Facioscapulohumeral dystrophy natural history study: standardization of testing procedures and reliability of measurements.

[Personitus KE, Pandya S, King WM, et al. Facioscapulohumeral dystrophy natural history study: standardization of testing procedures and reliability of measurements. Phys Ther. 1994;74:253-263.]

Key Words: Facioscapulohumeral muscular dystrophy, Functional testing, Isometric muscle testing, Manual muscle testing.

Facioscapulohumeral muscular dystrophy (FSHD) is a common form of muscular dystrophy, with an estimated incidence of 1:20,000.[1] The degree of involvement is extremely variable, ranging from minimal facial weakness to severe generalized weakness. Facioscapulohumeral muscular dystrophy initially affects facial, scapular, upper-arm, abdominal, and foot dorsiflexor muscles. The disease may progress to the proximal hip and distal arm and hand musculature. The course is usually slowly progressive, and 20% of those with the disease eventually progress to wheelchair dependence.[1] The mode of inheritance is autosomal dominant. Sporadic cases occur and are usually the result of a new mutation. Facioscapulohumeral muscular dystrophy has been linked to a locus at chromosome 4q35, but neither the gene nor the gene product have been identified.[2]

Descriptions of the clinical course of FSHD are based on cross-sectional studies and analyses of historical data obtained from clinical examinations.3 The natural history and variable patterns of the clinical progression of FSHD have not been objectively described in a prospective manner. Knowledge of the natural history of FSHD is necessary for designing clinical trials and for accurately assessing the efficacy of a therapeutic intervention.[7,8]

Various protocols have been shown to reliably document disease progression in patients with neuromuscular diseases.[7-9] These protocols have utilized manual muscle testing (MMT) and quantitative muscle testing (QMT) to document decline in strength. The protocols have included timed function tests and specific rating scales to document decline in function. Manual muscle testing provides reliable and sensitive measures of change in strength in patients with Duchenne muscular dystrophy.[10] Quantitative muscle testing also provides reliable and sensitive measures of decline in strength in patients with amyotrophic lateral sclerosis (ALS).[11] The timed function tests and rating scales have also been shown to be reliable.[7-11] The optimal strength testing procedure or combination of procedures that would most accurately document disease progression in patients with FSHD is not known. We therefore developed a standardized protocol utilizing MMT, QMT, and functional testing to study a well-defined population of patients and FSHD and nondiseased controls. This protocol would allow us to document the natural history of FSHD and to compare the reliability and sensitivity of MMT, QMT, and functional testing. This report presents the protocol design and reliability studies of the various measures of strength and functional abilty.

Method

Study Design

Subjects were tested at the clinical research centers of two university hospitals.[*] A physical therapist at each center acted as clinical evaluator and was responsible for performing QMT, MMT, and functional testing. For the purposes of this study, we defined functional testing as the subject's ability to do specified tasks. A study coordinator at each center was responsible for subject recruitment and monitoring data collection. A neurologist/principal investigator screened individuals with FSHD for their eligibility according to clinical, histologic, and electrophysiologic criteria.[12] For inclusion into the study, persons with FSHD must have shown evidence of facial weakness, scapular fixation, or foot dorsiflexor weakness. One affected member of the family underwent muscle biopsy to rule out myopathies such as mitochondrial myopathy, dermatomyositis, or congenital myopathy that may mimic the clinical presentation of FSHD. Electromyographic evaluation was also performed to rule out neuropathic disorders. All subjects with FSHD in this study were ambulatory.

All subjects with FSHD were admitted as inpatients and underwent 3 consecutive days of QMT, MMT, and functional testing. The order of testing was functional testing, MMT, and QMT. A complete test took 75 to 90 minutes. Subjects also underwent blood work and three consecutive 24-hour urine collections for determination of creatinine excretion as an indicator of muscle mass.

Volunteer controls were admitted as outpatients for three consecutive days of QMT, MMT, and functional testing. Two consecutive days of testing with the third day within the same work week was an acceptable alternative. All subjects, both patients with FSHD and volunteer controls, followed a weight-maintaining, meatfree diet for 3 days before and during the 24-hour urine collections.[13] Informed consent was obtained from all subjects in the presence of an auditor witness and one member of the investigative team. For subjects under 18 years of age, parental consent was obtained.

Subjects

Thirty-two subjects with FSHD and 32 age- and gender-matched volunteer controls with no known medical condition were studied at the two centers. The subjects with FSHD had a mean age of 36.1 years (SD=9.6, range=17-49). The volunteer controls had a mean age of 35.8 years (SD=8.0, range=23-50).

Both groups of subjects were comparable in height and weight, with the volunteer controls being slightly heavier, on average, than the subjects with FSHD. Subjects with FSHD had a mean height of 171.9 cm (SD=7.8, range=157.4-187.9) and a mean weight of 67.1 kg (SD=14.4, range=38.5-97.8). The volunteer controls had a mean height of 171.0 cm (SD=9.7, range=152.9-190.7) and a mean weight of 69.0 kg (SD=14.4, range=44.3-113.2).

Testing Procedures

The strength testing protocol was designed to evaluate the muscles most characteristically affected by FSHD. Eighteen muscle groups (9 right and 9 left) were evaluated by both MMT and QMT (Tab. 1).

Table 1. Muscle Groups (Right and
Left) Evaluated for Both Manual Muscle
Testing and Quantitative Muscle Testing

Shoulder abductors
Shoulder lateral (external) rotators
Shoulder horizontal adductors
Shoulder horizontal abductors
Elbow flexors
Elbow extensors
Knee extensors
Knee flexors
Dorsiflexors

Manual muscle testing. Manual muscle testing took approximately 10 to 15 minutes to complete. Muscle groups were scored using a modified Medical Research Council scale (Tab. 2).[14] Certain muscle groups were tested in one position only, whereas others needed alternate positions for maximal antigravity testing. Each muscle group was tested by procedures that standardized the subject's position, direction of movement, and joint angle for resistance and the examiner's stabilization and hand placement (Tab. 3).[15] If the clinical evaluator was uncertain about a muscle group grade (eg, 4+ versus 4), the lower score was chosen to ensure consistency. [TABULAR DATA 2 OMITTED] [TABULAR DATA 3 OMITTED]

Quantitative muscle testing. maximal voluntary isometric strength was tested on a QMT system.[dagger] The system uses an adjustable cuff to attach the subject's arm or leg to an inelastic strap that is attached to a force transducer with a load of 0.5 to 1,000 N (0.05-100.0 kg). Subjects were tested on an adjustable examining table enclosed in a frame of octagonal tubing, which provided a rigid and adjustable anchor for the transducer (Figure).

The physical therapist at each center who acted as clinical evaluator used photographs and written instructions that illustrated subject position, strap placement, examiner fixation, and common substitutions to ensure standardization (Tab. 4). Ninety-degree angles were estimated for joint and strap alignment. Three of the nine movements tested--elbow flexion, elbow extension, and ankle dorsiflexion--required the subject to hold his or her limb against the maximal gravitational vector. (Elbow extension and ankle dorsiflexion were the muscle groups that were most often untestable because of weakness [Tab. 5].) All other movements were tested in a maximal antigravity position (eg, the movement was directly opposed by gravitational force). [TABULAR DATA 4 OMITTED] [TABULAR DATA 5 OMITTED]

Each muscle group was tested three consecutive times for 5 seconds with 10 seconds of rest between trials. The maximum force generated over 5 seconds was recorded for each trial. The subject was vigorously coached to push or pull during the test. Auditory feedback was also provided by the computer, which emits a variable pitched sound in relation to the force generated. The QMT testing took approximately 45 to 60 minutes to complete.

Functional testing. This included a battery consisting of several objective tests and rating scales to document what we believe relate to functional capabilities. Timed tests included the amount of time taken to (1) climb four standard steps with a handrail, (2) traverse 9.14 m (30 ft), and (3) drink 180 mL (6 fl oz) of water through a straw placed in the middle of the subject's lips. Grip and pinch Jamar dynamometer[double dagger] and B&L pinch gauge (University of Rochester [UR]) and a Jamar pinch gauge[double dagger] (Ohio State University [OSU]). The best of three trials was recorded. Forced vital capacity (in milliliters) was measured with the subject in a sitting position using a Vanguard DS 500 electronic spirometer.[sections] Again, the best of three trials was recorded. Upper-extremity and lower-extremity functional capabilities were graded using the scales shown in Table 6. This testing took about 10 to 15 minutes to complete. [TABULAR DATA 6 OMITTED]

Reliability Testing

Intrarater reliability was examined for measurements of 32 subjects with FSHD and the 32 volunteer controls using data from the first 2 days of testing. Interrater reliability was examined on a subgroup of 7 subjects with FSHD. Subjects were seen for 2 consecutive days of testing (MMT and QMT tests), with different evaluators on each day. Each evaluator was blind to the other's results.

Machine-machine reliability was evaluated on 15 volunteer controls. The linear force transducer was the part of the QMT machine that was most likely to differ between the two centers. The OSU clinic's transducer and strap were sent to the UR clinic so that one evaluator could test the same subject with each of the two centers' transducers. The 15 volunteers were tested on the right side on 2 consecutive days. The transducer that was used on the first day (OSU versus UR) was randomly determined. Subjects were also tested on the two centers' Jamar dynamometers and B&L/Jamar pinch gauges.

Errata Forms/Weakness and Pain Protocols

Errata forms were designed to document any errors made during testing. They were used to document reasons for performing fewer than three trials for every muscle. An attempt was made to test all 18 muscle groups using QMT. For muscle groups that were suspected to be too weak to be accurately tested, the following steps were taken. The subject's limb was placed in the testing position and passively held to obtain the proper 90-degree alignment between the joint being tested and the force transducer strap. The resting force was noted. The clinical evaluator then removed his or her hand, stabilized the subject in the normal manner, and started the trial. If movement, attributable to the joint's primary mover, was seen at the joint and the subject attained at least resting force, then the trial was recorded. If the muscle group was judged to be too weak to test, three trials at 0 N were recorded.

When subjects experienced pain during QMT, one of two procedures was followed. If the subject was unable to complete a trial, or if there was a >50% decrease in strength during a trial due to pain, the trial was eliminated. If the subject was able to complete the trial without a significant decrease in strength, the trial was counted and the experience of pain was noted on the errata sheet. Subjects rarely complained of pain that limited their force generation.

Statistical Methods

The QMT data for each subject consisted of the peak force generated for each of three trials for each muscle on each day of testing. We considered three summary measures of force for each muscle on each day: the median, the mean, and the maximum of the three peak forces. To assess test-retest reliability for these measures, an intra-class correlation coefficient Icc[1,1])[16] was computed for each measure for each of the 18 muscles tested. The same statistic was also computed for assessing test-retest reliability of the grip and pinch strength measures, as well as measures of pulmonary function and timed functional testing. We chose the ICC model (1,1) because we did not believe it useful to further partition the error terms as occurs with other forms of the ICC.

The MMT data are ordinal; therefore, the weighted kappa statistic[17] was used to assess test-retest reliability for each of the 18 muscles separately. This statistic takes into account the relative seriousness of each possible disagreement through the assignment of weights inversely related to the number of grades that the scores for a particular subject differed from day 1 to day 2. Specifically, the weights were 1-([number of grades separating the two scores]/ 12), because there were 13 possible grades. Therefore, a subject who was assigned the same grade on day 1 and day 2 would have a weight of 1, and a subject who was assigned a score of 4- on day 1 and a score of 4+ on day 2 would have a weight of 5/6.

Interrater reliability, or agreement between raters, was assessed using the same statistical methods described earlier, except that ICC (2,1)[16] was used for assessing reliability of the QMT measurements. The use of ICC (1,1) for assessing intrarater reliability, as opposed to ICC (2,1), follows the development given in Fleiss[18] and is justified by the principle of selecting the most parsimonious statistical model that provides an adequate fit to the data. We felt that the systematic differences between days for tests performed by the same rater would be much less pronounced than systematic rater differences.

There is no universal agreement as to what values of weighted kappa or the ICC indicate acceptable reliability; however, Fleiss[18] recommends that ICC values greater than .75 be taken to represent excellent reliability. Landis and Koch[19] suggest the following criteria for kappa statistics in assessing agreement: O-.20=slight agreement, .21-.40=fair agreement, .41-.60=moderate agreement, .61-.80=substantial agreement, and .81-1.00=almost perfect agreement.

To explore the possibility of either learning or fatigue effects on the testing results, systematic differences among the results on days 1, 2, and 3 were examined using paired t tests. For each muscle and each subject group (FSHD and volunteer control), comparisons were made between days 1 and 2, 2 and 3, and 1 and 3.

Results

Reliability of Quantitative Muscle Testing Data

Intraclass correlation coefficients were found to be excellent for all QMT measurements (intrarater, interrater, and machine-machine reliability). Table 7 lists the individual ICCs for each motion tested.

There was very little difference in reliability among the three ways of summarizing the QMT measurements for each muscle for each day (median, mean, and maximum of the three peak forces). Only results for the median are shown in Table 7. Intrarater ICCs were also consistent across the two centers. [TABULAR DATA 7 OMITTED]

Reliability of Manual Muscle Testing Data

With few exceptions, all evaluated muscle groups of the volunteer controls had MMT grades of 5 (Normal strength). Therefore, reliability results are presented only for the subjects with FSHD. Table 8 lists the intrarater and interrater weighted kappa values for motions tested. Intrarater reliability was "almost perfect" and interrater reliability was "moderate" or better for all muscle groups. [TABULAR DATA 8 OMITTED]

Reliability of Functional Testing Data

Intrarater ICCs for functional testing are shown in Table 9. Excellent reliability was found for most measures, with the exceptions of test-retest reliability of drinking from a straw in subjects with FSHD (ICC=.63) and machine-machine reliability of the pinch-gauge measurements (ICC=.72). [TABULAR DATA 9 OMITTED]

Quantitative Muscle Testing Ranges

To investigate the validity of QMT measurements on weak subjects, the lowest QMT scores for each test are listed with their corresponding MMT scores (Tab. 10). The number of subjects with QMT scores of 0 N, representing muscle groups that were too weak to test using QMT, are also listed along with their corresponding MMT scores (Tab. 10). [TABULAR DATA 10 OMITTED]

Discussion

The natural history of FSHD has not been objectively described in a prospective manner. We have therefore developed and presented a standardized protocol designed to study subjects with FSHD and volunteer controls using various testing procedures. Intrarater reliability of measurements obtained by QMT, MMT, and functional testing was shown to be excellent in both groups in this study.

Each of the muscle strength testing procedures has distinct advantages and disadvantages. Combining all three procedures in a practical protocol provides a more comprehensive assessment of each subject. Furthermore, comparing data derived from MMT, QMT, and functional testing will allow for selection of the most appropriate method for use in future therapeutic trials with patients who have FSHD.

Functional testing was the most relevant and important procedure in the view of the patients with FSHD. Functional grade testing, although reliable, may be insensitive and may not closely correspond to a decline in muscle strength unless its grading system is differentiated to closely match the loss of function caused by the disease process.[20] In our subjects with FSHD, upper-extremity functional grading rarely exceeded a score of 3, even though there were a total of six grades. The grade 3 will be further broken down to improve the sensitivity of this test (ie, to include whether the subject can lift his or her arm to at least 90' of shoulder abduction).

The relatively low ICC for the machine/machine reliability of the pinch test measurements may be explained by the use of two different types of pinch gauges. We will use the same type of gauge (Jamar[double dagger]) in future studies. The drinking test was a novel and simple test designed to measure the strength of the lip and cheek muscles, muscle groups that are predominantly involved in FSHD. Because of the poor reliability of measurements obtained with this test, we will investigate other methods of quantitating facial strength.

Manual muscle testing is quickly performed and inexpensive. It has been found to yield reliable results in studies of Duchenne muscular dystrophy.[21] When used with a transformed scale and averaged over multiple muscle groups, the MMT score has been shown to be a valid and sensitive measure of disease progression in Duchenne muscular dystrophy.[21,22] This procedure can be used to test small individual muscles and can test a large number of muscle groups in a short period of time, allowing for a more comprehensive description of the subject and the disease process. Manual muscle testing, however, can be dependent upon the evaluator. Differences in evaluator strength and weight of the subjects' limbs are potential factors affecting MMT grades.[23] Also, for the same MMT grade, quantitative isometric force measurements can vary by as much 40%, which may result in a false impression of plateauing or stepwise progression in disease processes that are actually slowly progressive.[9,24]

Intrarater and interrater reliability of MMT grades were acceptable in our subjects with FSHD. The lower interrater reliability values may reflect the fact that only six subjects were tested or that certain muscle groups were difficult to standardize between two evaluators. Ankle dorsiflexion, shoulder abduction, shoulder lateral (external) rotation, and horizontal adduction were all problematic. Shoulder abduction and lateral rotation were the most difficult because of the scapular instability in our subjects with FSHD.

Quantitative testing is being used increasingly to measure muscle strength.[10,25] It was shown to give reliable results in Duchenne muscular dystrophy and ALS as well as to be sensitive to disease progression in ALS.[9,26] The three types of quantitative testing devices most often used are hand-held myometers, isokinetic dynamometers, and isometric testing machines. Hand-held myometers are portable and relatively inexpensive. The primary disadvantage of hand-held myometry is its dependence on the strength of the examiner. To obtain an accurate reading, the examiner must break the muscle contraction.[27] Even in moderately affected subjects with FSHD, some muscle groups maintain normal strength, thus possibly making it difficult for an examiner to break the muscle contraction.

Isokinetic testing may provide excellent standardization of test positions. isokinetic dynamometers, however, have several disadvantages. In addition to the expense of this equipment, muscles that have less than grade 3+ strength cannot be tested through the full arc of motion due to the weight of the lever arm unless active robotic systems are used.[10,28] Finally, because testing is time consuming, the number of muscles that can be practically evaluated is limited.

The isometric QMT machine used in this study allows for a greater number of muscle groups to be tested in a fixed amount of time than do isokinetic testing devices. Quantitative muscle testing also allows testing of normal and weak muscle groups in the 3- to 2 MMT range (Tab. 10). These characteristics are necessary in natural history studies. The ability of QMT to test weakened muscle groups may be further improved through changes in testing position or decreasing the weight of the cuff and strap. Both intrarater and interrater reliability were excellent for our subjects with FSHD tested by QMT. Muscles that were difficult to standardize between evaluators on MMT were reliably measured with QMT. Furthermore, muscle groups not commonly tested with QMT such as the ankle dorsiflexors, shoulder abductors and lateral rotators, and horizontal adductors and abductors were all found to be reliably tested. Because no subjects had grade 2 muscle strength in the right horizontal adductors, left knee extensors, and shoulder abductors and lateral rotators, QMT testing in the grade 2 MMT range for these muscles cannot be addressed.

The protocol incorporated 3 days of QMT testing at the baseline visit so that two important questions could be addressed: (1) Are there any systematic differences from one day to the next suggestive of either learning or fatigue effects? and (2) Is the average of measurements over 2 consecutive days any better (less variable) than a single measurement on the first day?

With regard to the first question, no important systematic differences were found among the QMT measurements on days 1, 2, and 3 for the subjects with FSHD. The control subjects tended to perform somewhat better than the subjects with FSHD for many muscles on the first day of testing. The magnitude of the decrease in force on the second and third days, however, was relatively small (approximately 5%), and it had very little effect on test-retest reliability for the control subjects. This effect could possibly be due to fatigue or to decreased subject effort on days 2 and 3.

We investigated the utility of using the average of the QMT measurements over the first 2 days, as opposed to a single measurement from the first day, by comparing the means and standard deviations of each of these scores. The results, shown in Table 5, indicate that no substantial gain is obtained by averaging measurements over 2 consecutive days. This observation is also evident from the excellent observed test-retest reliability, and it is extremely important for the design of therapeutic trials in FSHD. Based on the results of the baseline testing, only 1 day of QMT testing is necessary for patients with FSHD and volunteer controls.

As expected, we did not find substantial difference between the three ways of summarizing daily QMT measurements (median, mean, and maximum of three trials) for each muscle in terms of reliability. We used the median because it is more resistant to unusually high scores secondary to ballistic contractions or substitutions.

The sensitivity of all of our measures to a decline in muscle strength will be determined after collection of longitudinal data on our subjects. The volunteer controls will be used to estimate the decline in strength associated with normal aging and will allow us to distinguish between a decline in strength secondary to disease and that due to the normal aging process. This information will also allow us to quantify the degree of weakness (relative to average normal strength) in individual subjects with FSHD.

Conclusion

We have developed a standardized protocol utilizing QMT, MMT, and what we consider functional testing that produces reliable measurements of muscle strength and function in patients with FSHD. Combining QMT, MMT, and functional testing into one protocol allows for a more comprehensive evaluation of each subject. The yearly follow-up assessment of the study subjects will establish whether the protocol, as a whole or in part, provides sensitive measures of disease progression in FSHD. The knowledge gained about the natural history of FSHD will be essential in the design and accurate assessment of the efficacy of future therapeutic interventions.

Acknowledgments

Special thanks to Lynn Cos and Fran Rainey for coordinating the study and to Carol Bragg for typing the manuscript. (*) Strong Memorial, University of Rochester, NY, and The Ohio State University Hospitals, Columbus, Ohio. ([dagger]) Biomech Designs Ltd, 7955-98 Ave, Edmonton, Alberta, Canada T6A 0B5. ([double dagger]) JA Preston Corp, PO Box 89, Jackson, MI 49204.

References

[1] Lunt PW, Harper PS Genetic counselling in facioscapulohumeral muscular dystrophy. J Med Genet. 1991;28:655-664. [2] Wijmenga C, Frants RR, Brower OF, et al Location of facioscapulohumeral muscular dystrophy on chromosome 4. Lancet 1990;336: 651-653 [3] Padberg GV. Facioscapulohumeral Disease. Leiden, the Netherlands: Leiden University; 1982. Thesis. [4] Tyler FH, Stephens FE. Studies in disorders of muscle, II: clinical manifestations and inheritance of facioscapulohumeral dystrophy in a large family. Ann Intern Med. 1950;32:640-666. [5] Walton JN, Nattras FJ. On the classification, natural history and treatment of the myopathies. Brain. 1954;77:169-231. [6] Carroll DE. Facioscapulohumeral and scapuloperoneal syndromes, In: Vinken PJ, Bruyn GH, eds. Handbook of Clinical Neurology. Amsterdam, the Netherlands: Elsevier Science Publishers BV; 1979;40:415-431. [7] Brooke MH, Griggs RC, Mendell JR, et al. Clinical trials in Duchenne dystrophy, 1: the design of the protocol. Muscle Nerve. 1981;4: 186-197 [8] Munsat TL, Andres PL, Finison L, et al. The natural history of motor neuron loss in amyotrophic lateral sclerosis. Neurology. 1988;38: 409-443. [9] Andres PL, Thibodeau LM, Finison LJ, et al. Quantitative assessment of neuromuscular deficits in ALS. Neurol Clin, 1987;5:125-141. [10] Mendell JR, Moxley RT III, Griggs RC, et al. Randomized double-blind six-month trial of prednisone in Duchenne's muscular dystrophy. N Engl J Med. 1989;320:1592-1597. [11] Munsat TL. Quantification of Neurologic Deficit. Stoneham, Mass: Butterworth Publishers; 1989:87-100. [12] Tawil R, Griggs RC, Mendell J, et al. FSHD: design of natural history study and results of baseline testing. Neurology. In press. [13] Griggs RC, Forbes G, Moxley RT, et al. The assessment of muscle mass in progressive neuromuscular disease. Neurology. 1983;33:158-165. [14] Medical Research Council. Aids to the Investigation of Peripheral Nerve Injuries. London, England: Her Majesty's Stationary Office; 1976. [15] Daniels L, Worthingham C, Muscle Testing. Techniques of Manual Examination. 5th ed. Philadelphia, Pa: WB Saunders Co; 1986. [16] Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull. 1979;86:420-428. [17] Cohen J. Weighted kappa: nominal scale agreement with provision for scaled disagreement or partial credit. Psychol Bull. 1968;70: 213-220 [18] Fleiss JL. The Design and Analysis of Clinical Experiments. New York, NY: John Wiley & Sons Inc; 1986. [19] Landis JR, Koch GG, The measurement of observer agreement for categorical data. Biometrics. 1977;33:159-174, [20] Moxley RT. Functional muscle testing. Muscle Nerve. 1990;13(suppl):526-529. [21] Florence JM, Pandya S, King WM, et al. Clinical trials in Duchenne dystrophy: standardization and reliability of evaluation procedures. Phys Ther, 1984;64:41-45. [22] Florence JM, Pandya S, King WM, et al. Intrarater reliability of manual muscle test (Medical Research Council Scale) grades in Duchenne's muscular dystrophy. Phys Ther. 1992;72: 115-122. [23] Van der Ploeg RJO, Ossterhuis HJGH. Measuring muscle strength. J Neurol 1984;231: 200-203. [24] Beasley WC. Quantitative muscle testing: principles and applications to research and clinical services. Arch Phys Med Rehabil 1961; 42:398-425. [25] Pandya S, Personius K, Cos L, et al. Test/ retest reliability of isometric measurements in patients with muscle diseases, Phys Ther (Suppl). 1992;72:S113, Abstract. [26] Brussock CM, Haley SM, Munsat TL, et al. Measurement of isometric force in children with and without Duchenne's muscular dystrophy. Phys Ther. 1992;72:105-114. [27] Marino M, Gleim GW. The efficacy of manual assessment of muscle strength using a new device. Am J Sports Med. 1987;10:360-365. [28] Burnett C, Filush BE, Colby LA. Muscle testing for DMD. Clinical Management. 1991;2(2): 31-34.

KE Personius, PT, is a doctoral student in the Physiological Sciences Program, University of Arizo Tucson, AZ 85721. He was Staff Physical Therapist, Department of Neurology, University of Rochester, Rochester, NY 14642, when this study was conducted.

S. Pandya, PT, is Assistant Professor, Department of Neurology, University of Rochester, and Depar of Physical Therapy, Ithaca College, Rochester Campus, 300 E River Rd, Rochester, NY 14623 (USA). Address all correspondence to Ms Pandya.

WM King, PT, is Therapy Supervisor, Muscular Dystrophy Clinic, Department of Neurology, Ohio State University, Columbus, OH 43210.

R Tawil, MD, is Assistant Professor, Departments of Biostatistics and Neurology, University of Rochester.

Other members of the FSH DY Group are Jerry R Mendell, MD, John Kissell, MD, and Fran Rainey (Ohio State University); Robert C Griggs, MD, Richard T Moxley III, MD, Diane Storvick, Lynn Cos, RN, William Martens, Sandra Plumb, Carol Bragg, Nancy Giampietro, and Barbara Herr (University of Rochester).

The study protocol was approved by the institutional review boards of the University of Rochester and Ohio State University.

This work was supported in part by grants from the Muscular Dystrophy Association, New York State, and NIH grants NS 22099 and M01-RR00M.

This article was submitted January 25, 1993, and was accepted September 13, 1993.