Latest research in football - week 35 - 2019

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 Influence of poor preparation and sleep deficit on injury incidence in amateur small field football of both gender
Reference: Arch Orthop Trauma Surg. 2019 Aug 17. doi: 10.1007/s00402-019-03261-0. [Epub ahead of print]
Authors: Krutsch V, Clement A, Heising T, Achenbach L, Zellner J, Gesslein M, Weber-Spickschen S, Krutsch W
Summary: Amateur small-field football tournaments are rather common worldwide. Adequate preparation is essential for injury prevention. The consequences of insufficient injury preparation at this level are still unclear. This study investigates the factors influencing injuries in this football population. In 2017, medical students participating in a national amateur football tournament were analysed in a prospective cohort study. Injury incidence, injury pattern and factors influencing injuries were investigated according to the statement on data collection and injury definition of Fuller et al. (Br J Sports Med 40:193-201, 2006). Preparation for the tournament was assessed for both sexes by means of hours of sleep, alcohol consumption, training level and warm-up performance. Of 694 amateur football players (423 men and 271 women) with a mean age of 23 years (SD 2.5), 321 (21.1%) injuries happened during the tournament. 60% of injuries affected the lower extremity. The most common types of traumatic injury were skin abrasions (40.0%) and muscle strains (23.3%). The injury incidence of male players during match exposure was 469 per 1000 h football and significantly higher than in female players 313 (p = 0.025). One potential reason for the higher injury rate of male players as measure for inadequate preparation was significantly higher alcohol consumption the evening before the tournament (p < 0.001) and the after-effects on match day (p < 0.001). Additionally, male players reported less and inadequate sleep the night before the tournament (p < 0.007) and a lower warm-up rate before the matches compared to female players (p < 0.001). Small-field tournaments in football have a high injury incidence. Male players have a higher injury incidence than female players and show additionally a lack of sleep and alcohol consumption the night before the tournament and poor warm-up performance on match day. Adequate preparation for a football tournament is the key factor for preventing injuries, also in recreational football.

#2 Tattoos among elite football players during the 2019 FIFA Women's World Cup France
Reference: J Eur Acad Dermatol Venereol. 2019 Aug 17. doi: 10.1111/jdv.15890. [Epub ahead of print]
Authors: Kluger N
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Summary: Thirty-four percent of the men players harbored visible tattoos, without notable impact on performance or discipline on the field during the 2018 FIFA World Cup (FWC), [1]. In a spirit of gender equality, we performed the same study among elite women footballers enrolled in the 2019 FWC France with the same methodology [1]. Players' visible tattoos (location, colours) were reviewed using the Getty Images website [2]. We collected players and teams' statistics using the official FIFA website.

#3 Distribution of External Load During Acquisition Training Sessions and Match Play of a Professional Soccer Team
Reference: J Strength Cond Res. 2019 Aug 29. doi: 10.1519/JSC.0000000000003363. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Weston M, Yanci J
Summary: The aim of this study was to use global position systems to analyze the external loads of the 3 different acquisition training sessions (ATS) with competitive matches in professional soccer players over a 6-week period. Sixteen professional soccer players participated in the study, which analyzed the distribution of external load during the training microcycle of a professional soccer team. The 3 types of ATS undertaken by the players were as follows: ATS1 (strength), ATS2 (endurance), and ATS3 (speed). The total distance covered, the distance covered at above 14 km·h, the distance covered >21 km·h, the number of high accelerations (>3 m·s), and player load were recorded. The results showed that external loads were consistently higher during matches when compared with all training sessions (range of effect sizes: 1.06-3.38). Between training session comparisons revealed higher external loads during ATS1 and ATS2, when compared with ATS3 (range of effect sizes: 0.60-2.41). The only external load variable that differed between ATS1 and ATS2 was the distance covered >21 km·h, which was higher for ATS1. Our findings suggest that technical staff should consider the physical demands of weekly periodization to understand the training process regarding optimizing player physical performance.

#4 Relationship Among Biological Maturation, Physical Characteristics, and Motor Abilities in Youth Elite Soccer Players
Reference:  J Strength Cond Res. 2019 Aug 29. doi: 10.1519/JSC.0000000000003346. [Epub ahead of print]
Authors: Itoh R, Hirose N
Summary: Studies investigating skeletal maturity and motor abilities in youth Asian elite soccer players are lacking. We aimed to investigate the cross-sectional relationship among skeletal age (SA), physical characteristics, and motor abilities in youth elite soccer players. Skeletal age is commonly used to estimate the maturity status of youth athletes using a hand-wrist radiograph. We enrolled 49 youth elite male soccer players (12.7 ± 0.2 years). Height, body mass, body fat percentage, circumference (thigh/calf), flexibility, 10-m/50-m sprint, 10-m × 5 shuttle run, the crank test, 5-step bounding, Yo-Yo intermittent recovery test level 2, and cooper run were measured. Participants were divided into early (n = 14), average (n = 22), and late (n = 13) maturation groups according to their chronological age (CA) and SA based on the following criteria: SA-CA < -1 year, SA-CA = ±1 year, and SA-CA > +1 year, respectively. The difference in parameters among the groups was analyzed using one-way analysis of variance and Tukey's post hoc test. Statistical significance was set at p < 0.05. The early and average maturation groups were taller and heavier and had a larger circumference than the late maturation group (p < 0.05). Conversely, the early and average groups were significantly faster in 50-m sprint (p < 0.05) and scored higher in 5-step bounding (p < 0.05) than the late group. There was no difference in other parameters among the groups. In conclusion, the difference in biological maturity influences physical and physiological development, particularly height and muscular power, in youth elite soccer players.

#5 Competencies for rating perceived exertion in amateur soccer players with and without intellectual disabilities
Reference: J Appl Res Intellect Disabil. 2019 Aug 30. doi: 10.1111/jar.12668. [Epub ahead of print]
Authors: Schmitz G, Meis JM, Hafferkamp M, Schmitz S
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Summary: Perception of exertion is essential for self-regulation in sports. The ability to rate perceived exertion (RPE) is regarded as psychophysiological competence, although cognitive components of RPE are largely unknown. The present study tested the hypothesis that cognitive processing speed, perseveration and figural fluency correlate with RPE. The present study tested relationships between the performance in neuropsychological tests and the competence for RPE assessed during soccer training in 30 adults with and 22 adults without intellectual disabilities. Mean correlation coefficients for RPE and heart rate differed significantly between participants with intellectual disabilities (r = .41) and participants without intellectual disabilities (r = .71). The variance of RPE could be partially explained by neuropsychological performance measures reflecting cognitive processing speed and perseveration and by age. The results point to an impaired perception of exertion in people with intellectual disabilities, which can be partially explained by individual neuropsychological competencies.

#6 Sports Specialization Is Not Associated With Greater Odds of Previous Injury in Elite Male Youth Soccer Players
Reference: Clin J Sport Med. 2019 Sep;29(5):368-373. doi: 10.1097/JSM.0000000000000643.
Authors: Frome D, Rychlik K, Fokas J, Chiampas G, Jayanthi N, LaBella C
Summary: The purpose was to determine the relationship between sport specialization and previous injury in elite male youth soccer players. Male youth soccer players (N = 2123) participated in this study.  Sport specialization, weekly training volume, training ratio, and age were utilized as risk factors. Previous sports-related injury, injury type (traumatic vs overuse), injury severity, and injury location were main outcomes measures.  Of 2099 participants (average age 13.2 ± 1.8 years), 61.7% were specialized in soccer (played soccer >8 mo/yr and no other sports) and 38.3% were nonspecialized (played soccer >8 mo/yr and also played other organized sports). Specialized athletes were older than nonspecialized athletes (13.7 ± 1.9 vs 12.5 ± 1.4, P < 0.0001). Thirty-three percent (690/2099) of athletes reported at least one previous sports-related injury for a total of 765 traumatic injuries and 25 overuse injuries. Distribution of injury type was similar for specialized and nonspecialized athletes. Among athletes with overuse injuries, nonspecialized athletes were more likely to report upper-extremity and trunk overuse injuries than specialized athletes. After accounting for age and weekly training volume, specialized athletes had decreased odds of reporting any previous injury compared with nonspecialized athletes [odds ratio (OR), 0.78; 95% confidence interval (CI), 0.64-0.95], and similar odds of reporting a previous lower-extremity (LE) overuse injury as nonspecialized athletes (OR, 0.70; 95% CI, 0.56-1.1). However, specialized athletes missed more practices due to injury than nonspecialized players [median = 3, interquartile range (IQR) 2-4 vs median = 2, IQR 2-4, P = 0.0003]. In this national sample of elite, male youth soccer players, after accounting for age and weekly training volume, specialized athletes had decreased odds of reporting any previous injury and similar odds of reporting a previous LE overuse injury as nonspecialized athletes. These data suggest the need for further research to determine whether injury risk related to sports specialization depends on sex, chosen sport, and skill/competitive level.

#7 Comparative efficacy of active recovery and cold water immersion as post-match recovery interventions in elite youth soccer
Reference: J Sports Sci. 2019 Aug 28:1-9. doi: 10.1080/02640414.2019.1660448. [Epub ahead of print]
Authors: Pooley S, Spendiff O, Allen M, Moir HJ
Summary: The current study compared cold-water immersion (CWI) and active recovery (AR) to static stretching (SS) on muscle recovery post-competitive soccer matches in elite youth players (n = 15). In a controlled crossover design, participants played a total of nine competitive soccer games, comprising three 80 minute games for each intervention (SS, CWI and AR). Muscle oedema, creatine kinase (CK), countermovement jump performance (CMJA) and perceived muscle soreness (PMS) were assessed pre-, immediately post-, and 48 hours post-match and compared across time-intervals and between interventions. Following SS, all markers of muscle damage remained significantly elevated (P < 0.05) compared to baseline at 48 hours post-match. Following AR and CWI, CMJA returned to baseline at 48 hours post-match, whilst CK returned to baseline following CWI at 48 hours post-match only. Analysis between recovery interventions revealed a significant improvement in PMS (P < 0.05) at 48 hours post-match when comparing AR and CWI to SS, with no significant differences between AR and CWI observed (P > 0.05). Analysis of %change for CK and CMJA revealed significant improvements for AR and CWI compared to SS. The present study indicated both AR and CWI are beneficial recovery interventions for elite young soccer players following competitive soccer matches, of which were superior to SS.

#8 Does soccer play lower blood pressure?
Reference: Dtsch Med Wochenschr. 2019 Aug;144(17):1229-1232. doi: 10.1055/a-0953-6509. Epub 2019 Aug 27. [Article in German]
Summary: Playing football leads to a sustainable improvement of cardiovascular risk factors, especially to a reduction of blood pressure in hypertension. For certain target groups football is more attractive with its team character than individual sports. However, the existing studies are not sufficient for an evidence-based recommendation. Therefore, no medical society explicitly recommends football for lowering blood pressure. Urgent studies are needed to adequately evaluate the value of football as a health sport. This includes a special training program and rules, the involvement of football clubs in these programs, the training of appropriate coaches and the involvement of interested physicians. Football could, with its popularity, motivate more people to exercise and contribute to a sustained reduction in cardiovascular disease.

#9 Seasonal Accumulated Workloads in Collegiate Men's Soccer: A Comparison of Starters and Reserves
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003257. [Epub ahead of print]
Authors: Curtis RM, Huggins RA, Benjamin CL, Sekiguchi Y, M Arent S, C Armwald B, Pullara JM, West CA, Casa DJ
Summary: The purpose of this investigation was to quantify and compare player's season total-, match-, and training-accumulated workload by player status characteristics (i.e., starter vs. reserve) in American collegiate men's soccer. Global positioning system (GPS) and heart rate (HR)-derived workloads were analyzed from 82 collegiate male soccer athletes from 5 separate teams over the 2016 and 2017 seasons. Differences in total physical and physiological workloads (i.e., total distance, accelerations, and weighted HR-zone training impulse [TRIMP] score) as well as workloads over a range of intensity zones were examined using multilevel mixed models, with mean difference (MD) and effect size (ES) reported. Starters accumulated substantially more total distance (MD = 82 km, ES = 1.23), TRIMP (MD = 2,210 au, ES = 0.63), and total accelerations (MD = 6,324 n, ES = 0.66) over the season. Total accumulated distance in all velocity zones (ES [range] = 0.87-1.08), all accelerations zones (ES [range] = 0.54-0.74), and time spent at 70-90% HRmax (ES [range] = 0.60-1.12) was also greater for starters. Reserves accumulated substantially more total distance (MD = 20 km, ES = 0.43) and TRIMP (MD = 1,683 au, ES = 0.79) during training. Although reserves show elevated physical and physiological loads during training compared with starters, there is an imbalance in overall workloads between player roles, with starters incurring substantially more match and total seasonal workloads. These results indicate managing player workloads in soccer requires attention to potential imbalances between players receiving variable match times. Coaches and practitioners in collegiate men's soccer may consider implementing strategies to reduce discrepancies in loading between starters and reserves. Individualized monitoring of training and match workloads may assist in the implementation of more balanced load management programs.

#10 Contextual Variables and Training Load Throughout a Competitive Period in a Top-Level Male Soccer Team
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003258. [Epub ahead of print]
Authors: Rago V, Rebelo A, Krustrup P, Mohr M
Summary: The aim of the present study was to investigate and quantify the weekly training load (TL) according to different match-related contextual factors in a professional male soccer team (n = 23). Training load was quantified using a 10-Hz global positioning system with integrated 100-Hz accelerometer and heart rate recordings over a 3-month competitive period. Total distance (TD) covered and high-speed running (HSR, >16 km·h) during training were higher in the week after playing against a bottom-level or top-level opponent compared to a medium-level opponent (p < 0.05; effect size [ES] = 0.30-1.04). TD was also higher when preparing for a match against a bottom-level opponent (p < 0.05; ES = 0.39-0.76). In addition, the percentage of HSR was higher after playing a bottom-level compared to a medium-level opponent (p < 0.001; ES = 0.49 [0.27; 0.71]). TD covered was higher in the week following a draw or a win, and higher before a loss compared to a draw (p < 0.05, ES = 0.32-0.81). Both absolute HSR and HSR expressed as percentage of TD were higher before losing and winning a match compared to a draw (p < 0.05; ES = 0.72-0.98). Weekly TL seems to be slightly affected by match-related contextual variables, with special emphasis on the opponent standard and match outcome. Higher training volume was observed before and after playing against a top-level opponent, and after losing a match, whereas the volume of high-intensity training seems to be higher when preparing for a game against a top-level opponent. Future experimental research should clarify the interaction between match-related contextual variables (e.g., cause) and weekly TL (e.g., effect).

#11 Relative Age Effect in Collegiate Soccer: Influence of Nationality, Playing Position, and Class
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003356. [Epub ahead of print]
Authors: Hurley E, Comstock BA, Haile L, Beyer KS
Summary: The purpose of this study was to evaluate the existence of relative age effects (RAEs) in collegiate soccer. In addition, the impact of nationality, position, class, and National Collegiate Athletic Association (NCAA) tournament qualification status on the prevalence of RAEs was assessed. Birth dates from male NCAA Division I soccer athletes (n = 4,082) from the 2017/2018 season were categorized into quarters based on calendar and scholastic quarters. All athlete birth-date distributions were compared with the expected birth-date distributions for the United States. International-born athletes (INT) displayed a significant difference in birth-date distribution when assessed with calendar quarters, whereas American-born athletes (USA) showed a significant difference in birth-date distributions when assessed with scholastic quarters. Furthermore, INT showed significant RAEs for midfielders and defenders, whereas USA showed significant RAEs midfielders and goalkeepers. In terms of class, INT had significant RAEs for all classes, whereas USA had significant RAEs only for freshmen and sophomores. All INT had significant RAEs regardless of tournament qualification status; however, USA had significant RAEs only for nontournament teams. In summary, significant RAEs exist in male Division I college soccer; however, the presence of RAEs is influenced by nationality, position, class, and NCAA tournament qualification status. Coaches should be aware of RAEs during the recruitment process to avoid potential selection bias.

#12 High-intensity endurance capacity assessment as a tool for talent identification in elite youth female soccer
Reference: J Sports Sci. 2019 Aug 26:1-7. doi: 10.1080/02640414.2019.1656323. [Epub ahead of print]
Authors: Datson N, Weston M, Drust B, Gregson W, Lolli L
Summary: Talent identification and development programmes have received broad attention in the last decades, yet evidence regarding the predictive utility of physical performance in female soccer players is limited. Using a retrospective design, we appraised the predictive value of performance-related measures in a sample of 228 youth female soccer players previously involved in residential Elite Performance Camps (age range: 12.7-15.3 years). With 10-m sprinting, 30-m sprinting, counter-movement jump height, and Yo-Yo Intermittent Recovery Test Level 1 (IR1) distance as primary predictor variables, the Akaike Information Criterion (AIC) assessed the relative quality of four penalised logistic regression models for determining future competitive international squads U17-U20 level selection. The model including Yo-Yo IR1 was the best for predicting career outcome. Predicted probabilities of future selection to the international squad increased with higher Yo-Yo IR1 distances, from 4.5% (95% confidence interval, 0.8 to 8.2%) for a distance lower than 440 m to 64.7% (95% confidence interval, 47.3 to 82.1%) for a score of 2040 m. The present study highlights the predictive utility of high-intensity endurance capacity for informing career progression in elite youth female soccer and provides reference values for staff involved in the talent development of elite youth female soccer players.

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