Latest research in football - week 40 - 2020

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Reliability and Validity of Maximal Mean and Critical Speed and Metabolic Power in Australian Youth Soccer Players
Reference: J Hum Kinet. 2020 Jul 21;73:93-102. doi: 10.2478/hukin-2019-0135. eCollection 2020 Jul.
Authors: Cameron Lord, Anthony J Blazevich, Chris R Abbiss, Fadi Ma'ayah
Summary: The reliability and validity of maximal mean speed (MMS), maximal mean metabolic power (MMPmet), critical speed (CS) and critical metabolic power (CPmet) were examined throughout the 2016-2017 soccer National Youth League competitions. Global positioning system (GPS) data were collected from 20 sub-elite soccer players during a battery of maximal running tests and four home matches. A symmetric moving average algorithm was applied to the instantaneous velocity data using specific time windows (1, 5, 10, 60, 300 and 600 s) and peak values were identified. Additionally, CS and CP¬met values calculated from match data were compared to CS and CPmet values determined from previously validated field tests to assess the validity of match values. Intra-class correlation (one-way random absolute agreement) scores ranged from 0.577 to 0.902 for speed, and from 0.701 to 0.863 for metabolic power values. Coefficients of variation (CV) ranged from good to moderate for speed (4-6%) and metabolic power (4-8%). Only CS and CPmet values were significantly correlated (r = 0.842; 0.700) and not statistically different (p = 0.066; 0.271) to values obtained in a shuttle-running critical test. While the present findings identified match-derived MMS, MMPmet, CS and CPmet to be reliable, only CS and CPmet derived from match play were validated to a CS field test that required changes in speed and direction rather than continuous running. This suggests that both maximal mean and critical speed and metabolic power analyses could be alternatives to absolute distance and speed in the assessment of match running performance during competitive matches.

#2 Circulating Inflammatory Biomarkers and Endocrine Responses to Exercise in Female Soccer Players
Reference: J Hum Kinet. 2020 Jul 21;73:73-82. doi: 10.2478/hukin-2020-0005. eCollection 2020 Jul.
Authors: Grażyna Janikowska, Aleksandra Kochańska-Dziurowicz, Ilona Pokora, Aleksandra Żebrowska
Summary: The objective of the study to determine the effects of graded exercise on the cytokines and insulin-like growth factor-1 (IGF-1), growth hormone (hGH), testosterone (T), and cortisol (C) concentrations in the peripheral blood of female soccer players, and to evaluate if increased inflammatory biomarkers were related to these hormones and performance variables. Sixteen female soccer players (N = 16, age 19.3 ± 2.3 years) participated in this study. Blood samples were collected at three time points: pre-exercise, post-exercise, and in the 15th minute of recovery, to evaluate morphological and biochemical variables. The relative expression of IL-6 (interleukin 6) and serum concentrations of the cytokines were increased in the recovery period compared to pre-exercise levels (p = 0.03 and p=0.005, respectively). There was a significant effect of exercise on serum hGH level (p " 0.001), T/C ratio (p = 0.001), and C level (p=0.02). Positive correlations were found between: post-exercise IL-1β (interleukin 1 beta) and IL-6 (R = 0.84, p = 0.000), and the IL-6 and TNF-α (tumor necrosis factor alpha) gene expression during recovery (R = 0.65, p = 0.009), and serum IL-1β post-exercise and maximal power (R = 0.68; p = 0.004). Exercise-induced serum C levels positively correlated with IGF-1 levels (R = 0.52 p = 0.05). Negative associations were revealed between post-exercise T/C ratio and IGF-1 (R = - 0.58, p = 0.03) and serum free T and IL- β (R = -0.56, p = 0.04) levels. The low level of pre-exercise genes and protein of the IL-1β, IL-6 and TNF-α indicate a lack of inflammation signs in the female soccer players. This study shows significant effects of exercise on hormone levels and pro-inflammatory markers, which could be used to identify the role of female sex steroids on the immune function.

#3 Relationship Between the Session-RPE and External Measures of Training Load in Youth Soccer Training
Reference: J Strength Cond Res. 2020 Aug 6. doi: 10.1519/JSC.0000000000003785. Online ahead of print.
Authors: Jakub Marynowicz, Karol Kikut, Mateusz Lango , Damian Horna, Marcin Andrzejewski
Summary: The aim of this study was to identify the external training load (TL) markers (10 Hz Global Positioning System) that are most influential on the rating of perceived exertion (RPE) and session-RPE (sRPE) during youth soccer training. Data were collected from 18 youth soccer players during an 18-week in-season period. A total of 804 training observations were undertaken. We observed moderate to very large within-individual correlations between sRPE and measures of external load (r ranging from 0.36 to 0.76). Large, positive within-individual correlations were found between total covered distance, PlayerLoad, number of accelerations, and sRPE (r = 0.70, 0.64, and 0.62, respectively, p < 0.001). By contrast, small to moderate within-individual correlations were noted between RPE and measures of intensity (r ranging from 0.16 to 0.39). A moderate within-individual correlation was observed between high-speed running distance (HSR) per minute and RPE (r = 0.39, p < 0.001). The level of statistical significance was set at alpha = 0.05 for all tests. Two generalized estimating equation models were constructed, with RPE and sRPE as the response variables. The model identified by QIC for RPE contained 2 variables as follows: HSR per minute and distance in deceleration per minute, whereas sRPE was modeled with 3 predictors as follows: PlayerLoad, HSR, and distance in acceleration. The findings demonstrate that RPE does not reflect the intensity of a training session and that sRPE can be a useful, simple, and cost-effective tool for monitoring TL.

#4 Development and validation of the Referee Training Activity Questionnaire (RTAQ): Towards a better understanding of the training practices of soccer officials
Reference: J Sports Sci. 2020 Aug 10;1-12. doi: 10.1080/02640414.2020.1800371. Online ahead of print.
Authors: Gary P McEwan, Viswanath Unnithan, Chris Easton, Rosemary Arthur
Summary: The purpose was to develop and assess the validity of the Referee Training Activity Questionnaire (RTAQ), a systematic process was employed: 1) item generation; 2) assessments of content and face validity; and 3) assessments of criterion validity. In stage 1, items were generated following semi-structured interviews with an expert panel (n = 8). Following content analyses, the RTAQ was developed and comprised 3 primary sections (12 sub-sections) assessing: 1) attributes perceived to underpin soccer officiating performance; 2) general training information; and 3) specific training practices. In stage 2, the preliminary RTAQ was assessed for content and face validity by a sample of experts (n = 6). Based upon the content validity index (CVI), content validity was confirmed for 8 sub-sections (CVI ≥ 0.78) with 5 sub-sections being deemed invalid (CVI < 0.78). Various amendments were carried out in accordance with participant feedback. In stage 3, the RTAQ was completed by a cohort of officials (n = 25) who subsequently recorded a detailed training diary. Negligible mean biases, wide 95% LOA, and significant Pearson correlations were observed between the RTAQ and training diaries for most training activities, suggesting the RTAQ holds promise as a useful and effective alternative of acquiring insight into the training practices of soccer officials.

#5 Video assistant referees (VAR): The impact of technology on decision making in association football referees
Reference: J Sports Sci. 2020 Aug 14;1-7. doi: 10.1080/02640414.2020.1809163. Online ahead of print.
Authors: Jochim Spitz, Johan Wagemans, Daniel Memmert, A Mark Williams, Werner F Helsen
Summary: The use of technology has been proposed to improve decision-making in sport officials. The implementation of the video Assistant Referee (VAR) in association football is one example of how technology can be used to assist decision making, although its impact remains unknown. In 2195 competitive football matches across 13 countries, the VAR conducted 9732 checks for potential match-changing incidents, with the median duration of a check being 22 seconds. The checks resulted in a total of 795 reviews, with a median duration of 62.0 s for on-field reviews (N = 534) and 15.0 s for VAR-only reviews (N = 261).We report that the predictive odds for making the correct decision after VAR intervention were significantly higher than for the initial referee's decision, with accuracy increasing from 92.1% to 98.3%. Findings have implications for the current debate about the introduction of technology in association football and may help set guidelines regarding the use of technology across other sports and professional domains.

#6 What do you hear? The effect of stadium noise on football players' passing performances
Reference: Eur J Sport Sci. 2020 Aug 11;1-26. doi: 10.1080/17461391.2020.1809714. Online ahead of print.
Authors: Fabian W Otte, Sarah-Kate Millar, Stefanie Klatt
Summary: Stadium noise - created by spectators and fans - plays a critical part in the reality of professional sports. Due to a lack of research on the impact of these auditory cues and multimodal environments on motor performance, it is currently unclear how professional athletes experience and perceive stadium noise and how this potentially affects performance in practice. In order to explore the effect of stadium noise on athletes' performance, this paper presents an experimental design using the unique and standardised football training tool known as the 'Footbonaut'. Specifically, fifteen skilled German football players engaged in a standardised football-specific technical training program while subjected to four different auditory training conditions; these included both 'positive' and 'negative' stadium noise conditions, a 'baseline' condition providing auditory guidance, and a 'no (auditory) cue' condition. Performance data for passing accuracy and passing time were measured for training in each auditory condition. A repeated measures MANOVA revealed a significant main effect for passing time. Specifically, participants showed faster passing times in the baseline compared to the negative and no auditory cue conditions. Findings are presented and discussed from a constraints-led perspective, allied to principles of ecological dynamics and nonlinear pedagogy. Particularly, the use of representative training experiences (including multimodal sensory and emotional information) appears to underline training to refine expert athletes' adaptive coordination of complex motor actions.

#7 Neuropsychological Change After a Single Season of Head Impact Exposure in Youth Football
Reference: J Int Neuropsychol Soc. 2020 Aug 7;1-11. doi: 10.1017/S1355617720000685. Online ahead of print.
Authors: Arthur Maerlender, Eric Smith, P Gunnar Brolinson, Joseph Crisco, Jillian Urban, Amaris Ajamil, Steven Rowson, Eamon T Campolettano, Ryan A Gellner, Srinidhi Bellamkonda, Emily Kieffer, Mireille E Kelley, Derek Jones, Alex Powers, Jonathan Beckwith, Joel Stitzel, Richard M Greenwald, Stefan Duma
Summary: Head impact exposure (HIE) in youth football is a public health concern. The objective of this study was to determine if one season of HIE in youth football was related to cognitive changes. Over 200 participants (ages 9-13) wore instrumented helmets for practices and games to measure the amount of HIE sustained over one season. Pre- and post-season neuropsychological tests were completed. Test score changes were calculated adjusting for practice effects and regression to the mean and used as the dependent variables. Regression models were calculated with HIE variables predicting neuropsychological test score changes. For the full sample, a small effect was found with season average rotational values predicting changes in list-learning such that HIE was related to negative score change: standardized beta (β) = -.147, t(205) = -2.12, and p = .035. When analyzed by age clusters (9-10, 11-13) and adding participant weight to models, the R2 values increased. Splitting groups by weight (median split), found heavier members of the 9-10 cohort with significantly greater change than lighter members. Additionaly, significantly more participants had clinically meaningful negative changes: X2 = 10.343, p = .001. These findings suggest that in the 9-10 age cluster, the average seasonal level of HIE had inverse, negative relationships with cognitive change over one season that was not found in the older group. The mediation effects of age and weight have not been explored previously and appear to contribute to the effects of HIE on cognition in youth football players.

#8 Contextual factors influencing the characteristics of female football players
Reference: J Sports Med Phys Fitness. 2020 Jul 30. doi: 10.23736/S0022-4707.20.11182-4. Online ahead of print.
Authors: Jesse Griffin, Sean Horan, Justin Keogh, Karl Dodd, Melissa Andreatta, Clare Minahan
Summary: Women's football participation rates are projected to increase to 60 million worldwide by 2026, doubling the current participation. Growing investment and the increase in research in women's football has had a positive effect on the level of performance over the last 10 years. The present review will examine the literature on the physical and physiological characteristics of female football players from 2010 to 2019 to reflect the recent changes in professionalism. Characteristics investigated include anthropometry, strength, speed, endurance, power, change of direction and repeated sprint ability. These characteristics are presented in relation to playing position, age and competition-level. Results revealed that goalkeepers (171 cm, 66 kg) and defenders (168 cm, 61 kg) were the tallest and had the greatest body mass, while attackers were the fastest players over 20 m (3.05 s) and 30 m (4.38 s) and midfielders had the highest endurance (55.4 ml∙kg-1∙min-1) (p < 0.05). Characteristics tended to improve with age until full biological maturity around 17 to 18 years of age. Competition comparisons demonstrated international players have significantly greater speed, repeated sprint ability, power and endurance characteristics (p < 0.05). By identifying influential factors, coaches may be able to optimise their training and physical assessment practises, to better expose players to the required stimulus to develop these characteristics considered crucial to improved performance.

#9 Is the perception of intent by association football officials influenced by video playback speed?
Reference: R Soc Open Sci. 2020 Jun 3;7(6):192026. doi: 10.1098/rsos.192026. eCollection 2020 Jun.
Authors: George Mather, Simon Breivik
Download link:
Summary: Recent research on motion perception indicates that when we view actions in slow-motion, the perceived degree of intent behind those actions can increase. Slow-motion replays are widely used in the checking and review of refereeing decisions by video assistant referees (VAR) in association football. To test whether the decisions of referees are subject to such a bias, 80 elite English professional football officials made decisions about 60 incidents recorded in professional European leagues (recorded as fouls, yellow-card offences or red-card offences by the on-field referee). Both real-time (1×) and slow-motion (0.25×) playback speeds were used. Participants had no prior knowledge of the incidents, playback speeds or disciplinary sanctions relating to each clip. Three judgements were made about each incident: extent of contact, degree of intent, and disciplinary sanction. Results showed an effect of playback speed on decision-making, but not a consistent bias due to slow-motion. Instead the distinction between yellow-card and red-card offences was clearer: Under slow-motion, yellow-card incidents were judged as less severe, and red-card incidents are judged as more severe, thus enhancing the distinction between these offences. These results are inconsistent with previous scientific reports that perceived intent is heightened by slow video playback speed.

The Training Manager -