title: Front-crawl stroke descriptors variability assessment for skill characterisation.
abstract: The goal of this article is to characterise front-crawl swimming skill based on variability pattern of technique descriptors. Nine national level and nine recreational swimmers performed three 300 m trials in a 50 m outdoor pool, at 70%, 80% and 90% of their front-crawl 400 m personal best time. Using wearable inertial measurement units (IMUs) and validated algorithms we assessed the variability of technique descriptors at each arm cycle (139 ± 17 per trial). We calculated the duration of pull, push and non-propulsive phases, index of coordination (IdC), stroke length, stroke rate and intra-cyclic velocity variation. To track intra-trial technique variability, we calculated the Cauchy index to quantify the stability of multidimensional technique descriptors in space-time. Skilled swimmers, having access to divers motor solutions, achieved significantly higher velocities at similar intensities and similar IdC (P < 0.01) with more stable motor pattern (smaller Cauchy index). Besides, the similarity of intra-cyclic velocity variation at different intensities denotes that skilled swimmers used a wider dynamic range of velocity. We also introduced cycle velocity variation as a new metric of propulsive pattern repeatability and showed cycle velocity variation changes is correlated to the Cauchy index (rx,y = 0.72, P < 0.01). These findings indicate that IdC can be used as a predictor of performance only when swimmers of homogeneous expertise level are studied and suggest the scrutiny of both intra-cyclic velocity variation and cycle velocity variation as a requisite to study the motor adaptations of the swimmer in facing new constraints.
authors.affiliation: a Laboratory of Movement Analysis and Measurement , Ecole Polytechnique Fédérale de Lausanne (EPFL) , Lausanne , Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Dadashi
authors.affiliation: b Institute of Sport Sciences , University of Lausanne , Lausanne , Switzerland.
authors.forename: G P
authors.initials: GP
authors.lastname: Millet
authors.affiliation: a Laboratory of Movement Analysis and Measurement , Ecole Polytechnique Fédérale de Lausanne (EPFL) , Lausanne , Switzerland.
authors.forename: K
authors.initials: K
authors.lastname: Aminian
mesh_terms: D061725:Accelerometry / Q000379:methods; D000222:Adaptation, Physiological; D000293:Adolescent; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D009048:Motor Skills / Q000502:physiology*; D064797:Physical Conditioning, Human; D013550:Swimming / Q000502:physiology*; D013996:Time and Motion Studies; D055815:Young Adult
keywords: Performance; coordination; inertial sensor; motor adaptation; variability