Latest research in football - week 52 - 2018

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 field-based fitness tests in youth soccer players
Reference: Eur J Sport Sci. 2018 Dec 27:1-12. doi: 10.1080/17461391.2018.1556739. [Epub ahead of print]
Authors: Dugdale JH, Arthur CA, Sanders D, Hunter AM
Summary: This study aimed to establish between-day reliability and validity of commonly used field-based fitness tests in youth soccer players of varied age and playing standards, and to discriminate between players without ("unidentified") or with ("identified") a direct route to professional football through their existing club pathway. Three-hundred-and-seventy-three Scottish youth soccer players (U11-U17) from three different playing standards (amateur, development, performance) completed a battery of commonly used generic field-based fitness tests (grip dynamometry, standing broad jump, countermovement vertical jump, 505 (505COD) and T-Drill (T-Test) change of direction and 10/20 m sprint tests) on two separate occasions within 7-14 days. The majority of field-based fitness tests selected within this study proved to be reliable measures of physical performance (ICC = 0.83-0.97; p < .01). However, COD tests showed weaker reliability in younger participants (ICC = 0.57-0.79; p < .01). The field-based fitness testing battery significantly discriminated between the unidentified and identified players; χ2 (7) = 101.646, p < .001, with 70.2% of players being correctly classified. We have shown field-based fitness tests to be reliable measures of physical performance in youth soccer players. However, results from the 505COD and T-Test change of direction tests may be more variable in younger players, potentially due to complex demands of these tests and the limited training age established by these players. While the testing battery selected in this study was able to discriminate between unidentified and identified players, findings were inconsistent when attempting to differentiate between individual playing standards within the "identified" player group (development vs. performance).

#2 Factors influencing hydration status during a National Collegiate Athletics Association division 1 soccer preseason
Reference: J Sci Med Sport. 2018 Dec 14. pii: S1440-2440(18)31245-3. doi: 10.1016/j.jsams.2018.12.005. [Epub ahead of print]
Authors: Sekiguchi Y, Adams WM, Curtis RM, Benjamin CL, Casa DJ
Summary: The purpose was to investigate the roles that training load and environmental conditions have on fluid balance during a collegiate men's soccer preseason. Twenty-eight male collegiate soccer players (mean±SD; age, 20±1.7y; body mass (BM), 79.9±7.3kg; height, 180.9±6.8cm; body fat, 12.7±3.1%; VO2max, 50.7±4.3ml·kg-1·min-1) participated in this study. Prior to (PRE) and following (POST) each team session, BM, percent BM loss (%BML) and hydration status was measured. Participants donned a heart rate and GPS enabled monitor to measure training load. For all team activities, ambient temperature (TAMB) and relative humidity (RH) were obtained from the nearest local weather station. Participants consumed 500mL of water as part of the team-based hydration strategy before and after training session. Stepwise linear regression was used to identify the variables that predicted %BML. Significance was set a-priori p<0.05. Total distance covered predicted %BML during all preseason activities (r2=0.253, p<0.001), with TAMB and RH further adding to the model (r2=0.302, p<0.001). %BML never exceeded 2% of BM during any one session and daily variation in BM was <1% from baseline measures. Urine specific gravity was greater than 1.020 on 12/15days and UCOL was above 4 on 13/15days, indicating a state of hypohydration. Total distance covered was the best predictor for the extent of body water losses during a collegiate preseason. While the team-based hydration strategy during preseason was successful in minimizing fluid losses during activity, participants arrived hypohydrated 80% of the time, necessitating a greater focus on daily fluid needs.

#3 Assessing the validity of a video-based decision-making assessment for talent identification in youth soccer
Reference: J Sci Med Sport. 2018 Dec 21. pii: S1440-2440(18)30435-3. doi: 10.1016/j.jsams.2018.12.011. [Epub ahead of print]
Authors: Bennett KJM, Novak AR, Pluss MA, Coutts AJ, Fransen J
Summary: The aim was to investigate the construct and discriminant validity of a video-based decision-making assessment for talent identification in youth soccer. A total of 328 academy youth soccer players (tier one, tier two, and tier three) from three developmental stages (late childhood, early adolescence, and mid-adolescence) participated in this study. The control group consisted of 59 youth athletes with no soccer experience in the last five years. Players completed a video-based decision-making assessment on an iPad, with response accuracy and response time recorded for various attacking situations (2 vs. 1, 3 vs. 1, 3 vs. 2, 4 vs. 3, and 5 vs. 3). The video-based decision-making assessment showed some construct validity. Response times were significantly faster in early and mid-adolescent players when compared to those in the late childhood group. Furthermore, an overall decline in decision-making performance (i.e. decrease in response accuracy and increase in response time) was observed from the 2 vs. 1 to the 4 vs. 3 situations. The video-based decision-making assessment lacked discriminant validity as minimal differences between academies were evident for response accuracy and response time. Only response accuracy was able to discriminate youth academy soccer players from the control group to some extent. Coaches and sporting professionals should apply caution when interpreting data from practical, video-based decision-making assessments. There is currently limited conclusive evidence supporting the effectiveness of these assessments for talent identification.

#4 Influences of Synchronized Metronome Training on Soccer Players' Timing Ability, Performance Accuracy, and Lower-Limb Kinematics
Reference: Front Psychol. 2018 Dec 7;9:2469. doi: 10.3389/fpsyg.2018.02469. eCollection 2018.
Authors: Rönnqvist L, McDonald R, Sommer M
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Summary: Planning and performance of all complex movement requires timing, integration, and coordination between sensory-perception and motor production to be successful. Despite this, there is limited research into "if" and "how" timing training may influence movement performance in athletes. The aim of the present study was to investigate the effect of synchronized metronome training (SMT) on sensorimotor timing ability, and in view of that, if improved timing may be transferred to lower-limb movement planning, precision performance, and kinematics. The sample consisted of 24 female elite- and semi-elite soccer players, randomly assigned to receive SMT and a control group. The SMT group received 12 sessions of Interactive Metronome® (IM) training over 4 weeks. At pre- and post-test, timing-precision was assessed through hand and feet movement synchronization with rhythmic sound; and leg-movements performance accuracy, duration, and kinematics were recorded during embodied high cognitive-load stepping task (6 trials×20 s) by use of a optoelectronic motion capture system. Pre- to post-test comparisons showed significant timing improvements as an effect of the IM training. Significant pre- to post-test improvements on the stepping task performance were seen in an increasing number of accurate foot taps during the stepping task sequence and by shorter duration for the SMT-group only. No evident pre- to post-test effects of SMT on the kinematic parameters investigated were found. These findings signify that the guided attention and working-memory functioning may be positively affected by SMT training; thereby, resulting in better motor planning, performance, and movement precision. Still, independent of group and test-occasion, significant correlations were found between the participants' outcome performance differences and the kinematic parameters. It was found that a decreasing 3D movement distance and less segmented movements correlating negatively, and increasing velocity (speed) positively, with accuracy and performance duration, respectively. These findings are likely associated with inter-individual variations in the nature of higher-order cognitive processing capacity due to the highly cognitive demanding stepping task.

#5 Amyotrophic Lateral Sclerosis and soccer: an internet survey of 29 Italian players
Reference: Ann Ist Super Sanita. 2018 Oct-Dec;54(4):364-369. doi: 10.4415/ANN_18_04_14.
Authors: Vanacore N, Barbariol P, Caffari B, Lacorte E, Bacigalupo I, Spila Alegiani S
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Summary: Previous epidemiological studies reported a significantly higher risk of Amyotrophic Lateral Sclerosis (ALS) in Italian male soccer players. As a consequence, sports newspapers and news agencies focused on this issue and spread the news of 51 male soccer players with a reported diagnosis of ALS. We searched news on male Italian national soccer players with a reported diagnosis of ALS quoted from January 1, 1950 to July 31, 2016 in at least two Internet web sites or in books by journalists. A total of 39 male soccer players with a reported diagnosis of ALS were identified. Subjects were born from 1905 to 1973, 32 were currently deceased, 6 were still living, while the status of 1 player was unknown. All gathered information was available for 29 soccer players. The group had a mean age at diagnosis of 45.3 ± 12.2 years, a mean age at onset of symptoms of 46.4 ± 12.1 years, and a mean age at death of 50.9 ± 12.3 years. A significant inverse correlation between year of birth and age at onset of symptoms was observed, with a younger age at onset of symptoms in soccer players born in more recent years (r = -0.65, p < 0.01). Italian male soccer players with a reported diagnosis of ALS have a significantly younger age at diagnosis when compared to other European patients with ALS. Results support a possible relationship between soccer and the risk of ALS. We believe that further research is urgently needed in this field.

#6 Dark Chocolate Intake Positively Modulates Redox Status and Markers of Muscular Damage in Elite Football Athletes: A Randomized Controlled Study
Reference: Oxid Med Cell Longev. 2018 Nov 21;2018:4061901. doi: 10.1155/2018/4061901. eCollection 2018.
Authors: Cavarretta E, Peruzzi M, Del Vescovo R, Di Pilla F, Gobbi G, Serdoz A, Ferrara R, Schirone L, Sciarretta S, Nocella C, De Falco E, Schiavon S, Biondi-Zoccai G, Frati G, Carnevale R
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Summary: Intensive physical exercise may cause increase oxidative stress and muscular injury in elite football athletes. The aim of this study was to exploit the effect of cocoa polyphenols on oxidative stress and muscular injuries induced by intensive physical exercise in elite football players. Oxidant/antioxidant status and markers of muscle damage were evaluated in 24 elite football players and 15 controls. Furthermore, the 24 elite football players were randomly assigned to either a dark chocolate (>85% cocoa) intake (n = 12) or a control group (n = 12) for 30 days in a randomized controlled trial. Oxidative stress, antioxidant status, and muscle damage were assessed at baseline and after 30 days of chocolate intake. Compared to controls, elite football players showed lower antioxidant power and higher oxidative stress paralleled by an increase in muscle damage markers. After 30 days of dark chocolate intake, an increased antioxidant power was found in elite athletes assuming dark chocolate. Moreover, a significant reduction in muscle damage markers (CK and LDH, p < 0.001) was observed. In the control group, no changes were observed with the exception of an increase of sNox2-dp, H2O2, and myoglobin. A simple linear regression analysis showed that sNox2-dp was associated with a significant increase in muscle damage biomarker release (p = 0.001). An in vitro study also confirmed that polyphenol extracts significantly decreased oxidative stress in murine myoblast cell line C2C12-derived. These results indicate that polyphenol-rich nutrient supplementation by means of dark chocolate positively modulates redox status and reduced exercise-induced muscular injury biomarkers in elite football athletes.

#7 "Macro-structure" of developmental participation histories and "micro-structure" of practice of German female world-class and national-class football players
Reference: J Sports Sci. 2018 Dec 24:1-9. doi: 10.1080/02640414.2018.1558744. [Epub ahead of print]
Authors: Güllich A
Summary: The study examined the "micro-structure" of football practice and the "macro-structure" of participation history of female professional football players. Participants were 29 German 1st league (Bundesliga) players, 14 of whom played on the senior national team (Olympic Champion in 2016). A questionnaire recorded the players' positions, proportions of physical conditioning, drill-type skill exercises and playing forms within coach-led football practice, and the volume of coach-led practice and peer-led play, in both football and other sports, from childhood to adulthood. Analyses revealed that most athletes played various attacker and defender positions during development. National team players differed from their Bundesliga peers by less physical conditioning and greater proportions of playing forms within football practice. National team players also accumulated less total football practice until age 18 years, but more peer-led football and coach-led practice in other sports compared to their Bundesliga counterparts. Based on these variables, a binary logistic regression classified 93% of the national team and Bundesliga players correctly. Conclusion: A combination of long-term coach-led football practice involving a relatively large proportion of playing forms with considerable childhood/adolescent peer-led football play and coach-led practice in other sports may have facilitated adult performance among German female world-class football players.

#8 Comparison of head impact exposure in practice drills among multiple youth football teams
Reference: J Neurosurg Pediatr. 2018 Dec 21:1-9. doi: 10.3171/2018.9.PEDS18314. [Epub ahead of print]
Authors: Kelley ME, Espeland MA, Flood WC, Powers AK, Whitlow CT, Maldjian JA, Stitzel JD, Urban JE
Summary: Limiting contact in football practice can reduce the number of head impacts a player receives, but further research is needed to inform the modification of optimal drills that mitigate head impact exposure (HIE) while the player develops the skills needed to safely play the game. This study aimed to compare HIE in practice drills among 6 youth football teams and to evaluate the effect of a team on HIE. On-field head impact data were collected from athletes (ages 10-13 years) playing on 6 local youth football teams (teams A-F) during all practices using the Head Impact Telemetry System. Video was recorded and analyzed to verify and assign impacts to a specific drill. Drills were identified as follows: dummy/sled tackling, half install, install, install walk through, multiplayer tackle, Oklahoma, one-on-one, open field tackling, other, passing, position skill work, scrimmage, special teams, tackling drill stations, and technique. HIE was quantified in terms of impacts per player per minute (ppm) and peak linear and rotational head acceleration. Generalized linear models were used to assess differences in head impact magnitude and frequency among drills as well as among teams within the most common drills. Among 67 athlete-seasons, a total of 14,718 impacts during contact practices were collected and evaluated in this study. Among all 6 teams, the mean linear (p < 0.0001) and rotational (p < 0.0001) acceleration varied significantly among all drills. Open field tackling had significantly (p < 0.001) higher mean linear acceleration than all other drills. Multiplayer tackle had the highest mean impact rate (0.35 ppm). Significant variations in linear acceleration and impact rate were observed among teams within specific drills. Team A had the highest mean linear acceleration in install, one-on-one, and open field tackling and the highest mean impact rate in Oklahoma and position skill work. Although team A spent the greatest proportion of their practice on minimal- or no-player versus player contact drills (27%) compared to other teams, they had the highest median (20.2g) and 95th percentile (56.4g) linear acceleration in practice. Full-speed tackling and blocking drills resulted in the highest HIE. Reducing time spent on contact drills relative to minimal or no contact drills may not lower overall HIE. Instead, interventions such as reducing the speed of players engaged in contact, correcting tackling technique, and progressing to contact may reduce HIE more effectively.

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