Biomechanical aspects of postural balance strategy in dynamic sport activities

• Main Author: Jamkrajang, P.
• Other Authors: Robinson, M. ; Vanrenterghem, J. ; Limroongreungrat, W.
• Published: Liverpool John Moores University 2018
• Subjects: RC1200 Sports Medicine
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.762863

Postural balance is one of the most important aspects of everyday movement, especially in complex movements such as jumping, kicking or movements involving overhead/arm motion. In sporting activities, players often need to complete goal-directed tasks of an end-effector (e.g. tennis racket), while also needing to control their balance, in order to produce a successful task. However, studying the interaction between postural balance and end-effector control, in a biomechanical context and particularly in the tennis serve is difficult and remains largely unexplored. Traditionally, to explore postural balance researchers have to observe the whole-body centre of mass (CoM) location. However, for marker-based motion capture systems, collecting and processing data is time-consuming. If the researchers are interested in examining the movements of only some parts of the body, then reductions in model complexity may be possible while still retaining an ability to track CoM location. Therefore, the first aim of this research was to find an appropriate biomechanical model to quantify accurate whole-body (X)CoM representation. The second aim was then to investigate the interaction between postural balance control and end-effector performance, during the tennis serve, within a single target location and between different serving locations. The first study of this thesis showed that anteroposterior and medio-lateral displacement profiles of the CoM representation, based on the lower limbs, trunk and upper limbs showed strong agreement with the full-body model, and this only slightly reduced for the lower limbs and trunk only. Representations based on the lower limbs only showed less agreement, particularly for the extrapolated CoM (XCoM) in kicking. Our results justified the use of some model reductions for specific needs, saving measurement effort whilst limiting the error of tracking (X)CoM trajectories in the context of whole-body balance investigation. The second study of this thesis demonstrated that there is no direct interaction between the XCoM displacement, the changes in arms/trunk angular momentum, and maximum racket velocity during the preparation, propulsion and forward swing phases of a tennis serve. Only in the forward swing phase, a significant relationship between trunk angular momentum and maximum racket velocity was found which means the trunk segmental acceleration may play a role in controlling balance when generating the maximum racket velocity during the serve towards this target location. The third and final study in this thesis focussed on only the forward swing phase, and indicated that only the change in arms angular momentum influenced the maximum racket velocity. This was found specifically when serving into the wider part of the advantage court. Furthermore, individual relationships were evident between serving conditions. The novel approach introduced in this thesis, and the key outcomes of the work, have the potential to give researchers, coaches and athletes, who are working and playing in relevant dynamic sporting tasks, an opportunity to better understand the interaction between how control of the end-effector adapts while maintaining postural stability during the serve. Moreover, the work also guides the choice of biomechanical marker sets to estimate the centre of mass during dynamic activity.