title: Musculo-articular stiffness is affected by the magnitude of the impulse applied when assessed with the free-oscillation technique.
abstract: Musculo-articular stiffness (MAS) of the triceps surae can be assessed using the free-oscillation technique whereby an impulse is applied and the ensuing damped oscillations are recorded. The purpose of this study was to investigate if impulses of different magnitudes can affect the measurement of MAS. Twenty seven males (20.7±1.3 years) participated in this study. Three impulses of different magnitude (1.5, 2.3 and 3.1Ns) and four different loads (10, 20, 30, 40kg) were employed in the assessment of triceps surae MAS, which was quantified and compared across loads and perturbations. As the magnitude of the impulse applied increased, the MAS (p<0.0005, ES 1.20) and natural frequency of oscillation (f) decreased while the amplitude of movement (AM), angular velocity (ω) and damping coefficient (C) increased significantly. As the load level increased, the MAS (p<0.0005, ES 2.25) and the baseline ground reaction force (BGRF) increased whereas f, AM and ω decreased significantly. Even though the effect of the load is stronger, it appears that the level of MAS recorded (ranging from 24.0 to 21.3KN/m for the 10kg load and from 32.9 to 31.0KN/m for the 40kg load, for impulse 1 and 3 respectively), including several underlying factors, are affected by the magnitude of the impulse, therefore its accurate determination is pivotal. Caution should be exercised when comparing results from previous studies where the magnitude of the impulse has only been estimated but not controlled for.
authors.affiliation: Department of Sport Science CIDESD, University of Beira Interior, Covilhã, Portugal. Electronic address: afaria@ubi.pt.
authors.forename: Aurélio
authors.initials: A
authors.lastname: Faria
authors.affiliation: Department of Sport Sciences, Exercise and Health CITAB, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal.
authors.forename: Ronaldo
authors.initials: R
authors.lastname: Gabriel
authors.affiliation: Department of Sport Sciences, Exercise and Health CIDESD, University of Trás-os-Montes and Alto Douro, Vila Real, Portugal.
authors.forename: Helena
authors.initials: H
authors.lastname: Moreira
authors.affiliation: Department of Sport Science CIDESD, University of Beira Interior, Covilhã, Portugal.
authors.forename: Rui
authors.initials: R
authors.lastname: Brás
authors.affiliation: Department of Sport, Health and Exercise Science, Faculty of Science & Engineering, University of Hull, Hull, United Kingdom.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Ditroilo
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D007866:Leg; D008297:Male; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult
keywords: Ankle stiffness; Free-oscillation technique; Musculotendinous stiffness; Perturbation magnitude