GRIP AND
PINCH
STRENGTH VARIATIONS
TYPES OF WORKERS
IN DIFFERENT
I. C. JOSTY, M. P. H. TYLER, P. C. SHEWELL and A. H. N. ROBERTS
From the Plastic Surgery Department, Stoke Mandeville Hospital, Aylesbury, UK
We measured grip and pinch strengths in non-manual, light manual and heavy manual workers
using a Jamar dynamometer and a pinch measuring device. Heavy manual workers had the
strongest grips with the least difference between sides. Office workers had the weakest grips and
the greatest difference between sides. Light manual workers were between these two groups.
Consequently, the occupation of the patient must be taken into account when using grip and
pinch strength measurements to assess the need for rehabilitation and in medicolegal reports.
Journal of Hand Surgery (British and European Volume, 1997) 22B: 2." 266-269
Subjects were seated comfortably on a chair without
armrests. The shoulder was adducted and neutrally
rotated, the elbow flexed at 90 °, with the forearm and
wrist in neutral position. The same arm position was
used for testing both grip and pinch strengths. The
pinch device was held between the proximal interphalangeal joint of the index finger and the thumb tip. Before
testing, the reason for the study was explained, the
method of testing demonstrated and subjects were
allowed to practise once with their dominant hand.
Specific verbal instructions were given in the same
tone of voice, "I want you to hold the handle/button
and grip/pinch as hard as you can." An opportunity to
ask questions was provided. In order to eliminate the
effect of hand muscle fatigue, the test was performed on
one hand after another, always starting with the dominant hand. Two grip/pinch measurements were recorded
for each hand and, if the difference was more than 10%,
a third reading was taken. Grip strength measurement
was followed by pinch strength and the highest value
used.
Hand injuries usually affect grip and pinch strength,
temporarily or permanently. These parameters are often
used to assess progress during rehabilitation and the
need for further physiotherapy. Grip strength is also a
common assessment in medicolegal examinations and,
by comparison with the uninjured side, can provide
objective evidence of residual hand disability.
Traditionally, following the study by Bechtol (1954),
the dominant hand is regarded as being 10% stronger
than the non-dominant. We have observed, however,
that this might not be true for all working populations.
The aim of this study was to measure the grip and
pinch strengths in three different working populations:
non-manual workers (office workers), light manual
workers (car mechanics) and heavy manual workers
(farmers).
MATERIALS AND METHODS
All the subjects were right-handed male volunteers.
Subjects who had a history of hand injury or degenerative hand condition were excluded from the study. We
studied right-handed subjects only as Peterson et al
(1989) demonstrated that the 10% rule was not applicable to left-handed subjects.
Thirty-four non-manual workers (age range 19-45,
mean 29 years), 38 light manual workers (age range
16-56, mean 30 years) and 32 heavy manual workers
(age range 17-65, mean 43 years) were tested for grip
and pinch strength. The subjects were from local offices,
garages and farms, respectively.
Tests were performed using single, factory calibrated,
Jamar dynamometer and pinch measuring devices. The
third handle position on the dynamometer was used as
previous studies. H/~rkenOnen et al (1993) and Stokes
(1983) have demonstrated that maximal grip strength is
attained at this setting. Both the dynamometer and
pinch device were reset to zero prior to each reading
and were read to the nearest increment of the two scale
divisions.
Statistical methods
The data was analysed using SPSS for Windows v. 6.12.
Normality was assessed using a normal probability plot
and the Shapiro-Wilks statistic. A paired t-test was used
to determine the differences within groups and a single
factor analysis of variance (ANOVA) was used to
determine the differences between groups. A P value
<0.05 was taken as being statistically significant.
RESULTS
Grip strength
Table 1 and Figure 1 show that when non-manual workers are compared with heavy manual workers, the latter
show an increase in both dominant and non-dominant
grip strength values and a decrease in the mean percentage grip strength difference. We found that there was
no statistically significant difference between the dominant and non-dominant grip of heavy manual workers,
Testing
The American Society of Hand Therapists recommendation for testing was followed (Mathiowetz et al, 1984).
266
Downloaded from jhs.sagepub.com at PENNSYLVANIA STATE UNIV on May 11, 2016
267
GRIP STRENGTHS IN DIFFERENT WORKERS
Table 1--Grip strength within populations
Mean dominant
gr~ (kg)
(Range)
Mean non-dominant
grip (kg)
(Range)
Mean percentage grip
strength difference
Office workers
(n=34)
46.1
(33-62)
41.9
(25-60)
+9.1%
(P<0.001)
Car mechanics
(n=38)
52.5
(30-70)
50#
(30-65)
+ 3.4%
(P=0.002)
Farmers
(n=32)
53.7
(40-70)
53.6
(32 70)
+0.1%
(NS)
60
[]
O
tm
[]
55,
©
[]
50,
45,
"~
40
3s
Office workers
Fig 1
Car mechanics
Farm workers
Error bar chart showing grip strength comparisons within and between groups.
but there was in the other groups. Comparison between
groups revealed a significant difference in the mean
percentage grip strength difference between non-manual
and both light and heavy manual workers (P=0.015
and P=0.003, respectively), but not between light and
heavy manual workers.
Pinch strength
It can be seen from Table 2 and Figure 2 that heavy
manual workers show an increase in both dominant and
non-dominant pinch strength values. We found that the
mean percentage pinch strength difference within a
population was statistically significant in non-manual
and light manual workers but not in heavy manual
workers. There was no significant difference in mean
percentage pinch strength differences between the three
groups.
Figure 3 shows the boxplot of the percentage differences between the dominant and non-dominant grip and
pinch strength values for each group. The boxplot graph
shows a box with the upper border being the 75th centile
and the lower the 25th centile. The box contains the
median. The upper and lower limits represent the 95th
Table 2--Pinch strength within populations
Mean mdominant
pinch (kg)
(Range)
Mean non-dominant
pinch (kg)
(Range)
Mean percentage
pinch strength
difference
Office workers
(n= 34)
10.5
(7.5 14)
9.7
(6-12.5)
+ 7.6%
(P= 0.003)
Car mechanics
(n=38)
11.2
(7.5 16)
10.2
(6-15)
+ 8.9%
(e<o.ool)
11.9
(8-16)
11.4
(7.5-16)
+ 4.2%
(NS)
Farmers
(n = 32)
Downloaded from jhs.sagepub.com at PENNSYLVANIA STATE UNIV on May 11, 2016
268
T H E J O U R N A L OF H A N D S U R G E R Y VOL. 22B No. 2 APRIL 1997
13,
[]
[]
t¢3
i
°
3
11,
10'
"~
9'
8
Office workers
Fig 2
Car m e c h a n i c s
Farm
workers
Error bar chart showing pinch strength comparisons within and between groups.
-g
35,
'~
25,
-15
-25
-35
office workers(grip)
Farmers(grip)
Mechanics(pinch)
Mechanics(grip)
ONce worker(pinch)
Farmers(pinch)
O c c u p a t i o n and test
Fig 3
Boxplotto show range of percentagedifferencesfor each population.
and 5th centiles respectively and the dots represent
individual cases outside these limits.
DISCUSSION
Grip and pinch strength measurements are frequently
used to provide an objective outcome measurement for
hand injuries and operations (Macey and Burke, 1995).
They can also be used to gauge the need for further
physiotherapy during hand rehabilitation.
After hand injury or surgery, the grip strength in the
injured hand is compared with that in the uninjured
hand and a percentage difference may be calculated.
Figure 3 demonstrates that the range of this percentage
difference for grip strength decreases as the subjects'
work becomes more manual. We have demonstrated
that, when interpreting grip strength, the 10% rule is
only appropriate for non-manual workers. This implies
that if a manual worker has a high percentage difference
in grip strength following injury, it is more likely to be
a result of the injury rather than a pre-existing difference
between hands. This may indicate the need for further
physiotherapy.
Pinch strength is a useful determinant of thumb
function following injury and we have shown that a true
difference exists between the dominant and nondominant pinch strengths of non-manual and light
manual workers. In a manner analogous to grip strength,
percentage differences between the two sides can be
calculated and used to determine the degree of rehabilitation required.
From our investigation we conclude that the occupation of the patient must be taken into account when
using grip and pinch strength measurement in assessing
the outcome of hand injuries and when providing
medicolegal reports.
Downloaded from jhs.sagepub.com at PENNSYLVANIA STATE UNIV on May 11, 2016
G R I P S T R E N G T H S IN D I F F E R E N T W O R K E R S
Acknowledgements
We are grateful to D r Shine for his guidance with the statistical analysis.
References
Bechtol CO (1954). Grip test: use of a dynamometer with adjustable handle
spacings. Journal of Bone and Joint Surgery, 36A: 820-824.
H/irken6nen R, Piirtomaa M, Alaranta H (1993). Grip strength and hand position of the dynamometer in 204 Finnish adults. Journal of H a n d Surgery,
18B: 129 132.
Macey AC, Burke FD (1995). Outcomes of hand surgery. Journal of H a n d
Surgery, 20B: 841-855.
Mathiowetz V, Weber K, Volland G, Kashman N (1984). Reliability and validity
269
of grip and pinch strength evaluations. Journal of Hand Surgery, 9A:
222-226.
Peterson P, Petrick M, Connor H, Conklin D (1989). Grip strength and hand
dominance: challenging the 10% rule. American Journal of Occupational
Therapy, 43: 444-447.
Stokes H M (1983). The seriously uninjured hand-weakness of grip. Journal of
Occupational Medicine, 25: 683-684.
Received: 29 April 19,96
Accepted after revision: 4 July 1996
A. H. N. Roberts, Plastic Surgery Department, Stoke Mandeville Hospital, Aylesbury, Bucks
HP21 8AL UK.
© 1997 The British Society for Surgery of the Hand
Downloaded from jhs.sagepub.com at PENNSYLVANIA STATE UNIV on May 11, 2016