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

Abstract

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.

Results:

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.

Conclusion:

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.

Zusammenfassung

Fragestellung:

Eine isolierte Kraftmessung der Knieextensoren und -flexoren ist wichtig für die Identifikation potenzieller Risiken von Verletzungen und funktioneller Bewegungsdefizite im Alter. Verschiedene Methoden der dynamischen oder isometrischen Dynamometrie haben in der Rehabilitation und sportlichen Praxis Anwen­dung gefunden. Allgemein übliche isokinetische und tragbare Dynamometriegeräte haben eine hohe Zuverlässigkeit, aber die Wahl einer ge­­eigneten Kraftmessmethode führt oft zu einem Kompromiss von Kosten, Mobilität und Zuverlässigkeit. Aus diesem Grund wurde für das ­Forschungsprojekt „MOBIL“ (Interreg IVa) ein mobiler isometrischer Drehmomentmessstuhl für die Knieextensoren und -flexoren entwickelt. Das Ziel dieser Studie war es, die Zuverlässigkeit der Messwerte zu überprüfen.

Methodik:

22 gesunde junge Probanden nahmen an der Studie teil. Gemessen wurde das Spitzendrehmoment bei 60° Knieextension auf einem isometrischen Dynamometer. Jeder Proband absolvierte die Messung einbeinig – jeweils links und rechts – und beidbeinig. Es wurden 3 Versuche je Aufgabenstellung durchgeführt, um die Test-Reliabilität zu ermitteln. Für die Retest-Reliabilität wurde dasselbe Messprotokoll an einem anderen Tag wiederholt. Die Spitzendrehmomentmessungen wurden zur Berechnung des kontralateralen Kraftungleichgewichts und des bilateralen Kraftdefizits herangezogen. Intraklassen-Korrelationskoeffizient, Standardfehler und Variationskoeffizient wurden zur Beurteilung der Reliabilität verwendet.

Ergebnisse:

Den höchsten Intraklassen-Korrelationskoeffizienten für Test- und Retest-Reliabi­lität ergab die Spitzendrehmomentmessung. Das kontralaterale Kraftungleichgewicht und das bilaterale Kraftdefizit waren weniger zuverlässig verglichen mit dem Spitzendrehmoment. Generell war die Retest-Reliabilität geringer als die Test-Reliabi­lität. Den höchsten Variationskoeffizienten zeigen das kontrala­terale Kraftungleichgewicht und das bilaterale Kraftdefizit im Vergleich zur Spitzendrehmomentmessung. Sowohl Intraklassen-Korrelationskoeffizient als auch Variationskoeffizient für das kontralaterale Kraftungleichgewicht und das bilaterale Kraftdefizit können durch Mittelung aller Versuche einer Messung verbessert werden. Es wurden keine Verzerrungseffekte beobachtet.

Schlussfolgerung:

Diese Studie bestätigt die Zuverlässigkeit der isometrischen Drehmomentmessung und Auswertung. Das entwickelte Gerät und die Methodik werden in weiterführenden Studien über die Mobilität im Alter des internationalen Projekts „MOBIL“ verwendet.

Key words

assessment instruments - evaluation - reliability

Schlüsselwörter

Assessmentinstrumente - Evaluation - Reliabilität

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