The rapid exchange grip strength test and the detection of submaximal grip effort


Westbrook, A.P.; Tredgett, M.W.; Davis, T.R.C.; Oni, J.A.

Journal of Hand Surgery 27(2): 329-333

2002


This study assessed the reliability of the rapid exchange grip test for detecting submaximal grip effort, particularly evaluating its performance with motivated subjects with genuine hand weakness secondary to pain. Fifty normal participants performing with maximum effort then feigning hand weakness and 50 patients recovering from carpal tunnel surgery were studied. The results showed that the dynamic measure of grip strength equaled or exceeded the static measure in 28% of maximally performing participants (72% specificity), 58% of the carpal tunnel decompression patients (42% specificity), and 74% of participants giving submaximal grip effort (74% sensitivity). Sensitivities and specificities for other criteria of a positive test were also determined. Our findings suggest that the rapid exchange grip strength test cannot reliably detect voluntary submaximal effort.

The
Rapid
Exchange
Grip
Strength
Test
and
the
Detection
of
Submaximal
Grip
Effort
A.P.
Westbrook,
BM,BS,
M.W.
Tredgett,
MB
ChB,
T.R.C.
Davis,
ChM,
J.A.
Oni,
MB
ChB,
Nottingham,
England
This
study
assessed
the
reliability
of
the
rapid
exchange
grip
test
for
detecting
submaximal
grip
effort,
particularly
evaluating
its
performance
with
motivated
subjects
with
genuine
hand
weakness
secondary
to
pain.
Fifty
normal
participants
performing
with
maximum
effort
then
feigning
hand
weakness
and
50
patients
recovering
from
carpal
tunnel
surgery
were
studied.
The
results
showed
that
the
dynamic
measure
of
grip
strength
equaled
or
exceeded
the
static
measure
in
28%
of
maximally
performing
participants
(72%
specificity),
58%
of
the
carpal
tunnel
decompression
patients
(42%
specificity),
and
74%
of
participants
giving
submaxi-
mal
grip
effort
(74%
sensitivity).
Sensitivities
and
specificities
for
other
criteria
of
a
positive
test
were
also
determined.
Our
findings
suggest
that
the
rapid
exchange
grip
strength
test
cannot
reliably
detect
voluntary
submaximal
effort.
(J
Hand
Surg
2002;27A:329-333.
Copy-
right
©
2002
by
the
American
Society
for
Surgery
of
the
Hand.)
Key
words:
Grip
strength,
measurement,
submaximal
effort.
For
social,
financial,
or
psychological
reasons,
people
injured
at
work
may
not
give
their
true
max-
imal
effort
when
assessing
grip
strength.
Thus
it
is
important
to
develop
sensitive
and
specific
tests
to
detect
submaximal
grip
effort
after
injury
or
surgery.
A
number
of
techniques
have
been
described
to
detect
submaximal
effort.
Some
use
methods
more
appropriate
to
a
research
laboratory
1-4
;
others
can
be
more
readily
performed
in
the
clinical
setting
using
a
Jamar
dynamometer
(Asimov
Engineering,
Santa
Monica,
CA)
in
a
structured
test.
The
5-position
grip
strength
test
s
and
the
rapid
simultaneous
exchange
From
the
Department
of
Trauma
and
Orthopaedics,
Queen's
Medical
Centre,
University
Hospital,
Nottingham,
England.
Received
for
publication
July
24,
2001;
accepted
in
revised
form
October
26,
2001.
No
benefits
in
any
form
have
been received
or
will
be
received
from
a
commercial
party
related
directly
or
indirectly
to
the
subject
of
this
article.
Reprint
requests:
T.R.C.
Davis,
ChM,
Department
of
Trauma
and
Orthopaedics,
Queen's
Medical
Centre,
University
Hospital,
Notting-
ham
NG7
2UH,
England.
Copyright
©
2002
by
the
American
Society
for
Surgery
of
the
Hand
0363-5023/02/27A02-0079$35.00/0
doi:10.1053/jhsu .2002.30910
and
repeat
grip
strength
test
have
been
devised
to
detect
submaximal
effort
in
isolation
or
in
combina-
tion."
Previous
studies
by
our
group
and
others,
however,
suggest
that
the
sensitivity
and
specificity
of
both
the
5-position
grip
strength
test
and
the
rapid
repeat
measurement
of
grip
strength
are
unsatisfac-
tory.
9-
"
The
rapid
exchange
grip
(REG)
strength
test
6-12
is
used
in
clinical
practice
to
identify
submaximal
grip
effort.
Grip
strength
is
first
measured
at
each
of
the
5
settings
of
a
Jamar
dynamometer
in
both
hands.
The
dynamometer
is
then
set
to
the
handle
setting
at
which
maximum
grip
strength
was
mea-
sured
(static
measure)
and
the
patient
is
instructed
to
maximally
grip
the
dynamometer
with
each
hand
alternately
as
rapidly
as
possible.
Although
there
is
no
set
number
of
rapid
measurements,
5
to
10
are
routinely
obtained
for
each
hand.
The
max-
imum
recorded
grip
strength
during
the
rapid
ex-
change
is
the
dynamic
measure.
A
positive
REG
test,
indicating
feigned
weakness,
occurs
if
the
dynamic
measure
equals
or
exceeds
the
static
mea-
sure.
The
Journal
of
Hand
Surgery
329
330
Westbrook
et
al
/
Rapid
Exchange
Grip
Strength
Test
Although
the
REG
strength
test
has
been
found
to
discriminate
between
normal
subjects
and
ma-
lingerers
who
feign
hand
weakness,
6
.
8
.
13
its
valid-
ity
for
detecting
submaximal
effort
in
patients
complaining
of
genuine
hand
pain
is
uncertain.
It
is
not
known
whether
motivated
patients
with
gen-
uine
hand
pain
and
weakness
have
the
same
REG
strength
test
pattern
as
normal
people
or
if
the
pattern
between
the
former
group
is
indistinguish-
able
from
that
of
people
voluntarily
performing
submaximally.
This
study
investigates
the
pattern
of
the
REG
strength
test
in
patients
with
genuine
hand
pain
and
assesses
whether
it
can
differentiate
such
patients
from
those
giving
submaximal
effort.
Patients
and
Methods
Three
groups
of
subjects
underwent
REG
testing.
The
first
group
consisted
of
50
healthy
volunteers
with
no
history
of
upper
limb
pain,
injury,
or
disabil-
ity.
Twenty-five
were
women,
and
the
mean
age
was
38
years
(range,
22-66
years).
This
group
performed
an
REG
strength
test
on
both
hands
while
giving
maximum
effort.
The
second
group
consisted
of
the
same
50
healthy
volunteers
who
1
week
later
repeated
the
REG
strength
test.
This
time
they
were
instructed
to
feign
50%
weakness
of
their
dominant
hand.
The
third
group
consisted
of
50
patients
who
had
undergone
unilateral
open
carpal
tunnel
decompres-
sion
6
weeks
previously.
Thirty-one
of
these
patients
had
undergone
operations
on
their
dominant
hand.
Thirty-seven
of
the
50
were
women,
and
the
mean
age
was
53
years
(range,
22-85
years).
All
com-
plained
of
some
residual
pain
and
scar
tenderness.
Each
was
asked
to
perform
an
REG
strength
test.
The
strength
testing
procedure
was
identical
in
all
3
groups.
Two
calibrated
hydraulic
Jamar
dy-
namometers
were
used,
and
participants
received
standardized
instructions.
Each
subject
was
seated
with
both
shoulders
adducted
and
in
neutral
rota-
tion,
the
elbows
at
90°
flexion,
and
the
forearms
and
wrists
in
neutral
alignment.
Each
participant
first
performed
a
5-position
grip
strength
test
s
for
each
hand
to
ascertain
the
grip
width
at
which
maximum
static
grip
strength
occurred.
This
han-
dle
setting
was
then
used
for
the
rapid
exchange
test,
during
which
the
clinician
supported
both
dynamometers.
Participants
were
asked
to
alter-
nately
grip
each
dynamometer
as
hard
as
possible
at
a
rate
of
60
per
minute
on
10
occasions
or
until
the
subject
had
to
stop
because
of
fatigue
or
dis-
comfort.
The
maximum
dynamic
grip
strength
achieved
for
each
hand
was
then
expressed
as
a
percentage
of
the
initial
static
measure
at
the
same
grip
width
(dynamic/static
X
100%).
No
participant
had
any
prior
experience
or
knowl-
edge
of
either
the
REG
strength
test
or
of the
purpose
of
the
study,
and
a
single
investigator
supervised
all
the
tests.
Sensitivities,
specificities,
and
positive
and
nega-
tive
predictive
values
for
the
grip
test
were
calculated
using
8
different
criteria
to
indicate
a
positive
(sub-
maximal)
effort.
These
criteria
were
the
dynamic
measure
of
grip
strength
equaling
or
exceeding
85%,
90%, 95%,
100%,
101%,
105%,
110%,
and
115%
of
the
static
measure.
At
each
of
these
criteria
for
a
positive
test,
sensitivity
was
determined
by
calculat-
ing
the
percentage
of
participants
giving
submaximal
grip
effort
who
were
correctly
identified.
Specificity
was
calculated
by
using
the
results
for
the
normal
participants
when
performing
with
maximal
effort,
the
carpal
tunnel
surgery
patients,
and
both
these
groups
combined.
For
each
of
these
3
groups
the
specificity
was
equal
to
the
percentage
of
the
group
with
a
negative
test
(correctly
diagnosed
true
hand
weakness).
A
receiver
operating
characteristic
(ROC)
curve
of
sensitivity
and
specificity
of
the
REG
test
was
also
calculated
to
help
determine
the
optimum
criteria
for
a
positive
REG
test.
Results
All
50
normal
volunteers
and
the
50
carpal
tun-
nel
decompression
patients
completed
the
10
rep-
etitions
of
the
dynamic
grip
strength
measurement.
Values
for
mean
static
grip
strength
at
each
of
the
5
handle
settings
are
shown
in
Table
1.
In
37
of
the
50
normal
participants,
maximum
grip
strength
of
the
dominant
hand
occurred
at
the
second
position.
Mean
grip
strength
was
lower
in
the
operated
hands
of
the
carpal
tunnel
decompression
patients,
but
maximum
grip
strength
was
at
position
2
in
33
of
the
50.
The
results
for
the
nondominant
hands
of
the
normal
participants
and
the
nonoperated
hands
of
the
carpal
tunnel
patients
showed
similar
results.
The
maximum
grip
strength
in
the
partic-
ipants
asked
to
feign
50%
weakness
was
at
posi-
tion
2
in
24
and
position
3
in
20
of
the
50.
The
mean
dynamic
grip
strength
was
94%
(95%
CI,
92-96)
of
the
static
measure
for
the
normal
moti-
vated
group
and
95%
(95%
CI,
91-99)
of
the
static
measure
for
the
carpal
tunnel
decompression
group.
The
mean
dynamic
grip
strength
was
126%
MI
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40
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20
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0
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Normals
ificity:Com
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cificity:CTD
nts
sitivity
The
Journal
of
Hand
Surgery
/
Vol.
27A
No.
2
March
2002
331
Table
1.
Mean
(Range)
Grip
Strength
as
Measured
by
a
Jamar
Dynamometer
Mean
Grip
Strength
(kgf)
Grip
Normal,
Motivated
Participants
Carpal
Tunnel
Handle
Participants
Feigning
50%
Weakness
Decompression
Patients
Position
(Dominant
Hand)
(Dominant
Hand)
(Operated
Hand)
1
26
(10-68)
14
(1-32)
11
(2-25)
2
41
(18-67)
18
(3-44)
18
(6-39)
3
38
(18-71)
18
(2-49)
16
(4-38)
4
35
(12-59)
17
(3-44)
14
(3-34)
5
29
(10-55)
15
(1-38)
12
(2-30)
Position
1
is
the
narrowest
handle
setting
and
position
5
is
the
largest
handle
setting.
(95%
CI,
114-138)
of
the
static
measure
for
the
normal
subjects
when
asked
to
feign
50%
hand
weakness.
If
dynamic
grip
equaling
or
exceeding
(100%)
static
grip
is
used
to
indicate
a positive
test,
6
as
is
usually
the
case,
then
14
of
50
maximally
perform-
ing
participants
(72%
specificity)
and
29
of
50
carpal
tunnel
decompression
patients
(42%
speci-
ficity)
would
be
suspected
of
voluntary
submaxi-
mal
effort
(Fig.
1),
and
26%
of
participants
asked
to
feign
50%
hand
weakness
would
not
have
been
detected
(74%
sensitivity).
Using
the
data
from
the
ROC
curve
(Fig.
2)
and
Table
2,
we
found
the
optimum
criterion
for
a
positive
test
if
the
dynamic
measure
equaled
or
exceeded
the
static
measure
by
105%.
Using
this
criterion
gave
a
specificity
of
90%
for
the
maximally
performing
participants
and
82%
for
the
carpal
tunnel
decompression
pa-
tients.
The
sensitivity
of
the
test
using
this
crite-
rion
was
70%.
Table
2
shows
the
specificities
and
sensitivities
and
positive
and
negative
predictive
values
of
the
REG
test
at
the
other
criteria
of
a
positive
test.
These
values
enable
an
examiner
to
calculate
from
the
results
of
a
given
patient
the
chances
of
voluntary
submaximal
effort
going
un-
detected
or
being
falsely
diagnosed.
Further
analysis
of
our
data
revealed
that
the
spec-
ificity
of
the
test
for
the
nondominant
hand
was
similar
to
that
for
the
dominant
hand
and
that
the
pattern
of
strength
in
the
normal
hands
of
patients
with
real
and
voluntary
hand
weakness
behaved
as
our
normal
controls.
Discussion
The
Jamar
dynamometer
provides
an
accurate,
re-
liable,
and
valid
measure
of
isometric
grip
strength
in
motivated
participants.
14
It
is
also
used
in
a
number
85
90
95
100
101
105
110
115
Positive
Test
Criterion
(dynamic/static
x
100%)
Figure
1.
Graphs
of
the
sensitivity
and
specificity
of
the
REG
test
using
different
normal
control
groups
to
determine
specificity
and
different
criteria
for
a
positive
(feigned
weakness)
test.
332
Westbrook
et
al
/
Rapid
Exchange
Grip
Strength
Test
100
80
-
60-
ti
40
a)
(i)
20
0
20
40
60
80
100
Specificity
(%)
Figure
2.
ROC
of
sensitivity
against
specificity
for
the
REG
test.
of
structured
tests
that
attempt
to
determine
sincerity
of
effort.
The
rapid
exchange
and
rapid
simultaneous
grip
strength
tests
have
been
reported
to
accurately
detect
submaximal
grip
effort
with
up
to
80%
sensi-
tivity
and
87%
specificity.
6
'
7
The
5-position
grip
strength
test
exhibits
a
skewed
bell-shaped
curve
when
grip
strength
is
plotted
against
grip
handle
position
for
both
nor-
mal
motivated
subjects
and
those
with
genuine
hand
weakness.
A
flatter
plot
has
been
described
for
participants
with
voluntary
submaximal
ef-
fort.
5
This
difference
could
theoretically
be
used
to
distinguish
between
these
populations;
however,
considerable
variability
exists
between
individu-
als,
and
this
makes
it
difficult
to
detect
submaxi-
mal
effort.
The
REG
test
was
devised
to
over-
come
this
problem.
6.12
The
present
study
found
that
the
standard
criterion
for
a
positive test,
a
dy-
namic
measure
equal
to
or
greater
than
(100%)
the
static
measure,
has
reasonable
specificity
(72%)
in
normal
subjects
and
sensitivity
(74%),
although
it
is
not
as
high
as
previously
reported.
6
7
Furthermore,
the
results
for
the
post—carpal
tunnel
decompression
group
show
that
the
specificity
(42%)
of
the
test
is
much
less
if
it
is
used
to
assess
weakness
in
people
with
hand
pain
and
incorrectly
labels
58%
of
such
motivated
patients
as
voluntarily
performing
sub-
maximally.
If
the
criterion
of
a positive
test
is
changed
to
the
dynamic
measure
(105%)
of
the
static
measure,
however,
the
REG
test
has
reason-
able
specificity,
both
for
normal
subjects
(90%)
and
subjects
with
valid
weakness
caused
by
hand
pain
(82%).
Hildreth
et
a1
6
reported
that
in
normal
healthy
motivated
participants
the
dynamic
measure
of
grip
strength
should
be
approximately
85%
of
the
static
measure.
According
to
our
results,
if
this
criterion
of
a
positive
test
is
used,
it
has
very
poor
specificity
(14%
to
20%),
although
the
sensitivity
of
the
test
is
very
high
(86%).
We
cannot
generalize
from
our
results
to
say
that
a
positive
REG
test
for
a
specific
individual
indicates
malingering
because
it
cannot
consis-
tently
distinguish
between
maximal
and
submaxi-
mal
performance.
It
is,
however,
more
effective
than
the
5-position
grip
strength
test
and
rapid
repeat
measurement
of
grip,
and
our
results
allow
clinicians
to
estimate
the
likelihood
of
falsely
de-
tecting
or
failing
to
detect
voluntary
submaximal
grip
effort.
Table
2.
Sensitivity
and
Specificity
of
the
Rapid
Exchange
Grip
Test
Using
Different
Control
Groups
to
Determine
Specificity
and
Different
Criteria
for
a
Positive
Test
Positive
Test
Sensitivity
Criterion
Specificity
(%)
(%)
Dynamic
Normal Motivated
CTD
Combined
Normal
Participants
Positive
Negative
X
100
Participants
Patients
and
CTD
Patients
Feigning
50%
Predictive Predictive
Static
(n
=
50)
(n
=
50)
(n
=
100)
Weakness
(n
=
50)
Value
(%)
Value
(%)
85%
14
20
17
86
34
71
90%
28 32
30
86
38
81
95%
52
36
44
78
41
80
.
100%
72
42
57
74
46
81
88
78
83
70
67
85
.
105%
90
82
86
70
71
85
.110%
98
90
94
56
82
81
.115%
100
96
98
54
93
81
CTD,
carpal
tunnel
decompression.
The
Journal
of
Hand
Surgery
/
Vol.
27A
No.
2
March
2002
333
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