Isokinetic evaluation of knee: what about compatibility between different dynamometers?
Mr Julien PAULUSa, Mr Laurent RADRIZZIb, Mr Jérôme PAULSb, Mr Roland KRECKÉb, Prof Jean-Michel CRIELAARDa, Prof Jean-Louis CROISIERa
a Université de Liège - Département des Sciences de la Motricité & de Kinésithérapie et Réadaptation, b Centre Hospitalier de Luxembourg - Clinique du Sport et Centre d'Orthopédie
The aim of this study was to assess the compatibility between dynamometer Biodex System 3 Pro, Con-Trex MJ PM-2 and Cybex Humac CSMI of knee extensors and flexors.
Twenty-one subjects, moderately active, performed three isokinetic evaluation sessions with six to ten days of rest between each. Each of it, performed on a dynamometer in accordance with a different randomized order, included a concentric evaluation (60°.s-1 & 240°.s-1), eccentric (30°.s-1) and fatigue-resistance protocol (30 concentric repetitions maximum 180°.s-1) for the knee extensors and flexors.
The peak torque (PT) and the maximal work (MW) of each repetition were recorded, as well as concentric and mixed agonists/antagonists ratios, to measure the compatibility inter-dynamometer two by two through their respective ICC (3.1), SEM and MD.
For the short maximal strength test, ICC values for the extensors are almost always higher than 0.85 in concentric mode although they don't exceed 0.61 in eccentric mode. The ICC values for the flexor in slow concentric and eccentric mode are above 0.7, 0.75 and 0.8 for pairs Biodex/Cybex, Biodex/Con-Trex and Cybex/Con-Trex. None of ICC value exceeds 0.75 in fast concentric mode for the flexors.
The ratios have ICC values lower than 0.6 except concentric ratio at 60°.s-1 for the pair Cybex/Con-Trex (0.83) and mixed ratio for the pairs Biodex/Cybex (0.73) and Cybex/Con-Trex (0.77).
The ICC values of the parameters measured during the extensors fatigue-resistance protocol are mostly above 0.8 regardless of the pair of dynamometers considered. The ICC values of these parameters for the flexors are almost all lower than 0.7.
Although the reproducibility of extensors in concentric mode is high, it's important to inform users, whether in clinical or scientific domain, that different dynamometers provide regular incompatible results and we draw attention to the little reproducibility of the agonist/antagonist ratios. Our results justify the establishment of norms for each dynamometers brand in order to interpret, with relevance, the isokinetic test, either for short maximal strength evaluation or fatigue-resistance protocol.
Keywords : isokinetic; short maximal strength test; fatigue-resistance protocol; Biodex; Cybex; Con-Trex; inter-dynamometer; compatibility; reproductibility