Author(s): VAMPOLA, J., ŠTASTNÝ, P., VARJAN, M., MALÝ, T., MUSÁLEK, M., CASTELLANO, J., KOKŠTEJN, J., Institution: CHARLES UNIVERSITY, Country: CZECH REPUBLIC, Abstract-ID: 970

INTRODUCTION:
According to previous studies on the neuromuscular demands (Harper et al., 2019), professional football is more decelerative than accelerative. However, it is not known whether this is respected in terms of intensity ranges. The aim of the study is to compare whether this trend in favor of deceleration is maintained in the different intensity ranges.
METHODS:
External load from official competitions in three age categories (2nd team, 20.8 ± 4.4 yrs; U19, 17.0 ± 0.7 yrs; and U17, 15.8 ± 0.6 yrs) of elite football academy were measured by 10 Hz GPS technology during two consecutive seasons, 2021/22 and 2022/23. 2nd team played in third and second professional Czech leagues, both youth teams played the highest youth competitions. Various thresholds were used for examining the number of accelerations (ACC) and decelerations (DEC): ACC12 (from 1 to 2 ms-2), ACC23 (2-3 ms-2), ACC34 (3-4 ms-2), ACC45 (4-5 ms-2), ACC5 (>5 ms-2), with negative sign for decelerations (from DEC12 to DEC5), respectively. From official matches with 4-3-3 formation in which the players participated for the entire duration (>90 minutes), were calculated averages for every player/season. Repeated measures ANOVA with Bonferroni’s post-hoc test, Student t pair test and Wilcoxon signed-rank test were used (JASP, Version 0.18.3). Cohen´s d values were employed to assess effect sizes. Effect magnitude was interpreted according to power analysis (G*power, version 31.9.7).
RESULTS:
ANOVA revealed a significant influence of category on the results. Significant differences were found in all parameters only between the 2nd team and U17, although with small effect sizes according to power analysis (p<0.05, d= 0.47-0.60). There were found, in all categories, greater number of ACC than DEC in thresholds of 2-3 ms-2 (ACC23>DEC23) and 3-4 ms-2 (ACC34>DEC34). In all other thresholds more decelerations were found (ACC12 < DEC12, ACC45 < DEC45, and ACC5 < DEC5). In the lowest level ACC12 and DEC12, there were found statistically significant differences only in U17 (p< 0.01, d= 0.38) and U19 (p< 0.01, d= 0.53) categories with low and high effect size, respectively. For all other thresholds statistically very significant differences were found for all the categories (p<0.01). Magnitude of effect size exceed the counted thresholds by power analysis in all other thresholds except for U17 ACC34 versus DCC34 (d= 0.49) and ACC45 versus DCC45 (d=0.51).
CONCLUSION:
The results confirm that more DEC than ACC occur in football matches when higher thresholds are considered. On the contrary, the opposite is true in lower speed changes. Additionally, the team category significantly impacts the results, with U17 showing significantly lower number of ACC and DEC compared to the 2nd team in all thresholds. In addition, one of the main findings for practice is, that integrating accelerations and decelerations into one variable (i.e. mean value) is not recommended for greater thresholds (>4 ms-2), where the difference between ACC a DEC is greater.