Test-Retest Reliability of Hand-Held Dynamometry During a Single Session of Strength Assessment

RICHARD W. BOHANNON

This retrospective study was undertaken to determine the test-retest reliability of hand-held dynamometer strength testing for 18 extremity muscle groups. To assess reliability, I compared three dynamometer strength scores recorded for each muscle group on the strength score forms of 30 neurologically involved patients, using the Pearson product-moment correlation and a one-way analysis of variance (ANOVA) for repeated measures. All correlations were significant (p < .01); the median and modal correlations were all .97 or .98. The ANOVA revealed significant differences in repeated dynamometer test scores only for hip and shoulder abduction. The results suggest that hand-held dynamometry can be a reliable assessment technique when practiced by a single experienced tester.

Key Words: Muscle contraction, Musculoskeletal system, Physical therapy.

Beasley, in 1956, clearly established the need for muscle strength testing methods that are more precise and objective than manual muscle testing.1 Using a manual force gauge, he demonstrated that differences in strength of 20% to 25% are not distinguished by manual muscle tests and that manual muscle tests sometimes fail to identify weakness in knee extensor muscles with a 50% loss in strength. Since Beasley's important work, numerous reports have been published de­scribing the use of both isokinetic2-4 and hand-held dynamometers5-7 in strength testing. Although a number of reports have described the reliability of testing with isokinetic dynamometers8.9 and fixed force gauges,10-12 little information is available regarding the reliability of testing with hand-held dynamometers. The only statement of which I am aware that addresses the reliability of hand-held dynamometry is that of Hosking and associates who reported that "the variation in repeated strength measurements in 18 children did not often exceed ±15 percent of the initial values.",3

If the practicing clinician is to have confidence in hand­held dynamometry, evidence that the procedure is reliable is needed. On the basis of previous test results, I expected to prove that hand-held dynamometry is a highly reliable assess­ment technique. The purpose of this paper is to describe the reliability of three consecutive isometric strength measure­ments obtained during the testing of 18 different muscle groups.

METHOD

Procedures I examined the dynamometer strength score forms com­

pleted by one tester during the initial evaluation of 30 consec­utive patients. The patients had a mean age of 51.9 years (range, 17-82 years). All could follow complex instructions. Sixteen patients were diagnosed as having cerebrovascular

accidents, four had closed head injuries, two had incomplete spinal cord injuries, and two had peripheral neuropathies. The remaining six patients had various individual neurologi­cal diagnoses.

Three dynamometer strength scores were recorded on the form for each muscle group tested; therefore, the scores could be used to calculate test-retest reliability. Because each patient was tested with the dynamometer only as appropriate or possible considering the patient's condition and the range of the dynamometer, all 18 muscle groups were not tested with the same frequency.

All dynamometer tests were performed by one clinician who had completed over 5,000 dynamometer muscle tests before testing the 30 patients in this sample. The dynamom­eter tests consisted of isometric "make contractions" in which the patients used each tested muscle group to push maximally against the plate and the piston of the hand-held dynamom­eter for four to five seconds. All tests were performed with the tested limb segment in a position that was not affected by gravity. A commercially available hand-held dynamometer* was used for testing. The tester manually stabilized the body parts proximal to the tested limb segment during testing. Before testing each muscle group, the tester demonstrated to the patient the muscle contraction to be performed. Retests of specific muscle groups were performed 10 to 30 seconds after the initial test. During testing, the tester kept the dyna­mometer scale turned from view to remain blind to the score until after a four- to six-second muscle group contraction effort was completed. The scale was then read, and the score was recorded to the nearest kilogram. The piston of the dynamometer always was held perpendicular to the limb segment toward which it was directed, and the plate of the dynamometer always was placed in the same position on the tested limb. Specific testing positions are reported in Table 1.

Data Analysis

Reliability was determined using Pearson product-moment correlations of the first and second, second and third, and Mr. Bohannon is Chief, Department of Physical Therapy, Southeastern

Regional Rehabilitation Center, Cape Fear Valley Medical Center, PO Box 2000, Fayetteville, NC 28302 (USA).

This article was submitted October 22, 1984; was with the author for revision one week; and was accepted March 21, 1985. * Spark Instruments and Academics, Inc, PO Box 5123, Coralville, IA 52241.

206 PHYSICAL THERAPY

RESEARCH

first and third test scores. Because reliability determined by such correlations may be insensitive to systematic differences in scores, a one-way analysis of variance (ANOVA) for re­peated measures also was used to compare the three trials. All statistical procedures were performed using the Stats Plus14

and Anova II15 software programs.

RESULTS

Table 2 reports the mean values, the correlations, and the ANOVA F scores and p values for all three tests. The corre­lations calculated for the pairs of strength scores obtained during the testing of all muscle groups ranged from .84 to .99. All correlations, therefore, were significant (p < .01) and demonstrative of good to high reliability. The median and modal correlations for all muscle groups were either .97 or .98. Most ANOVA p values were high. Only two values were less than .05; these values were associated with hip and shoulder abduction.

DISCUSSION

The results of this study suggest that hand-held dynamom-etry is a reliable procedure when practiced by a clinician who is experienced with the technique. Correlation coefficients similar to those in this report, calculated using the scores on the dynamometer score forms of other therapists in my de­partment, support this conclusion (unreported data). The therapists in my department, therefore, now record a single test score for each muscle group when they believe the patient has exerted a maximum effort. Although the percentage var­iations in retest scores were not determined for each patient whose record was reviewed, the percentage difference of the mean of the first, second, and third test trials of each muscle group were all less than the 15% reported by Hosking and associates.13

The low p values associated with the repeated measures ANOVA used to compare the shoulder and hip abduction scores suggest that a systematic variation may exist in the

TABLE 1 Positions for Muscle Groups Tested

Muscle Group

Wrist flexors

Wrist extensors

Elbow flexors

Elbow extensors

Shoulder internal rotators

Shoulder external rotators

Shoulder extensors

Shoulder flexors

Shoulder adductors

Shoulder abductors

Ankle plantar flexors

Ankle dorsiflexors

Knee flexors

Knee extensors

Hip flexors

Hip extensors

Hip abductors

Hip adductors

Patient Position Supine

Supine

Supine

Supine

Supine

Supine

Supine

Supine

Supine

Supine

Supine

Supine

Sitting

Sitting

Supine

Supine

Supine

Supine

Limb Positions

Arm beside trunk, elbow flexed 90°, forearm in neutral supi­nation, wrist in neutral flex­ion

As wrist flexors

As wrist flexors

As wrist flexors

As wrist flexors

As wrist flexors

Shoulder flexed 90°, shoulder in neutral horizontal adduc­tion

As shoulder extensors

Elbow extended, shoulder ab­ducted 45°

As shoulder adductors

Hip and knee extended

As ankle plantar flexors

Knee and hip flexed to 90°

Knee and hip flexed to 90°

Hip flexed to 90°, knee relaxed

As hip flexors

Knee extended, hip in neutral abduction

Knee extended, hip in neutral abduction

Manually Stabilized Body Part

Arm and forearm

As wrist flexors

Arm

Arm

Arm

Arm

Shoulder

Shoulder

Trunk

Trunk

Lower limb proxi­mal to ankle

As ankle plantar flexors

Thigh

Thigh

Trunk

Trunk

Contralateral lower extremity

Contralateral lower extremity

Dynamometer Placement

Just proximal to metacarpophalan­geal joints on extensor surface of hand

Just proximal to metacarpophalan­geal joints on flexor surface of hand

Just proximal to wrist joint on radial surface of forearm

Just proximal to wrist joint on ulnar surface of forearm

Just proximal to wrist joint on flexor surface of forearm

Just proximal to wrist joint on exten­sor surface of forearm

Just proximal to elbow on extensor surface of arm

Just proximal to elbow on flexor sur­face of arm

Just proximal to elbow on medial sur­face of arm

Just proximal to elbow on lateral sur­face of arm

Just proximal to metatarsophalangeal joints on plantar surface of foot

Just proximal to metatarsophalangeal joints on dorsal surface of foot

Just proximal to ankle on posterior surface of leg

Just proximal to ankle on anterior surface of leg

Just proximal to knee on extensor surface of thigh

Just proximal to knee on flexor sur­face of thigh

Just proximal to knee on lateral sur­face of thigh

Just proximal to knee on medial sur­face of thigh

Volume 66 / Number 2, February 1986 207

TABLE 2 Test-Retest Reliability of Isometric Strength Testing Using a Hand-Held Dynamometer

Muscle Group Action

Wrist flexion Wrist extension Elbow flexion Elbow extension Shoulder internal rotation Shoulder external rotation Shoulder extension Shoulder adduction Shoulder flexion Shoulder abduction Ankle dorsiflexion Ankle plantar flexion Knee flexion Knee extension Hip extension Hip flexion Hip abduction Hip adduction

Na

26 45 44 51 42 45 39 32 25 45 36 25 47 33 25 44 37 14

Mean Force Produced (kg)

Test 1

s 6.4 7.7

11.4 9.3 8.6 8.2

11.8 9.7

10.1 9.9 9.9

17.9 9.0

11.0 17.8 7.9

12.1 7.8

4.5 5.3 6.6 6.0 4.1 4,4 6.0 5.0 5.1 5.6 6.2 7.3 5.5 6.4 5.4 5.6 5.6 2.0

Test 2

s 6.7 7.9

11.3 9.1 8.5 8.2

11.9 9.7

10.0 9.9 9.9

17.6 9.0

11.0 17.4 8.1

12.0 7.6

4.7 5.2 6.4 5.8 4.2 4.5 6.0 5.3 5.1 5.7 6.1 7.2 5.9 6.7 5.2 5.6 5.6 1.9

Test 3

s 6.6 7.8

11.1 9.0 8.4 8.1

11.8 10.1 10.0 10.2 9.6

17.8 9.0

10.7 17.7 8.0

12.6 8.0

4.5 5.1 6.1 5.6 4.0 4.0 6.1 5.2 5.0 5.9 5.6 7.4 5.7 6.4 5.1 5.6 5.9 2.4

Test 1-Test 2

.97

.98

.99

.99

.99

.98

.97

.97

.98

.99

.98

.98

.99

.98

.93

.98

.98

.91

r

Test 2-Test 3

.98

.98

.99

.98

.98

.97

.99

.95

.99

.99

.98

.97

.98

.98

.95

.99

.98

.95

Test 1-Test 3

.96

.97

.99

.98

.98

.98

.97

.97

.96

.98

.99

.97

.98

.97

.87

.97

.98

.84

Repeated Measures Analysis of Variance

F

.817

.388 1.852 2.650 1.081 .169 .314

1.755 .042

4.007 1.028 .330 .013

1.912 .301

1.278 5.392 1.072

P

NS NS NS NS NS NS NS NS NS

.021 NS NS NS NS NS NS

.006 NS

repeated dynamometer scores of these muscle groups. Al­though these variations are not substantial, they have served as an impetus for attempting alternative methods of testing.

The test-retest reliability of tests repeated within a short period of time (as in this study) may differ from that of tests repeated days or weeks apart. Because patients' physical status may change over a period of days or weeks, the comparison of records obtained over such time periods would be inappro­priate for establishing the reliability of the measurement. Test-retest reliability determined by retesting healthy subjects after a longer period of time may provide information regarding reliability under conditions in which test learning may not be a factor.

Reliability may be higher for tests performed on adult patients than for tests performed on healthy adults. Because patients generally are weaker than healthy persons, stabiliza­tion and meeting muscle force production with the dynamom­eter is easier with patients. Stabilization and meeting muscle force production may be particularly difficult for clinicians who are not physicially strong.

The test-retest reliability described in Table 2 is relevant only when muscles are tested by an experienced clinician using the positions described in Table 1. The reliability of tests performed on other muscle groups and intertester relia­bility are not established in this study. Such reliability should be established before the comparison of test scores obtained by different testers.

For most of the muscle groups that were tested, reliability is comparable to that obtained with isokinetic dynamome­ters.8,9 I was unable to determine muscle force measurements

exceeding 27.2 kg (60 lb) with the hand-held dynamometer. Clinicians who are strong enough physically may wish to consider using dynamometers with higher muscle force meas­uring capacities.

Although the upper limit of measurement is not a problem with isokinetic dynamometers and with many fixed force gauges, the ease and speed with which patients can be tested with hand-held dynamometers makes them clinically more practical. Given their reliability, precision, and objectivity, I recommend hand-held dynamometers as an alternative to manual muscle testing. I currently am gathering normative isometric strength data using the hand-held dynamometer. Such information should increase further the value of hand­held dynamometry in patient assessment.

CONCLUSION

I found three repeated hand-held dynamometer strength scores, obtained by a single clinician during one test session of 30 patients, to be highly correlated. Hand-held dynamom­etry, therefore, may be considered reliable under the condi­tions of its application described in this report. As intertester reliability and normative data are established for hand-held dynamometry, this technique may prove to be of great value to the clinician.

Acknowledgment. I greatly appreciate the assistance of Marian Geddie in the preparation of this manuscript.

a N = number of muscle groups.

208 PHYSICAL THERAPY

RESEARCH

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Volume 66 / Number 2, February 1986 209