Reliability of Maximal Voluntary Contraction Related Parameters Measured by a Novel Portable Isometric Knee Dynamometer

Authors: N. Sarabon 1,2,3, J. Rosker 1,2, H. Fruhmann 3, S. Burggraf 3, S. Loefler 3, H. Kern 3

Source: Phys Rehab Kur Med 2013; 23(01): 22-27

Keywords: assessment instruments, evaluation, reliability


Problem: Isolated strength measurements of knee extensors and flexors are important for identifying potential risks of injury and functional movement deficits in elderly. Various methods, measuring dynamic or isometric torque, have been used in rehabilitation and sports practice. Commonly used isokinetic and hand-held-dynamometry strength measurements have been shown to be highly correlated. Choosing the appropriate strength measuring method often requires a compromise between cost, mobility and reliability. For the purpose of “MOBIL “ (Interreg IVa) research project, a portable isometric knee dynamometer was developed. The goal of the study was to examine reliability of the peak torque and peak toque derived parameters.

Method: 22 healthy young subjects participated in the study. Peak torque during maximal knee extension was measured with isometric dynamometer. Each subject performed maximal knee extension with each leg and bilaterally. 3 repetitions of each task were performed, for the analysis of intra-session repeatability. Identical measurement protocol was repeated on another separate day, for studying inter-session repeatability. Peak torque measurements were used to calculate contra-lateral strength imbalance and bilateral deficit. Interclass-correlation-coefficient, typical error and coefficient of variation were used to describe reliability.

Highest interclass-correlation-coefficient for intra-session and inter-session repeatability was observed for peak torque measurements. Contra-lateral strength imbalance and bilateral deficit had lower repeatability compared to peak torque. Generally inter-session reliability was lower compared to intra-session reliability. Highest coefficient of variation was observed for contra-lateral strength imbalance and bilateral deficit respectively and lowest for peak torque. Interclass-correlation-coefficient as well as coefficient of variation for contra-lateral strength imbalance and bilateral deficit could be improved by averaging all trials in a session. No bias effects were observed.

This study confirmed isometric dynamometer measurements and analysis approach used, to be reliable. The device and methodology will be used in further research in the international project “MOBIL” on mobility in aging.


1 Institute for Kinesiology Research, University of Primorska, Science and Research Center, Koper, Slovenia
2 Laboratory for Motor Control and Motor Behaviour, S2P Ltd., Ljubljana, Slovenia
3 Ludwig Boltzmann Institute of Electrical Stimulation and Physical Rehabilitation, Vienna, Austria