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PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 38th ANNUAL MEETING-1994
EFFECTS OF GRIP SPAN, WRIST POSITION, HAND
AND GENDER ON GRIP STRENGTH
B. Ramakrishnan, Lisa A. Bronkema, and M. Susan Hallbeck
Center for Ergonomics and Safety Research
University of Nebraska - Lincoln
175 Nebraska Hall
Lincoln, Nebraska 68588-0518
Extensive literature is available which has examined the effects of grip span, wrist
position, hand, gender, and anthropometric dimensions on grasp strength, but none have
looked at all the factors combined. A thorough understanding of the relations between
these various factors would help minimize workplace risks and improve safety. Thus, a
study was performed to relate these factors. Twenty subjects (10 male and 10 female)
performed maximal exertions with both hands in three wrist positions (45" flexion, 45"
extension, and neutral), for three Jamar hand dynamometer spans. Thus, the model was
a 2 (gender) x 2 (hand) x 3 (wrist position) x 3 (dynamometer span) x 20 (subjects)
mixed effects model with blocking on subjects. Anthroponietric dimensions of the
subjects' hands were utilized to establish correlation between basic hand dimensions and
grasp strength. A stepwise regression analysis established correlation between basic
hand dimensions with grasp strength. An R2 value of 0.82 was obtained for the
regression equation developed for the largest span ( 6 cm) of the dynamometer with palm
thickness, wrist circumference and forearm length as the independent variables and grasp
strength as the dependent variable. For the middle span of 4.7 cm, however, it was seen
that palm thickness, wrist circumference, and hand breadth were the only significant
variables, with a coefficient of determination of 0.79. Therefore, these four dimensions
were chosen for a correlation study with grasp strength. The correlation study revealed
that wrist circumference has a reasonably good correlation between the non-dominant
hand and the largest span of the handle in the neutral wrist position. Palm thickness and
hand breadth yielded significance in two of the three handle spans. The ANOVA
showed that all main effects, namely, wrist position, grip span, gender, and hand were
significant at the 0.01 level.
INTRODUCTION
Because of the high incidence of
cumulative trauma disorders (CTD's) in the work
place, much emphasis has been placed upon the
study of the factors which are believed to be
causes, such as repetitive motions, the application
of high forces, and awkward postures (PutzAnderson, 1988). Therefore, it is useful to
understand the relations between various factors
and grip strength, factors such as deviated
postures, handedness, anthropometric dimensions,
grip span, gender and their interactions.
REVIEW OF THE LITERATURE
A literature survey indicates that the
relations between grip strength and individual
factors such as wrist position, gender, hand, and
grip span have been studied by several
researchers. A neutral wrist position is preferable
to a flexed or extended position because higher
forces can be exerted and it is less likely to
contribute to the development of a CTD (PutzAnderson, 1988). While in a 45" extended
position, forces of approximately 75-82% of the
neutral position are possible, while forces of only
60-72% can be exerted when the hand is in a 45"
flexed position (Hallbeck and McMullin, 1993;
McMullin and Hallbeck, 1991; and PutzAnderson, 1988). O'Driscoll, Horii, Ness,
Cahalan, Richards, and An (1992) compared the
grip strengths achieved with a flexion or extension
of 10-15 degrees with that achieved in a selfselected wrist position. Grips strength achieved in
a flexed or extended position was found to be
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PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 38th ANNUAL MEETING-1994
approximately 75-80% of the strength in a selfselected position. The reduced forces with a
deviated wrist have been attributed to the fact that
the ability of a musculotendinous unit to generate
force is dependent upon its functional length
(Hazelton, Smidt, Flatt, and Stephens, 1975).
The percentage of strength of the nondominant hand as compared to the dominant hand
has been cited in several studies. The nondominant hand has been found to generate forces
of approximately 90% (O'Driscoll, et al., 1992),
93% (Swanson, Matev, and de Groot, 1970 and
Hunter, Schneider, Mackin, and Bell, 1978),94%
(McMullin and Hallbeck, 1991), 95% (Hallbeck
and McMullin, 1993), and 97% (McMullin and
Hallbeck, 1992) that of the dominant hand in
grasp. Harkonen, Piirtomaa an Alaranta (1993)
found no significant difference between the
dominant and non-dominant hand.
The distance spanned by the dynamometer
handle was studied by Wang (1982). T h e
dynamometer used in his study was set at spans of
3.5, 4.7, and 6.0 cins. Paired t-tests that were
performed on this data showed the 3.5 and 4.7 cm
handles to be in one grouping, and the 4.7 and 6.0
cm handles to be in another grouping. Harkonen
et al., (1993) also studied this, including 5 spans
in their study. The third handle position (6 cm) of
the Jamar hand dynamometer was found to yield
the highest grip strength for both male and female
subjects.
Gender has been shown to have a
significant effect on grip strength. Females have
been found to possess 51% (Hunter, et al., 1978),
66% (Mathiowetz, Kashman, Volland, Wcber,
Dowe, and Rogers, 1985; McMullin and Hallbeck,
1992; and Putz-Anderson, 1988), 6 0 - 7 0 %
(Harkonen, et al., 1993), 68% (Williamson and
Rice, 1992), 74% (Hallbeck and McMullin,
1993), and 76% (McMullin and Hallbeck, 1991)
that of males in grasp strength.
Several attempts have been made to derive
empirical equations for grip strength, associating
with it the subjects' anthropometric dimensions.
Schmidt and Toews (1970) found grip strength to
be proportional to height and weight, up to a
maximum of 75 inches and 215 pounds. Lunde,
Brewer, and Garcia (1972) derived equations to
predict both dominant and non-dominant hand grip
strength using height and weight, but these
equations had relatively low coefficients of
determination. Wang ( 1982) correlated grip
strength to anthropometric data of the hand for
males and females, separately. He found thumb
circumference to be a good correlate (R2 = 0.5) of
grip strength for males, and hand breadth and
555
finger crotch length to be a good correlate (R2 =
0.8) for females. Harkonen et al., (1993) found
hand length did not significantly predict grip
strength in their study.
The main objective of this study was to
analyze grip strength in relation to the various
factors, cited above, which affect it. Because none
of the previously cited studies have determined the
effects of all these factors combined, and how they
interrelate, an experiment was set up in which grip
strength, of both hands, three wrist positions, and
three dynamometer positions, was measured and
related to basic anthropometric dimensions such as
forearm length, forearm circumference, wrist
circumference, palm thickness, palm breadth, palm
length, and hand length."
METHOD
A 3 * 3 * 2 full factorial model was
developed, consisting of three wrist positions (45"
extended, 45" flexed, and neutral), three
dynamometer grip spans (1=3.5 cm, 2=4.7 cm,
and 3 = 6.0 cm), and two hands (dominant and
non-dominant). Two trials for each of t h e
combinations were taken, giving a database of 36
data elements per subject. Ten male and ten female
participants volunteered for the study. All these
were university students in the age group of 21 to
35.
A Jainar (Model 1) hand dynamometer was
used for the strength measurement tasks. The
anthropometric dimensions were taken using a
standard anthropometric measuring kit (GPM Swiss). A table of adjustable height with an arm
restraint and positions marked for neutral, 45"
flexed, and 45" extended positions of the wrist was
used. The restraint helped position the arm at a 90"
included elbow angle with the upper arm adducted,
and the markings enabled the participants to
position their hands at a repeatable angle while the
study was conducted.
The subjects placed their forearm in the
restraint and were instructed to align their hands
and arms in the same fashion for each trial. The
trials were performed according to the Caldwell
regimen (Caldwell, Chaffin, Dukes-Dobos,
Kroemer, Laubach, Snook, and Wasserman,
1974) and were administered in a random order.
Two minutes of rest time was given between each
trial.
T o find the relation between the
anthropometric dimensions, namely forearm
length, forearm c i r c u m f e r e n c e , wrist
circumference, palm length, palm thickness, palm
breadth and hand length and the grip strength, a
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PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 38th ANNUAL MEETING-1994
span 3 in all the three positions of the wrist namely
neutral, flexion and extension. There is also a high
correlation at span 2 of the handle for the neutral
position of the wrist of both hands and at 45"
extension of the non-dominant hand. Span 3 of the
handle for both the dominant and the nondominant hand shows a significant correlation with
the forearm length in the neutral and the 45" flexion
positions of the wrist, while for the 45" extended
position, a good correlation is indicated only for
the dominant hand.
forward stepwise regression analysis was carried
out for the neutral wrist position with a
significance level of entry of 0.10. The regression
analysis was aimed at identifying the best subset
of anthropometric dimensions to be used for the
correlation analysis.
Furthermore, an analysis of variance was
run to identify the nature of the variance of the
independent variables with respect to the grip
strength. Post-hoc (Tukey) tests was a l s o
performed on significant main effects to illustrate
which level or condition was significantly different
from others.
Table 1. Correlation
Circumference.
RESULTS
Matrix
f o r Wrist
Regression Analysis:
For span 1, no independent variable was
significant enough to enter the stepwise regression
model even at the 0.10 level of significance.
However, for handle span 2, wrist circumference,
palm thickness, and hand breadth were found to be
significant and the model deveIoped had an r2 of
0.79. For handle span 3, wrist circumference,
palm thickness, and forearm length were
significant enough to enter the model at the 0.10
level of significance. This model had an r2 value
of 0.82. The high r2 values of both the models
suggest that a substantial amount of the variation in
the data is explained by the variables chosen.
Hence four anthropometric dimensions were
chosen for a correlation study with the grip
strength : wrist circumference, palm thickness,
hand breadth and forearm length.
Hand
Handle
Corr.
Wrist
position Condition Span
Coefficient
-
1
Neutral
i
Dominant
i
3
I
0.7956
1
Correlation Analysis:
A correlation analysis was conducted for
all four anthropometric dimensions chosen using
the best subset indicated by the stepwise
regression analysis, with wrist position, handle
spacing and hand. A brief summary of the results
of the correlation analysis are given in Tables 1-4
for wrist circumference, palm thickness, hand
breadth and forearm length. Only correlation
coefficients greater that 0.70 and significant at the
0.001 level have been included in the summary
tables. The results of the correlation matrix show
that wrist circumference has a reasonably good
correlation with the non-dominant hand at span 3
of the dynamometer handle for the wrist in the
neutral position. Similarly, for the palm thickness
and hand breadth, there is a high correlation for
both the dominant and non-dominant hands in
11
It
Table 3. Correlation Matrix for Hand Breadth.
Wrist I Hand I Handle I Corr.
position Condition
span Coefficient
Neutral
Neutral
Neutral
Neutral
45" Flex.
45" Flex.
Dominant
Dominant
Non dom.
Non dom.
Dominant
Non dom.
2
45" Ext.
450Ext.
Non dom.
Non dom.
2
3
i
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(R)
3
2
3
i
1
I
I
0.7581
0.7955
0.7303
0.8057
0.7667
0.7171
0.7807
0.7047
0.7635
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PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 38th ANNUAL MEETING-1994
Wrist
Hand
position Condition
II-Neutral
Neutral
45" Flex.
45" Flex.
45" Ext.
Dominant
Non dom.
Dominant
Non dom.
Dominant
Handle
Corr.
span Coefficient
-3
I
3
0.7592
0.7121
0.7907
0.7830
0.7635
557
grip span of the hand dynamometer also showed
that grip strength with spans 2 and 3 was
significantly higher than that of span 1.
Differences between the dominant and the non
dominant hand were also found to be statistically
significant, though the actual differenoe in the
mean values were not appreciably different. The
Tukey analysis is summarized below in Tables 6,
7, 8 and 9 for wrist position, handle span, hand
and gender.
Analysis of Variance:
The ANOVA results are summarized in
Table 5. It may be noted that all the main effects,
namely the wrist position, handle spacing, hand,
and gender are significant at the 0.01 level. The
handle spacing*gender effect was significant as
was the wrist p o s i t i o n * h a n d ,
wrist
position*handle spacing and handle spacing*hand.
Post-hoc (Tukey) tests were performed o n
significant main effects.
Table 5. ANOVA Results.
11t Variable
I DF I s s l - r , l
Gender = G
1
12713.4 0.0033
Subject(Gen) = S(G) 18 20009.7
0.0001
Wrist
Position
=
WP
2
3258.1
L
WP* G
2
253.1
0.2123
WP*S(G)
36
2814.3
Hand
1
377.7
0.0037
Hand* G
1
33.6
0.3339
Hand*S(G)
18
613.1
I
6937.6
71.1
Wrist
Position
Neutral
45" Flexion
45" Extension
Mean
Strength
32.5875
28.4646
27.7667
Tu key
Grouping
A
B
B
Table 7. Tukey test of strength by handle span.
I
I
Mean
I Tukey
11
Table 8. Tukey test of strength by hand.
It
I
Mean
I Tukey II
Hand
Strength
Grou ping
Dominant
30.3306
A
Non dominant
28.8819
B
d
0.0415
DISCUSSION AND CONCLUSIONS
T h e Tukey groupings show that grip
strength with the wrist in neutral position is
significantly different from that when the wrist is
either flexed or extended. However, between the
flexed and the extended positions there is no
significant difference. Similarly, analysis of the
The regression models developed here
have an r2 value of about 0.80 indicating that over
80% of the variation in grip strength is being
explained by the anthropometric dimensions,
namely, wrist circumference, palm thickness, hand
breadth and forearm length.
Palm thickness and hand breadth were
found to be significant correlates of grip strength
of both the dominant and non-dominant hand for
all wrist positions. As the handle span increases
the forearm length was also found to be a good
correlate. Wrist circumference had a good
correlation only with the non-dominant hand in
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558
PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 38th ANNUAL MEETING-1994
handle span 3. Thus, these anthropometric
dimensions could be used to develop empirical
models to predict grip strength. Such models could
help draw standards for work in critical areas
where grip strength is an important factor.
It was found that the grip strength was
significantly higher when the wrist was in the
neutral position as compared to when the wrist
was either flexed or extended. Other points noted
are that the grip strength in flexion was about 87%
that of the neutral wrist grip strength, much higher
than in previous studies (Hallbeck and McMullin,
1993, Hallbeck and McMullin, 1991, and PutzAnderson, 1988). The grip strength with the wrist
extended was about 85%of neutral grip strength.
Between the flexed and the extended positions no
statistically significant difference was noted, in
contrast to that found by Hallbeck and McMullin
(1993) and Putz-Anderson (1988). The mean
difference between the grip strength of t h e
dominant and the non-dominant hand was
comparable to previous studies, showing the nondominant strength to be approximately 95% that of
the dominant hand. Similarly, there was a
significant difference in grip strength between span
1 and spans 2 and 3. This information is of
importance to hand tool designers. Span 1 of the
dynamometer yielded only 61% of the grip
strength as compared to when the handle was in
spans 2 and 3. This works out to an optimum
range of 4.7 to 6.0 cm for grip span.
A significant gender effect was found with
respect to the grip strength. For span 1, the female
participants were found to have about 91% as
much strength as that of the male participants.
However this decreased markedly as the positions
of the handle became larger, with span 2 indicating
about 75% and span 3 yielding only 68% that of
the males. This could well be explained by the
natural anthropometric differences between males
and females.
Wrist position, handle span and their
interaction were also significant. This indicates
that as the wrist deviated from neutral, the
differences between handle spans became more
pronounced.
Some of the factors not considered in this
study are the variations in grip strength with the
hand in the pronated and supinated positions.
Similarly, this study confined itself to an adducted
arm with the elbow at 90". Many practical
applications and work situations call for use of
hand tools with the hands in postures with the arm
extended or abducted, and the palm in pronated or
supinated positions. Further studies on such
aspects would be beneficial to the ergonomist.
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