Time series of ground reaction forces following a single leg drop jump landing in elite youth soccer players consist of four distinct phases

Abstract

A B S T R A C TThe single leg drop jump landing test may assess dynamic and static balance abilities in different phases of the landing. However objective definitions of different phases following landing and associated reliability are lacking.Therefore, we determined the existence of possible distinct phases of single leg drop jump landing on a force plate in 82 elite youth soccer players. Three outcome measures were calculated over moving windows of five sizes: center of pressure (COP) speed, COP sway and horizontal ground reaction force (GRF).Per outcome measure, a Factor Analysis was employed with all windows as input variables. It showed that four factors (patterns of variance) largely (>75%) explained the variance across subjects/trials along the 12 s time series. Each factor was highly associated with a distinct phase of the time series signal: dynamic (0.4-2.7 s), late dynamic (2.5-5.0 s), static 1 (5.0-8.3 s) and static 2 (8.1-11.7 s).Intra-class correlations (ICC) between trials were lower for the dynamic phases (0.45-0.68) than for the static phases (0.60-0.86). The COP speed showed higher ICC's (0.63-0.86) than COP sway (0.45-0.61) and GRF (0.57-0.71) for all four phases.In conclusion, following a drop jump landing unique information is available in four distinct phases. The COP speed is most reliable, with higher reliability in the static phases compared to the dynamic phases. Future studies should assess the sensitivity of information from dynamic, late dynamic and static phases.

The assessment of single-leg drop jump landing performance by means of ground reaction forces: A methodological study

“…Players took off by means of a small drop jump with two feet, landed on the testing leg at the center of the force plate, and stabilized as quickly as possible. They kept all movement to a minimum standing on the testing leg for 15 s, while keeping their hands on the iliac crest [23]. Players were instructed to look at a visual target 4 m ahead on a blank wall.…”

“…Most jump tasks consists of a jump movement in vertical and anterior direction, and the impact forces in these directions are common outcome measures [6,9]. As these high impact GRF specifically yield information about the kinetic energy absorption [23,24], they are usually considered separately from dynamic postural stability measures [6,9]. As the calculation of DPSI includes the impact forces, DPSI holds information about both kinetic energy absorption and the subsequent postural sway up to 3 s post landing.…”

“…This could be important since kinetic energy absorption and postural stabilization may be independent aspects of jump landing performance. In a recent study, it was shown that the magnitude of the horizontal GRF (HGRF) during 0.4-2.4 s following a single-leg drop jump landing holds different information compared to the time periods of 0-0.4 s and 3.0-5.0 s [23]. The time period of 0-0.4 s was likely affected by the high impact force in anteroposterior direction.…”

“…The time period of 0-0.4 s was likely affected by the high impact force in anteroposterior direction. Between 0.4 and 2.4 s the drop in COM accelerations was still rather large, between 3.0 and 5.0 s the drop was small, and after 5 s following landing the single-leg stance was considered as a static balance [23,25]. To date, the interrelations among improved TTS, DPSI, peak forces, dynamic HGRF, and static HGRF are largely unknown.…”

Age-Matched Z-Scores for Longitudinal Monitoring of Center of Pressure Speed in Single-Leg Stance Performance in Elite Male Youth Soccer Players

“…Commonly, center of pressure (COP) trajectory parameters are used, such as the averaged distance to the COP origin, a 95% COP area, the averaged COP speed, or various nonlinear measures (25,26,36,40,47,51,64). In general, these COP parameters provide very similar information (8,11,12,51). This is important because the application of more outcome measures will reduce the power or increase the like-lihood of type I errors.…”