a strain-gauge dynamometer (figure 2). Figure 3 shows the device for measuring the FF. A fixture was designed to apply a small commercial load-cell (Sensotec; Subminiature Load Cell, model 13) to the lower leg of the pliers. In
C. Fransson and J. Winkel
884
Table 2. H a n d size measurements used in the study. Finger length refers to mean length of fingers 11-V. Finger length (mm) Mean SD Range -
-
Women (n-8) Men (n = 8) Total (n- 16)
-
Hand breadth (mm) Mean SD Range
-
66 72 69
-
9 9 9
48-80 55-90 48-90
79 90 84
-
7
5 8
Hand length (mm) Mean SD Range
-
72-92 83-99 72-99
171 186 178
7 8 11
159-183 175-197 159-197
addition, three dummy fixtures were used to provide a similar grip surface for all fingers. The four fixtures were freely movable along the handle of the pliers. Only the perpendicular composant of the FF could be measured by the load cell. The actual FF was calculated as shown in figures 3(a)-(c). The finger grip span was defined as the shortest distance between the handles of the tool directly under the finger; the hand grip span was defined as the shortest distance between the handles at the position between middle and ring finger (figure 4(a)). The RF and the FF from one finger at a time were measured simultaneously (figure 4(b)). The RE- and FF-signals were amplified (time-constant 1 s) and .monitored on pen recorder and oscilloscope. A screen separated the subject from the recording devices to avoid visual feedback (figure 2).
2.3. Procedure The subject stood in a standardized position (figure 2). Using the right hand, maximal force was exerted steadily without jerking. Each test session comprised seven measurements, separated by a 2min rest. The resting time between test sessions was at least 4 h. All fingers were engaged in the grip although the FF was measured for only one finger at a time. The investigated finger grip spans were 41, 50, 60, 70, 80, 90 and 100mm. 41 mm was the narrowest handle separation possible for our equipment. This finger grip span was studied 6 months later, since the optimal hand and finger grip span appeared to be narrower than 50 mm for some of the subjects. Each subject performed 1 12 exertions: 4 fingers x 2 grip types x 7 finger grip spans x 2 (the measurements were repeated after 2-3 weeks).
2.4. Statisrical methodr Mean values and standard deviations were calculated by standard methods. Linear correlation analysis was applied to study the relationship between RF and hand size as well as between the RF and hand grip spans over 60mm. Analysis of variance (ANOVA) was used to study the effects of finger, finger grip span, grip type, sex and subject on the FF as well as the effects of hand grip span, grip type, sex and subject on the RF. An unpaired t-test was used to test for differences in hand size between males and females and a paired t-test was used to test for effects of training. Multiple regression analysis was used to study the influence of hand size parameters on the RF.
885
Grip and hand strength
a
=distance between finger and the centre line of tool when the pliers are closed x =opening distance 1 =distance between finger and rotation axis of the tool, measured along the handle s =distance between finger and rotation axis of the tool, measured along the centre line d =distance between finger and the intercept between (centre line+a) and its perpendicular line at the level of the rotation axis a! =angle of inclination p, =angle between finger and the centre line of tool when the pliers are closed 8 =angle between finger and the centre line of tool when the pliers are open 8, r, p, c: are introduced variables, used for description and calculation only sinyl =all sin8 = (a+x)ll /9 =180D-8 y =xitan8 s =(P-a2)l r =(x2-t$)i
d
a
p =I--r c =@2-a2)i d =($+$-2cr s i n d r = sinpld
cosp)h
a =amin(rsu@/d)
Figure 3. (a) The device used for measuring finger force. F (finger force), Fcosa! (finger force composant recorded by the Load cell). All fixtures were movable along the handle. (b) Symmetrically opened pliers: designation of angles and distances. (c) Calculation of the angle of inclination (a).
886 Finger grip span
C. Fransson and J. Winkel Hand grip span
Finger force
Resultant force, RF
Figure 4. (a) The arrows show how finger and hand grip spans were measured. (b) Illustration of how finger force (FF) and resultant force between the jaws of the tool (RF) were measured.
3. Results 3.1 Finger force (FF) Data concerning the FF are shown in figure 5. The FF differed from finger to finger (p
