Understanding biomechanical differences in technique between phases of a sprint
thesisposted on 31.10.2019 by Hans Christian von Lieres und Wilkau
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Sprinting requires the rapid development of velocity while technique changes across multiple steps. Research Themes (Phase analysis, Technique analysis and Induced acceleration analysis) were formulated to investigate and understand the biomechanical differences in technique between the initial acceleration, transition and maximal velocity phases of a sprint.
Theme 1 (Phase analysis) revealed relatively large changes in touchdown variables (e.g. centre of mass height, touchdown distances, shank angles) during the initial acceleration phase. This likely reflects an increasing need to generate larger vertical forces early during stance as a sprint progresses. At toe-off, smaller yet progressive changes in variables (e.g. trunk angles and centre of mass height) across the initial acceleration and transition phases reflect a constraint determining decreases in propulsive forces during a sprint. Theme 2 (Technique analysis) revealed a trend linking smaller horizontal foot velocities and touchdown distances with smaller braking impulses during the transition and maximal velocity phases. Furthermore, moderate to large increases in negative work by the ankle plantar flexors and knee extensors suggests an increased contribution to absorb forces at those joints and maintain the height of the centre of mass as a sprint progresses. Finally, theme 3 (Induced acceleration analysis) revealed that the braking impulses relative to body mass (expressed in m·s-1) due to the accelerations at contact point, which largely resulted from the foot being decelerated at touchdown, increased from -0.01 ± 0.01 m·s-1 to -0.08 ± 0.02 m·s-1 between steps three to 19 of a sprint. The ankle moment provided the largest contributions to centre of mass acceleration throughout stance with the changing orientation of the ground reaction force vector ultimately determined by the increasing foot, shank and trunk angles as the sprint progressed.
This thesis developed the conceptual understanding of the technical differences between different phases of sprinting. It will contribute to the development and evaluation of sprinting technical models associated with different phases of the event and provide a greater understanding of key contributors to performance. As a sprint progresses, sprinters should emphasise the development of the leg mechanics during the terminal swing and early stance phases to ensure step-to-step changes in braking impulses are managed.
Thesis completed in 2017.