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258 International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5
Research
Research
Hand grip strength is a measure of
the force exerted by the hand dur-
ing a maximum isometric contrac-
tion (Stechtman et al, 2003; Svens
and Lee, 2005). The purpose of grip strength
evaluation is to measure a person’s grip strength
relative to normative data, and to monitor a per-
son’s progress following hand injury or surgery
(Stechtman et al, 2003; Svens and Lee, 2005).
While there are a variety of instruments avail-
able for measuring grip strength, not all instru-
ments have been proven to be reliable or valid
(Stechtman et al, 2005). Fess (1968) stressed
that the reliability and validity of a grip strength
instrument is crucial to the quality of the results
obtained. Therefore, establishing reliability and
validity of an instrument is essential for clinical
practice. Hand grip dynamometry is used for
assessing upper limb impairment, work capacity
following injury or disease and rehabilitation
progression and/or potential following injury or
surgery (Reuter et al, 2011).
Reliability and validity of an
electronic dynamometer for
measuring grip strength
Reliability is the extent to which a measure-
ment is consistent and free from error. Good
test-retest reliability is the ability of an instru-
ment to measure accurately and consistently
over time (Stechtman et al, 2005). Intraclass
correlation coefficient (ICC) is recommended
for determining reliability, as it assesses
the degree of association and agreement
among instruments (Portney and Watkins,
2008; Vincent, 2005). Validity is the extent
to which an instrument measures what it is
intended to measure, and t he most effective
form of validity is criterion related validity
(Mathiowetz, 2002; Stechtman et al, 2005).
Criterion related validity is also defined as
concurrent validity, and involves comparing
an instrument to a ‘gold standard’ in order to
prove that the outcomes of one instrument can
be used as a substitute measure for an estab-
lished gold standard criterion test (Stechtman
et al, 2005; Vincent, 2005). The Jamar hydrau-
lic dynamometer was developed by Bechtol
Aims: This article describes a study aiming to establish the concurrent validity and test-retest reliability
of the Biometrics E-LINK EP9 electronic dynamometer.
Methods: Grip strength testing was performed on 49 healthy participants. Three trials were
completed for the right and left hands on the Biometrics and Jamar dynamometers, using a repeated
measures design. Data was compared and used to establish concurrent validity of the Biometrics
dynamometer. Fifteen participants repeated the testing a week later, for test-retest reliability of the
Biometrics dynamometer.
Findings: The Biometrics E-LINK EP9 evaluation system was found to have excellent validity (ICC
0.983–0.986). However, a small but statistically signicant difference between the right hand grip
strength scores of the Biometrics (31.65 ± 8.89) and Jamar (30.44 ± 9.49) dynamometer was revealed
(p ≤ 0.05). Test-retest reliability of the Biometrics system proved excellent, with ICC scores of 0.986
for the left hand and 0.996 for the right hand.
Conclusions: The results indicate that the Biometrics E-LINK EP9 evaluation system is valid, reliable
and comparable to the Jamar hydraulic dynamometer, when used for measuring grip strength with
the second handle position. However, due to the statistically signicant differences found for the right
hand grip strength scores, therapists should exercise caution when interchanging instruments.
Key words: n dynamometer n grip strength n test-retest
Submitted 6 September, sent back for revisions 1 November; accepted for publication following double-blind peer review
19 November 2010
Deborah Allen, Fiona Barnett
Deborah Allen is
Honours Graduate,
Occupational Therapy
Discipline, James Cook
University; and Fiona
Barnett is Senior
Lecturer, Occupational
Therapy Discipline,
James Cook University,
Townsville, Australia
Correspondence to:
F Barnett
E-mail: ona.barnett@
jcu.edu.au
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International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 259
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betw een the Jama r dynam ometer and the ir
respective electronic dynamometers (ICC=
0.957–0.990) when using the second han-
dle position (Stechtman, 2003; Bohannon,
2005; Stechtman et al, 2005). In contrast,
one study reported reasonable to good con-
current validity (ICC<0.900) (Svens and Lee,
2005). Therefore, the purpose of this study
was to establish the concurrent validity and
test-retest reliability of the Biometrics elec-
tronic dynamometer, and compare it with the
criterion standard hydraulic Jamar dynamom-
eter for measurement of grip strength among
healthy participants. This study aims to prove
the hypothesis that the Biometrics E-LINK
EP9 evaluation system is reliable, valid and
comparable to the Jamar hydraulic dynamom-
eter, when used for measuring grip strength on
the second handle position.
METHODS
Participants
The participants were a convenient sample.
Forty nine university students (seven males
and 42 females) volunteered for this project.
Participants were aged between 18 and 25
years with no known history of impaired cog-
nitive functioning, physical disability, or cur-
rent upper extremity injury. On meeting the
(1954) and is the tool most widely used by
clinicians for hand grip measurement (Innes,
1999). Studies have since reported high valid-
ity and/or reliability of this instrument, and
normative data referencing healthy popula-
tions have been developed for it (Stechtman et
al, 2005; Svens and Lee, 2005). For these rea-
sons, the Jamar is considered to be one such
‘gold standard’ instrument, and many authors
have used the Jamar as a criterion standard
to validate other instruments, both hydraulic
and electronic (Mathiowetz, 2002; Stechtman
et al, 2003; Bohannon, 2005; Stechtman et
al, 2005; Svens and Lee, 2005). Examples
of hydraulic dynamometers with proven
reliability and validity include the Baseline
and Rolyan dynamometers, while exam-
ples of electronic dynamometers include the
BTE-Primus and the DynEx dynamometers
(Mathiowetz et al, 2000; Mathiowetz, 2002;
Stechtman et al, 2003; Stechtman et al, 2005).
Electronic or computer connected
dynamometers offer advantages over hydrau-
lic dynamometers including identifying
fatigue index during a prolonged isometric
contraction, increased sensitivity to applied
force, digital readouts which increase inter-
rate reliability and a decrease in manual
reading errors, and automated calculations
(Stechtman et al, 2005; Svens and Lee, 2005).
One such electronic dynamometer that has
recently become available is the Biometrics
E-LINK EP9 evaluation system (Biometrics
Ltd, Gwent, UK, 2006). The website of the
Biometrics E-LINK EP9 dynamometer
describes it as a computerised tool for evaluat-
ing grip strength in 0.1 increments (kg or lbs),
and can perform tests that could not be done
with manual devices (Biometrics Ltd, 2010.).
The instrument is connected to the E-LINK
software and measures grip strength with three
different tests available:
n Standard peak force grip test
n Sustained grip test
n Rapid exchange test.
While there are no current data available on
the reliability and validity of the Biometrics
elec troni c dyn amome ter, four studie s have
used the criterion standard Jamar hydrau-
lic dynamometer to evaluate the reliability
and validity of other electronic dynamome-
ters, including the GripTrack, BTE-Primus,
MicroFET 4 and the DynEx dynamom-
eters (Mathiowetz, 2002; Stechtman et al,
2003; Stechtman et al, 2005; Svens and Lee,
2005). Three of the four studies reported
very good to excellent concurrent validity
Figure 1. Biometrics E-LINK EP9 Hand grip dynamometer.
260 International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5
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above requirements for inclusion, participants
completed the informed consent approved
by a University Human Research Ethics
Committee. Eighty-six percent of participants
were right handed.
Instruments
One Jamar hydraulic dynamometer and one
Biometrics E-Link grip strength attach-
ment (G200) (Figure 1) were used to obtain
static grip strength measurements on the sec-
ond handle position of each dynamometer.
Maximal grip strength was recorded in kilo-
grams of force as the mathematical average of
three successive trials. The Jamar dynamom-
eter was calibrated using known weights to
ensure accuracy prior to data collection. The
Biometrics E-Link system was calibrated by
the manufacturer prior to the study. Prior to
the trials, familiarisation occurred via a dem-
onstration by the test administrator and a prac-
tice trial by the participants.
Procedure
Participants’ grip strengths were evaluated
using the Biometrics E-LINK EP9 system and
Jamar hydraulic dynamometer to measure con-
current validity. Each grip strength test con-
sisted of three maximal repeated contractions
(trials) for each hand on the second handle
position of the dynamometer. The testing was
performed in a non-alternating manner in line
with previous studies comparing electronic
dynamometers with the Jamar (Bohannon,
2005; Svens and Lee, 2005; Stechtman et al,
2005): three grip strength trials were obtained
for the right hand using the Jamar dynamom-
eter then three trials were obtained for left
hand using the Jamar. The process was then
repeated using the Biometrics E-LINK EP9
evaluation system. The duration of each con-
traction was three seconds, with a 15 second
break between trials, and a five minute break
between instruments. Mathiowetz (1990)
found that 15 second breaks between trials
and five minute break between instruments is
sufficient to reduce the impact of fatigue. Trial
duration and rest periods were timed with a
stopwatch. Fifteen of the forty-nine partici-
pants were re-tested a week later using the
Biometrics evaluation system, using the above
testing procedure to examine test-retest reli-
ability.
Specific positioning protocols were used
throughout testing. Participants were posi-
tioned in the appropriate seated position as
recommended by the American Society of
Hand Therapists (ASHT): shoulders adducted
and neutrally rotated, elbow flexed to 90º,
forearm in neutral and wrist between 0–30º of
extension and 0–15º of ulna deviation and feet
flat on the floor (Bohannon and Schaubert,
2005). The participants were instructed to
maintain this position throughout testing.
To ensure consistency, participants received
no visual or auditory feedback during testing,
and were coached using the same standardised
verbal directions. The directions given were as
follows: ‘First we will test your left hand. You
will be required to grip the dynamometer as
hard as you can, and then relax. I’ll count for
you and tell you when to relax. Go. One, two,
three, relax. Ok, that was good. Again, grip
as hard as you can, One, two, three, release.
Good.’ The same standardised and reserved
instructions and feedback were given for each
trial, hand and instrument.
Data analysis
For the participant data, the average of the
three trials was calculated and used as the grip
strength score for each test. All grip strength
measurements were expressed in kilograms of
force. Concurrent validity was calculated to
indicate consistency between the Biometrics
E-Link EP9 Evaluation System dynamome-
ter and the Jamar dyn am om eter. Tes t- retest
reliability was calculated to indicate consist-
ency of force measurements of the Biometrics
evaluation system.
Intraclass correlations (ICC) were per-
formed to determine concurrent validity and
test-retest reliability. ICC reliability has pre-
viously been determined to be an appropri-
ate indicator of test retest reliability (Vincent,
2005). In addition, a repeated measures anal-
ysis of variance (ANOVA) with one within-
participants factor of instrument (Biometrics
versus Jamar) was conducted to deter-
mine whether differences in strength scores
existed between instruments. Differences
were considered significant at the 0.05 level
of significance.
Findings
Prior to statistical analysis, data were exam-
ined to ensure that the assumption of normal-
ity were met. Variables were examined for
kurtosis and skewness and the data were deter-
mined to be normally distributed. Normally
distributed variables will have kurtosis val-
ues not exceeding 3, and skewness values not
exceeding 2 (Vincent, 2005). Kurtosis val-
ues for the current study ranged from 0.533
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International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 261
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to 0.674 and skewness values ranged from
1.182 to 1.249. Data were also screened for
outliers by examining box plots. Participant
4 was determined to be an outlier, and the
data were excluded from further analysis.
Descriptive statistics of grip strength scores
for the Biometrics and Jamar dynamometers
are provided in Table 1.
The Biometrics E-LINK EP9 evaluation
system was found to have excellent validity
(r = 0.983; 0.986). The repeated measures
ANOVA revealed no significant differences
between the left hand grip strength scores,
however a small but significant difference
between the right hand grip strength scores of
the Biometrics and Jamar dynamometer was
found ( F = 14.81; p = 0.000) (Table 2).
Test-retest reliability of the Biometrics
sy ste m proved ex cel lent for t he lef t ha nd
(r = 0.986) and for the right hand (r = 0.996).
This suggests that the grip strength scores
obtained with the Biometrics system were sta-
ble over the two testing periods.
DISCUSSION
The advantages of using a computerised
dynamometer include increased sensitivity to
applied force, digital readouts which increase
inter-rate reliability, a decrease in manual
reading errors and the ability to evaluate grip
strength to the closest 0.1 increments (kg or
lbs) compared to the closest 5lb increments on
the Jamar hydraulic dynamometer. However,
the concurrent validity and reliability of the
Biometrics E-LINK EP9 Evaluation System
for measuring grip strength have not been
reported. This study compared the electronic
Biometrics dynamometer and the hydraulic
Jamar dynamometer to provide the valid-
ity and reliability values of the Biometrics
E-LINK EP9 Evaluation System based on data
derived from healthy human participants.
Validity and Reliability
Concurrent validity
Correlation coefficients greater than 0.750
are considered reasonable for validity, how-
ever to fulfil the requirements of comparabil-
ity of the instruments, the ICC value should
exceed 0.900 (Svens and Lee, 2005). The con-
current validity between the Biometrics and
Jamar dynamometers was found to be excel-
lent for both the right (0.986) and left hands
(0.983), and indicates that both the Jamar
and Biometrics dynamometers measure the
same construct of grip strength. Results also
indicate that the Biometrics is a valid tool
for measuring grip strength. These findings
are similar to previous studies (Stechtman et
al, 2003; Bohannon, 2005; Stechtman et al,
2005; Svens and Lee, 2005) that have used the
‘gold standard’ Jamar dynamometer as a cri-
terion standard, correlating it to various grip
strength electronic tools (DynEx, GripTrack,
BTE-Primus and MicroFET 4) to establish
concurrent validity and inter-instrument relia-
bility. These studies revealed good to excellent
concurrent validity and inter-instrument reli-
ability scores, with values ranging from 0.800
to 0.990 (Stechtman et al, 2003; Bohannon,
2005; Stechtman et al, 2005; Svens and
Lee, 2005).
Despite the excellent concurrent valid-
ity values, significant differences in the right
grip strength scores between the Jamar and
Biometrics dynamometers were revealed.
Mean grip strength scores of the right hand
measured with the Biometrics dynamom-
eter were slightly but significantly higher
than those measured with the Jamar. This
indicates that the Biometrics is comparable
to the Jamar dynamometer when measur-
ing the left hand, however it is not as com-
parable when measuring the right. One
previous study that compared an electronic
dynamometer to a hydraulic dynamometer
revealed similar results, with the MicroFET
4 having significantly higher average means
for the left hand than the Jamar (Bohannon,
2005). Although the high correlation coef-
ficient indicates association between two or
more scores (in this case the grip strength
scores obtained on the two instruments),
comparison testing (ANOVA) revealed sig-
nificant statistical differences between scores
Table 1.
Mean ± SD of grip strength scores (kg) of the
Biometrics and Jamar dynamometers
n = 48 Biometrics Jamar
Right hand 31.65 ± 8.89 30.44 ± 9.49*
Left hand 28.54 ± 9.76 28.65 ± 9.62
*p <0.05
Table 2.
ANOVA results for Biometrics
and Jamar dynamometers
Wilks’
Lambda Df F Sig of F
Left Hand 0.998 1/47 0.095 0.759
Right Hand 0.760 1/47 14.811 0.000*
* Signicant difference
262 International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5
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obtained on the two instruments. Therefore,
if one instrument demonstrates consistently
higher scores than the other, it is possible
to find significant differences between the
scores obtained on the two instruments, and
yet obtain a high concurrent validity correla-
tion coefficient between the two instruments
(Stechtman et al, 2005). Despite the signifi-
cant differences found in the current study
between mean grip strength scores for the
right hand, the high concurrent validity sug-
gests that the Biometrics is equivalent to the
Jamar in obtaining grip strength scores. Only
instruments that have low values and signifi-
cantly different statistical results for concur-
rent validity are determined to not measure
grip strength with reasonable comparability
to the Jamar dynamometer (Stechtman et al,
2005). The findings of this study indicate that,
when used under the same conditions as out-
lined in the methodology, clinicians can use
the Biometrics on the second handle position
and know that it is reliable, valid and com-
parable to the second hand position of the
Jamar dynamometer.
Test re-test reliability
According to Fess (1968), the effective-
ness of an instrument cannot be determined
without reliability and validity values.
Good reliability is indicated by correlation
coefficients of greater than 0.750, however
with clinical measurement reliability values
should exceed 0.900 (Stechtman et al, 2003).
The findings of the present study revealed
excellent test-retest reliability values for
the Biometrics dynamometer. This indicates
that the Biometrics is consistent in measur-
ing grip strength scores, and suggests the grip
strength scores were stable over the two test-
ing sessions for the Biometrics dynamome-
ter. Previous studies (Stechtman et al, 2003;
Stechtman et al, 2005) of test-retest reliabil-
ity of electronic dynamometers including the
DynEx and BTE-Primus, have shown high
test-retest reliability values ranging from
0.970 to 0.984.
Handle position
Throughout this study, data was obtained
using the Jamar and Biometrics dynamom-
eters, with both instruments set to the second
handle position. As the Jamar and Biometrics
have different handle shapes, and the Jamar
handle is positioned at a slightly further dis-
tance from the base of the dynamometer than
the Biometrics when in the second handle
position, depending on hand size, many par-
ticipants may not have been able to obtain
optimum hand and finger position to produce
maximal grip strength. A study of 288 par-
ticipants by Firrell and Crain (1995) found
that 89% of participants had maximal grip
strength on the second handle position, how-
ever since no clear significant correlation
between hand size and maximal handle set-
ting was evident, it was recommended that
grip strength of all participants should be
consistently measured at the second han-
dle setting irrespective of age, weight or
hand dimensions.
Instrument design
While there are several instruments avail-
able for measuring grip strength, the Jamar
hydraulic dynamometer is used most often
and is regarded as the ‘gold standard’ of grip
strength measuring devices. For this reason
it is most often used as a criterion standard
to establish the reliability and validity of
newer grip strength measuring instruments
(Stechtman et al, 2005). However, differences
in the design of the instruments being com-
pared, including handle shape, weight and
data display, may contribute to significantly
different results between the two instruments,
as seen with the current study (Bohannon,
2005; Svens and Lee, 2005).
The handle of the load cell of the Biometrics
is a slightly different shape and, when in
the second handle position, results in a grip
expanse that is several millimetres larger than
the hydraulic Jamar in the same handle posi-
tion. This would increase the force exerted
by the subject onto the Biometrics grip
strength attachment.
Although the hydraulic Jamar dynamometer
measures grip strength accurately (±3%), it
incorporates a dial display which is differenti-
ated by 5lb intervals (Stechtman et al, 2003;
Stechtman et al, 2005). As a result, this dis-
play feature has the potential to contribute to
measurement error through manual reading
error, as the tester had to estimate the grip
strength score when the needle stopped out-
side the marked numbers. The Biometrics
electronic dynamometer, however, is computer
connected, and records grip strength measure-
ments to the nearest tenth of a kilogram, on a
digital display. This decreases the potential of
measurement error and increases inter-rater
reliability, as results obtained by differ-
ent testers are automatically recorded by the
software. Electronic dynamometers also have
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International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 263
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increased sensitivity to applied force, which
therefore enables electronic dynamometers,
such as the Biometrics to record low grip
strength scores that may not have registered
on the Jamar.
Testing procedure
A wide range of testing positions and proce-
dures have been developed for grip strength
testing, however it is generally agreed that
standardised testing position and procedure
are necessary when establishing the reliabil-
ity and validity of new instruments. As with
the current study, the standard seated posi-
tion recommended by the ASHT for measur-
ing grip strength is generally used by authors
when comparing electronic dynamometers to
the hydraulic Jamar dynamometer in order
to establish concurrent validity and inter-
instrument reliability (Stechtman et al, 2003;
Bohannon, 2005; Stechtman et al, 2005; Svens
and Lee, 2005).
Testing procedures used when establishing
the reliability and validity of a new instru-
ment vary widely. Basic testing procedure
involved obtaining grip strength measure-
ments from three trials of each hand with
both instruments, in this case, the Jamar and
Biometrics dynamometers. This repeat test-
ing often causes a noticeable decrease of grip
strength over time, and this is an indication
that fatigue is present (Svens and Lee, 2005).
Fatigue is a compounding variable that should
be avoided to in order to ensure consistency of
results. To decrease the risk of fatigue impact-
ing on the study results, rest periods between
trials and instruments were used. Rest period
durations used in this study were 15 seconds
between trials, and a five minute interval
between instruments.
Previous studies (Stechtman et al, 2003;
Bohannon, 2005; Stechtman et al, 2005; Svens
and Lee, 2005) have used rest periods of 15,
30, and 60 seconds between trials, and no sig-
nificant differences between the rest period
durations were found. A study conducted by
Mathiowetz (1990) found that rest periods of
15 seconds between trials and five minutes
between instruments were adequate to reduce
the effects of fatigue when using three second
trials. Stetchman et al (2003), however, found
that rest periods as outlined by Mathiowetz
(1990) were insufficient to reduce the effects
of fatigue when using trials longer than three
seconds. Therefore, fatigue was determined
not to be a contributing factor to the signifi-
cantly different results revealed in this study,
as three second trials and appropriate rest
breaks, as outlined by Mathiowetz (1990),
were used.
Limitations
The main limitation of this study was the
small sample size (n = 49) which may have
reduced the generalisability of this study.
Although the sample was sufficient to pro-
vide adequate statistical power for the intra-
class correlation coefficients, it may have
prevented the realisations of significant dif-
ferences in some comparisons. The small sam-
ple size of unequal demographics (males =
7, females = 42; right hand dominant = 86%)
meant that the study was not representative
of the target population, and the application
of more detailed analysis and the influence
of confounders, e.g., effects of hand domi-
nance and gender, could not be explored ade-
quately. The small age range present in the
convenience sample also meant that this study
was unable to establish age norms for the
Biometrics dynamometer.
Another limiting factor may have been
related to the handle position of the instru-
ment during testing. The handles of the
dynamometers, when in the second handle
position, are slightly different in regards to
the distance from the bases of the instruments.
This d ifference in the dist an ce between the
instruments, in combination with differences
in hand size, may have resulted in participants
not being able to obtain optimal hand and
finger position in order to produce maximal
grip strength.
The dial display of the Jamar dynamometer
was another limitation of the instrument, as the
tester was required to estimate results when
the needle stopped outside one of the 5kg
interval readings. This may have contributed to
measurement error and in turn impacted on the
results of the study.
Practical implications
The successful undertaking of many activi-
ties of daily living requires a certain
degree of hand grip strength. As hand
grip strength is affected by injury and dis-
eas e it is i m p o rtant t h a t accur a t e grip
strength measurement is employed for reha-
bilitation progression in clinical practice
(Reuter et al, 2011). It is therefore vital
that validity and reliability data be estab-
lished for electronic hand grip dynamom-
eter systems as they become available. This
study has established that the Biometrics
264 International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5
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E-LINK EP9 evaluation system is a valid
and reliable measurement tool to use by
rehabilitation professionals.
Recommendations
Future studies into the reliability and validity
of the Biometrics E-LINK EP9 evaluation sys-
tem should be conducted using a larger sample
that is representative of the target population
in age, gender and hand dominance. Results
from such studies could then be generalised to
the larger population, and normative data for
the Biometrics dynamometer could be estab-
lished and programmed into the software.
While this study determined the second handle
position of the Biometrics E-LINK EP9 evalu-
ation system to be reliable, valid and compara-
ble to the second handle position of the Jamar
dynamometer, future studies should be con-
ducted to determine the reliability and validity of
the other four handle positions of the Biometrics
in relation to the Jamar dynamometer.
The accuracy of the Jamar and the
Biometrics dynamometers were established
using known weights prior to data collec-
tion, however the instruments were not cali-
brated throughout the study as they were only
used for two testing sessions. It is recom-
mended that when using hand dynamometers
frequently in clinical practice that they are
calibrated at least every three months (Svens
and Lee, 2005). Even though the accuracy of
an electronic dynamometer may have been
established using known weights and the
concurrent validity with a Jamar dynamom-
eter has been established, the ability to inter-
change grip strength dynamometers should
never be assumed. This is due to the differ-
ences in calibration and age of the individual
instruments, and for these reasons it is rec-
ommended that the same instrument should
be used throughout a person’s rehabilitation
period, until inter-instrument reliability is
established (Stechtman et al, 2005; Svens and
Lee, 2005).
CONCLUSION
Despite the limitations of this study, the
results suggest that the Biometrics E-LINK
EP9 evaluation system is valid, reliable and
comparable to the Jamar hydraulic dynamom-
eter when used for measuring grip strength
on the second handle position. However, due
to significant differences found between the
right hand grip strength scores between the
two instruments, therapists should exercise
caution when interchanging instruments and
it is recommended that the same dynamometer
be used to measure grip strength of a patient
throughout their treatment programme. IJTR
Conflict of interest: none
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n Determining the reliability and validity of an instrument is essential before it
is applied to clinical practice.
n The Biometrics E-LINK EP9 evaluation system is a valid and reliable tool for
measuring grip strength.
n The Biometrics E-LINK EP9 evaluation system allows for ease and accuracy
when assessing or monitoring patients.
KEY POINTS
Research
International Journal of Therapy and Rehabilitation, May 2011, Vol 18, No 5 265
Research
COMMENTARIES
Therapists require accurate data
for hand grip strength to assess
impairment and evaluate reha-
bilitation following injury, surgery, or
disease. Recent advances in technol-
ogy have produced several promising
tools that may make this assessment
more reliable and accurate. For exam-
ple, electronic and computer-linked
dynamometers have several advan-
tages over conventional hydraulic
dynamometers, including increased
sensitivity and automated data entry
and calculation.
This article
The article evaluates the validity and reli-
ability of an electronic dynamometer, the
Biometrics E-LINK EP9, and compares it
directly with an industry standard, the
Jamar hydraulic. The results indicate that
the Biometrics system is valid, reliable,
and comparable to the Jamar system
under the experimental conditions. The
difference in sensitivity (increments of
0.1 kg or lb for the Biometrics versus 5 lb
for the Jamar) alone makes the electronic
dynamometer attractive to therapists eval-
uating injured patients.
I liked this article. The methods and
results are presented clearly, the conclu-
sions are straightforward, and the find-
ings are put into context of previous
research in the field. It remains to be seen
if the small, albeit statistically significant,
difference in right hand strength meas-
ured by the two instruments is of “practi-
cal” significance in the clinical setting.
In any case, therapists may want to use
the same instrument when evaluating an
individual patient. I would have liked to
seen a comparison of price of the instru-
ments, but this is a minor point. I suggest
that future studies include a wider range
of age and demographics (with respect
to gender and hand dominance) of the
test subjects in order to generate a more
comprehensive set of norms.
Conclusions
I am concerned, however, with the
design of the handles of both instru-
ments. This is not a shortcoming of
the article, but there is a lack of
available instrumentation for measuring
grip or pinch strength of people with
reduced web spaces. The handles of the
dynamometers are too thick to measure
grip or pinch strength of a patient who
has lost multiple fingers and/or has
reduced prehension. I would like to
see development of electronic- or com-
puter-linked dynamometers that can
accurately and reliably measure grip or
pinch strength for these extreme cases.
Martin A. Stapanian, Ph.D.
Research Ecologist
Huron, Ohio, USA
mastapanian@bex.net
“The results indicate that the Biometrics system is
valid, reliable, and comparable to the Jamar system
under the experimental conditions.”
The background for all treatment
should be evidence based. For
an occupational therapist work-
ing in a clinical practice it is very
important to use equipment that is
validated, and reliability evaluated.
Most therapists working with patients
following hand injury or surgery evalu-
ate the progress of a treatment using
the Jamar dynamometer for the grip
strength test. The reason is, of course,
because the Jamar dynamometer is
tested for reliability and validity. The
use of Jamar dynamometer is well
described and easy to follow.
This article evaluates one of the newer,
computerised, dynamometer systems that
have appeared on the arena for measur-
ing grip strength. Examples of these
systems are the GripTrack, BTE-Primus,
MicroFET 4 and the DynEx dynamom-
eters. Earlier articles have found that by
using the Jamar Dynamometer as a ‘gold
standard’, those dynamometers can be
evaluated for reliability and validity, and
three out of the four studies described
very good to excellent concurrent valid-
ity between the Jamar dynamometer
and their respective electronic dynamom-
eters. The Biometrics electronic dynamom-
eter has not been evaluated before, there-
fore this study compares the criterion
standard hydraulic Jamar dynamometer
with the Biometrics electronic dynamom-
eter for validity and test-retest reli-
ability by measuring grip strength on
healthy participants.
The study
The methodology of the study is clearly
described, and uses the manual from the
Jamar dynamometer; the same proce-
dures for testing the hand grip strengths
are used for the two instruments accord-
ing to the recommendation by the
American Society of Hand Therapists
(ASHT). I found it interesting that I could
not tell from this article if the same
test administrator was in charge of all
the measurements.
The authors have shown that the
Biometrics E-LINK EP9 has excellent
validity, with a small but notable differ-
ence between the right hand strength
scores. The test-retest reliability showed
excellent for the both hands. However,
the small sample size (n = 49) and the
unequal demographics made the result
less powerful, and also made it impos-
sible to establish age norms for the
Biometrics dynamometer.
Conclusions
This article shows the importance of
using instruments that are evaluated
and proven valid and reliable for thera-
pists working in this area. It is also
important to use new computerised sys-
tems because they decrease the likeli-
hood of recording error, since the meas-
urements are automatically recorded by
the software.
Hélène Fitinghoff
Occupational Therapist,
University Lecturer,
Karolinska Institutet,
Stockholm
Helene.fitinghoff@ki.se
“It is very important to use equipment that is vali-
dated, and reliability evaluated.”
