PATIENTS WITH fibromyalgia (FM) present with diffuse

Transcription

1 1646 ORIGINAL ARTICLE Test-Retest Reliability of Isometric and Isokinetic Knee Extension and Flexion in Patients With Fibromyalgia: Evaluation of the Smallest Real Difference Jose C. Adsuar, MSc, Pedro R. Olivares, MSc, Borja del Pozo-Cruz, MSc, Jose A. Parraca, MSc, Narcis Gusi, PhD ABSTRACT. Adsuar JC, Olivares PR, del Pozo-Cruz B, Parraca JA, Gusi N. Test-retest reliability of isometric and isokinetic knee extension and flexion in patients with fibromyalgia: evaluation of the smallest real difference. Arch Phys Med Rehabil 2011;92: Objective: To investigate the reliability of isokinetic peak torque and work and isometric peak torque measurements for knee flexion and extension in fibromyalgia (FM) patients by determining the smallest real difference (). Design: Test-retest reliability study. Setting: University laboratory. Participants: Women with FM (N 37) aged between 34 and 74 years. Interventions: Not applicable. Main Outcome Measures: The participants performed isometric, concentric, and eccentric tests of the knee. Unilateral maximal peak torque and average work were measured for each direction (flexion, extension) and contraction (isometric, concentric, eccentric) type. Relative reliability, absolute reliability, and were calculated. The 3 tests were repeated after an interval of 7 days. Results: With the exception of eccentric flexion, all peak torque measures had an intraclass correlation coefficient (ICC) of 0.90, and all work measures had an ICC of The ranged between 21% and 37% for all peak torque measures and between 40% and 73% for all work measures. Conclusions: Isokinetic dynamometry provides reliable measurement of peak torque and work for isometric, concentric, and eccentric knee flexion and extension in patients with FM. The present study has generated novel data, which will assist physicians, therapists, and clinicians in interpreting posttreatment changes in patients with FM. Key Words: Fibromyalgia; Rehabilitation; Reproducibility of results; Isokinetic dynamometry; Muscle strength by the American Congress of Rehabilitation Medicine PATIENTS WITH fibromyalgia (FM) present with diffuse and widespread musculoskeletal pain, 1 which interferes with everyday activities such as walking and climbing stairs. They have less muscle strength in the lower extremities than healthy subjects and thus display weaker concentric, eccentric, and isometric contractions. 2-9 Research has shown that isokinetic dynamometry of the knee during isometric, concentric, and eccentric muscle contraction is reliable in healthy individuals provided that they receive adequate instruction and are familiar with the equipment and that the test procedures are standardized Several isokinetic dynamometry studies of the knee have evaluated joint function and the effect of therapy 16,17 in patients with FM. However, to our knowledge, no previous study has evaluated the smallest real difference () in this population. is very important in determining whether a change observed during reassessment is genuine or simply within the boundaries of assessment error. Reliability is an important prerequisite for the correct interpretation of isokinetic dynamometry data, which indicate to the clinician whether or not a genuine change has occurred. This is dependent on the consistency of the results and thus on a relatively low rate, or absence, of measurement error. Reliability over 2 sessions, that is, test-retest reliability, is particularly important clinically, in view of the importance of long-term follow-up. Consistent test-retest reliability allows comparisons to be made over time. 18 The aim of the present study was to determine the relative and absolute test-retest reliability of peak torque and work measurements for isokinetic concentric, eccentric, and isometric knee extension and flexion in patients with FM by calculating the. METHODS Participants A letter containing preliminary information about the study was sent to all members of the 3 local FM associations (n 221). A total of 37 women requested further information and were informed of the details of the study protocol by letter. All 37 individuals agreed to participate and provided written informed consent. Each participant was then assessed by an experienced rheumatologist in a university laboratory. A diagnosis of FM, as defined by the criteria of the American College of Rheumatology, 19 was confirmed by reviewing medical records and clinical status. The clinical examination included an assessment of tender points. The participants reported no history of the following disorders: other rheumatic diseases, other severe somatic or psychiatric disorders, severe coronary disease, hypertension, or any disorder of the shoulder or spine. The study was approved From the Faculty of Sports Sciences, University of Extremadura, Caceres, Spain. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Correspondence to Narcis Gusi, PhD, Faculty of Sports Sciences, University of Extremadura Caceres, Spain, ngusi@unex.es /11/ $36.00/0 doi: /j.apmr FM ICC J List of Abbreviations fibromyalgia intraclass correlation coefficient smallest real difference joule

2 RELIABILITY OF ISOKINETIC TESTS IN FIBROMYALGIA, Adsuar 1647 by the bioethics committee of our university in accordance with the Helsinki Declaration. Instrumentation All tests were performed using a Biodex System 3 Quick-Set isokinetic dynamometer a and System 3 software (version 3.40). a All participants were asked to complete the Spanish version of the Fibromyalgia Impact Questionnaire 20,21 to measure the subjective severity of FM symptoms. Procedures The same test procedure was performed on 2 separate occasions (days 1 and 2), which were separated by an interval of 7 days, in accordance with previous studies of the reliability of isokinetic parameters in healthy subjects. 12,22 For each participant, the 2 test sessions were conducted at the same time of day to reduce the effect of diurnal variation. All participants were asked not to take pain medication 24 hours before the tender points evaluation and the strength assessments. All tests were conducted by the same investigator. Only the dominant knee was tested, and this was defined as the preferred kicking leg. The participant was seated in a comfortable position with the seatback at an angle of 85 to the seat. The mechanical axis of the dynamometer was aligned with the axis of movement of the knee in accordance with standardized protocols 11 and as performed previously in patients with FM. 16 Familiarization with the 3 tests involved the performance of 3 submaximal and 3 maximal isometric, concentric, and eccentric actions of the flexor and extensor muscles of the knee at the beginning of the first testing session. Concentric and eccentric movements were performed at 60 per second. 23 The weight of the knee was recorded using the dynamometer software, and gravity adjustments were made. All participants were asked to perform the following 3 tests: 1. Isometric test: 3 maximal isometric contractions involving both extensor and flexor muscles of the knee (extensor and flexor muscle contractions alternating with each other), with the knee flexed at Concentric/concentric test (con/con test): 3 concentric movements of the knee involving alternate extension and flexion. The motion ranged from 80 of knee flexion to full extension. 3. Concentric/eccentric test (con/ecc test): 3 concentric extension movements of the knee followed by an eccentric flexion movement. Concentric extension and the eccentric flexion movements were both targeting the quadriceps muscle. The motion ranged from 80 of knee flexion to full extension. The participants were verbally encouraged during the tests, and were allowed a rest for a period of 2 minutes between each of the 3 tests. Measures Peak torque and work (J) were downloaded from the System 3 software for each direction (flexion, extension) and contraction (isometric, concentric, and eccentric) type. Peak torque is defined as the single highest torque output recorded throughout the range of motion of each repetition. 24(p2) Work is defined as the output of mechanical energy 24(p2) and is represented by the area under the torque versus angular displacement curve. 24 Statistics A paired t test was used to analyze differences between test and retest values. The significance level was set at P.05. Table 1: Characteristics of Women With FM (N 37) Group Age (y) Weight (kg) Height (cm) Number of tender points (1 18) Duration of symptoms (y) FIQ (points) Mean SD Abbreviation: FIQ, Fibromyalgia Impact Questionnaire total score. Relative reliability was determined according to the intraclass correlation coefficient (ICC 3,1 ) with 95% confidence intervals across the 2 test sessions. 25 Absolute reliability was determined according to the standard error of measurement [ SD (1 ICC); where indicates the standard error of measurement and the SD is the mean SD of days 1 and 2] and the ( ). 26 Bland-Altman plots were constructed to illustrate a random relationship between individual differences and the peak torque and work measurements of days 1 and RESULTS Table 1 shows the characteristics of the study participants. None of the study participants dropped out. None of the participants had any prior experience with isokinetic dynamometry, and none reported any disabling pain on days 1 or 2. Table 2 shows the peak torque and work values during the isometric, concentric, and eccentric contractions. No statistically significant differences were observed between the values for days 1 and 2 for any of the variables. Table 3 shows the ICC values and their 95% confidence intervals for all measurements and. With the exception of eccentric flexion, all peak torque measures had an ICC of greater than 0.90, and all work measures had an ICC of greater than Figure 1 shows Bland-Altman plots of the isometric, concentric, and eccentric tests on days 1 and 2. The bias represents the average difference for peak torque between days 1 and 2. All bias in the present study was negative, indicating that day 2 had higher peak torque values than day 1. All bias ranged from 0 to 5. Similar results were obtained for work (fig 2). DISCUSSION Strength values in our participants with FM were similar to those reported in previous studies of women with FM. 16,28 The present results indicate that women with FM had less force during isometric, concentric, and eccentric contraction, as measured by both peak torque and work, compared with healthy women described in previous reports. 12,29 No statistical differences were found between day 1 and day 2 tests. Isometric extension values were approaching significance, but it could be due to the lower SD (SD 24.11) compared with the mean of the test. Despite this approaching significance, the effect size of the mean difference was small (Cohen d.18). The ICC values for all peak torque measurements in the present study can be considered very high, with the exception of those for eccentric flexion contractions which can be considered high, according to previous studies. 29 The ICC values for work can be considered high, with the exception of those for eccentric flexion contractions, which can be con-

3 1648 RELIABILITY OF ISOKINETIC TESTS IN FIBROMYALGIA, Adsuar Table 2: Summary of Isokinetic Peak Torque and Work at 60 /s on 2 Occasions (N 37) Peak Torque Work (J) Test Measurement* Day 1 Day 2 P Day 1 Day 2 P Con/con test Concentric extension contractions Concentric flexion contractions Con/ecc test Concentric extension contractions Eccentric flexion contractions Isometric test Isometric extension contractions NA NA NA Isometric flexion contractions NA NA NA NOTE. Values are mean SD or as otherwise indicated. Abbreviations: Con/con, concentric/concentric; con/ecc, concentric/eccentric; NA, not applicable. *Maximum of 3 repetitions. Isometric test: consists of 3 isometric movements of the knee in 45 of knee flexion involving both extensors and flexors knee muscles; con/con test: consists of 3 concentric movements of the knee with alternate extension and flexion; con/ecc test: consists of 3 concentric extension movements of the knee followed by an eccentric flexion movement. sidered moderate. 29 To our knowledge, no previous study has reported the reliability of isokinetic knee measurements in FM patients. Studies of healthy participants have reported slightly higher ICC values 29 than those calculated in the present study. The standard error of measurement for all peak torque measurements ranged between 8% and 13%, and those for all work measurements ranged between 14% and 27%. These values are thus higher than those reported from studies of healthy participants. 12 The standard error of measurement value is crucial in the correct interpretation of isokinetic dynamometry data, because it indicates the degree of measurement noise (ie, change that is unlikely to be of clinical significance). The standard error of measurement findings of the present study suggest that the test-retest differences of less than 14% for peak torque and 28% for work should be considered measurement noise in FM patients and are likely to be of no clinical significance. The clinical significance of posttreatment change that lies between the standard error of measurement and is less certain. 30 In the case of isometric peak torque differences of between 10% and 28%, eccentric flexion peak torque differences of between 12% and 33%, and concentric extension and flexion peak torque differences of between 13% and 36%, a decision as to whether a genuine change has occurred would need to be made clinically by taking all aspects of patient assessment into account. This is also true for eccentric flexion work differences of between 27% and 73% and concentric extension and flexion work differences of between 10% and 60%. On the basis of the percentage of observed in the present study, a general guideline for FM patients would be that a 22% change in the peak torque of isometric extension contractions and a 28% change in the peak torque of isometric flexion contractions are indicative of genuine clinical change. Similarly, a 33% change in the peak torque of eccentric flexion contractions, a 30% change in the peak torque of concentric extension, and a 36% change in the peak torque of concentric flexion indicate genuine clinical change. For work measures, a change of 42% for concentric extension and flexion and 59% to 73% for eccentric flexion indicate genuine clinical change. An of 73% could indicate that this is not a useful measure in clinical practice, because a substantial improvement needs to be demonstrated before considering it a real difference. These results are very similar to those reported for stroke 31 and patients with musculoskeletal disorder. 32 Reliability may be affected by several factors. These include: the technological capability of the dynamometer, data Table 3: Reliability of Isokinetic Isometric, Concentric, and Eccentric Knee Measurements (N 37) Peak Torque Work (J) Test Measurement* ICC (95% CI) (%) (%) ICC (95% CI) Con/con test Concentric extension contractions.92 (.85.96) (.72.92) Concentric flexion contractions.92 (.85.96) (.73.92) Con/ecc test Concentric extension contractions.91 (.82.95) (.73.92) Eccentric flexion contractions.83 (.68.91) (.26.80) Isometric test Isometric extension contractions.91 (.82.95) NA NA NA NA NA Isometric flexion contractions.91 (.83.95) NA NA NA NA NA Abbreviations: CI, confidence interval; con/con, concentric/concentric; con/ecc, concentric/eccentric; NA, not applicable;, standard error of measurement; %, standard error of measurement as the percentage of the group average; %, as the percentage of the group average. *Maximum of 3 repetitions. Isometric test: consists of 3 isometric movements of the knee in 45 of knee flexion involving both extensors and flexors knee muscles; con/con test: consists of 3 concentric movements of the knee with alternate extension and flexion; con/ecc test: consists of 3 concentric extension movements of the knee followed by an eccentric flexion movement. (%) (%)

4 RELIABILITY OF ISOKINETIC TESTS IN FIBROMYALGIA, Adsuar 1649 Fig 1. The differences between day 1 and day 2 sessions plotted against the means of the 3 test sessions for the peak torque of the participants. processing, examiner- and subject-related variability, 33 and whether patients are on pain medications or not. Demonstrated reliability and validity is fundamental to the establishment of a credible measure of human muscle function. 34 The Biodex System 3 has been shown to have excellent reliability and validity, with an ICC of 0.99 having been reported for force recorded at the strain gauge. 35 To minimize examiner-related variability, the same examiner experimenter conducted all of the sessions and gave standardized instructions and verbal encouragement. Protocol-related measurement error was minimized by the use of standardized procedures for warm-up, stabilization, seating, and alignment of the dynamometer and lever. The present study has generated novel data, which will assist physicians, therapists, and clinicians in interpreting post-

5 1650 RELIABILITY OF ISOKINETIC TESTS IN FIBROMYALGIA, Adsuar Fig 2. The differences between day 1 and day 2 sessions plotted against the means of the 2 test sessions for the work of the participants. treatment changes in isometric and isokinetic knee extension and flexion in patients with FM. Study Limitations Alignment of the mechanical axis of the Biodex System 3 isokinetic dynamometer to the knee is performed manually, and placement of the seat relative to the dynamometer is dependent on visual inspection. Thus, there may have been a minimal difference in placement between days 1 and 2. In addition, the participants did not undergo a familiarization session because of time and financial constraints. 12 This study found high relative reliability and high ; this may be due to including participants with a wide range of age, which could have contributed toward the between-subject variability. The measurements are acceptably sensitive for groups of patients, but to monitor individual progress, we would need reliability studies by age group. CONCLUSIONS Isokinetic dynamometry provides reliable measurement of peak torque and work for isometric (ICC.91), concentric (ICC of torque.92; ICC of work.85), and eccentric (ICC of torque.83; ICC of work.61) knee flexion and extension in patients with FM. The present study has generated novel data, which will assist physicians, therapists, and clinicians in interpreting posttreatment changes in isometric and isokinetic knee extension and flexion in patients with FM. References 1. Cassisi G, Sarzi-Puttini P, Alciati A, et al. Symptoms and signs in fibromyalgia syndrome. Reumatismo 2008;60 (Suppl 1): Valkeinen H, Alen M, Hannonen P, Hakkinen A, Airaksinen O, Hakkinen K. Changes in knee extension and flexion force, EMG and functional capacity during strength training in older females with fibromyalgia and healthy controls. Rheumatology (Oxford) 2004;43: Hakkinen A, Hakkinen K, Hannonen P, Alen M. Force production capacity and acute neuromuscular responses to fatiguing loading in women with fibromyalgia are not different from those of healthy women. J Rheumatol 2000;27: Dombernowsky T, Dreyer L, Bartels EM, Danneskiold-Samsoe B. [Muscular strength in patients with fibromyalgia. A literature review] [Danish]. Ugeskr Laeger 2008;170:

6 RELIABILITY OF ISOKINETIC TESTS IN FIBROMYALGIA, Adsuar Mengshoel AM, Forre O, Komnaes HB. Muscle strength and aerobic capacity in primary fibromyalgia. Clin Exp Rheumatol 1990;8: Norregaard J, Bulow PM, Lykkegaard JJ, Mehlsen J, Danneskiold-Samsooe B. Muscle strength, working capacity and effort in patients with fibromyalgia. Scand J Rehabil Med 1997;29: Norregaard J, Bulow PM, Vestergaard-Poulsen P, Thomsen C, Danneskiold-Samoe B. Muscle strength, voluntary activation and cross-sectional muscle area in patients with fibromyalgia. Br J Rheumatol 1995;34: Norregaard J, Bulow PM, Danneskiold-Samsoe B. Muscle strength, voluntary activation, twitch properties, and endurance in patients with fibromyalgia. J Neurol Neurosurg Psychiatry 1994; 57: Jacobsen S, Holm B. Muscle strength and endurance compared to aerobic capacity in primary fibromyalgia syndrome. Clin Exp Rheumatol 1992;10: Frontera WR, Hughes VA, Dallal GE, Evans WJ. Reliability of isokinetic muscle strength testing in 45- to 78-year-old men and women. Arch Phys Med Rehabil 1993;74: Dvir Z. Isokinetics: muscle testing, interpretation and clinical application. 2nd ed. London: Churchill Livingstone; Sole G, Hamren J, Milosavljevic S, Nicholson H, Sullivan SJ. Test-retest reliability of isokinetic knee extension and flexion. Arch Phys Med Rehabil 2007;88: Maquet D, Croisier JL, Renard C, Crielaard JM. Muscle performance in patients with fibromyalgia. Joint Bone Spine 2002;69: Panton LB, Kingsley JD, Toole T, et al. A comparison of physical functional performance and strength in women with fibromyalgia, age- and weight-matched controls, and older women who are healthy. Phys Ther 2006;86: Henriksen M, Lund H, Christensen R, et al. Relationships between the fibromyalgia impact questionnaire, tender point count, and muscle strength in female patients with fibromyalgia: a cohort study. Arthritis Rheum 2009;61: Gusi N, Tomas-Carus P, Hakkinen A, Hakkinen K, Ortega-Alonso A. Exercise in waist-high warm water decreases pain and improves health-related quality of life and strength in the lower extremities in women with fibromyalgia. Arthritis Rheum 2006; 55: Martin L, Nutting A, MacIntosh BR, Edworthy SM, Butterwick D, Cook J. An exercise program in the treatment of fibromyalgia. J Rheumatol 1996;23: Meeteren J, Roebroeck ME, Stam HJ. Test-retest reliability in isokinetic muscle strength measurements of the shoulder. J Rehabil Med 2002;34: Wolfe F, Smythe HA, Yunus MB, et al. The American College of Rheumatology 1990 Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee. Arthritis and rheumatism 1990;33: Burckhardt CS, Clark SR, Bennett RM. The fibromyalgia impact questionnaire: development and validation. J Rheumatol 1991;18: Esteve-Vives J, Rivera J, Salvat MI, De Gracia M, Alegre C. Propuesta de una versión de consenso del Fibromyalgia Impact Questionnaire (FIQ) para la población española. Reumatología clínica 2007;3: Larsson B, Karlsson S, Eriksson M, Gerdle B. Test-retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions. J Electromyogr Kinesiol 2003;13: Shklar A, Dvir Z. Isokinetic strength relationships in shoulder muscles. Clin Biomech (Bristol, Avon) 1995;10: Kannus P. Isokinetic evaluation of muscular performance: implications for muscle testing and rehabilitation. Int J Sports Med 1994;(15 Suppl 1):S Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull 1979;86: Weir JP. Quantifying test-retest reliability using the intraclass correlation coefficient and the. J Strength Cond Res 2005; 19: Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: Tomas-Carus P, Gusi N, Hakkinen A, Hakkinen K, Raimundo A, Ortega-Alonso A. Improvements of muscle strength predicted benefits in HRQOL and postural balance in women with fibromyalgia: an 8-month randomized controlled trial. Rheumatology (Oxford) 2009;48: LeBreton J, Senter J. Answers to 20 questions about interrater reliability and interrater agreement. Organizational Research Methods 2008;11: McKenna L, Cunningham J, Straker L. Inter-tester reliability of scapular position in junior elite swimmers. Phys Ther Sport 2004; 5: Flansbjer UB, Holmback AM, Downham D, Lexell J. What change in isokinetic knee muscle strength can be detected in men and women with hemiparesis after stroke? Clin Rehabil 2005;19: Keating J, Matyas T. Unpredictable error in dynamometry measurements: a quantitative analysis of the literature. Isokinet Exerc Sci 1998;7: Farrell M, Richards JG. Analysis of the reliability and validity of the kinetic communicator exercise device. Med Sci Sports Exerc 1986;18: Feiring DC, Ellenbecker TS, Derscheid GL. Test-retest reliability of the biodex isokinetic dynamometer. J Orthop Sports Phys Ther 1990;11: Drouin JM, Valovich-mcLeod TC, Shultz SJ, Gansneder BM, Perrin DH. Reliability and validity of the Biodex system 3 pro isokinetic dynamometer velocity, torque and position measurements. Eur J Appl Physiol 2004;91:22-9. Supplier a. Biodex Medical Systems, 20 Ramsay Rd, Shirley, NY