Latest research in football - week 5 - 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 Iron, Hematological Parameters and Blood Plasma Lipid Profile in Vitamin D Supplemented and Non-Supplemented Young Soccer Players Subjected to High-Intensity Interval Training
Reference: J Nutr Sci Vitaminol (Tokyo). 2017;63(6):357-364. doi: 10.3177/jnsv.63.357.
Authors: Jastrzebska M, Kaczmarczyk M, Suarez AD, Sanchez GFL, Jastrzebska J, Radziminski L, Jastrzebski Z
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Summary: Vitamin D deficiency has been associated with increased risk for cardiovascular disease and anemia. Vitamin D-related changes in lipid profile have been studied extensively but the relationship between vitamin D and lipid metabolism is not completely understood. As both vitamin D and intermittent training may potentially affect iron and lipid metabolism, the aim of the study was to evaluate whether a daily supplementation of vitamin D can modulate the response of hematological and lipid parameters to high-intensity interval training (HIIT) in soccer players. Thirty-six young elite junior soccer players were included in the placebo-controlled, double-blind study. Participants were non-randomly allocated into either a supplemented group (SG, n=20, HIIT and 5,000 IU of vitamin D daily) or placebo group (PG, n=16, HIIT and sunflower oil). Hematological parameters were ascertained before and after the 8-wk training. The change score (post- and pre-training difference) was calculated for each individual and the mean change score (MCS) was compared between SG and PG using the t test and analysis of covariance. There were no differences between SG and PG at baseline. The red and white cell count, hemoglobin, hematocrit, MCHC, ferritin, and HDL-cholesterol changed significantly over the 8-wk HIIT. However, no significant differences in MCS were observed between SG and PG for any variable. A daily vitamin D supplement did not have any impact on alteration in hematological or lipid parameters in young soccer players in the course of high-intensity interval training.

#2 Impact of the EURO-2016 football cup on emergency department visits related to alcohol and injury
Reference: Eur J Public Health. 2018 Jan 15. doi: 10.1093/eurpub/ckx233. [Epub ahead of print]
Authors: Noel GN, Roch AR, Michelet PM, Boiron LB, Gentile SG, Viudes GV
Summary: In Marseille, the 2016 EURO football cup days were independently associated with a 43% increase in alcohol-related visits in the Emergency Department (ED). Patients admitted for alcohol consumption were younger (41 vs. 46.6;P < 0.001), more often male (82.8% vs. 60.1%; P < 0.001) and more often admitted as inpatients (24.0% vs. 16.5%; P = 0.03) than those admitted for injury. Unlike reported in previous studies, injury-related visits did not increase. This could be explained by coding practice variability between EDs (alcohol or injury). To account for this variability, both diagnosis groups must be separately included when using ED data for preparing and monitoring major gatherings.

#3 Exploring the effects of playing formations on tactical behaviour and external workload during football small-sided games
Reference: J Strength Cond Res. 2018 Jan 4. doi: 10.1519/JSC.0000000000002445. [Epub ahead of print]
Authors: Baptista J, Travassos B, Goncalves B, Mourao P, Viana JL, Sampaio J
Summary: This study aimed to identify the effects of playing formations on tactical behaviour and external workload during football small-sided games. Twenty-three semi-professional footballers integrated three different playing formations in a 7-a-side small-sided game, according to their specific player positions: team 4:3:0 (4 defenders, 3 midfielders); team 4:1:2 (4 defenders, 1 midfielder, 2 forwards); and team 0:4:3 (4 midfielders, 3 forwards). Based on players' movement trajectories, the following individual and collective tactical variables were calculated: total distance covered and distance covered while walking, jogging, running and sprinting, distance from each player to both own and opponent's team centroid (Dist CG and Dist OPP CG, respectively), individual area, team length, team width and surface area. Approximate entropy (ApEn) was computed to identify the regularity of each variable. The team 4:3:0 promoted players' space exploration with moderate physical efforts. The team 4:1:2 promoted compactness and regularity of the team with increase in the physical efforts. The team 0:4:3 promoted team balance and adaptability on space coverage with increase in physical efforts. Concluding, different playing formations support different game dynamics, and variations on external load were directly linked with the variations on tactical behaviour. The analysis tactical behaviour through quantification of variability of patterns of play and quantification of distance covered at different velocities were the most useful information for the analysis of the effects of practice task manipulations. Therefore, in a practical sense, strength and conditioning coaches should plan and monitor these tasks in interaction with the head coaches.

#4 The Importance of Strength and Power on Key Performance Indicators in Elite Youth Soccer
Reference: J Strength Cond Res. 2018 Jan 24. doi: 10.1519/JSC.0000000000002446. [Epub ahead of print]
Authors: Wing CE, Turner AN, Bishop CJ
Summary: The purpose of this investigation was to examine the importance of strength and power in relation to key performance indicators (KPI's) within competitive soccer match play. This was achieved through using an experimental approach where fifteen subjects were recruited from a professional soccer club's scholarship squad during the 2013/14 season. Following anthropometric measures, power and strength were assessed across a range of tests which included the squat jump (SJ), countermovement jump (CMJ), 20 metre (m) sprint and arrowhead change of direction test. A predicted 1-repetition maximum (RM) was also obtained for strength by performing a 3RM test for both the back squat and bench press and a total score of athleticism (TSA) was provided by summing z-scores for all fitness tests together, providing one complete score for athleticism. Performance analysis data was collected during 16 matches for the following KPIs: passing, shooting, dribbling, tackling and heading. Alongside this, data concerning player ball involvements (touches) was recorded. Results showed that there was a significant correlation (p < 0.05) between CMJ (r = 0.80), SJ (r = 0.79) and TSA (r = 0.64) in relation to heading success. Similarly, a significant correlation (p < 0.05) between predicted 1RM squat strength and tackle success (r = 0.61). These data supports the notion that strength and power training are important to soccer performance, particularly when players are required to win duels of a physical nature. There were no other relationships found between the fitness data and the KPI's recorded during match play which may indicate that other aspects of player's development such as technical skill, cognitive function and sensory awareness are more important for soccer-specific performance.

#5 The Effect of Heat Stress on Measures of Running Performance and Heart Rate Responses During A Competitive Season in Male Soccer Players
Reference: J Strength Cond Res. 2018 Jan 24. doi: 10.1519/JSC.0000000000002441. [Epub ahead of print]
Authors: Coker NA, Wells AJ, Gepner Y
Summary: Measures of running performance (RP) and heart rate responses (HR) to matchplay during three different heat stress (HS) conditions were assessed in seven National Collegiate Athletic Association (NCAA) Division I male soccer players. Total distance (TD), as well as distance covered within distinct velocity zones [walking (WALK), jogging (JOG), low speed running (LSR), high-speed running (HSR), sprinting (SPRINT), low-intensity running (LIR), and high-intensity running (HIR)] were assessed using GPS units over 12 matches. HS was monitored during each match, and matches were defined as low (HSlow, n=4), moderate (HSmod, n=4), or high (HShigh, n=4) HS. Minutes played were significantly different across HS conditions (p=0.03). Therefore, distance covered within each movement velocity was assessed relative to minutes played, and as a percentage of total playing time. WALKrel was significantly greater during HShigh compared to HSlow (p=0.035). LIRrel was significantly greater during HSmod (p=0.015) compared to HSlow. A trend was observed for %WALK being higher during HShigh compared to HSlow (p=0.066). %LIR was significantly greater during HShigh compared to HSlow (p=0.048). HIR was not significantly different across HS conditions. Percent of time spent >85% HRmax was significantly greater during HShigh (p=0.002) and HSmod (p<0.001) compared to HSlow. Percent of time spent between 65-84% HRmax was significantly greater during HSlow compared to HShigh (p<0.001). Results indicate that HS resulted in increased LIR and %HR≥85, while HIR was maintained. HIR performance may be conserved through decreased playing time and/or the adoption of pacing strategies. This may assist coaches in altering player management strategies to optimize team performance.

#6 Combined Anterolateral, Anterior, and Anteromedial Ankle Impingement in an Adolescent Soccer Player-A Case Report and Review of the Literature
Reference: Clin J Sport Med. 2018 Jan 24. doi: 10.1097/JSM.0000000000000576. [Epub ahead of print]
Authors: Cosma DI, Vasilescu DE, Corbu A, Todor A, Valeanu M, Ulici A
Summary: A unique case of combined anterolateral, anterior, and anteromedial ankle impingement in an adolescent soccer player is presented in this article. To the best of our knowledge, this is the only report of circumferential, massive, anterior ankle impingement in children described in the literature. The importance of proper diagnosis and treatment of such a lesion is illustrated in this case report. We also emphasize that clinical examination combined with 3D computed tomography scan reconstruction is an excellent and cost-effective imaging modality that can help with the diagnosis of anterior ankle impingement. Finally, open surgical treatment showed excellent results in an elite athlete.

#7 Match Situations Leading to Head Injuries in Professional Male Football (Soccer)-A Video-based Analysis Over 12 Years
Reference: Clin J Sport Med. 2018 Jan 19. doi: 10.1097/JSM.0000000000000572. [Epub ahead of print]
Authors: Beaudouin F, Aus der Funten K, Troß T, Reinsberger C, Meyer T
Summary: The purpose was to identify risk situations promoting head injuries in professional male football (soccer) and to investigate the impact of a rule change in 2006 punishing elbow-head contacts. Professional football players of the first male German Bundesliga participated in this study.  Observational criteria of head impacts on video recordings (players' actions preceding head injuries, foul play-referee's decision and assessment of rater, ball possession, on-pitch medical treatment, and consequences of head impact). Three hundred thirty-four head injuries were reported in kicker Sportmagazin corresponding to an incidence rate of 2.25 (95% confidence interval 2.01-2.51) per 1000 player match hours. The injured player predominantly jumped (60%), headed the ball (36%), or ran forwards (20%); the noninjured players mainly jumped (64%), headed the ball (27%), or raised the elbow to the head (23%). Free ball situations (2 players challenge for the ball) caused most of the head injuries (81%). The players' action "raising the elbow" during a head injury seemed to be lower after the rule change. Jumping for the ball with the intention of heading is the predominant action associated with head injury risk. Head injuries occur most often when players challenge for the ball in a header duel. As head injuries bear the potential risk of long-term health sequelae, the identification of situational circumstances is essential to develop preventative means in the future.

#8 Linear Acceleration in Direct Head Contact Across Impact Type, Player Position, and Playing Scenario in Collegiate Women's Soccer
Reference: J Athl Train. 2018 Jan 26. doi: 10.4085/1062-6050-90-17. [Epub ahead of print]
Authors: Caccese JB, Lamond LC, Buckley TA, Glutting J, Kaminski TW
Summary: Heading, an integral component of soccer, exposes athletes to a large number of head impacts over a career. The literature has begun to indicate that cumulative exposure may lead to long-term functional and psychological deficits. Quantifying an athlete's exposure over a season is a first step in understanding cumulative exposure. The objective was to measure the frequency and magnitude of direct head impacts in collegiate women's soccer across impact type, player position, and game or practice scenario. Twenty-three collegiate women's soccer athletes participated in this study. Athletes wore Smart Impact Monitor accelerometers during all games and practices Impacts were classified during visual, on-field monitoring of athletic events. All direct head impacts that exceeded the 10 g threshold were included in the final data analysis. The dependent variable was linear acceleration, and the fixed effects were (1) type of impact: clear, pass, shot, unintentional deflection, or head-to-head contact; (2) field position: goalkeeper, defense, forward, or midfielder; (3) playing scenario: game or practice. Shots (32.94 g ± 12.91 g, n = 38, P = .02) and clears (31.09 g ± 13.43 g, n = 101, P = .008) resulted in higher mean linear accelerations than passes (26.11 g ± 15.48 g, n = 451). Head-to-head impacts (51.26 g ± 36.61 g, n = 13, P < .001) and unintentional deflections (37.40 g ± 34.41 g, n = 26, P = .002) resulted in higher mean linear accelerations than purposeful headers (ie, shots, clears, and passes). No differences were seen in linear acceleration across player position or playing scenario. Nonheader impacts, including head-to-head impacts and unintentional deflections, resulted in higher mean linear accelerations than purposeful headers, including shots, clears, and passes, but occurred infrequently on the field. Therefore, these unanticipated impacts may not add substantially to an athlete's cumulative exposure, which is a function of both frequency and magnitude of impact.

#9 Preseason Maximal Aerobic Power in Professional Soccer Players Among Different Divisions
Reference: J Strength Cond Res. 2018 Feb;32(2):356-363. doi: 10.1519/JSC.0000000000001810.
Authors: Marcos MA, Koulla PM, Anthos ZI
Summary: The purpose of this study was to examine and compare the anthropometric, maximal oxygen uptake (V[Combining Dot Above]O2max), and positional differences of first division (D1) professional football players from players of second (D2) and third (D3) divisions in Cyprus football leagues. Four hundred twenty-one professional male football players participated in this study. All subjects underwent anthropometric and body composition evaluation. In addition, they performed an incremental cardiopulmonary exercise testing (CPET) on a treadmill for V[Combining Dot Above]O2max evaluation. The results were analyzed using 1-way analysis of variance, between subjects design revealing significant effects among the divisions. Tukey's honest significant difference (HSD) tests demonstrated that players from D1 scored significantly higher on V[Combining Dot Above]O2max and lasted significantly longer on the treadmill than participants of D2 and D3 (p ≤ 0.05). Similar findings were demonstrated when D2 was contrasted against D3 players. Goalkeepers, defenders, and forwards demonstrated significantly higher anthropometric measurements, whereas wingers and midfielders demonstrated significantly higher V[Combining Dot Above]O2max (p ≤ 0.05) than goalkeepers and defenders. The findings of this study clearly demonstrated that cardiovascular fitness, as determined by CPET, is an important fitness parameter that differentiates professional football players who play at a more advanced level. This could be attributed to the different seasonal schedules that allow for longer transition time for lower division players and thus favoring greater detraining effects. Emphasis should be given by fitness professionals on transition period training to minimize the detraining effects especially in lower divisions.

#10 Performance Differences Among Skilled Soccer Players of Different Playing Positions During Vertical Jumping and Landing
Reference: J Strength Cond Res. 2018 Feb;32(2):304-312. doi: 10.1519/JSC.0000000000002343.
Authors: Harry JR, Barker LA, James R, Dufek JS
Summary: Both jumping and landing performance of skilled soccer players is diminished when task demands are increased. However, it is unclear if performance changes are specific to players of certain playing positions. Therefore, we assessed jumping and landing performance among skilled soccer players of different playing positions. Twenty-five National Collegiate Athletic Association (NCAA) Division 1 male soccer players (179.5 ± 7.8 cm, 75.5 ± 7.1 kg, 19.7 ± 1.2 years) performed maximum effort vertical jump landings (VJLs), whereas vertical ground reaction force (vGRF) data were obtained. Participants were stratified into goalkeeping (GK), defensive (DEF), midfield (MID), and attacking (ATT) group according to their primary playing position. One-way analyses of variance (α = 0.05) and effect sizes (ESs; large ≥ 0.80) were used to compare differences among groups. The jumping phase variables evaluated were jump height, unloading and amortization vGRF magnitudes, eccentric rate of force development, and the reactive strength index. Landing phase variables included the peak vGRF magnitude, vGRF loading rate, vGRF attenuation rate, and landing time. No statistically significant differences were detected for any jumping or landing variable (p ≥ 0.05). However, a number of large magnitude differences were detected during landing after ES calculations. Specifically, greater peak vGRF magnitudes were detected in DEF vs. both MID (ES = 1.08) and ATT (ES = 0.93), a greater vGRF loading rate occurred in DEF vs. MID (ES = 0.93), and a greater vGRF attenuation rate occurred in DEF vs. both MID (ES = 1.00) and AT (ES = 0.80). It is concluded that highly skilled soccer players possess position-specific abilities with respect to the landing phase of VJL. Skilled soccer players might experience enhanced training outcomes after VJL training regimens tailored to the specific demands of their primary playing position.

#11 Importance of Speed and Power in Elite Youth Soccer Depends on Maturation Status
Reference: J Strength Cond Res. 2018 Feb;32(2):297-303. doi: 10.1519/JSC.0000000000002367.
Authors: Murtagh CF, Brownlee TE, OʼBoyle A, Morgans R, Drust B, Erskine RM
Summary: Importance of speed and power in elite youth soccer depends on maturation status. J Strength Cond Res 32(2): 297-303, 2018-Maturation status is a confounding factor when identifying talent in elite youth soccer players (ESP). By comparing performance of ESP and control participants (CON) matched for maturation status, the aims of our study were to establish the importance of acceleration, sprint, horizontal-forward jump, and vertical jump capabilities for determining elite soccer playing status at different stages of maturation. Elite youth soccer players (n = 213; age, 14.0 ± 3.5 years) and CON (n = 113; age, 15.0 ± 4.4 years) were grouped using years from/to predicted peak height velocity (PHV) to determine maturation status (ESP: pre-PHV, n = 100; mid-PHV, n = 25; post-PHV, n = 88; CON: pre-PHV, n = 44; mid-PHV, n = 15; post-PHV, n = 54). Participants performed 3 reps of 10- and 20-m sprint, bilateral vertical countermovement jump (BV CMJ), and bilateral horizontal-forward CMJ (BH CMJ). Elite youth soccer players demonstrated faster 10-m (p < 0.001) and 20-m sprint (p < 0.001) performance than CON at all stages of maturation. Mid-PHV and post-PHV ESP achieved greater BV CMJ height (p < 0.001) and BH CMJ distance (ESP vs. CON; mid-PHV: 164.32 ± 12.75 vs. 136.53 ± 21.96 cm; post-PHV: 197.57 ± 17.05 vs. 168.06 ± 18.50 cm; p < 0.001) compared with CON, but there was no difference in BV or BH CMJ between pre-PHV ESP and CON. Although 10 and 20 m and sprint performance may be determinants of elite soccer playing status at all stages of maturation, horizontal-forward and vertical jumping capabilities only discriminate ESP from CON participants at mid- and post-PHV. Our data therefore suggest that soccer talent identification protocols should include sprint, but not jump assessments in pre-PHV players.

#12 Direct player observation is needed to accurately quantify heading frequency in youth soccer
Reference: Res Sports Med. 2018 Jan 24:1-8. doi: 10.1080/15438627.2018.1431534. [Epub ahead of print]
Authors: Harriss A, Walton DM, Dickey JP
Summary: In soccer, heading may be related to subsequent neurological impairment. Accurate measures of heading exposure are therefore important. This study evaluated whether 12 female youth players accurately recalled their average number of headers over an entire soccer season (20 games total). Their self-reported average number of headers per game was multiplied by the number of games that they participated in, and were compared to actual number of headers extracted from game video. All players overestimated the number of headers compared to game video. Linear regression analysis indicated that self-reported headers overestimated the number of headers by 51%. While self-reports are a convenient way to estimate heading behaviour, they do not accurately represent the number of headers that players perform. Self-reports of heading exposure should be interpreted with caution.

#13 Dietary habits and energy balance in an under 21 male international soccer team
Reference: Res Sports Med. 2018 Jan 25:1-10. doi: 10.1080/15438627.2018.1431537. [Epub ahead of print]
Authors: Caruana Bonnici D, Akubat I, Greig M, Sparks A, Mc Naughton LR
Summary: Soccer presents a metabolic challenge which is not necessarily matched by players' habitual dietary intake. To examine the effects of a bespoke diet, 22 players completed the Ball Sport Endurance and Sprint Test (BEAST90mod) protocol, followed by 4 days of regulated nutritional intake. The diet consisted of 10 g∙kg-1 body mass (BM) and 1.7 g∙kg-1 BM of carbohydrate and protein, respectively. On day 5, players followed a prematch nutritional strategy of 7 g∙kg-1 BM of carbohydrate and 1 g∙kg-1 BM of protein divided into three meals and then repeated the BEAST90mod. The players' pre-intervention intake consisted of 49 ± 7.1% or 3.5 g ± 1.0 g∙kg-1 BM for carbohydrate and 19 ± 3.8% of total daily energy intake or 1.3 g ± 0.5 g∙kg-1 BM for protein. Following the tailor-made dietary intervention, players ran an additional 887 ± 233 m (8.1%; d = 2.4). An acute dietary intervention provided a positive effect on a valid simulated soccer match play test.

American Football
#1 Fatal Exertional Heat Stroke and American Football Players: The Need for Regional Heat-Safety Guidelines
Reference: J Athl Train. 2018 Jan 13. doi: 10.4085/1062-6050-445-16. [Epub ahead of print]
Authors: Grundstein AJ, Hosokawa Y, Casa DJ
Summary: Weather-based activity modification in athletics is an important way to minimize heat illnesses. However, many commonly used heat-safety guidelines include a uniform set of heat-stress thresholds that do not account for geographic differences in acclimatization. The purpose was to determine if heat-related fatalities among American football players occurred on days with unusually stressful weather conditions based on the local climate and to assess the need for regional heat-safety guidelines. Incidents of fatal exertional heat stroke (EHS) in American football players were obtained from the National Center for Catastrophic Sport Injury Research 5 and the Korey Stringer Institute. Sixty-one American football players at all levels of competition with fatal EHSs from 1980 to 2014. We used the wet-bulb globe temperature (WBGT) and a z-score WBGT standardized to local climate conditions from 1991 to 2010 to assess the absolute and relative magnitudes of heat stress, respectively. We observed a poleward decrease in exposure WBGTs during fatal EHSs. In milder climates, 80% of cases occurred at above-average WBGTs, and 50% occurred at WBGTs greater than 1 standard deviation from the long-term mean; however, in hotter climates, half of the cases occurred at near-average or below-average WBGTs. The combination of lower exposure WBGTs and frequent extreme climatic values in milder climates during fatal EHSs indicates the need for regional activity-modification guidelines with lower, climatically appropriate weather-based thresholds. Established activity-modification guidelines, such as those from the American College of Sports Medicine, work well in the hotter climates, such as the southern United States, where hot and humid weather conditions are common.

#2 Balance Regularity Among Former High School Football Players With or Without a History of Concussion
Reference: J Athl Train. 2018 Jan 13. doi: 10.4085/1062-6050-326-16. [Epub ahead of print]
Authors: Schmidt JD, Terry DP, Ko J, Newell KM, Miller LS
Summary: Subclinical postural-control changes may persist beyond the point when athletes are considered clinically recovered postconcussion. The purpose was to compare postural-control performance between former high school football players with or without a history of concussion using linear and nonlinear metrics. A total of 11 former high school football players (age range, 45-60 years) with 2 or more concussions and 11 age- and height-matched former high school football players without a history of concussion. No participant had college or professional football experience. Participants completed the Sensory Organization Test. We compared postural control (linear: equilibrium scores; nonlinear: sample and multiscale entropy) between groups using a 2 × 3 analysis of variance across conditions 4 to 6 (4: eyes open, sway-referenced platform; 5: eyes closed, sway-referenced platform; 6: eyes open, sway-referenced surround and platform). We observed a group-by-condition interaction effect for medial-lateral sample entropy ( F2,40 = 3.26, P = .049, ηp2 = 0.140). Participants with a history of concussion presented with lower medial-lateral sample entropy values (0.90 ± 0.41) for condition 5 than participants without a history of concussion (1.30 ± 0.35; mean difference = -0.40; 95% confidence interval [CI] = -0.74, -0.06; t20 = -2.48, P = .02), but conditions 4 (mean difference = -0.11; 95% CI: -0.37, 0.15; t20 = -0.86, P = .40) and 6 (mean difference = -0.25; 95% CI: -0.55, 0.06; t20 = -1.66, P = .11) did not differ between groups. Postconcussion deficits, detected using nonlinear metrics, may persist long after injury resolution. Subclinical concussion deficits may persist for years beyond clinical concussion recovery.


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