Original article
Inter- and Intrarater Reliability of Isokinetic Thigh Muscle Strength Tests in Postmenopausal Women With Osteopenia

https://doi.org/10.1016/j.apmr.2011.10.001Get rights and content

Abstract

Eitzen I, Hakestad KA, Risberg MA. Inter- and intrarater reliability of isokinetic thigh muscle strength tests in postmenopausal women with osteopenia.

Objective

To evaluate inter- and intrarater reliability of isokinetic muscle strength measurements during knee extension 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 (ICC2,1). Mean difference between tests, standard error of measurement (SEM and SEM%), and smallest 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

ICC2,1 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. Agreements were overall higher for assessments during knee extension 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 reliability, 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.

Section snippets

Methods

Twenty-seven postmenopausal women with osteopenia who were already attending an ongoing randomized controlled trial (RCT) (www.clinicaltrials.gov; reference number NCT01357278) were included. The inclusion criteria were osteopenia defined from a proven low BMD (T score <–1.5).24 BMD was measured by means of dual-energy x-ray absorptiometry (DXA).25, 26 To establish the level of physical activity, we used the self-reported form Physical Activity Scale for the Elderly (PASE),27, 28 with a range

Results

The subjects included in the study had a mean age ± SD of 68.2±7.3 years and were all residents in the Oslo region in Norway. All 27 subjects completed tests 1 and 2, but 1 subject got sick and was restricted from participating in test 3. For the 26 subjects completing all 3 tests, the interval between test day 1 and test day 2 was 7 days, except for 1 subject who showed up 1 day early, and therefore had 6 days between test days 1 and 2. DXA testing was performed a mean ± SD of 10.6±2.3 days

Discussion

To our knowledge, this is the first study to address the inter- and intrarater reliability of isokinetic dynamometry during knee extension and flexion in postmenopausal women with osteopenia. The main finding of this study is that the levels of agreement across both the 2 different raters and the different times are high, with ICC levels comparable to those of previous reliability studies concerning both healthy adults and adults with different health conditions.5, 7, 8, 9, 10, 11, 14, 16, 17,

Conclusions

Isokinetic assessments of thigh muscle strength in postmenopausal women with osteopenia are of high reliability, with a level of agreement comparable to the levels found in previous reliability studies concerning the elderly population.

Suppliers

  • a

    Biodex Medical Systems, Inc, 20 Ramsay Rd, Shirley, NY 11967-4704.

  • b

    SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.

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    The authors acknowledge the Musculoskeletal and Sports Medicine Clinic Hjelp24NIMI, Oslo, Norway (www.hjelp24.no) for supporting the Norwegian Research 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 organization with which the authors are associated.

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