Hand-held Dynamometer Measurements: Tester Strength

Transcription

1 Hand-held Dynamometer Measurements: Tester Strength JOAN B. WIKHOLM, BA, BS,' RICHARD W. BOHANNON, EdD, MS, BS~ Three examiners with measurably different strengths and three muscle groups with distinctly different maximum force productions were used to investigate the effect of tester strength on the magnitude and reliability of hand-held dynamometer (HHD) force measurements. Each examiner measured the shoulder external rotator, elbow flexor, and knee extensor muscles of 27 healthy adults twice during two sessions (one week apart). lntrarater/intrasession, intraraterlintersession, and interraterlintrasession reliability coefficients (ICCs) were calculated. Interrater ICCs decreased in magnitude f.92 to.226) as the tested muscle groups increased in force production. lntraraterl intersession ICCs indicated a similar trend. High intrarater/intrasession and interrater1 intrasession ICCs calculated from shoulder external rotator measurements indicated that HHD testing for muscle groups generating a mean maximum force of about 120 N may be reliable for clinicians with strengths equal to or exceeding those of the weakest tester in this study. Above 120 N, tester strength appeared to be a major determinant of the magnitude and reliability of the forces measured with a HHD. Further investigation into the relationship between tester strength and the intrarater and interrater reliability of HHD measurements is warranted. Accurate muscle strength measurement is an integral and essential component of physical therapy assessment for many patients. Objective strength measurements provide baseline data and information about rate of change and intervention efficacy. Manual muscle testing (MMT) remains the conventional measurement method despite research indicating an associated high degree of subjectivity that threatens accuracy (, 5, 16). Beasley's classic study of poliomyelitis patients demonstrated that MMT grades of normal were given to certain patient groups whose subsequent dynamometric force measurements revealed approximately 50 percent strength deficits (). Beasley also noted that MMT failed to distinguish 20 to 25 percent differences in strength in the 0 to 50 Ib range and was inaccurate in estimating small percentage differences at lower ' Physical therapist at Mt. Sinai Hospital. 500 Blue Hills Ave.. Hartford. CT *Associate professor at the School of Alli Health. U101. University Of CT. Stons. CT and coordinator for clinical research in the Dept. of Rehabilitation. Hartford Hospital, Harfford. CT so-s011p1l $ THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAPY Copynght by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association force levels (). He and others since have advocated the clinical use of quantitative force measuring devices to increase objectivity, precision, and reliability of strength measurements. The quest for quantification has led to the development and testing of a variety of fixed and hand-held dynamometers (HHDs). Portability and ease of application have made HHDs desirable for general clinical use. Researchers have found that HHD measurements are both valid and reliable when used to test naturally weak and pathologically weakened muscle groups (1, 5, 6, 10-12, 18, 20, 22). Although quantitative and more precise than MMT (2-S), HHD measurements, like MMT measurements, can be influenced by the strength of the examiner (). Beasley raised this issue over 0 years ago regarding MMT when he stated that "all estimates of normality are marked off by the dividing line determined by the examiner's own ability to apply force" (, p 41). The literature abounds with references to limitations that tester strength imposes on HHD reliability. Clark (1) described the Newman myometer as limited to muscle strength measurements not exceeding 60 Ibs (266.9 N). Edwards and McDonnel (14) wrote that an examiner must JOSPT 1:4 April 1991 HAND-HELD DYNAMOMETER MEASUREMENTS 191

2 be very strong to use a HHD with a force range greater than 12 kg ( N). Hosking et al (1 7) noted that tester strength limited measurements from the knee extensor and hip flexor muscle groups when the Hammersmith myometer (range N) was used. Hyde (1 8) indicated that regardless of tester experience, the upper limit of ability to offer resistance was 0 kg (294.2 N) of force. Wiles (26) agreed that attempts to perform break tests against forces greater than 0 kg (294.2 N) were "clumsy or impossible for the average examiner." Stuberg (22) found that knee extension and elbow flexion strength measures of healthy children exceeded the dynamometer's 27.2 kg (266.7 N) capacity. He questioned the usefulness of a higher force measuring range because of limitations resulting from increased stabilization difficulties. Van der Ploeg (24) stated that a HHD range beyond 220 N is not helpful due to stabilization and strength issues. Others have also raised the issue of tester strength as a variable (8, 9, 19). Although finding high intrarater correlations for both MMT and the HHD with five different muscle groups, Wadsworth et al (25) recognized tester strength as an important variable. Agre et al (1) obtained intrarater and interrater reliability coefficients of for HHD measurements of peak isometric force of upper extremity muscle groups but reported poor reliability for lower extremity muscle groups that generated higher forces. Saranti (21) eliminated 50 cases from his subject pool of 21 9 due to tester inability to overcome the subject's resistance during the break test approach to muscle strength testing of hip flexion and hip abduction using the HHD. Strength differences between examiners may result in divergent force readings despite apparently successful testing applications. Byl et al found that the strength measured by examiners increased 10 to 0 percent when additional stabilizing procedures were used to test normal elbow flexion and shoulder abduction with the HHD. Mean strength measurements increased with stabilization, but they remained significantly different between examiners for all tests except one. The significant variation in maximum force recorded was thought to be due to inherent strength differences in the examiners (1 2). Common sense dictates that inherent tester strength and ability to hold a HHD against a patient's effort are related. To date, however, tester strength has not been isolated as a variable or examined to ascertain its effect on HHD muscle strength measurements. Therefore, the purpose of this study was to investigate the effect of tester strength on the magnitude and reliability of HHD force measurements obtained from three muscle groups. METHOD The study design was an 'explicatory experiment" as defined by Feinstein (15). The investigators intended to reveal differences in force readings accompanying different testers' strengths. Thus, three examiners with considerably different strength abilities were chosen to repeatedly test the same variable (muscle strength). Each examiner tested the same three muscle groups of 27 healthy adults at two sessions spaced one week apart. Testers Nine volunteer testers, who were experienced in MMT but had no previous clinical experience with the HHD, were solicited from the rehabilitation department of a major metropolitan hospital. They were not informed of the project's specific purpose or the selection process by which three would be chosen. Each volunteer performed two trials each of maximum isometric shoulder flexion/elbow extension and shoulder extension/elbow flexion efforts with their dominant side. The efforts were performed against a Cybex isokinetic dynamometer (Cybex, Division of Lumex, Inc., 2100 Smithtown Avenue, Ronkonkoma, NY 11779). Test efforts were designed to approximate requirements made of the upper extremity during HHD testing of elbow flexion, shoulder external rotation, and knee extension. Means of the four efforts were ranked. Testers with scores that were highest (170.2 Nm), lowest (70.24 Nm), and closest to the overall mean (87.5 Nm) were chosen to represent a strong, weak, and average strength tester. Tester one was cm tall and weighed 72.6 kg; tester two was cm tall and weighed 62.6 kg; and tester three was 161. cm tall and weighed 56.0 kg. All testers were right-handed, and their mean age was 27 years. Subjects Subject participation and consent forms were approved by the University of Connecticut Committee on the Use of Human Subjects in Research. Twenty-two women and five men (Table 1) volunteered to participate, again unaware of the investigation's specific purpose. All volunteers, including the testers, signed release forms stating that they had no knowledge of musculoskeletal or neurological problems that might affect their ability to generate maximum force. They also agreed to report any changes in status during testing, not to change any existing pattern of physical activity, and not to undertake a new strengtheningltraining program. WlKHOLM AND BOHANNON JOSPT 1:4 April 1991

3 TABLE 1 Characteristics of subjects who were tested by three examiners with a hand-held dynamometer 'im Right = 20 Right = 10 N = 22 Left = 2 Left = 12!en Right = 5 Right = N-5 Left = 0 Left = 2 otal Right = 25 Right = 1 N = 27 Left = 2 Left = 14 A subject pool of healthy normals was chosen to provide a strength range wide enough to challenge the HHD ability of all testers. Using healthy normals also eliminated questions regarding consistency of effort resulting from ongoing disease processes, recovery rate, or neurological or cognitive deficits. The investigators were interested only in comparing the magnitude and reliability of force measurements obtained by testers with different strength abilities. Procedure The shoulder external rotator, elbow flexor, and knee extensor muscle groups were chosen for testing due to their widely different force production abilities. In this study, they represented weak, average, and strong muscle groups, respectively. Each of the three groups had been previously investigated using a HHD (1, 7, 8, 10, 12, 20). The three testers attended an orientation session where they learned and practiced the test positions and stabilization procedures for the three muscle groups. Each tester received written instructions concerning proper procedure, ensuring that subjects received consistent verbal instructions and feedback. Testers also attended review sessions prior to each testing date. Subjects were scheduled three at a time and assigned by random draw to one of three previously labeled testing sessions. Dominant side was recorded, and tested side was chosen by a coin toss. Testers were assigned to their first station by a random draw that was repeated with each group of three subjects. Testers performed two blind trials at 0 seconds apart and then rotated to the next station. A one-minute rest period was allowed between testers. Subjects remained at each station until all testers had performed the station-appropriate test and then moved to the next station. The entire procedure was repeated one week later at the same time of day. Side tested remained the same across weeks. Testers employed a make type test before which subjects were instructed to come to a maximum effort over a one- to two-second period. The subjects were told to sustain the effort for three to four seconds until the tester instructed them to relax. The HHD was placed perpendicular to the limb segment tested in a location specified by landmark during the instruction sessions to assure that the lever arm length remained constant. The landmarks were the extensor surface of the forearm just proximal to the styloids for shoulder external rotation (Figure I), the flexor surface of the forearm just proximal to the styloids for elbow flexion (Figure 2), and the anterior surface of the leg just proximal to the malleoli for knee extension. Subjects were positioned supine on padded tables in separate booths for shoulder external rotation (Figure 1) and elbow flexion (Figure 2) testing. For both tests, the elbow was placed in 90 degrees of flexion and the shoulder was put in neutral rotation and about 40 degrees of abduction. Subjects were positioned upright, sitting on a Cybex testing chair with the knee in about 90 degrees of flexion and waist and leg straps in place for knee extension testing (Figure ). Testers used manual stabilization during all tests. During knee extension testing, the metal bar under the Cybex chair was used for additional stabilization (Figure ). The HHD was held as stationary as possible during each test. Testers used Ametek dynamometers (Ame- Figure 1. Subject position and tester stance and stabilization for shoulder external rotation muscle force testing with a hand-held dynamometer. JOSPT 1:4 April 1991 HAND-HELD DYNAMOMETER MEASUREMENTS 19

4 Figure 2. Subject position and tester stance and stabilization for elbow flexion muscle force testing with a hand-held dynamometer. tek/mansfield & Green Division, 8600 Somerset Drive, Largo, FL 54), which were calibrated by vertical loading with weights prior to the start of each session. The dynamometer's range is zero to 650 N (1 N =.2248 Ib); its precision is to.i N. The dynamometer remained at each station. Shoulder rotation and elbow flexion were tested with dynamometers affixed with rectangularshaped padded heads, while knee extension was tested with a curved, padded head to better accommodate the shape of the lower leg. Data Analysis The maximal force readings recorded were subjected to statistical analysis using the SYSTAT program (27). Descriptive statistics for the magnitude of force measured for each muscle group during each session by each tester were determined. The grand mean magnitudes of force measured by each tester from each of the three muscle groups during each session were compared between the three testers using one-way analysis of variance (ANOVA) procedures. From the ANOVA results, intraclass correlation coefficients (ICCs) were calculated to provide Figure. Subject position and tester stance and stabilization for knee extension muscle force testing with a hand-held dynamometer. an indication of interrater/intrasession reliability. The mean magnitude of force measured by each tester from each muscle group during each session was compared between trials using ANOVA procedures. lntraraterlintrasession lccs were calculated from the ANOVA results. The grand mean magnitudes of force measurements obtained by each tester from each muscle group during each session were compared between sessions using ANOVA procedures. Intraraterlintersession lccs were calculated from the ANOVA results. RESULTS The ANOVA results in Table 2 demonstrate that for each muscle group during each test sessionexcluding the shoulder rotator muscles during the second session-there was a significant difference in the magnitude of force measured by the three examiners. Examiner one, the strongest tester, consistently recorded higher maximal force readings for all three muscle groups than the other examiners. The gap between examiner one and examiners two and three widened as the strength of the muscle group tested increased. Differences 194 WIKHOLM AND BOHANNON JOSPT 1:4 April 1991

5 TABLE 2 Interrater/intrasession comparison of force measurements (N) of three muscle groups obtained by three examiners of different strengths during two sessions at one week apart Elbow flexors Force Analysis of Variance lntredass Muscle Grwp Session Examiner Measurements Conelation (Week) Grand Mean Fratio P Coeffiaent Shoulder external rotators o m Knee extensors between means of maximal force generated for both sessions of shoulder external rotation were small, with only 10.9 N separating examiners one and two. The elbow flexion mean maximal force difference during week one increased to 62.8 N between examiner one and examiner three, who recorded the second highest mean. A marked difference of 170 N between examiner one and two for mean maximum knee extension force illustrates a similar trend. Tester two, the average strength tester, measured notably greater force than tester one only for the knee extensor force tests. Interrater/intrasession lccs (Table 2) were least for the knee extensor muscle group, which was the strongest examined (session one ICC =.226). The lccs were in the intermediate range for the elbow flexor muscles (.799 and.768 for sessions one and two, respectively). The lccs were highest for the shoulder external rotator muscles, which were the weakest muscle group examined (.92 and.927 for sessions one and two, respectively). Table summarizes the differences in force measured between trials by each examiner for each muscle group during each session. The ANOVA procedures revealed no significant differences in the magnitude of force measured between trials, regardless of the muscle group, session, or examiner. lntraraterlintrasession lccs for shoulder external rotation and elbow flexion were above.900, except for second session elbow flexion lccs of.825 and.852 for examiners two and three, respectively. Knee extension force measurement lccs ranged from.i61 to.950, revealing a marked difference between testers. Examiners two and three had very poor lccs and did not repeat the knee extension tests during the second week because they were unable to hold without losing stabilization during the first session. Intraraterlintersession lccs varied considerably, depending on the muscle group and tester. Table 4 summarizes the differences in forces measured between sessions by the three examiners for the three different muscle groups. The ANOVAs demonstrate that only the shoulder external rotation force measured by the strongest examiner differed significantly between sessiom. Intraraterlintersession lccs for shoulder external rotation were all high, and reliability increased in order from examiner three (.926) to examiner one (.976). Examiner one demonstrated continued high reliability with an ICC of.98 for elbow flexion, despite an increase in force magnitude of N between his grand mean measurements for shoulder external rotation and elbow flexion. In contrast, examiners two and three had poor elbow flexion lccs of.64 and.676, respectively. These decreases in intrarater/intersession reliability occurred with overall increases of just 52.8 N and 58.2 N between grand mean shoulder external rotation and elbow flexion force measurements. Only examiner one retested knee extension during the second session. The resulting intersession ICC was.821. DISCUSSION It appears that tester strength effects the magnitude and reliability of HHD measurements. Magnitude measurements differed between testers, with the strongest tester routinely measuring greater forces than the other testers for the same JOSPT 1:4 April 1991 HAND-HELD DYNAMOMETER MEASUREMENTS 195

6 TABLE Intrarater/intrasession comparison of two repeated force measurements (N) of three muscle groups obtained by three examiners of different strengths during two sessions Muscle Group Examiner Measurements Trial 1 Trial 2 F-ratio Analysis of Vanance Inhadass Conelation Coefficient Shoulder external 1 1 rotators <nee extensors Elbow flexors TABLE 4 lntrarater/intersession comparisons of repeated force measurements (N) of three muscle groups obtained by three examiners of different strengths Muscle Group Exarnir ler Ooe Session Two X S X S Analysis of Variance lntrac dass Conel ation F-ratio P Coeffi cient Shoulder external rotators Knee extensors Elbow flexors muscle groups. Moreover, differences in forces measured between the examiners increased as the strength of the muscle group tested increased. The effect of tester strength was further demonstrated by the differences in reliability coefficients. lnterrrater lccs showed an unmistakable trend of quickly diminishing reliability (.92 to.226) as the muscle groups tested increased overall force production. Intrarater/intersession lccs indicated a similar trend of decreasing reliability with increasing force measurements for all three examiners. Examiner one, however, maintained an overall high degree of reliability throughout the tests. Although many studies have been published regarding both intrarater and interrater reliability, tester strength is rarely considered when assessing reliability. However, predictions of upper force range limits for HHD reliability have been published. In this study, the high intraraterlintersession and interraterlintrasession lccs calculated for shoulder external rotation testing indicate that HHD testing for muscle groups generating a mean maximum force of 120 N may be reliable for clinicians regardless of their strength. Results of this study also indicate that high interrater reliability for forces under 120 N can be expected between clinicians having less than average strength if they are provided with proper instruction. This generalization is warranted since testers representing clinicians of typical strength were solicited from a pool of practicing therapists in a large metropolitan hospital. Examiner one, the strongest tester, was able to reliably (intrarater/intersession ICC =.821) record mean maximum knee extension forces exceeding 400 N without previous experience using 196 WIKHOLM AND BOHANNON JOSPT 1:4 April 1991

7 HHDs. These force measurements far exceed previously postulated limits (1, 14, 18, 2, 24, 26). Examiner one's ability to do so appears to be primarily a result of his greater than average strength. Examiner one's consistently high reliability for all muscle groups lends support to HHD use by strong examiners for muscle strength screening of healthy populations. Examiners two and three recorded similar force readings for elbow flexion. These unexpectedly close readings may be explained in part by results of the initial tester screening strength tests. During the shoulder extension/elbow flexion portion of the test, examiner two generated only 6.1 Nm more torque than examiner three. During the shoulder flexion/elbow extension portion of the test, however, the difference in torque generated between the two examiners was 28.5 Nm. The shoulder extension/elbow flexion test most closely approximated the stabilizing pattern used during actual elbow extension testing. Intrarater/intrasession lccs of.825 to.976 for shoulder external rotation and elbow flexion indicate that, regardless of strength, the testers were consistent within themselves. However, as mentioned previously, examiner one recorded higher maximum force efforts for each session and each muscle group than the other examiners. Many of the upper extremity tests were performed successfully by examiners two and three with no observed loss of stabilization. Subsequently, they obtained lower mean maximum force readings than examiner one. Some subjects may have subconsciously inhibited their force efforts so they would not exceed the stabilizing force generated by the examiner. Feedback provided by some subjects suggests that this might be the case. Further investigation into the relationship of tester strength to both intrarater and interrater reliability in HHD use is warranted. Upper limits of reliability should be established to further define appropriate clinical usage. If HHD is proven unreliable for strong muscle groups and/or less reliable for weak testers, then MMT reliability under the same circumstances must be strongly questioned. Beasley has cautioned against the hazards of relying on internally based judgment systems (). A visible and unquestionable loss of stabilization of the dynamometer occurs when a subject overcomes a tester. This undeniably demonstrates that an accurate muscle force measurement is not possible under certain circumstances. Therapists require reliable, objective measures to help establish baseline data, track strength gains and losses, predict functional capabilities, and report on the success of chosen treatment interventions. The issue of tester strength is in- tegral to HHD reliability. This study has begun the investigation of the relationship between them. CONCLUSION Based on the results of this study, the investigators conclude that differences in correlations for repeated measurements of shoulder external rotator, elbow flexor, and knee extensor forces obtained by different examiners are related to previously established differences in the examiners' inherent strength levels. 0 REFERENCES Agre JC. Megness JL, Hull SZ. Wright KC, Baxter TL. Patterson R. Stradd L: Strength testing with a portable dynamometer: reliability for upper and lower extremities. Arch Phys Med Rehabil 68: Appletown RE. Sykanda AM: Objective assessment of rnusde strength in chron~c relapsing dysimmune pdyradiculoneuropathy. Dev Med Child Neurol 0: Beasley WC: Influence of method on estimates of normal knee extensor force among normal and postpolio children. Phys Ther Rev 6: Bohannon RW: Results of resistance exercise on a patient with amyotrophic lateral sclerosis. Phys Ther 6: , 198 Bohannon RW: Manual muscle test scores and dynamometer test scores of knee extension strength. Arch Phys Med Rehabil 67: Bohannon RW: Test retest reliability of hand-held dynamometry dunng s~ngle session of strength assessment. Phys Ther 66: Bohannon RW: Llpper extremity strength and strength relationsh~ps among young women. J Orthop Sports Phys Ther 8: Bohannon RW: Hand-held dynamomehy: Stability of musde strength over multiple measurements. Clin B i i h 2: Bohannon RW: The clinical measurement of strength. Clin Rehabil 1: Bohannon RW. Andrews AW: lnterrater reliability of hand-hcld dynamometry. Phys Ther 67: Bohannon RW. Smith MB: Upper extremity strength deficits in hemiplegic stroke patients: relationship between admission and d~scharge assessment and time sinceonset. Arch Phys Med Rehab 68: Byl NN. Richards S. Asturias J: Inherater and interrater reliability of strength measurements of the biceps and deltoid using a handheld dynamometer. J Orthop Sports Phys Ther 9: Clark HH: Comparison of instruments for recording muscle strength. Res 0 25: Edwards RHT. McDonnel M: Hand-held dynamometer for evaluating voluntary muscle function. Lancet , 1974 Fe~nstem AR: Clincal Epidemiology. The Architecture of Clinical Research. WB Saunders. Philadelphia Frese E. Brown M. Norton BJ: Cl~nlcal reliability of manual musde testmg middle trapenus and gluteus rned~us muscles. Phys Ther 67: ,1987 Hoskmg GP. Bhat US. Dubowitz V. Edwards RHT: Measurements of muscle strength and performance in children with normal and diseased muscle. Arch Dis Child 51: Hyde SA. Scott OM. Goddard CM: The myometer: the develop ment of a cl~n~cal tod. Physiotherapy 6R Mayhew TP. Rothstein JM: Measurement of muscle performance w~th instruments. Clin Phys Ther 7: Riddle DL. Finucane SD. Rothstein JM, Walker ML: lntrasession and mtersession reliability of handheld dynamometer measurements taken on bramdamaged patients. Phys Ther 69: Saraniti AJ. GUm GW, Melvin M. N i a s JA: The relationship between subjective and objective measurements of strength. J Orthop Sports Phys Ther 2: ,1980 Stuberg WA. Metcalf WK: Rehabihty of quantiiative musde testing in healthy children and in ch~ldren with Duchenne muscular dystre phy usmg a hand-held dynamometer in assessing isometric external rotator performance. J Orthop Sports Phys Ther 10:21-217, 1988 JOSPT 1:4 April 1991 HAND-HELD DYNAMOMETER MEASUREMENTS 197

8 2. Sullivan SI. Chesley A. Hebert G. McFaull S. Sarlli D: The lntrarater reliability of manual muscle testing and handhdd dynavalidity and reliability of the hand-hekl dynamometer in assessing metric muscle testing. Phys Ther 67: isometric external rotator performance. J Orthop Sports Phys Ther 26. Wiles CM, Kami Y: The measurement of muscle strength in patients 10: with peripheral neuromuscular disorders. J Neurd Neurosurg Psy- 24. Van der Ploeg RJO. Dosterhuis HJGH. Reuvekamp J: Measuring ch~atty 46: muscle strength. J Neurol21: Wtlkinson L: SYSTAT: The System for Statistics. Evanston. IL: 25. Wadsworth CT. Krishnan R. Sear M, Harrold J. Nisen DH: SYSTAT. lnc WIKHOLM AND BOHANNON JOSPT 1:4 April 1991