The aim of this study was to examine the influence of skill of expert triple jumpers on the coordination variability of lower extremity intra-limb couplings. In contrast to the traditional motor learning perspective, we hypothesized that as skill and thus performance increases, movement coordination variability will also increase. Three-dimensional kinematic and ground reaction force data were collected during the hop-step transition phase of the triple jump. Relative motion plots and a modified vector coding technique were used to quantify the coordination variability across the trials. The results were consistent with a U-shaped curve, representing coordination variability, as skill increases. The high coordination variability in less skilled athletes is present while the appropriate characteristics defining the movement coordination patterns are acquired. This coordination variability may not be beneficial to performance. As the refinement of these characteristics is achieved, coordination variability decreases, resulting in a more consistent or regulated performance. In the final stages of developing a skilled performance, a functional variability is accessed that brings flexibility to the system allowing it to cope with perturbations. This study highlights the need to address the learning effect when analysing coordination variability from a dynamical systems perspective.

1The aim of this study was to investigate spatiotemporal and kinematic changes between the 2 initial acceleration, transition and maximum velocity phases of a sprint. Sagittal plane 3 kinematics from five experienced sprinters performing 50 m maximal sprints were collected 4 using six HD-video cameras. Following manual digitising, spatiotemporal and kinematic 5 variables at touchdown and toe-off were calculated. The start and end of the transition phase 6 were identified using the step-to-step changes in centre of mass height and segment angles. Mean step-to-step changes of spatiotemporal and kinematic variables during each phase were 8 calculated. Firstly, the study showed that if sufficient trials are available, step-to-step changes 9 in shank and trunk angles might provide an appropriate measure to detect sprint phases in 10 applied settings. However, given that changes in centre of mass height represent a more 11 holistic measure, this was used to sub-divide the sprints into separate phases. Secondly, 12 during the initial acceleration phase large step-to-step changes in touchdown kinematics were 13 observed compared to the transition phase. At toe-off, step-to-step kinematic changes were 14 consistent across the initial acceleration and transition phases before plateauing during the 15 maximal velocity phase. These results provide coaches and practitioners with valuable 16 insights into key differences between phases in maximal sprinting.

Elite female soccer athletes are susceptible to stress fractures and menstrual dysfunction and have delayed onset of menarche despite normal BMI and appropriate body perception and attitudes towards eating. Further studies are needed to better understand stress fracture risk in female soccer athletes and in other team sports to determine how these findings relate to long-term bone health in this population.

II.