ORIGINAL ARTICLE Inter- and Intrarater Reliability of Isokinetic Thigh Muscle Strength Tests in Postmenopausal Women With Osteopenia Ingrid Eitzen, PT, PhD, Kari Anne Hakestad, RN, MSc, May Arna Risberg, PT, PhD ABSTRACT. Eitzen I, Hakestad KA, Risberg MA. Inter- and intrarater reliability of isokinetic thigh muscle strength tests in postmenopausal women with osteopenia. Arch Phys Med Rehabil 2012;93:420-7. Objective: To evaluate inter- and intrarater reliability of isokinetic muscle strength measurements during knee exten- sion and flexion in postmenopausal women with osteopenia. Design: Reliability study assessing inter- and intrarater reliability. Setting: General community. Participants: A convenience sample of 27 postmenopausal women (mean age  SD, 68.27.3y) with defined osteopenia from a bone mineral density T score of less than 1.5 and a wrist fracture within the last 2 years. Interventions: Not applicable. Main Outcome Measures: Isokinetic concentric muscle strength during knee extension and flexion was measured for 2 test conditions: 5 repetitions at 60°/s, and 25 repetitions at 180°/s. Agreement between tests was evaluated with the intraclass correlation coefficient (ICC 2,1 ). Mean difference between tests, standard error of measurement (SEM and SEM%), and small- est real difference (SRD and SRD%) were calculated with 95% confidence intervals. SRD% and SEM% are emphasized in the results to allow congruent comparisons between the different test conditions. Results: ICC 2,1 reflected high agreement both for inter- and intrarater reliability, with most of the values .90 or greater. There were no significant differences between the left and the right leg at any of the 3 tests. Some differences were apparent between the test sessions, but these were not systematic. Agree- ments were overall higher for assessments during knee exten- sion than knee flexion. The SEM% was between 3.5% and 10.2% for knee extension, and 7.0% and 17.7% for knee flexion. SRD% was suggested to be between 15% and 20% for knee extension, and 25% and 30% for knee flexion. Conclusions: Isokinetic assessments of thigh muscle strength in postmenopausal women with osteopenia are of high reliabil- ity, with a level of agreement comparable to the levels found in previous reliability studies concerning both the healthy elderly and elderly with different health conditions. The measurement errors are small to moderate. The established SRD% provides thresholds for whether observed changes in strength in this patient group represent true change, which allows evaluations of minimal clinical importance in future studies. Key Words: Muscle strength; Osteopenia; Outcomes as- sessment; Rehabilitation; Reproducibility of findings. © 2012 by the American Congress of Rehabilitation Medicine P OSTMENOPAUSAL WOMEN ARE particularly exposed to reductions in muscle strength and bone mineral density (BMD), which increase their risk of fractures. 1,2 Since main- tenance or improvement of muscle strength will decrease the loss of BMD, muscle strength assessments are of high rele- vance for elderly women. Isokinetic dynamometry is today an established method for evaluation of muscle strength during knee extension and flexion for different conditions and diag- noses, 3,4 and the reliability of the method has been investigated in a number of studies concerning both the healthy elderly, 5-8 as well as elderly persons with knee osteoarthritis, 9,10 knee arthroplasty, 11 stroke, 12-16 late effects of polio, 17 different neu- rologic disorders, 18 and heart failure. 19 In total, these studies have found isokinetic dynamometry to be an adequate test method for thigh muscle strength for elderly people, with or without dysfunctions. However, to our knowledge, no studies have evaluated the reliability of isokinetic dynamometry in postmenopausal osteopenic or osteoporotic women. Because osteopenia and osteoporosis might be associated with an inher- ent fear of fractures during physical performance, it could be spurious to rely on reliability studies investigating dissimilar populations. Further, to evaluate strength development after exercise therapy interventions, it is important to know the standard error of measurement (SEM) and the threshold for the smallest change in score that must be surpassed to regard the change as real—that is, the smallest real difference (SRD). 20-23 The purpose of the present study was, therefore, to evaluate the inter- and intrarater reliability of selected isokinetic muscle strength outcomes during knee extension and flexion in post- From the Norwegian Research Center for Active Rehabilitation (Eitzen, Hakestad, Risberg); the Norwegian School of Sport Sciences (Eitzen, Risberg) and the Orthopedic Department, Oslo University Hospital (Eitzen, Hakestad, Risberg), Oslo, Norway. The authors acknowledge the Musculoskeletal and Sports Medicine Clinic Hjelp24NIMI, Oslo, Norway (www.hjelp24.no) for supporting the Norwegian Re- search Center for Active Rehabilitation (www.active-rehab.no) with rehabilitation facilities and research staff. Supported by a grant from the South-Eastern Norway Regional Health Authority (grant no. 2009056). 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 organi- zation with which the authors are associated. Reprint requests to Ingrid Eitzen, PT, PhD, Hjelp24 NIMI, Pb 3843 Ullevaal Stadion, 0805 Oslo, Norway, e-mail: Ingrid.Eitzen@hjelp24.no. 0003-9993/12/9303-00698$36.00/0 doi:10.1016/j.apmr.2011.10.001 List of Abbreviations BMD bone mineral density CI confidence interval CV coefficient of variance DXA dual-energy x-ray absorptiometry ICC intraclass correlation coefficient MIC minimally important change PASE Physical Activity Scale for the Elderly RCT randomized controlled trial ROM range of motion SEM standard error of measurement SRD smallest real difference 420 Arch Phys Med Rehabil Vol 93, March 2012