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Ph~iohrcq? 7hmq and Prulim (1994) 10, 27-34 0 Lawrence Erlbaum Associates Limited 1994
Handgrip and fingerpinch strength
Tommy Oberg, Ulrika Oberg and Alek Karsznia
A total of 128 subjects (55 males, 73 females) were examined for isometric handgrip and fingerpinch strength using a VigorimeteP, a simple hand-held dynamometer, suitable for everyday medical and physiotherapy practice. Preliminary age- and sex-specific data are presented together with data for the difference between the strongest and weakest hands. A statistically significant age-related reduction in handgrip strength was found for the males but not for the females. For fingerpinch strength, there were only minor, non-significant changes with age. Basic facts concerning strength and strength measurement are discussed.
I NTRO D U CTI 0 N
Handgrip and fingerpinch strength are import- ant for most hand functions. The normal hand is supplied with receptors which mediate the touch, pressure and joint senses. In the brain, large areas of the cortex are involved with the co- ordination of hand functions. Evaluation of the different aspects of hand function is important not only in physiotherapy practice, but also in neurology, orthopaedics, rehabilitation and in follow-up studies. The measurement of strength is part of such an evaluation. Consequently, there is a need for simple, yet valid and reliable equipment, and for reference data suitable for everyday clinical practice.
There are two main types of grip: power grip and precision grip (Napier, 1956; Landsmeer, 1962; Bejjani and Landsmeer, 1989). These grip patterns ‘either separately or in combination,
T. ()berg, Director and Associate Professor, A. Karsznia, Department of Biomechanics and Orthopaedic Technology, University College of Health Sciences, PO Box 1038, S-551 11 Jonkoping, Sweden U. Oberg, Director, Department of Physical Therapy, County Hospital, S-575 28 Eksjo, Sweden (Reprint requests to TO) Accepted for publication September 1993
provide the anatomical basis for all prehensile activities, whether skilled or unskilled’ (Napier, 1956). They can be further divided into sub- groups (Stoner, 1965; Nielsen and Rodgers, 1986). In the power gr$, the fingers are flexed at all three joints, and the object is held between the fingers and the palm. For such a grasp, the optimum diameter for force development is 40- 50mm (Drury and Coury, 1982; Nielsen and Rodgers, 1986). The power grip - and a vari- ation of it, the oblique grasp - is used to control the application of force in lifting objects, grasping handles, moving cylindrical objects transversely, and gripping handtools such as wrenches, screwdrivers, etc. (Bejjani and Lands- meer, 1989). In theprecisiongrip, the object is held between the thumb and the volar aspects of the fingers, with the thumb in opposition. The preci- sion grip is used to oppose one surface against another, for example in lifting a paper bag in the upright position, for stabilising loose sheets, etc. The pinch or precision grip is considered to have 25% of the power grip strength (Nielsen and Rodgers, 1986).
It is common knowledge that females generally have less muscle strength than males and that muscle strength decreases with age (Grimby and Saltin, 1983; Kiser and Rodgers,
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28 PHYSIOTHERAPY THEORY AND PRACTICE
1986; McArdle, Katch and Katch, 1986; Astrand and Rodahl, 1986; Shephard, 1987; Pheasant, 1988; Chaffin and Andersson, 1991). This loss of muscle strength seems to be closely related to a reduced muscle mass, brought about by ageing, inactivity or both (McArdle et al, 1986; Kstrand and Rodahl, 1986; Shephard, 1987). Only a few reports have been concerned with handgrip or fingerpinch strength. For example, Montoye and Lamphiear (1977) examined grip strength in males and females aged 10-69 years, Hoag 1982) reported grip strength in female workers
and An et a1 (1985) examined grip strength for tip pinch, key pinch, pulp pinch and different types of grasps. Such data are often related to specific groups of subjects or to specific equip- mmt. Often strength is measured in units that are not suitable for comparison. Thus, i t is hard to apply the results from one study to another.
In Sweden, Collin's dynamometer and Vigorimeter n have been used in routine clinical practice for the determination of handgrip strength. Collin's dynamometer is a simple ellip- tic metal frame that can be squeezed in the hand. Inside the frame is a pointer, which shows the degree of deformation. There is no simple-to-use calibration method for this dynamometer, and at maximal squeezing i t causes discomfort in the hand. I n this study, we concentrate on the Yigorimeter", a simple manometer for measure- ment of handgrip strength. It has frequently been used, but no reliable reference data exist. This dynamometer will be described in detail in the Llethods section.
T h r aim of the present study is to produce preliminary- age- and sex-specific data for hand- grip and fingerpinch strength, measured using a \.,*igorimrterg, and to compare the results with those reported in the literature and obtained \cith other measurement devices.
METHODS
Subjects I n total. 128 subjects (55 males, 73 females) aged 20 -69 ) r a n were examined. Most were staff from the County Council visiting an occupa-
tional health unit for reasons other than disease. No-one had a disease that could influence the outcome of the handgrip and fingerpinch strength measurements. Their occupations are shown in Table 1 and their age distribution in Table 2.
Table 1 Subjects by occupation (n=128)
Occupational group n
Males (n=55) Repairman, porter 19 Administrative staff 12 Hospital staff 9 Officer 8 Teacher 4 Ambulance driver 2 Other 1
Females (n = 73) Cleaner 29 Hospital staff 12 Kitchen worker 12 Administrative staff 8 Secretary 7 Teacher 3 Social worker 2
Table 2 Age dis t r ibut ion
Age group Males Females Total (years) (n=55) (n=73) (n=128)
20-29 11 10 21 30-39 11 15 26 40-49 10 20 30 50-59 13 18 31 60-69 10 10 20
The Vigorimeter8 dynamometer*
The Vigorimeter& is a dynamometer constructed for measuring handgrip and fingerpinch strength. I t consists of a manometer with a display similar to a clockface. A pointer shows the pressure in bar or kPa. The pointer stops at its maximum position and can be restored to zero using a small button. The manometer is con- nected to a rubbrr ball via a rubber tube. The balls come in three sizes: large (60 mm diameter),
.-____ __ -~ ~- 'Gebruder Martin, Bahnhofstrasse 124, Postfach 60, D-7200 Tuttlingen, Germany.
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PHYSIOTHERAPY THEORY AND PRACTICE 29
Fig. 1 The VigorimeteQ. The manometer and the three sizes of balls are shown.
medium (47 mm diameter) and small (42mm diameter). The equipment was calibrated against a mercury manometer via a Y-ramifica- tion of the rubber tube. The equipment is shown in Fig. 1.
Test procedure
3
- / The measurements were performed by a nurse instructed in the procedure. The subject's arm was kept hanging down at an elbow angle of 90". The hand was kept with the wrist in a neutral functional position, i.e. with a slight ulnar and dorsal deviation. All subjects performed three
Fig. 2 (a) The force grip for the testing of handgrip strength; (b) the precision grip for the testing of fingerpinch strength.
different measurements with a 10 sec interval between the measurements. The mean of the three measurements was recorded as the indi- vidual strength value. The subject could not see the display. Right and left hand grip strength, and right and left fingerpinch strength, were measured. At the measurement of handgrip strength, the ball was squeezed using a power grip (Fig. 2a). At the measurement of finger- pinch strength, the smallest ball was squeezed using a precision grip, with the index finger and middle finger parallel on one side of the ball and the thumb in opposition on the other side (Fig. 2b). The subject was asked to squeeze the ball as much as possible for 2-3 sec, and the maximum reading was recorded. All of the males used the large ball and all of the females used the medium-sized ball.
Statistical met hods
cients of variation, confidence intervals and pre- diction intervals were calculated using standard methods. For evaluation of variation between the age groups, one-way analysis of variance (ANOVA) was applied. Correlations were estim- ated using Pearson's product-moment cor- relation (Armitage and Berry, 1987).
R ES U LTS
For handgrip strength (Tables 3 and 4), both the males and females showed declining strength with age. For the males, one-way ANOVA revealed a statistically significant difference between the age groups ( P < O . O O I ) for both the right and left hands. The Pearson correlation between age and handgrip showed a coefficient of -0.63 (P<O.OOl) for the right hand and -0.54 (P<O.OOl) for the left hand. For the
Means, medians, standard deviations, coeffi- females, there was a slight, but non-statistically
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30 PHYSIOTHERAPY THEORY AND PRACTICE
Table 3 Handgrip strength: Males
Age f * S D 95%CI 95%PI (years) n &Pa) cv &Pa) (kPa)
Right hand 20-29 11 144*13 0.09 135-153 115-173 30-39 11 138*31 0.22 1 17-1 59 69-207 40-49 10 121i20 0.1 7 107-1 35 76-1 66 50-59 13 110*26 0.24 96124 60-160
Left hand
30-39 11 133*29 0.22 114-152 68-198
60-69 10 94*18 0.1 9 81-1 07 53-1 35
20-29 11 131 *23 0.1 8 1 16-1 46 80-1 82
40-49 10 117*20 0.1 7 103-1 31 72-1 62 50-59 13 112*20 0.1 8 100-1 24 68-1 56 60-69 10 92*14 0.1 5 82-102 60-124
Abbreviations: CV. coefficient of variation; CI, confidence interval; PI, prediction interval.
Table 4 Handgrip strength: Females
Right hand 20-29 10 30-39 15 4 0 4 9 20 50-59 18 60-69 10
Left hand 20-29 10 30-39 15 40-49 20 50-59 18 60-69 10
101 *25 104*31 94*21 92*18 90+10
93*20 99*27 91*19 90*18 84*10
0.25 0.30 0.22 0.20 0.1 1
0.22 0.27 0.21 0.20 0.1 2
83-1 19 96-1 12 84-1 04 83-1 01 83-97
79-1 07 84-1 14 82-1 00 81 -99 77-91
45-1 57 37-1 71 50-1 38 54-1 30 67-1 13
48-1 38 41 -1 57 51-1 31 53-1 28 61 -1 07
Abbreviations: CV, coefficient of variation; CI, confidence interval; PI, prediction interval.
significant decrease. The correlation between age and grip strength was -0.21 for the right hand and - 0.1 1 for the left hand. For fingerpinch strength (Tables 5 and 6), one-way ANOVA did not reveal any statistically significant differences between age groups, neither for the right or left hand, nor for males or females. The Pearson correlation coefficients were low and non-signi- ficant. For both handgrip and fingerpinch strength, Student’s t-test revealed a statistically significant difference between the males and females ( P < O . O O l ; Tables 7 and 8). There was no obvious trend in the distribution of occupa- tions over age groups.
For handgrip strength, Student’s t-test
revealed no significant difference between the right and left sides. However, for fingerpinch strength, there was a significant difference (P<O.Ol) between sides for the females but not the males (Table 7 , Fig. 3 ) . Figure 3 shows the strongest side. Most people were, as expected, strongest on the right side: left handgrip was strongest for 31 and 32% of the males and females, respectively. For fingerpinch strength, the corresponding figures were 36 and 25%. However, for many of the subjects, there was a discrepancy betweeen handgrip and fingerpinch with respect to which side was strongest. For those who exhibited greater right handgrip and/ or fingerpinch strength, 59% of the males and
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PHYSIOTHERAPY THEORY AND PRACTICE 3 1
Table 5 Fingerpinch strength: Males
Age f * S D 95%CI 95%PI (years) n W a ) cv W a ) W a )
Right hand
30-39 11 54*12 0.22 46-62 27-81
5&59 13 53* 8 0.1 5 48-58 36-70
Left hand 20-29 11 49* 9 0.1 8 42-56 29-69 30-39 11 56*13 0.23 4 7 4 4 28-84 40-49 10 54*16 0.30 43-65 18-90 50-59 13 50* 7 0.1 4 46-54 35-65 60-69 10 50* 6 0.1 2 46-54 36-64
Abbreviations: CV. coefficient of variation; CI, confidence interval; PI, prediction interval.
20-29 11 50*13 0.26 41 -59 21 -79
40-49 10 60*14 0.23 50-70 28-92
60-69 10 49*10 0.20 42-56 26-72
Table 6 Fingerpinch strength: Females
~
Age R*SD 95%CI 95%PI (years 1 n (kPa) cv (kP4 &Pa)
Right hand 20-29 10 46* 9 0.20 40-52 26-66 30-39 15 49*11 0.22 43-55 25-73 4049 20 48* 9 0.1 9 44-52 29-67 50-59 18 45* 7 0.1 6 42-48 30-60 60-69 10 47* 9 0.20 41 -53 27-67
Left hand 20-29 10 46*10 0.22 39-53 23-69 30-39 15 45*10 0.22 39-51 24-66 40-49 20 44* 9 0.20 40-48 25-63 50-59 18 39*10 0.26 34-44 18-60 60-69 10 44* 7 0.1 6 39-49 28-60
Abbreviations: CV, coefficient of variation; CI, confidence interval; PI, prediction interval
50% of the females showed greater strength in both. In contrast, only about 20% of the subjects who showed a left hand advantage for one grip showed a similar advantage in the other.
In relation to the difference between the strongest and weakest sides (Table 9), the distri- bution of data was skewed. For this reason, the median difference between the strongest and weakest sides was calculated. The 5th percentile was also calculated. In many situations, refer- ence values are defined within an interval includ- ing 95% of normal individuals. Differences exceeding the value for this percentile may be regarded outside a reference interval, and thus unusual.
DISCUSSION
Shephard et a1 (1991) examined isometric hand- grip force in 67 males and females aged 45-75 years. They found a linear decrease in muscle strength of 6 8 % per decade over the span examined (45-75 years), but in the males the loss was most marked in terms of handgrip. Similar age-related reductions in grip strength have been reported by others (e.g. Burke et al, 1953; Miles, 1950; Montoye and Lamphiear, 1977; Sperling, 1980; Imrhan and Loo, 1989; Chatterjee and Chowdhuri, 1991; Nygird, Luopajarvi and Ilmarinen, 1991). In this study, we found a similar, statistically significant, age-related
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32 PHYSIOTHERAPY THEORY AND PRACTICE
Table 7 Mean ( i S D ) handgrip power (kPa)
Right hand Left hand t-test
Males (n=55) 122*23 117i22 F1.16, P>0.05 Females (n=73) 96*21 91 i 2 0 ~ 1 . 2 8 , P>0.05 r-test p6.66 t-6.97
P< 0.001 P< 0.001 ~~ ~~
Table 8 Mean (*SD) fingerpinch power (kPa)
Right hand Left hand t-test
Males (n=55) 53i11 5 2 i l l F0.78, P> 0.05 Females (n=73) 47* 9 43* 9 F2.69, P<O.Ol r-test F3.39 t-5.09
P< 0.001 P< 0.001
Left hand strongest Men
Right hand strongest Men
Handgrip Fingerpinch
Left hand strongest Women
Handgrip Fingerpinch
Right hand strongest Women
Handgrip Fingerpinch Handgrip Fingerpinch
Fig. 3 Handgrip and fingerpinch strength in males and females. The numbers indicate numbers of individuals.
reduction in handgrip strength among the males for both the right and left sides. For the females, there was a less marked, non-significant reduc- tion in handgrip strength, Thus our findings agree with those of Shephard et al (1991). Sim- ilar sex-specific differences in losses in grip strength have been reported by others. For ex- ample. Sperling (1980) compared the static strength in the transversal volar grip in 70-year- olds with that of 20- to 30-year-olds and found a smaller decrease among the females than among the males. Chatterjee and Chowdhuri (1991)
noted correlations between age and handgrip strength, with coefficients of r = -0.74 for the right hand and r = -0.69 for the left hand. We found slightly lower, but statistically significant correlations for handgrip strength in the males ( r = - 0.63 and r = - 0.54 for the right and left hands, respectively), but not in the females.
In comparing adult and elderly males and females, Imrhan and Loo (1989) report similar age-related reductions in fingerpinch strength. In our study, however, we found no age-related changes in fingerpinch strength. Imrhan and Loo found a coefficient of variation of 19-41%; in our study, it was slightly less, i.e. 12-30%. There is no obvious explanation for the differences between our findings and those of Imrhan and Loo. It may be that pinch grip is unstable and therefore makes it difficult to squeeze maximally. In other words, there may be a limit to how hard one can squeeze due to grip stability rather than strength. To test such an assumption, there is a need for a study where fingerpinch strength is tested with some device where grip stability is not of importance. Using our study design, finger- pinch strength was 45-50% of handgrip strength.
Generally, females have less muscle strength than males. According to Astrand and Rodahl (1986), this ratio is 0.50-0.75: 1 for females and males. Similar figures are given by others (Kiser and Rodgers, 1986; Pheasant, 1988). Such sex differences have also been reported for handgrip and fingerpinch strength (Miles, 1950; Montoye
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PHYSIOTHERAPY THEORY AND PRACTICE 33
Table 9 Differences between strongest and weakest hands
Difference Handgrip Fingerpinch ( k W
Males ( n ) Females ( n ) Males (n ) Females (n )
1 4 5-9
10-14 15-1 9 20-24 25-29 30-34 35-39 40-44 45-49
Median p,
14 16 6 9 5 1 1 1 1 1
9 36
25 25 25 21 14 31 10 14 12 11 3 6 1 2
1
8 5 7 22 15 17
and Lamphiear, 1977; Imrhan and Loo, 1989). In our study, we found statistically significant sex differences for handgrip and fingerpinch strength. Thus, our findings agree with those reported in the literature. The female: male ratio was slightly higher than generally reported, about 0.83: 1.
The question about handedness may at first seem simple, but it is in fact not so. Handedness has primarily been studied by psychologists and brain physiologists, rather than by general physi- ologists and clinicians. Handedness is related to such factors as genetics, brain damage and de- gree of brain lateralisation (Levy and Reid, 1976; Rasmussen and Milner, 1977; Springer and Deutsch, 1982; Kupfermann, 199 I ) , but these factors will not be discussed further here. Most investigators just ask subjects, ‘Are you right- or left-handed?’ However, such a proced- ure may be misleading. Most researchers now agree that the best way to decide handedness is by observation of the subject in a performance situation (Springer and Deutsch, 1982). In some tasks, the subject uses his or her right hand, but in others his or her left hand. Thus handedness is task-specific. However, not even the most thor- ough procedures will always show a clear prefer- ence for one hand over the other. Examinations of handedness most often give controversial or contradicting results. Sometimes, the figure 10% left-handedness is referred to in the literature (e.g. Springer and Deutsch, 1982). We therefore avoid the concept ‘handedness’ and prefer task-
specific descriptions such as right-hand-writer, left-hand-gunshooter.
If a performance definition is adopted in a force measurement situation, handedness will be interpreted in terms of the strongest hand. Because of the theoretical difficulties and the variation we observed in hand strength, we de- cided to focus on the difference between the strongest and weakest hand, and the 5th percent- ile was regarded as the upper limit of reference data (Tables 7 and 8). In many situations, ‘normal values’ or reference values are defined within an interval including 95% of representat- ive healthy subjects. With such an approach, 95% of healthy individuals have a side dif- ference of less than the 5th percentile. A dif- ference above the 5th percentile value may be considered unusual, just like any laboratory measurement outside the reference interval. This does not necessarily mean pathology, but it is an indication for further questioning or examina- tion.
CONCLUSIONS
We have presented preliminary sex- and age- specific data for right and left handgrip and fingerpinch strength as measured with a Vigori- meter”. The prediction intervals can be used for evaluation of single observations, and the confid- ence intervals for evaluation of means of group data. Data for differences between the strongest
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34 PHYSIOTHERAPY THEORY AND PRACTICE
and weakest sides are also given. For a complete reference data set, further work is required. It is our opinion that the Vigorimeterg is suitable as a standard measuring device in ordinary medical or physiotherapy practice.
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