Kinematic factors associated with start performance in World-class male sprinters.

The aim was to investigate the kinematic factors associated with successful performance in the initial acceleration phase of a sprint in the best male athletes in the World at the 2018 World Indoor Athletics Championships. High speed video (150 Hz) was captured for eight sprinters in the men's 60 m final. Spatio-temporal and joint kinematic variables were calculated from the set position to the end of the first ground contact post-block exit (GC1). Normalised average horizontal external power (NAHEP) defined performance and was the dependent variable for a series of regression analyses. Clear relationships were found between GC1 NAHEP and 10-m time, 60-m time, change in velocity, acceleration and contact time in the first ground contact (r = -0.74, -0.64, 0.96, 0.91 and -0.56, respectively). Stepwise multiple linear regression of joint kinematic variables in the first ground contact revealed that trunk angle at take-off and thigh separation angle at take-off explained nearly 90% of variation in GC1 NAHEP (R2 = 0.89). The athletes' projection at take-off with a forward leaning trunk and large thigh separation is characteristic therefore of excellent initial acceleration performance and this will be a good visual guide for technical coaching instruction. This was the first study of its kind to adopt such a research design in a World-class sample in a representative environment. Future studies that combine detailed kinematic and kinetic data capture and analysis in such a setting will add further insight to the findings of this investigation.

The importance of duration and magnitude of force application to sprint performance during the initial acceleration, transition and maximal velocity phases.

Successful sprinting depends on covering a specific distance in the shortest time possible. Although external forces are key to sprinting, less consideration is given to the duration of force application, which influences the impulse generated. This study explored relationships between sprint performance measures and external kinetic and kinematic performance indicators. Data were collected from the initial acceleration, transition and maximal velocity phases of a sprint. Relationships were analysed between sprint performance measures and kinetic and kinematic variables. A commonality regression analysis was used to explore how independent variables contributed to multiple-regression models for the sprint phases. Propulsive forces play a key role in sprint performance during the initial acceleration (r = 0.95 ± 0.03) and transition phases (r = 0.74 ± 0.19), while braking duration plays an important role during the transition phase (r = -0.72 ± 0.20). Contact time, vertical force and peak propulsive forces represented key determinants (r = -0.64 ± 0.31, r = 0.57 ± 0.35 and r = 0.66 ± 0.30, respectively) of maximal velocity phase performance, with peak propulsive force providing the largest unique contribution to the regression model for step velocity. These results clarified the role of force and time variables on sprinting performance.

Phase analysis in maximal sprinting: an investigation of step-to-step technical changes between the initial acceleration, transition and maximal velocity phases.

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

World-Class Male Sprinters and High Hurdlers Have Similar Start and Initial Acceleration Techniques.

The effect of the inclusion of a high hurdle 13.72 m after the start line on elite sprint start and initial acceleration technique has yet to be investigated or understood. This highly novel study addresses that lack of information in an exceptional manner, through detailed biomechanical analysis of the world's best sprint and hurdle athletes, with data collected in situ at the 2018 IAAF World Indoor Championships, held in Birmingham, UK. High speed videos (150 Hz) were compared for eight sprinters and seven hurdlers for the start and initial acceleration phase of the finals of the men's 60 m and 60 m hurdles. Temporal and kinematic data were supplemented by vector coding analysis to investigate mechanisms by which these world-class athletes translate their centres of mass (CM) up to the fourth touchdown post-block exit. The sprinters and hurdlers coordinated their lower limb and trunk movement in a similar manner throughout the start and initial acceleration phases, which contributes new conceptual understanding of the mechanisms that underpin start and initial acceleration performance. Differences between groups were initiated from block set-up, with the hurdlers utilising a larger block spacing, but with the front block nearer to the start line than sprinters. Even after accounting for stature, the biggest differences in the raising of the CM occurred during the block phase, with hurdlers greater than sprinters (difference in vertical CM displacement scaled to stature = -0.037, very large effect size). Subsequent flight phases showed the biggest differences in the translation of the CM, in part due to longer flight times in the hurdlers, whilst the techniques of the two groups generally converged during the ground contact phases of initial acceleration. In highlighting that similar techniques are used by world-class sprinters and hurdlers, despite differing task constraints, this study has provided invaluable insights for scientists, coaches, and athletes, that will inform further developments in understanding and practice across both sprints and hurdles.