Date Published: May 31, 2019
Publisher: Public Library of Science
Author(s): Lars Reinhardt, René Schwesig, Andreas Lauenroth, Stephan Schulze, Eduard Kurz, Moacir Marocolo.
The aim of this investigation was to establish the validity of a GPS-based tracking system (Polar Team Pro System, PTPS) for estimating sprint performance and to evaluate additional diagnostic indices derived from the temporal course of the movement velocity. Thirty-four male soccer players (20 ± 4 years) performed a 20 m sprint test measured by timing gates (TG), and while wearing the PTPS. To evaluate the relevance of additional velocity-based parameters to discriminate between faster and slower athletes, the median-split method was applied to the 20-m times. Practical relevance was estimated using standardized mean differences (d) between the subgroups. Differences between the criterion reference (TG) and PTPS for the 10 and 20 m splits did not vary from zero (dt10: -0.01 ± 0.07 s, P = 0.7, d < -0.1; dt20: -0.01 ± 0.08 s, P = 0.4, d < -0.2). Although subgroups revealed large differences in their sprint times (d = -2.5), the average accelerations between 5 and 20 km/h as well as 20 and 25 km/h showed merely small effects (d < 0.5). Consequently, analyses of velocity curves derived from PTPS may help to clarify the occurrence of performance in outdoor sports. Thus, training consequences can be drawn which contribute to the differentiation and individualization of sprint training.
As in most team sports, soccer is about scoring and preventing goals, whereas straight sprinting with and without the ball was found to occur in approximately every second goal situation in the first German national league . Since all players on the pitch are involved in these situations, sprinting is of outstanding importance and thus a crucial element of the requirement profile. This estimation was also shared by many authors [2–5], although the cumulative sprint distance is below 5% relative to the total distance covered during a match. Furthermore, the vast majority of sprint displacements are below 20 m [6–9]. Moreover, investigations in the English Premiere League across seven seasons from 2006/07 to 2012/13 showed a massive increase in the distance covered in the high-intensity (24–36%) and sprinting (36–63%) zone in all playing positions although the total distance only changed marginally [2, 3]. Following common conventions, high-speed running and sprinting are achieved when at least 20 or 25 km/h are reached, respectively [3, 7, 10–12]. As a matter of course, every sprint consists of an initial acceleration phase in order to gain running velocity. Nevertheless, accelerating is more energetically demanding than moving at constant velocity . In spite of an 8-fold higher number of maximal accelerations than sprints per game, this phase is frequently excluded from analysis, since the high-intensity running threshold is not crossed .
This study investigated the validity of the PTPS to estimate short-distance linear sprint performance using velocity profiles. The analyses of velocity curve progressions enabled a section-wise evaluation. Within the distance of eight to ten meters, two characteristic slopes of the velocity curve were identified. These phases represented different average accelerations which could not predict the sprint time over 20 m distance.
In conclusion, the results of this study indicate that velocity curves derived from a GPS-based tracking system are a valid and useful database to analyze sprint performance. Especially the section-wise calculation of kinematic parameters in defined velocity ranges leads to additional perspectives on the occurrence of sprint performance in outdoor sports. Thus, specific training consequences can be drawn which contribute to the differentiation and individualization of short-distance sprint training. Due to the fact that these technologies are used by the majority of the elite soccer teams on a daily basis, it is reasonable to use the data captured as a source of additional information concerning the sprint performance. This compensates for the disadvantage of existing measurement inaccuracy.