Short communication Reliability of isokinetic normalized peak torque assessments for knee muscles in post-stroke hemiparesis Shohreh Noorizadeh Dehkordi a,1 , Saeed Talebian a, * , Gholamreza Olyaei a,1 , Ali Montazeri b a Tehran University of Medical Sciences, Rehabilitation Faculty, Department of Physiotherapy, Enghelab Avenue, Piche Shemiran, P.O. Box 11365-1683, Tehran, Iran b Iranian Institute for Health Sciences Research, P.O. Box 13185-1488, Tehran, Iran Received 12 February 2007; received in revised form 17 July 2007; accepted 22 July 2007 Abstract The purpose of this study was to establish test–retest reliability of measurement procedures for quantifying isokinetic concentric peak torque (PT) at the knee using normalization methods post-stroke. A second aim was to estimate the change required to show clinically significant improvements in knee muscles strength. The isokinetic normalized PT (NPT) values for the knee extensors and flexors were measured in each participant at two different angular velocities during two sessions 1 day apart. Thirty participants with mild to moderate hemiparesis after stroke who were able to walk were tested. The normalized PT measures for the knee muscles of the affected lower extremity were highly reliable (intraclass correlation coefficients ranged from 0.85 to 0.98; p < 0.05). Size of relative changes (the percent smallest real difference, SRD%) for extensors NPT (ranged from 22.35% to 25.68%) were lower than flexors NPT (ranged from 74.01% to 76.31%), indicating that the affected isokinetic knee flexors had more random variation than the knee extensors. This study supports the use of isokinetic dynamometers for the assessment of knee muscle strength in participants with chronic mild to moderate post-stroke hemiparesis and to measure clinical improvements. Established measurement error and smallest real differences in normalized PT will aid interpretation of real changes in muscle strength in this clinical population. # 2007 Elsevier B.V. All rights reserved. Keywords: Hemiparesis; Reliability; Weakness; Stroke 1. Introduction Muscle weakness is a primary source of motor impairment amongst stroke survivors [1]. It is associated with reductions in peak muscle torque, decreases in the velocity of force development, lack of sustaining force output, rapid onset of fatigue and ineffective force production within the context of a task [1,2]. In addition, several studies have shown weakness of the ipsilesional side as early as 1 week following stroke [3,4]. Isokinetic dynamometers are frequently used to assess muscle strength at different velocities in both health and disease. There is preliminary evidence of high relative test–retest reliability of repeated measures of knee muscles strength in patients more than 6 months post-stroke [5–10]. Nevertheless, few studies demonstrated measurement errors and systematic changes in the mean for peak torque (PT) in isokinetic dynamometers [5,7]. No studies have quantified the smallest real difference (SRD) in PT measures quantified with the normalization methods at angular velocities of 608/s and 1208/s for the lower limbs using isokinetic dynamometry. The objectives of this study were therefore to: (i) determine values of concentric PT quantified with the normalization method in the affected and unimpaired knee flexors and extensors, (ii) establish the relative and absolute reliability of concentric knee extensors and flexors PT within www.elsevier.com/locate/gaitpost Gait & Posture 27 (2008) 715–718 * Corresponding author. Tel.: +98 21 77533939; fax: +98 21 77534133. E-mail addresses: Noorizadeh@razi.tums.ac.ir (S. Noorizadeh Dehkordi), talebian@sina.tums.ac.ir (S. Talebian), olyaeigh@sina.tums.ac.ir (G. Olyaei), Montazeri@acecr.ac.ir (A. Montazeri). 1 Tel.: +98 21 77533939; fax: +98 21 77534133. 0966-6362/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2007.07.013