Differences in ground reaction waveforms between elite senior and junior academy sprinters during the block phase and first two steps

Philip Graham-Smith,Steffi L Colyer,Aki It Salo

doi:10.1177/1747954120917537

Abstract

The block start and initial steps following block exit are fundamental aspects of sprinting and their development is key to junior athletes’ progression. This study assessed the difference in force production between elite senior (including two sub-10 s 100-m sprinters) and junior academy sprinters during the block phase and the first two steps of a sprint. Thirty-seven male sprinters (17 senior, 20 junior) performed a series of maximal effort 20–40 m acceleration from blocks on an indoor track, with the ground reaction forces produced during the block phase and first two steps measured using force platforms. Senior athletes produced better block-phase performances (average horizontal external power; 15.52 ± 1.48 W/kg, M ± SD) compared with the juniors (12.37 ± 2.21 W/kg; effect size ± 90% confidence interval = 1.28 ± 0.38). However, force production during the initial two steps was comparable across groups. Specifically, senior athletes exhibited higher relative force production and ratio of forces during the early (∼15–35%) block phase and higher anteroposterior forces during the transition from bilateral to unilateral pushing (58–62% of the block phase). Front foot force production was also found to differentiate senior and junior groups at rear block exit (∼55% of the block phase). This may be a required response to the greater centre of mass displacement in order to prevent over-rotation in the senior athletes during the front block pushing phase. Collectively, these results indicate that the progression of junior athletes is non-uniform across the block phase and subsequent two contacts, which should be considered when attempting to progress junior athletes towards senior ranks.

Highlights

In order to guide athletic development and support the transition of young sprinters to senior status in sprinting, one important issue is to identify any kinetic factors that differentiate junior and senior athletes
There was a large effect size between the average horizontal external power produced by the senior compared with the junior athletes on the blocks
Senior athletes produced this higher average horizontal external power on the blocks both by generating greater (6% higher) horizontal block exit velocity and spending less time pushing against the blocks (11% lower) compared with the junior athletes (Table 1)

Summary

Introduction

In order to guide athletic development and support the transition of young sprinters to senior status in sprinting, one important issue is to identify any kinetic factors that differentiate junior and senior athletes. The sprint start is a highly complex skill with high-level performances characterised by coordinated movement about multiple joints.[1,2] Undoubtedly, large capacities of lower limb strength and power are essential to the sprint start as the rate at which an athlete can increase their kinetic energy (average horizontal external power) dictates performance level.[3] better sprint starters have consistently been found to be those who exhibit greater anteroposterior components of force[4,5] and higher rates of force development,[6] in the early parts of the rear block push.[7]. Waveform analyses have revealed that it could be the application of forces lower than the applied peak force that are related to better sprint start performance, for the front block.[7,9,10] discrete analysis of peak forces may neglect important information and the consideration of the entire one-dimensional curves relating to both the force orientation and magnitude in the analysis of sprint start performance is important

Methods

Results

Conclusion