title: Sources of variability in musculo-articular stiffness measurement.
abstract: The assessment of musculo-articular stiffness (MAS) with the free-oscillation technique is a popular method with a variety of applications. This study examined the sources of variability (load applied and frequency of oscillation) when MAS is assessed. Over two testing occasions, 14 healthy men (27.7±5.2 yr, 1.82±0.04 m, 79.5±8.4 kg) were measured for isometric maximum voluntary contraction and MAS of the knee flexors using submaximal loads relative to the individual's maximum voluntary contraction (MAS%MVC) and a single absolute load (MASABS). As assessment load increased, MAS%MVC (coefficient of variation (CV)  =  8.1-12.1%; standard error of measurement (SEM)  =  51.6-98.8 Nm⁻¹) and frequency (CV  =  4.8-7.0%; SEM  =  0.060-0.075 s⁻¹) variability increased consequently. Further, similar levels of variability arising from load (CV  =  6.7%) and frequency (CV  =  4.8-7.0%) contributed to the overall MAS%MVC variability. The single absolute load condition yielded better reliability scores for MASABS (CV  =  6.5%; SEM  =  40.2 Nm⁻¹) and frequency (CV  =  3.3%; SEM  =  0.039 s⁻¹). Low and constant loads for MAS assessment, which are particularly relevant in the clinical setting, exhibited superior reliability compared to higher loads expressed as a percentage of maximum voluntary contraction, which are more suitable for sporting situations. Appropriate sample size and minimum detectable change can therefore be determined when prospective studies are carried out.
authors.affiliation: School of Public Health, Physiotherapy and Population Science, University College Dublin, Dublin, Ireland. m.ditroilo@hull.ac.uk
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Ditroilo
authors.forename: Mark
authors.initials: M
authors.lastname: Watsford
authors.forename: Aron
authors.initials: A
authors.lastname: Murphy
authors.forename: Giuseppe
authors.initials: G
authors.lastname: De Vito
mesh_terms: D000328:Adult; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D015203:Reproducibility of Results; D018401:Sample Size; D016474:Weight-Bearing / Q000502:physiology*