Biomechanical characterisation of the three fundamental karate-dō stances: load distribution, stability, and postural control in elite karateka

Abstract

This dissertation offers a biomechanical characterisation of the three fundamental stances of contemporary karate-dō - zenkutsu-dachi, kōkutsu-dachi and kibadachi - and, as a distinctive complementary contribution, traces the historicalinstitutional path along which they hardened into the postural canon now regulated by the World Karate Federation. It follows the Scandinavian, article-based model of _3.2.1 of the FADEUP norms: four article-chapters built around an experimental study that is the dissertation's primary contribution and sequenced to follow the logic of the inquiry, each chapter leading towards that experimental core. Chapter 1 places the study within the karate-dō biomechanics literature through a scoping review carried out under the PRISMA-ScR guidelines and the JBI Manual; it maps the five methodological pillars - kinematics, kinetics, electromyography, anthropometry and thermography - as an evidence gap-map, and finds that the diachronic dimension has gone unexamined. Chapter 2, the distinctive complementary contribution, traces four documentable institutional interventions - Matsumura's Jigen-ryu menkyo (S1, c. 1840), Itosu's pedagogical reform (S2, 1901-1922), Funakoshi Gichin's Tokyo period (S3, 1922-1935) and the stabilisation of the canon by Funakoshi Yoshitaka and the Japan Karate Association (S4, 1936-1955) - and shows that the canon preserves no intact Okinawan inheritance but is, rather, the residue of an institutionally codified history. Chapter 3 places the dataset behind the experimental study in open access under a Creative Commons Attribution 4.0 International licence, deposited on Figshare with the processing and analysis code in a public repository, so that the experimental claims can be audited in full. Chapter 4 - the primary contribution and the dissertation's centre of gravity - characterises the three stances in twelve elite karateka (four men, eight women; 91.7% black belt; 66.7% international competitors; seven Shōtōkan, five Gōju-ryu), each performing five gyaku-zuki repetitions from each base under a standardised protocol at the Porto Biomechanics Laboratory, recorded with three-dimensional markerless kinematics (Theia3D, 180 Hz) and two synchronised force platforms (Bertec FP4060-15, 1000 Hz). Generalised linear mixed-effects models with Bonferroni-adjusted contrasts show the three stances to be distinct neuromechanical specialisations - anteriorised propulsion, lateralised structural robustness and posteriorised ballistic readiness - separable by load distribution, base-of-support geometry, three-dimensional centre-ofmass / centre-of-pressure divergence and the vectorial margin of stability (operationalised through the Relative Stability Radius), with direct implications for highperformance training. The two contributions speak to each other: the experimental study settles what the stances are and how they work for the high-performance practitioner, while the historical reconstruction explains why they take the form the laboratory records.