U.S. patent number RE35,598 [Application Number 08/551,692] was granted by the patent office on 1997-09-02 for strength analyzer and method of using same.
Invention is credited to Joseph Johnstonbaugh, Richard C. Nelson, Armin M. Sadoff, Steven J. Sadoff, Gerald A. Smith.
United States Patent |
RE35,598 |
Sadoff , et al. |
September 2, 1997 |
Strength analyzer and method of using same
Abstract
An otherwise conventional Jamar dynamometer is provided with a
force transducer. The analog output of the force transducer is
sampled at regular intervals and converted to a sequence of digital
values by a conventional analog-to-digital converter. The digital
output of the converter is processed by a conventional computer in
real time to produce an output that clearly indicates the maximum
force exerted by the subject and whether or not the subject was
sincerely attempting to exert a maximum force while the test was in
process. Preferably the output comprises both a graphic display of
the forces exerted by the subject over a predetermined interval of
time and a statistical analysis of those forces. The output data
includes calculated discriminator variables which indicate with a
high statistical accuracy whether the subject was sincerely
exerting a maximal force on the dynamometer when instructed to do
so. In an exemplary embodiment, the computer is a MSTM DOS
compatible microcomputer and the analog-to-digital converter is a
conventional accessory device that is adapted to be mounted in an
expansion slot of such a microcomputer.
Inventors: |
Sadoff; Armin M. (Beverly
Hills, CA), Nelson; Richard C. (State College, PA),
Smith; Gerald A. (Philomath, OR), Johnstonbaugh; Joseph
(Port Matilda, PA), Sadoff; Steven J. (Tokyo 100,
JP) |
Family
ID: |
27490770 |
Appl.
No.: |
08/551,692 |
Filed: |
November 1, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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329678 |
Oct 26, 1994 |
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69453 |
Jun 11, 1993 |
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575920 |
Aug 31, 1990 |
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Reissue of: |
276716 |
Nov 28, 1988 |
04884445 |
Dec 5, 1989 |
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Current U.S.
Class: |
73/379.01;
73/379.02 |
Current CPC
Class: |
A61B
5/225 (20130101) |
Current International
Class: |
A61B
5/22 (20060101); G01L 003/24 () |
Field of
Search: |
;73/379.01,379.02,379.03
;482/46,49,50,112,113,5,901 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Simple Method to Determine Sincerity of Effort During a Maximal
Isometric Test of Grip Strength", Gilbert et al, Amer. Jour. of
Physical Medicine, vol. 62, No. 3, pp. 135-144 (1983). .
"Muscle Strength Assessment from EMG Analysis", Chaffin et al,
Medicine & Science in Sports & Medicine, vol. 12, No. 3,
pp. 2-5-211, 1980. .
"Grip Strength as Measured by the Jamar Dynamometer", Archives of
Physical Medicine & Rehabilitation, Jun. 1970, pp.
321-327..
|
Primary Examiner: Chilcot; Richard
Assistant Examiner: Dougherty; Elizabeth L.
Attorney, Agent or Firm: Cislo & Thomas
Parent Case Text
.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No.
08/329,678, filed Oct. 26, 1994, abandoned, which is a continuation
of application Ser. No. 08/069,453, filed Jun. 1, 1993, abandoned,
which is a continuation of application Ser. No. 07/575,920, filed
Aug. 31, 1990, abandoned, which is a reissue application of
application Ser. No. 276,716, filed Nov. 28, 1988, now U.S. Pat.
No. 4,884,445. .Iaddend.
Claims
What is claimed is:
1. A method for measuring grip strength of a subject, comprising
the steps of:
(a) providing a grip strength dynamometer with a transducer having
an electrical output which produces an analog signal representative
of the force with which the dynamometer is gripped;
(b) coupling the electrical output from the transducer to an input
of a digital computer via an analog to digital converter;
(c) having the subject grip the dynamometer with a maximal
contraction effort for a first predetermined period of time using a
designated first hand;
(d) inputting to the computer digital data representative of
samples of the gripping force applied to the dynamometer during the
first predetermined period;
(e) calculating for the first hand from the sampled force data a
first value for a first discriminator;
(f) inputting to the computer digital data samples of the applied
force while the subject is gripping the dynamometer with a maximal
contraction effort for a second predetermined period of time but
with his other hand;
(g) calculating a second value for said first discriminator from
the sampled second hand force data;
(h) comparing the calculated first and second hand values of the
first discriminator to calculate a value for a second discriminator
based on the difference thereof;
(i) combining the calculated second discriminator value with the
calculated value of another discriminator having a different
statistical distribution to that of the second discriminator to
form a combined discriminator value; and
(j) determining whether the combined discriminator value is within
a range that has been previously determined experimentally to
indicate with a predetermined level of confidence the sincerity of
the subject.
2. The method of claim 1 wherein said calculated value of another
discriminator is calculated from only data samples that are input
while the subject is gripping the dynamometer with his first
hand.
3. The method of claim 1 wherein
said computer determines the beginning and end of each said
predetermined period and a value for the average force applied to
the dynamometer during a defined portion of each said predetermined
period, and
at least one of said first discriminator and said another
discriminator is a function of both the thus-determined value for
the average force and of a calculated value of a peak force.
4. The method of claim 3 wherein said first discriminator is the
ratio of the calculated average force value to the calculated peak
force value.
5. The method of claim 4 wherein
said another discriminator is also a function of said calculated
average force value and of said calculated peak force value,
and
said another discriminator has a different distribution than that
of said first discriminator.
6. The method of claim 3 wherein each said predetermined period is
a five second period commencing with the application of a threshold
force and said defined portion is the terminal 60% of said five
second period.
7. The method of claim 1 further comprising the step of
(k) outputting the sampled force data in graphic form.
8. Apparatus for determining .[.grip.]. strength comprising:
a .[.grip strength.]. dynamometer .Iadd.responsive to a force
applied thereto by a subject.Iaddend.;
an electrical transducer attached to the dynamometer and having an
analog output which produces an analog signal representative of the
force .[.with which.]. .Iadd.applied to .Iaddend.the dynamometer
.[.is gripped.].;
an analog to digital converter having an analog input for receiving
analog data and a digital output for outputting digital data
corresponding to the analog data at said analog input, said analog
input being coupled to said analog output .Iadd.of said electrical
transducer.Iaddend.;
a digital computer having a digital input for digital data coupled
to said digital output from the analog to digital converter, said
digital computer further comprising:
timer means for establishing a first predetermined period of time,
and
calculating means for deriving from the digital data applied to
said digital input during said first predetermined period of
time:
a first calculated value corresponding to the average force applied
to the dynamometer during a defined portion of said first
predetermined period,
a second calculated value corresponding to the peak force applied
to the dynamometer during said first predetermined period,
third and fourth calculated values for respective first and second
discriminator functions, said first and second discriminator
functions each being a function of the average force and the peak
force, but having different statistical distributions for sincere
and faking subjects, and
a fifth calculated value for a combined discriminator function
which is derived from said first and second discriminator
functions, said combined discriminator function being such that it
more reliably differentiates between sincere and faking subjects
than either of said first or second discriminator functions.
9. The apparatus of claim 8 .Iadd.wherein said dynamometer is
adapted to be gripped by either hand of the subject, said apparatus
.Iaddend.further comprising means for inputting to the computer
digital data samples of the applied force while the subject is
gripping the dynamometer with a maximal contraction effort for a
second predetermined period of time but with his other hand.
10. The apparatus of claim 9 further comprising means for
determining a sixth calculated value corresponding to said first
discriminator function but using the second hand force data sampled
during said second predetermined period of time.
11. The apparatus of claim 10 further comprising means for using
the difference between said third calculated value and said sixth
calculated value in determining said fourth calculated value.
12. The apparatus of claim 11 further comprising means for
combining said fourth calculated value with a seventh calculated
value corresponding to a third discriminator function having a
different statistical distribution than that of the second
discriminator to form a combined discriminator value.
13. The apparatus of claim 9 further comprising
recording means coupled to said computer and responsive to said
calculating means, for providing a permanent record of the use of
the apparatus for measuring the grip strength of both hands of a
single subject, including graphical data representative of force
applied by the subject, and alphanumeric data presenting the test
results in summary form.
14. The apparatus of claim 13 further comprising
display means coupled to said computer and responsive to said
calculating means, for providing a display of selected data while
the apparatus is being used to measure the grip strength of said
single subject, including graphical data representative of the
variations of the force applied by the subject over said first and
second predetermined periods of time and alphanumeric data
presenting the test results.
15. The apparatus of claim 8 further comprising means for
determining whether the calculated value of said combined
discriminator function is within a range that has been previously
determined experimentally to indicate with a predetermined level of
confidence the sincerity of the subject.
16. The apparatus of claim 8 further comprising
display means coupled to said computer and responsive to said
calculating means, for providing a display of selected data while
the apparatus is being used to measure the grip strength of a
single subject, including graphical data representative of the
variations of the force applied by the subject over said first
predetermined period of time and alphanumeric data presenting the
test results in summary form. .Iadd.17. The apparatus of claim 8
wherein
said fifth calculated value is substantially equal to said third
calculated value and said combined discriminator function is
substantially equal to said first discriminator function if the
subject is male, and
said fifth calculated value is substantially equal to said fourth
calculated value and said combined discriminator function is
substantially equal to said second discriminator function if the
subject is female. .Iaddend..Iadd.18. The apparatus of claim 17
wherein
said first discriminator function is substantially proportional to
the ratio of the difference of the peak and average forces to their
product, and
said second discriminator function is substantially proportional to
the ratio of the difference of the n.sup.th root of the peak and
average forces to their product. .Iaddend..Iadd.19. The apparatus
of claim 18
wherein n is equal to 4. .Iaddend..Iadd.20. Apparatus for
determining muscle strength comprising:
a dynamometer responsive to a force applied to the dynamometer by a
contracted muscle of a human subject;
an electrical transducer attached to the dynamometer and having an
analog output which produces an analog signal representative of the
force applied to the dynamometer;
an analog to digital converter having an analog input for receiving
analog data and a digital output for outputting digital data
corresponding to the analog data at said analog input, said analog
input being coupled to said analog output;
a digital computer having a digital input for digital data coupled
to said digital output from the analog to digital converter, said
digital computer further comprising:
timer means for establishing a first predetermined period of time,
and
calculating means for deriving from the digital data applied to
said digital input during said first predetermined period of
time;
a first calculated value corresponding to the average force applied
to the dynamometer during a defined portion of said first
predetermined period,
a second calculated value corresponding to the peak force applied
to the dynamometer during said first predetermined period,
a third calculated value for a respective first discriminator
function substantially proportional to the ratio of the difference
of the peak and average forces to their product,
a fourth calculated value for a respective second discriminator
function substantially proportional substantially proportional to
the ratio of the difference of the nth root of the peak and average
forces to their product,
wherein said third calculated value is used to differentiate
between sincere and faking male subjects and said fourth calculated
value is used to differentiate between sincere and faking female
subjects. .Iaddend..Iadd.21. The apparatus of claim 20 wherein n is
equal to 4.
.Iaddend..Iadd.22. A method for determining whether or not a human
subject is making a sincere effort to apply maximum force, the
method comprising the steps of:
(a) having the subject apply force to a dynamometer with a
purported maximal effort for a predetermined period of time;
(b) determining a maximal force and an average force applied during
a designated portion of the predetermined period of time;
(c) calculating at least one of a first discriminator value
proportional to a ratio of a difference of the maximal and average
forces and a product of the maximal and average forces, and a
second discriminator value proportional to a ratio of a difference
of nth roots of the maximal and average forces and the product of
the maximal and average forces, wherein the first discriminator
value is calculated according to the following equation:
and the second discriminator value is calculated according to the
following equation: ##EQU4## where D4 and D5 are the first and
second discriminator values, respectively, and F.sub.max and
F.sub.ave are the maximal and average forces, respectively, and
K.sub.1 and K.sub.2 are constants; and
(d) comparing at least one of the first and second discriminator
values to a corresponding one of first and second predetermined
discriminator values, respectively, and determining whether the
subject is making a sincere effort based on the comparison,
wherein the first and second predetermined discriminator values are
previously obtained by performing steps (a) to (c) for members of
an
experimental group. .Iaddend..Iadd.23. The method of claim 22
wherein both the first and second discriminator values are
calculated and compared to the first and second predetermined
discriminator values in the step of
comparing for male and female subjects. .Iaddend..Iadd.24.
Apparatus for determining strength comprising:
a dynamometer responsive to a force applied to the dynamometer by a
human subject;
an electrical transducer attached to the dynamometer and having an
analog output which produces an analog signal representative of the
force applied to the dynamometer
an analog to digital converter having an analog input for receiving
analog data and a digital output for outputting digital data
corresponding to the analog data at said analog input, said analog
input being coupled to aid analog output of said electrical
transducer;
a digital computer having a digital input for digital data coupled
to said digital output from the analog to the digital converter,
said digital computer further comprising:
timer means for establishing a first predetermined period of time,
and
calculating means for deriving from the digital data applied to
said digital input during said first predetermined period of
time;
a first calculated value corresponding to the average force applied
to the dynamometer during a defined portion of said first
predetermined period,
a second calculated value corresponding to the peak force applied
to the dynamometer during said first predetermined period,
third and fourth calculated values for respective first and second
discriminator functions, said first and second discriminator
functions each being a function of the average force and the peak
force, but having different statistical distributions for sincere
and faking subjects, wherein the first discriminator value is
calculated according to the following equation:
and the second discriminator value is calculated according to the
following equation: ##EQU5## where D4 and D5 are the first and
second discriminator values, respectively, and F.sub.max and
F.sub.ave are the maximal and average forces, respectively, and
K.sub.1 and K.sub.2 are constants,
wherein the computer comprises means for comparing at least one of
the third and fourth calculated values to a corresponding one of
first and second predetermined stored discriminator values,
respectively, and for determining whether the subject is making a
sincere effort based on the comparison,
wherein the first and second predetermined discriminator values are
obtained for members of an experimental group and stored in the
computer.
.Iaddend..Iadd.25. The apparatus of claim 24 wherein the means for
calculating calculates both the first and second discriminator
values, and the means for comparing compares these values with a
combination of the first and second predetermined discriminator
values. .Iaddend..Iadd.26. The method of claim 22 wherein the force
applied to the dynamometer is by the subject gripping the
dynamometer. .Iaddend..Iadd.27. The apparatus of claim 24, wherein
the dynamometer comprises a grip strength dynamometer.
.Iaddend..Iadd.28. The apparatus of claim 22, wherein n equals 4.
.Iaddend..Iadd.29. The method of claim 24, wherein n equals 4.
.Iaddend..Iadd.30. A method for determining whether or not a human
subject is making a sincere effort to apply maximum force using a
contracted muscle group, the method comprising the steps of:
(a) having the subject apply force to a dynamometer with a
purported maximal effort for a predetermined period of time;
(b) determining a maximal force and an average force applied during
a designated portion of the predetermined period of time;
(c) calculating at least one of a first discriminator value (D4)
proportional to a ratio of a function of a difference of the
maximal and average forces and a function of a product of the
maximal and average forces, and a second discriminator value (D5)
proportional to a ratio of a function of a difference of nth roots
of the maximal and average forces and a function of the product of
the maximal and average forces, and
(d) comparing at least one of the first and second discriminator
values to a corresponding one of first and second predetermined
discriminator values, respectively, and determining whether the
subject is making a sincere effort based on the comparison,
wherein the first and second predetermined discriminator values are
previously obtained by performing steps (a) to (c) for members of
an experimental group. .Iaddend..Iadd.31. The method of claim 30
wherein both the first and second discriminator values are
calculated and compared to the first and second predetermined
discriminator values in the step of
comparing for male and female subjects. .Iaddend..Iadd.32.
Apparatus for determining sincerity of effort comprising:
a dynamometer responsive to a force applied to the dynamometer by a
contracted muscle of a human subject;
an electrical transducer attached to the dynamometer and having an
analog output which produces an analog signal representative of the
force applied to the dynamometer;
an analog o digital converter having an analog input for receiving
analog data and a digital output for outputting digital data
corresponding to the analog data at said analog input, said analog
input being coupled to said analog output of said electrical
transducer;
a digital computer having a digital input for digital data coupled
to said digital output from the analog to digital converter, said
digital computer further comprising:
timer means for establishing a first predetermined period of time;
and
calculating means for deriving from the digital data applied to
said digital input during said first predetermined period of
time:
a first calculated value corresponding to the average force applied
to the dynamometer during a defined portion of said first
predetermined period,
a second calculated value corresponding to the peak force applied
to the dynamometer during said first predetermined period,
third and fourth calculated values for respective first and second
discriminator functions (D4, D5), said first and second
discriminator functions each being a function of the average force
and the peak force, but having different statistical distributions
for sincere and faking subjects, wherein the first discriminator
value is proportional to a ratio of a function of the difference of
the peak and average forces to a function of a product of the peak
and average forces, and
the second discriminator value is proportional to a ratio of a
function of the difference of nth roots of the peak and average
forces to a function of a product of the peak and average
forces,
wherein the computer comprises means for comparing at least one of
the third and fourth calculated values to a corresponding one of
first and second predetermined stored discriminator values,
respectively, and for determining whether the subject is making a
sincere effort based on the comparison,
wherein the first and second predetermined discriminator values are
obtained for members of an experimental group and stored in the
computer.
.Iaddend..Iadd.33. The apparatus of claim 32 wherein the means for
calculating calculates both the first and second discriminator
values, and the means for comparing compares these values with a
combination of the first and second predetermined discriminator
values. .Iaddend..Iadd.34. The method of claim 30 wherein the force
applied to the dynamometer is by the subject gripping the
dynamometer. .Iaddend..Iadd.35. The apparatus of claim 32 wherein
the dynamometer comprises a grip strength dynamometer.
.Iaddend..Iadd.36. The method of claim 30 wherein the nth roots are
the 4th roots. .Iaddend..Iadd.37. The apparatus of claim 32 wherein
the nth roots are the 4th roots. .Iaddend.
Description
TECHNICAL FIELD
The present invention relates to apparatus and method for assessing
.[.grip.]. strength in an ergonomic or clinical setting, as well as
for determining whether the test subject's response is sincere when
he is instructed to apply a maximum contraction force to the test
apparatus.
BACKGROUND ART
An article by Schmidt published in 1970 in Archives of Physical
Medicine & Rehabilitation, June 1970 pp 321-327 is exemplary of
the use of a so-called Jamar dynamometer with adjustable hand
spacing and a sealed hydraulic system as a standardized instrument
for determining grip strength, and notes that grip strength has
been correlated with hand dominance, overall "physical fitness",
normal growth, seriousness of upper extremity injuries, and the
success of physical rehabilitation programs.
Van Patten (U.S. Pat. No. 3,672,219) discloses a handgrip
dynamometer equipped with an electric transducer which is connected
to a volt meter. Kroemer (U.S. Pat. No. 3,670,573) shows a digit
dynamometer with a strain gauge transducer whose output is applied
to a chart recorder.
A paper by Gilbert et al. published in 1983 in American Journal of
Physical Medicine, vol 62 No. 3 pp 135-144 discloses the
desirability of providing a graphical record of force in response
to a single request for maximal voluntary contraction using a force
transducer whose electrical output is recorded on a strip chart,
for the purpose of determining whether an apparent inability to
produce a normal gripping force is faked, or is genuine. The
authors concluded that the ratio of average force to peak force is
statistically correlated to the subject's sincerity, and suggested
that a "minimum standard indicative of a sincere effort" should be
that the average force during the final three seconds of a 5 second
contraction should be at least 90% of the peak force. However, such
a ratio is not believed to discriminate between a sincere and
insincere subject with sufficient reliability to serve as the sole
basis for determining a claim for workman's compensation.
Ruis et al. (U.S. Pat. No. 4,235,437) discloses a microcomputer
having among its inputs electrical signals indicative of user
exerted force from respective transducers and analog-to-digital
converters. The microcomputer samples the measured values including
various force values and uses that information to calculate the
required counterforce to constrain the group of muscles being
exercised to a particular path/resistance profile. The force
information is also stored for possible subsequent (unspecified)
use. Brentham (U.S. Pat. No. 4,566,692) shows another complex
computerized exercising device which includes a microprocessor and
an analog-to-digital converter which may be used in the
rehabilitation field, which has an electrical input provided by a
pressure transducer with the data being either stored for
"observation at a later date" and/or illustrated graphically to the
user.
A study of Chaffin et al published in 1980 in Medicine and Science
in Sports and Exercise, vol 12 No. 3, pp 205-211 concerns the use
of electromyography in connection with force measurements of both a
"maximum" and an extended submaximal contraction to estimate the
subject's true maximum voluntary contraction. In theory such a
procedure would be applicable to the measurement of grip strength,
but the accurate collection of EMG data presents considerable
technical difficulty.
It is to be noted that none of known prior art discloses a simple
and accurate apparatus for automatically converting the forces
exerted by a subject into a reliable indication of whether the
subject is sincerely exerting a true maximal contraction.
DISCLOSURE OF THE INVENTION
It is thus an overall objective of the present invention to
facilitate an easily administered analysis of possible loss of
.[.grip.]. strength including the sincerity of the subject when
using a grip strength dynamometer .Iadd.or other similar means for
measuring the force exerted by a contracted muscle (or related
group of muscles) in a human subject.Iaddend.. It is another
related overall objective to record and display the exerted
"maximal" contraction in a way that permits convenient assessment
of the subject's sincerity and a ready comparison of the strength
of .[.the.]. .Iadd.an .Iaddend.injured hand with the other
(uninjured) hand of the subject.
According to .Iadd.a preferred embodiment of .Iaddend.the present
invention, an otherwise conventional .[.grip.]. .Iadd.muscle
contractive force .Iaddend.dynamometer (for example, the above
mentioned Jamar apparatus) is provided with a force transducer. The
analog output of the force transducer is sampled at regular
intervals and converted to a sequence of digital values by a
conventional analog-to-digital converter. The digital output of the
converter is processed by a conventional computer in real time to
produce an output that clearly indicates the maximum force exerted
by the subject and whether or not the subject was sincerely
attempting to exert a maximum force while the test was in process.
Preferably the output comprises both a graphic display of the
forces exerted by the subject over a predetermined interval of time
and a statistical analysis of those forces. In an exemplary
embodiment, the computer is a portable MSTM DOS compatible
microcomputer and the analog-to-digital converter is a conventional
accessory device that is adapted to be mounted in an expansion slot
of such a microcomputer.
In accordance with one specific aspect of the invention, a number
of variables--each having a statistical correlation with the
sincerity of a representative cross section of typical
subjects--are individually calculated and then combined into a
"discriminant" which is a more reliable indicator of the sincerity
for a given individual than any single component thereof. To that
end, the computer is preferably programmed to calculate each of the
following variables:
Peak Force
Average Force (from threshold +2 seconds to threshold +5seconds,
i.e., over the last three seconds of the trial)
Ratio of Average Force to Peak Force
Coefficient of Variation (standard deviation of the Average Force
over the last three seconds, divided by the Average Force)
Elapsed Times from threshold to
50% of Peak,
90% of Peak and
100% of Peak.
Peak-Average Difference (proportional to the difference between the
inverses of the maximum and average forces, i.e., the ratio of the
difference of the two forces to their product), and
Peak-Average Root Difference (similar to the Peak-Average
Difference, but forming the numerator from the difference of the
fourth root of the two forces)
The data for each hand is stored and compared to calculate
Ratio Difference (an additional discriminator of subject sincerity
formed by subtracting the Ratio of the two forces for one hand from
the corresponding Ratio for the other hand; this has been found to
be particularly useful for female subjects)
Obviously, such a two-handed calculation will not be meaningful for
a subject not having a "normal" hand, for example, a subject with a
bilateral injury.
The computer has the capability to summarize the test results
as
Faking or sincere
Percent Loss, and
Rating Reduction Fraction.
In accordance with another more specific aspect of the invention,
the programmed microcomputer not only analyzes the output data from
the transducer, but also ensures that the entire test is conducted
and documented in accordance with a standardized test protocol and
to that end preferably:
generates a beep to indicate the subject should immediately try to
exert the maximum force
verifies that there is zero force prior to the beep
samples for six seconds after the beep
analyzes the force output for a five-second interval starting when
a threshold force value has been reached.
Such an automated procedure thus produces output data in the form
of a standardized snapshot.
BRIEF DESCRIPTION OF DRAWINGS
For a better understanding of the present invention and how to make
and use what is presently considered to be the best mode thereof,
reference should be made to the appended drawings of an exemplary
embodiment in which
FIG. 1 is a block system diagram of the various system
components;
FIG. 2 shows the hardware used to practice the invention ready for
use;
FIG. 3 shows the main menu as it appears to the operator;
FIG. 4 comprising FIGS. 4a and 4b shows the two information screens
used to input subject information;
FIG. 5 shows a screen plot of a single test trial;
FIG. 6 shows a printed summary of a full test sequence for a single
subject; and
FIG. 7 is a flowchart of the computerized test procedure.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIGS. 1 and 2, it will be seen that a standard Jamar
Dynamometer 10 includes a chamber 12 filled with hydraulic fluid 14
which is responsive to pressure 16 applied by means of an
adjustable handle 18. Chamber 12 has an outlet port 20 to which is
normally attached a mechanical pressure gage (not shown) which
measures the peak force applied to the handle, which is linearly
proportional to the pressure of the fluid inside the dynamometer.
Such a standard Jamar instrument is easily modified by removing the
usual pressure gage and replacing it with a conventional force
transducer 22 connected to a battery 24 (or a small transformer) to
provide at an output 26 a voltage relative to ground 28 ranging
from 0 to 5 volts, thereby producing an electric signal on an
output line 30 having an amplitude proportional to the pressure and
thus to the applied force. A supporting stand 32 may be constructed
to hold the dynamometer 10 loosely in an upright position on the
table top such that the dynamometer remains freely moveable. The
handgrip dynamometer is preferably supplied with two accessory
support stands: one relatively rigid (not shown) for calibration
procedures and another more flexible stand 32 for the normal grip
testing.
The analog dynamometer output is sampled at a frequency of 200 Hz
using a Metrabyte DAS-8 analog-to-digital board 34 in an MS-DOSTM
compatible microcomputer 36 (for example, a CompaqTM Portable II)
having a screen 38 and a keyboard 40. The computer is equipped with
the MS-DOSTM operating system 42, CGA graphics 44, a parallel port
46 for an EpsonTM compatible printer 48, a serial port 50 for a
Hewlett-Packard Graphics Language compatible plotter 52, and an
expansion slot 54 in which is mounted the analog-to-digital
converter 34. Such an arrangement provides a force measurement
accuracy of better than .+-.0.2 pounds. A computer program 56
controls the analog-to-digital board as well as the testing
protocol and data analysis. A program listing for a preliminary
version of such a program (written in Microsoft QuickBasic) has
been submitted to the Register of Copyrights in the Library of
Congress under the title "Grip Test Program Version 3" by Armin M.
Sadoff and is hereby incorporated by reference.
Although this application is believed to set forth sufficient
information for the average artisan to make and use what is
presently considered to be the best mode of the invention claimed
herein, a copy of that commonly owned program is also being filed
concurrently herewith in the file wrapper of this application and
members of the public are hereby given a limited license to obtain
single copies of the program listing from either the Commissioner
of Patents or from the Library of Congress for the purpose of
obtaining any additional information it may provide which may be of
assistance in understanding the use and function of the present
invention.
Prior to use, the handle 18 of the dynamometer 10 is adjusted to
the subject's preferred spacing and several practice contractions
are made to acquaint the subject with the feel of the device during
a test.
At this point, reference should also be made to the exemplary
screen layouts of FIGS. 3, 4 and 5, to the examplary printout
layout of FIG. 6 and to the program flowchart of FIG. 7.
Under the control of the program 56, the microprocessor 58
contained in the computer 36 commands the converter 34 via control
line 60 to sample the output 30 from the transducer 22 and to
output via data line 62 digital data signals 200 times each second
which correspond to the analog output of the transducer 22. This is
done for six seconds (block 100) following an audible signal
generated by the processor (block 102) and output from a speaker 64
contained within the computer which indicates the start of the
test. A second such beep (block 104) indicates the end of the data
collection for a particular trial.
The sampled data is converted to force units in pounds (block 106)
using a calibration constant previously obtained in the
conventional manner (block 108) by applying a known force to the
dynamometer 10. The individual data for each trial are analyzed
(block 110) to determine several characteristic parameters:
T.sub.0 =time when the force first reaches an arbitrarily set
threshold of 3 pounds (the beginning of the 5 second
contraction)
F.sub.max =peak force throughout the trial
F.sub.avg =average force through the final 60% of the trial (the
final 3 seconds for a 5 second contraction)
T.sub.90 =time to 90% of peak (time 90)
F.sub.fin =average force during the "plateau" region of the curve
(defined as T.sub.90 until the end of the contraction period)
.sigma.=Standard deviation of the force data during the "plateau"
region of the curve
Each trial results in a screen display of test results (block 112;
FIG. 5) which is validated by the operator (block 114); if the
operator does not accept the results of a given trial, the data
collection process is repeated without incrementing the trial
counter (blocks 116, 118, 120).
The results of six such trials (block 122) (one "round") are pooled
together (block 118), in which case a single mean value for each of
the previously described parameters can be determined for the
entire round and used in any subsequent analysis. At the end of
each round, the alphanumeric printer optionally may be commanded to
print (block 124, FIG. 6) summary information, including the
above-defined characteristic values and further "discriminator"
values which are derived therefrom, as well as identified
information which is input (block 126; FIG. 4) by the computer
operator (subject's name, social security number; right or left
hand) and time/date information derived from a clock internal to
the computer 36.
The computer generated force-time plots for each trial which are
displayed on the screen 38 (block 112; FIG. 5) may also be recorded
on the plotter 52 to permit qualitative comparisons to be made
between the various conditions. These plots therefore bear the
relevant identifier and time/date information.
The first discriminator (D1) involves a fractional comparison of
average (A) and peak (P) forces, and is defined as follows:
##EQU1## The second discriminator assesses the variability of the
plateau region and is defined as: ##EQU2## A third discriminator
variable called the Ratio Difference (D3) uses data from both
hands. It is calculated by subtracting the above defined Ratio
measured for the other hand. Preferably, it is output as part of
the summary data which is normally printed after both hands have
been tested.
Two other discriminator variables which are also based on the mean
peak and mean average forces may be conveniently calculated for
each test trial to spread the characteristic ranges upon which
discrimination between sincere and faking maxima was observed:
##EQU3## The five discriminator variables, D1=Ratio, D2=Coefficient
of Variation, D3=Ratio Difference, D4=Peak-Average Difference, and
D5=Peak-Average Root Difference, have been subjected to extensive
statistical analysis in an experiment involving a number of male
and female subjects who were instructed to fake a submaximal
contraction at certain points in the above-described procedure. The
frequency distributions were estimated for each discriminator from
the mean and standard deviation of the variable for the various
conditions (assuming each distribution was approximately normal).
Based on the "sincere" distribution, criterion values (Table 1)
were determined for each discriminator such that 95% of the sample
would be included in the sincere distribution (thus establishing a
theoretical type I error level of 5%). Finally, several multiple
variable prediction relationships were determined. These were
derived by first calculating a z score for each discriminator value
(based on the standard deviation of the sincere distribution of
each variable). A mean z score was obtained from the variables
involved in each relationship. The 95% z score (1.645) was used as
a criterion value for discrimination into sincere and faking
designations. The true sincere and true faking percentages were
determined for each single and multiple variable relationship
(Tables 2 and 3).
TABLE 1 ______________________________________ CRITERION VALUES TO
DETERMINE FAKING (95% CONFIDENCE LEVEL): MALE FEMALE
______________________________________ D1. (RATIO): <84.9
<75.5 D2. (COEF. VARIATION): >8.85 >14.14 D3. (RATIO
DIFFERENCE): >6.88 >8.46 D4. (PEAK-AVE DIFF.): >0.18
>0.53 D5. (PEAK-AVE ROOT DIFF.): >0.28 >3.13
______________________________________
TABLE 2 ______________________________________ PREDICTION ACCURACY
FOR EACH DISCRIMINATOR VARIABLE*: MALE SIN- FAK- FEMALE CERE: ING:
SINCERE: FAKING: ______________________________________ D1.
(RATIO): 90.0% 95.0% 93.5% 58.7% D2. (COEF. 90.0% 92.5% 95.7% 52.2%
VARIATION): D3. (RATIO 100% 100% 96.0% 78.3% DIFFERENCE): D4.
(PEAK-AVE 97.5% 100% 95.7% 71.7% DIFF.): D5. (PEAK-AVE 95.0% 97.5%
97.8% 87.0% ROOT DIFF.): ______________________________________
TABLE 3 ______________________________________ PREDICTION ACCURACY
FOR MULTIPLE DISCRIMINATOR VARIABLES*: MALE FEMALE SINCERE: FAKING:
SINCERE: FAKING: ______________________________________ D1 + D3 +
92.5% 100% 95.7% 87.0% D4 + D5: D1 + D4 + 90.0% 97.5% 95.7% 76.1%
D5: D3 + D4 + 95.0% 100% 95.7% 89.1% D5: D3 + D5 95.0% 100% 97.8%
93.5% D4 + D5 92.5% 97.5% 95.7% 84.8%
______________________________________ *Based on criterion values
established using a normal distribution approximation (confidence
level = 95%)
Referring specifically to Table 3, it may be seen that several
combinations of discriminators were found to result in improved
detection of faking over any one single discriminator--this notably
enhanced the possibility of detection of faking, particularly for
females and only slightly increased the risk of labeling a sincere
trial as faked.
Each of the 5 discriminators was found to yield quite divergent
distributions for sincere and faking conditions of the male
population. Because of the relatively large separation between the
distributions in these cases, each variable provided good
discrimination between the sincere and faking conditions and thus
proved to be highly sensitive tests of faking while being
conservative in falsely categorizing sincere trials. However, the
values for the female population exhibited less separation between
the sincere and faking distributions and were also more variable.
This widened each of the distributions in comparison to the male
population. The greater variability resulted in criterion values
more distant from the sincere means for each variable.
Consequently, smaller proportions of the faking distribution were
beyond the criterion resulting in less sensitivity in faking
detection.
Subject by subject analysis indicated that the 5 discriminators
were often "catching" different faking subjects. A combination of
variables thus increased the successful detection rates. The
coefficient of variation was found to duplicate the results of the
ratio variable and was not included in the multiple variable
predictions. Table 3 lists five of the combinations tested. The
inclusion of the ratio variable (D1) was found to decrease the
female detection rate below the levels of D5 alone. The combination
of D3 and D5 proved to be the best predictor. It maximized the
female "true faking" detection to about 93% while maintaining a
relatively conservative error rate with sincere trials of about
2-3%. Discriminator D3 used in this combination involved the
comparison of ratios between hands. In the case of a bilateral
injury where faking might be expected on both hands, the use of
this variable would not be appropriate. In such cases, the best
predictive combination was found to be D4 and D5.
For the male population slight improvement in an already high level
of predictive ability was found with the various discriminator
combinations; however, the female predictions were found to improve
substantially. The best combination of variables was D3 and D5
which yielded a correct prediction of female faking of 93.5%.
It will thus be appreciated that for both men and women, the
above-described system and method of force-time curve analysis
allows for detection of more than 92% of insincere grip force
maxima.
Reference should again be made to FIG. 7. The program file itself
is under the filename GRIPTEST.EXE. Another file (GRIPPER.CAL)
contains calibration information used by the program. In the
process of testing a patient's grip strength a data file (whose
filename is the subject ID number plus an optional extension) is
stored at the completion of the test on a previously formatted
floppy disk.
The program is loaded by typing the name of the program: GRIPTEST,
whereupon an opening title screen will appear. After the program
title screen, typing any key takes the operator to the main program
menu (FIG. 3). Three choices are presented. The operator can (1)
test the subject, (2) calibrate the equipment (blocks 128, 108), or
(3) print or plot results (blocks 130, 124) from previous files
(stored on disk). While testing will be the primary mode of
operation, calibration of the equipment is a necessary prerequisite
to testing.
CALIBRATION
When doing normal testing the program accesses the information in
the calibration file (GRIPPER.CAL) on the program disk. If for some
reason that calibration file is not available (perhaps
inadvertently erased, or the disk was removed from the drive), the
program will automatically go into the calibration mode to generate
a calibration file before testing.
The calibration mode provides the means of relating the electrical
signals produced by the dynamometer to the real world forces
exerted on it. A baseline reading with zero force application is
initially taken, followed by a reading with some known force
application. The known difference in forces is input into the
computer where it is divided by the measured difference in signals
to form a conversion factor which can be used during subsequent
tests as the required multiplier to convert the subsequently
measured difference between the baseline signals and those
generated during the testing of a subject into corresponding force
values.
The actual calibration procedure preferably begins with the
dynamometer 10 placed in the bottom half of a conventional
calibration support (palmar grip surface down). The computer 36
activates the analog-to-digital convertor 34 to sample the output
signal (for six seconds) and uses the arithmetical average of the
corresponding digital output 62 from the converter to determine a
baseline signal value. Then the upper half of the calibration
support is placed on top of the dynamometer and a reference weight
on top of this upper support. The program prompts the operator to
input the amount of weight put on the device and then samples the
resultant signal (again for six seconds). A calibration file will
then be created on the disk in drive A. The Jamar dynamometer 10
and the transducer 22 exhibit a relatively linear signal output;
however, for most accurate calibration, the reference weight chosen
should be near the upper end of the expected forces (probably 75 to
150 pounds). Also the operator should include the weight of the
upper half of the calibration support in the reference weight
(about 4 pounds). Thus, if a 75 pound weight is put on the
calibration stand, the reference weight value input into the
computer should be 79 pounds.
TESTING GRIP FORCE
Testing the subject is the primary mode of operation of the program
and is the first choice listed on the main menu (FIG. 3). Choosing
this mode from the main menu begins a strict testing protocol.
Initially the operator is prompted for certain subject information:
Name, Social Security number, California ID number, gender, age,
major hand and injured hand (block 126). Following this is a set of
six grip trials, alternating right and left hands. The computer
prompts the operator in each case (block 120) for the proper hand
the subject should be using. The subject is alerted to the
beginning of each trial by a "beep" from the computer (blocks 122,
102. A second beep (block 104) signals its completion. To be
meaningful, each trial should begin with zero force on the
dynamometer (i.e., the sampled digital signal exceeds the baseline
value by at most a nominal amount, such as three pounds). If the
computer senses more than a nominal initial force, it will
immediately respond with a series of warning beeps and the test
will be re-initialized. The subject should be instructed to respond
after the starting beep completes sounding. The time between beeps
is six seconds. The program samples the data for the whole time
(block 100) but only displays the force output for the five second
interval beginning from when the calculated force exceeds a
threshold value of 3 pounds.
After recording the force-time data from the dynamometer, several
variables are calculated (block 106) and the force-time curve is
graphically displayed (block 112) on the monitor 38. Each of these
variables is displayed at the top of the trial results screen (FIG.
5).
The tester can scan the trial results screen and judge whether the
trial was satisfactory. Pressing any key will open a small window
on the graphical display with the message "Accept Last Trial?
(Y/N)." Responding with "Y" for yes (block 116) will then continue
with the testing of the subsequent hand, while "N" will redo the
previous trial (entry point "C" to block 120). At the completion of
six acceptable trials, three on each hand, the data is available
for printing. At this time, the data should be stored on the disk
in drive B.
After storage of the data on disk, the operator is prompted (block
124) to indicate whether output is desired immediately or later. In
either case, printed or plotted results can be obtained as
described below.
OUTPUT OF RESULTS
The selection of main menu choice three (Output of Results from a
Previous File) or an indication that immediate output (after
testing) is desired will display the Final Results Output menu.
From this menu several choices of output mode are available:
a printed summary table;
a plotted summary table;
a plotted summary table and right/left hand force curves.
The distinction between output modes is one of time, complete data
and perhaps aesthetics. The printed output includes the individual
trial variables as well as means and standard deviations across the
three trials (FIG. 6), but no force-time graphs. Printed output
takes less than 30 seconds to produce. The plotted outputs are
somewhat slower to produce (about 10 minutes for the three pages)
but present a complete record of each trial in a standard report
format (FIG. 5).
Whichever the operator's choice from the output menu, a prompt is
then given to prepare the appropriate device for output. In the
case of the plotter, if at the end of a page's output the results
are unacceptable (pen ran dry, paper wrinkled, etc.), the plot may
be repeated by typing "R" from the screen's prompt. Otherwise,
output will be continued with the subsequent page, or if complete,
return to the Output menu.
Two other menu choices are available. Number 4 will restart the
program ready for testing the next subject, while No. 5 will
terminate the program, returning to the computer's operating
system.
SUBJECT INFORMATION
Two screens of information (FIGS. 4a and 4b) are requested for each
test subject. The name entered must be less than 16 characters
total. For names longer than this, some appropriate abbreviation
will be necessary (such as first initial, or perhaps truncating a
particularly long last name). The capitalization used will carry
over to the output, therefore capitalize as desired for the output
format.
The hand information (FIG. 4b) gives several choices. The major
hand (dominant hand) entry allows designation as (R/L/A) which
stand for Right, Left, and Ambidextrous. The injured hand selection
allows choices of (R/L/B/N) which stand for Right, Left, Both and
Neither.
SCREEN PLOT OF FORCE-TIME
Each trial is presented graphically on the screen with subject
information and calculated variables (FIG. 5). The Peak Force is
the greatest force observed throughout the 5 second sample. Average
Force is the mean of the force data over the last 3 seconds
samples. Ratio is the calculated percent of the Average Force to
the Peak Force. The Coefficient of Variation is a measure of the
variability of the force over the last 3 seconds. It is calculated
based on the standard deviation of the force data during the last 3
seconds divided by the average force during that interval. Several
times are also displayed on the screen. These are measured to the
nearest hundredth of a second beginning from the sample immediately
prior to the crossing of the threshold force.
FINAL RESULTS OUTPUT
The final results output can be of several forms. Printed output
goes just to the printer 48. The plotter 52 may also be used to
generate a similar summary table (FIG. 6) as well as force graphs
for each of the individual trials which are similar to the
graphical display on the screen (FIG. 5) shown at the end of each
trial. The graph scaling is determined by the maximum obtained on
any of the six trials.
The present invention has been described above with regard to the
structure, function and use of a presently contemplated specific
embodiment of the invention. It should be appreciated by those
skilled in the art that many modifications and variations are
possible. Accordingly the exclusive rights afforded hereby should
be broadly construed, limited only by the spirit and scope of the
appended claims.
* * * * *