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Accuracy

of

Spring and Strain Gauge

Hand-held Dynamometers

RICHARD W BOHANNON, A WILLIAMS ANDREWS2

The accuracy of tw o spring gauge and two strain gauge hand-held dynamometers

was determined using certified weights. Each dynamometer, which had extensive prior

use, was vertically loaded with the certified weights in 5 Ib increments from 5-55 Ibs.

Analysis of variance was used to compare the actual certified weights with the weights

measured by each dynamometer. Additionally, Pearson product moment correlations

were calculated between the weights measured by e ach device. T he two spring gauge

dynamometers measured comparably as did the two strain gauge dynamometers. Only

the two strain gauge dynamometers, however, registered (measured) weights not

differing significantly from the actual weights with which they were loaded. The corre-

lations between each device s measurements were 0.98 or above. If the dynamometers

tested are indicative, strain gauge dynamometers may be more accurate than spring

gauge dynamometers after extensive use .

The imprecision of subjective manual muscle

test grades and their insensitivity to changes in

muscle strength provide clinicians with an impetus

for using more objective instruments for measur-

ing muscle strength (1). Among the instruments

that have been used extensively for this purpose

in a clinical environment are hand dynamometers,

fixed dynamometers, isokinetic dynamometers,

and hand-held dynamometers

(2).

Unlike that of

some other instruments (3-6), the accuracy of

specific hand-held dynamometers has not been

determined and reported. Before clinicians can

make informed decisions regarding the purchase

and use of instruments, they must be aware of

the instruments' accuracy. The purpose of this

brief report is to compare the accuracy of two

spring gauge and two strain gauge dynamome-

ters. We expected from previous informal calibra-

tion checks that the two strain gauge dynamom-

eters, unlike the two spring gauge dynamometers,

would be accurate. We expected the measure-

ments obtained with all the dynamometers to be

highly correlated.

Associate Professor, School of Allied Health. University of Connecti-

cut. U-101. Storrs. CT 06269.

Graduate student. Division of Physical Therapy. University of North

Carolina. Chapel Hill. NC.

0196-6011/89/1008/0323 02.00/0

THEJOURNAL

F

ORTHOPAEDIC

ND

SPORTSHYSICALHERAPY

Copyright

Q

1989 by The Orthopaedic and Sports Physical Therapy

Sect~ons f the American Physical Therapy Association

METHOD

Two different types of gauges were com-

pared. The two spring gauge dynamometers were

the same model (Spark hand-held dynamometer,

Spark Instruments and Academics, Inc, P.O. Box

5123, Coralville, IA 52241). They had a range of

0 to 60 Ibs and registered orce with a dial display.

The dial face was divided into half-pound incre-

ments. The two strain gauge dynamometers were

the same model (Chatillon model DFG-100, John

Chatillon and Sons, 83-30 Kew Gardens Road,

Kew Gardens, NY 11415-1

999 .

They had a range

of 0 to 115 Ibs and registered force with a digital

display. The display registered to 0.1 Ibs of sen-

sitivity. All four dynamometers were over 2 years

old and had been used in thousands of clinical

tests.

To measure instrument accuracy, each in-

strument was placed vertically in a vise and a

pendulum goniometer was used to assure that its

flat end piece was perpendicular to the pull of

gravity. Certified weights were then placed on the

flat end piece of each device in 5 Ib increments

from 5-55 Ibs. (Fig. 1). Each dynamometer was

reset (zeroed) between the application of each

calibration load.

The weight indicated (measured) by each

dynamometer was compared to the actual certi-

fied weight it was measuring as well as to the

weight measured by the other three dynamome-

ters. An analysis of variance (ANOVA) procedure

JOSPT February

989

SPRING AND STRAIN HAND-HELD DYNAMOMETERS

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and a Tukey HSD post hoc test were used for

this purpose. In addition, Pearson product mo-

ment correlations were calculated between each

instrument s measurements of the weights.

RESULTS

Figure

2

illustrates the measurements of the

certified weights obtained using each dynamom-

eter. A close inspection of the figure reveals that

throughout the range of weights applied, the two

spring gauges measured higher weights than the

two strain gauges. At every 5 Ib increment both

spring gauges measured at least 1 Ib high. The

mean weight of the certified weights was 30 Ibs,

whereas the mean of the weights measured by

the dynamometers were strain gauge one (30.0

Ibs), strain gauge two (30.0 Ibs), spring gauge one

(31.7 Ibs) and spring gauge two (31.8 Ibs). The

ANOVA results are reported in Table 1. They

reveal that the actual certified weights and the

weights measured by the four dynamometers

were significantly different

p