Reproducibility of an Isokinetic Strength-Testing Protocol of the Knee and Ankle in Older Adults

Background: Muscle power assessed by isokinetic dynamometers has the potential for playing an important role in investigating functional status in older subjects. Researchers and clinicians are interested in the reliability of isokinetic test protocols for the confidential assessment of status, as this affects the interpretation of the results of an intervention program. Objective: The current study investigated the inter- and intrarater reliability of an isokinetic strength-testing protocol of the knee and ankle preceded by a familiarization session. Methods: Twenty-four independently living elderly subjects (6 males, 18 females, mean age 71.2 +/- 5.5 years) were assessed 3 times in two test sessions. The main outcomes were the intraclass correlation coefficient, standard error of measurements (SEM) and ratio of limits of agreement (RLOA) for isokinetic knee and ankle contractions, as measured with the Biodex System 3. Results: The intraclass correlation coefficients of the isokinetic variables varied from 0.81 to 0.99 representing 'good' to 'very good' reliability. Most SEM and RLOA indexes represented acceptable agreement which varied from 6 to 13 and 18 to 37%, respectively. Nonacceptable agreement was found for ankle plantar flexion with SEMs that varied from 14 to 17% and RLOAs from 39 to 48%. Conclusion: The results of this study demonstrate that the Biodex System 3 is a reliable device when used for elderly living independently. The ability of the device to determine a real change in isokinetic ankle and knee contractions is better on a group level than on an individual level. The Biodex System 3 can be employed with confidence in studies to determine the effect of exercise intervention programs on physical activity. Copyright (C) 2008 S. Karger AG, Basel