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 (ICC(2,1)). 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: 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. 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.