Latest research in football - week 20 - 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 Risk Factors for Groin Injury and Symptoms in Elite Level Soccer Players: A Cohort Study in the Dutch Professional Leagues
Reference: J Orthop Sports Phys Ther. 2018 May 23:1-30. doi: 10.2519/jospt.2018.7990. [Epub ahead of print]
Authors: Langhout R, Tak I, van Beijsterveldt AM, Ricken M, Weir A, Barendrecht M, Kerkhoffs G, Stubbe J
Summary: Groin injury and symptoms are common in soccer players. Their relationship with reduced hip range of motion (ROM) and previous injury is unclear. The purpose was to conduct a retrospective assessment of associations between previous injury and pre-season hip ROM and pre-season prevalence of severe groin symptoms; and prospective identification of risk factors for within-season groin injury. During 2015-2016, 190 players from 9 Dutch professional soccer clubs participated. Univariate and multivariate logistic regression were used to predict pre-season severe groin symptoms, identified using the Copenhagen Hip And Groin Outcome Score, from a history of previous groin injury, general injury (minimum 1 week duration) in previous season, and hip ROM. Cox regression was used to predict within-season groin injury. Point-prevalence of severe groin symptoms was 24% and within-season incidence of groin injury 11%. Total/training/match groin injury incidence was 0.5/0.2/2.6 injuries/1000 playing hours. A history of more than 1 previous groin injury was associated with current severe groin symptoms (Odds Ratio=3.0; 95% CI=1.0, 8.3; P=.038). General injury sustained in the previous season (ankle, knee, thigh, shoulder; median 9 weeks time-loss) was a risk factor for groin injury (Hazard Ratio=5.1; 95% CI=1.1, 14.6; P=.003). Severe injuries in the previous season to locations other than the groin increase the risk of groin injury the next season. A history of groin injury is associated with current severe groin symptoms. Pre-season hip ROM does not identify players at risk for groin injury.

#2 Talent identification for soccer: Physiological aspects
Reference: J Sci Med Sport. 2018 Jan 31. pii: S1440-2440(18)30027-6. doi: 10.1016/j.jsams.2018.01.009. [Epub ahead of print]
Authors: Dodd KD, Newans TJ
Summary: Soccer coaches are always looking to discover the next star player, without investing the necessary resources, time, and effort into a player's development. In the modern era, talent identification in soccer seems to be a comparative process rather than a developmental process. This article will look at the physiological profiles of soccer players in the modern era and how testing and talent identification processes should coincide with this data. An extensive literature search identifying the physiological attributes of soccer players that are required to compete at an elite level was conducted. An examination of the methods to test these attributes was also conducted. Studies were assigned into three areas to understand the physiological aspect of soccer: physiological testing methods, benchmark values, and correlations between different tests. A testing battery was established to test the key physiological attributes of prospective youth soccer players. Benchmark levels were also identified to allow coaches to understand areas of improvement. Using a physiological testing battery will allow teams to track their players' progress throughout their developmental years. This allows coaches to consistently identify a player's strengths and weaknesses, as well as allow players who may experience late maturation to still be identified.

#3 Influence of Team's Rank on Soccer Referees' External and Internal Match Loads During Official Matches
Reference: J Strength Cond Res. 2018 Jun;32(6):1715-1722. doi: 10.1519/JSC.0000000000002040.
Authors: Castillo D, Castagna C, Camara J, Iturricastillo A, Yanci J
Summary: The aim was to examine the external and the internal match loads (ML) of field referees (FRs) attending teams of different ranking during championship matches. Twenty FR who officiated in 30 official soccer matches (30 observations) participated in our study. The criteria for allocating the soccer referees' ML results were based on the teams' final league positions as follows: matches performed by Top 10 teams (TOP10), matches performed by bottom 10 teams (BOT10), and matches played among TOP10 and BOT10 teams (MIXED). External (match activities, accelerations [Acc], and decelerations [Dec]) and internal MLs (Edwards' heart rate [HR]-derived training impulse [TRIMPEDW], HRmean expressed as a percentage of HRpeak [%HRpeak], and differentiated rating of perceived exertion [dRPE]) were recorded. The main results showed that FR, who officiated TOP10 matches, covered more distance at a low walking speed (<3.6 km·h) and performed a higher percentage of high-intensity accelerations and decelerations than those FR who officiated lower ranked teams' matches. Moreover, FR who officiated MIXED matches registered lower values of TRIMPEDW MLs and %HRpeak and declared higher respiratory (sRPEres ML) and muscular (sRPEmus ML) perceived MLs during the second half. Considering those FR who officiate matches between teams of a higher competitive level will need to produce higher match responses, especially regarding the percentage of distance covered at high intensity, accelerations, and decelerations; physical trainers of soccer referees at a high competitive level should implement these high-intensity short-term actions in specific training regimes.

#4 Association of Physical and Technical Activities With Partial Match Status in a Soccer Professional Team
Reference: J Strength Cond Res. 2018 Jun;32(6):1708-1714. doi: 10.1519/JSC.0000000000002033.
Authors: Moalla W, Fessi MS, Makni E, Dellal A, Filetti C, Di Salvo V, Chamari K
Summary: The purpose of this study was to examine the association between physical and technical activities and partial match status (winning, drawing, or losing) in a professional soccer team over 2 seasons. Physical and technical activities of 52 official matches were collected and analyzed at each 15-minute interval, for each half (45 minutes), and full match (90 minutes) using a multiple-camera computerized tracking system. The results indicated that according to full match outcome: winning status was characterized by players covering more total distance (p ≤ 0.05) and low-intensity running (<14.4 km·h) (p ≤ 0.05), whereas, losing status induced more sprinting (≥25.2 km·h) (p < 0.01) and high-intensity running (≥19.8 km·h) (p ≤ 0.05). However, according to partial match status (i.e., 15 minutes and half time), players covered more distance for all running intensities while winning (p < 0.01). Technical match performance scores were not influenced by match status. In conclusion, the present study showed that the physical activities including high-intensity running and total distance covered were related to the match status, whereas technical activities were not. The overall outcome shows that higher physical activity was associated with winning partial match periods. This approach highlights the importance of physical fitness in soccer and may help coaches to better modulate players' roles and team tactical organization throughout the match.

#5 Observation of Women Soccer Players' Physiology During a Single Season
Reference: J Strength Cond Res. 2018 Jun;32(6):1702-1707. doi: 10.1519/JSC.0000000000002025.
Authors: Paulsen KM, Butts CL, McDermott BP
Summary: The purpose of this study was to observe heart rate (HR) responses in match settings over the course of a conference season in National Collegiate Athletic Association Division I women's soccer. Twenty-one female collegiate soccer players were provided a HR monitor and instructed to wear it for the duration of match play. Player positions included 6 defenders (DEF), 6 midfielders (MID), and 9 forwards (FWD). Defenders were further identified as either center defenders (CD) or outside defenders (OD). A 1-way analysis of variance was used to determine if mean HR varied between FWD, MID, and DEF. An independent t-test was used to determine if there was a difference between CD and OD HRs. The FWD, MID, and DEF did have significantly different mean HR (p ≤ 0.05), but post-hoc analysis revealed no significant differences (p ≥ 0.05). However, CD demonstrated significantly lower HRs than OD (p = 0.009). Player position, specifically in the CD and OD role, impact the intensity of exercise in match settings and may be used to specify training and conditioning sessions.

#6 Alpha-Actinin-3 R577X Polymorphism Influences Muscle Damage and Hormonal Responses After a Soccer Game
Reference: J Strength Cond Res. 2018 May 17. doi: 10.1519/JSC.0000000000002575. [Epub ahead of print]
Authors: Coelho DB, Pimenta EM, Rosse IC, Veneroso C, Pussieldi GA, Becker LK, Oliveira EC, Carvalho MRS, Silami-Garcia E
Summary: Alpha-actinin-3 R577X polymorphism influences muscle damage and hormonal responses after a soccer game. J Strength Cond Res XX(X): 000-000, 2018-The purpose of this study was to evaluate indicators of muscle damage and hormonal responses after soccer matches and its relation to alpha-actinin-3 (ACTN3) gene expression (XX vs. RR/RX), considering that the R allele produces alpha-actinin-3 and provides greater muscle strength and power. Thirty players (10 XX and 20 RR/RX) younger than 16 years were evaluated in this study. Blood samples were collected immediately before, after, 2, and 4 hours after the games to assess muscle damage (creatine kinase [CK] and alpha-actin) and hormonal responses (interleukin-6 [IL-6], cortisol, and testosterone). Postgame CK was higher as compared to the pregame values in both groups and it was also higher in the RR/RX (p < 0.05) than in the XX. The concentrations of alpha-actin and IL-6 were similar for both groups and did not change over time. Testosterone was increased after the game only in the RR/RX group (p < 0.05). Cortisol concentrations in group RR/RX were higher immediately after the game than before the game, and 2 and 4 hours after the game the concentration decreased (p < 0.05). The RR and RX individuals presented higher markers of muscle microtrauma and hormonal stress, probably because they performed more speed and power actions during the game, which is a self-regulated activity. From the different responses presented by RR/RX and XX genotypes, we conclude that the genotypic profile should be taken into account when planning training workloads and recovery of athletes.

#7 Psychosocial predictors and psychological prevention of soccer injuries: A systematic review and meta-analysis of the literature
Reference: Phys Ther Sport. 2018 May 15. pii: S1466-853X(17)30491-1. doi: 10.1016/j.ptsp.2018.05.006. [Epub ahead of print]
Authors: Slimani M, Bragazzi NL, Znazen H, Paravlic A, Azaiez F, Tod D
Summary: The purpose was To examine (a) the relationships between the psychosocial risk factors and injury rates and (b) the effects of psychological-based prevention interventions on the injury risk of soccer players. Scholarly electronic databases (PubMed/MEDLINE, Google Scholar, Scopus) were searched on 1 January 2017, complemented by manual searches of bibliographies. We identified 13 eligible studies, including a total of 1149 injured soccer players aged between 14 and 36 years. Psychosocial risk factors, psychological-based prevention interventions and injury risk in soccer players were set as main outcome measures. Personality traits, such as trait anxiety and perceived mastery climate, along with a history of stressors, like negative-life-event stress or high level of life stress, daily hassle, and previous injury, are the main predictors of injury rates among soccer players. Also, from injury prevention studies, it has been shown that psychological-based interventions reduce injury rates (effect size = 0.96; 95% CI 0.34-1.58; p = 0.002) in senior soccer players. Practitioners need to ensure injured soccer players are psychologically and socially ready to play. They should also employ psychological-based interventions (i.e., mindfulness, imagery, self-talk, stress management, relaxation, goal setting) when designing injury prevention programs.

#8 A review advocating caution with Major League Soccer expansion and investment in more rehabilitation professionals
Reference: Phys Ther Sport. 2018 May 9. pii: S1466-853X(18)30010-5. doi: 10.1016/j.ptsp.2018.05.008. [Epub ahead of print]
Authors: Mansfield CJ, Ferkovic-Mack C, Eibensteiner J, Zwolski C
Summary: Major League Soccer (MLS) has aggressively expanded from 10 teams to 23 teams. With the addition of more teams, the league will have to dictate a schedule that maximizes the league's popularity, while also maintaining the health of the players. A longer season and congested game schedule could increase the risk of injury for players. The purpose of this commentary is to make recommendations for the prevention of injuries among MLS players with respect to proposed league expansion. MLS has lengthened the regular season with each expansion in teams. An increase in season length was seen in conjunction with the MLS expansion from 14 to 19 teams during the 2008 through 2013 seasons. Data from the inaugural MLS season found injury rates were higher in games compared to practices and more injuries occurred later in the season. With the expansion of MLS, anterior cruciate ligament tears appeared to have increased each year. Current evidence suggests the implementation of a proper preseason in addition to the once-per-week game frequency would best promote player health and well-being. Players may benefit from in-season injury prevention training and weekly load monitoring.

#9 Strength recovery after anterior cruciate ligament reconstruction with quadriceps tendon versus hamstring tendon autografts in soccer players: A randomized controlled trial
Reference: Knee. 2018 May 15. pii: S0968-0160(18)30123-6. doi: 10.1016/j.knee.2018.03.011. [Epub ahead of print]
Authors: Martin-Alguacil JL, Arroyo-Morales M, Martin-Gomez JL, Monje-Cabrera IM, Abellan-Guillen JF, Esparza-Ros F, Lozano ML, Cantarero-Villanueva I
Summary: The comparison between HT and QT grafts in strength recovery and function after an ACLR is scarce in the literature. A total of 56 participants were enrolled in this randomized controlled trial and placed into two groups: HT or QT. The hamstring/quadriceps (H/Q) ratio was the primary end-point measured with a Genu-3 dynamometer. Peak torque, functional assessment (Lysholm knee scoring scale and Cincinnati Knee Rating System), and anteroposterior laxity (KT-2000™ arthrometer) were also assessed. An intention-to-treat analysis was performed. The results of the H/Q ratio analysis of the participants over time revealed significant differences at 60, 180, and 300°/s at three, six, and 12months of follow-up (60°/s: F=5.3, p=0.005; 180°/s: F=5.5, p=0.004; 300°/s: F=5.1, p=0.005). Furthermore, they revealed significant differences at 60°/s, 180°/s, and 300°/s in the participants over time for peak torque in the extensor muscle strength at three and six months of follow-up, with higher values in the hamstring tendon group but not at 12months of follow-up. There were no significant differences in functional endpoints or arthrometer assessments at 24months of follow-up. An ACLR with a QT graft showed similar functional results with a better isokinetic H/Q ratio compared to an ACLR with the HT at 12months of follow-up in soccer players. This higher H/Q ratio observed with the QT could be an advantage of this graft over the HT for an ACLR.

#10 No association between rate of torque development and onset of muscle activity with increased risk of hamstring injury in elite football
Reference: Scand J Med Sci Sports. 2018 May 23. doi: 10.1111/sms.13224. [Epub ahead of print]
Authors: van Dyk N, Bahr R, Burnett AF, Verhagen E, von Tiggelen D, Witvrouw E
Summary: Hamstring injuries remain a significant burden in sports that involve high speed running. In elite male football, hamstring injury has repeatedly been identified as the most common noncontact injury, representing 12% of all injuries. As the incidence remains high, investigations are aimed at better understanding how to improve prevention efforts. Intrinsic risk factors such as strength have been investigated extensively in a cohort of professional football players; however, other intrinsic measures of neuromuscular function have not been studied in this cohort. This study aims to investigate the association between timing of hamstring muscle activity onset and the rate of torque development during the early phase of isokinetic strength testing with risk of hamstring injury in professional football players in a prospective cohort study. All teams (n=18) eligible to compete in the premier football league in Qatar underwent a comprehensive strength assessment during their annual periodic health evaluation at Aspetar Orthopaedic and Sports Medicine Hospital in Doha, Qatar. Variables included rate of torque development and timing of muscle activity onset. A total of 367 unique players (60.6% of all QSL players) competed for 514 player seasons (103 players competed both seasons) and sustained 65 hamstring injuries. There was no difference in the onset of muscle activity between the biceps femoris and medial hamstrings comparing the injured to uninjured players. For both onset of muscle activity and rate of torque development, there were no significant differences between any of the variables (p>0.05), with small effect sizes detected across all the different variables (d<0.3). Rate of torque development and onset of muscle activity were not associated with a risk of future hamstring injury. The use of these measures as part of a periodic health evaluation to identify risk of hamstring injury is unsupported.

#11 A History of Anterior Cruciate Ligament Reconstruction at the National Football League Combine Results in Inferior Early National Football League Career Participation
Reference: Arthroscopy. 2018 May 19. pii: S0749-8063(18)30238-X. doi: 10.1016/j.arthro.2018.03.018. [Epub ahead of print]
Authors: Provencher MT, Bradley JP, Chahla J, Sanchez A, Beaulieu-Jones BR, Arner JW, Kennedy NI, Sanchez G, Kennedy MI, Moatshe G, Cinque ME, LaPrade RF
Summary: The purpose was to evaluate whether players with a history of an anterior cruciate ligament reconstruction (ACLR) before the National Football League (NFL) Combine played or started fewer games and/or participated in fewer eligible snaps compared with NFL Combine participants without a history of knee injury or surgery. We performed a retrospective review of all players who participated in the NFL Combine between 2009 and 2015 and who had a history of an ACLR. NFL Combine participants were included if they had a previous ACLR or combined anterior cruciate ligament (ACL) injury and nonoperatively managed medial collateral ligament injury. The number of games started, number of games played, draft number, overall draft pick, and snap percentage for each position were determined. The mean value of each outcome metric was compared between case and control players. We identified 110 players who had an ACL injury (n = 76) or a combined ACL and medial collateral ligament injury (n = 34). Players in the ACLR group had a significantly worse mean draft pick number (difference of 30.2, P = .002) and mean draft round (difference of 0.8, P = .019) versus controls. Compared with control players, players in the ACLR group started and played significantly fewer games in both season 1 (difference of 2.7 games started, P < .001; difference of 2.7 games played, P < .001) and season 2 (difference of 7.4 games started, P < .001; difference of 3.0 games played, P = .003) and had a significantly lower snap percentage in both season 1 (difference of 23.1%, P < .001) and season 2 (difference of 24.0%, P < .001). Athletes at the NFL Combine who previously underwent an ACLR had significantly lower early-career NFL player metrics, including fewer games started, fewer games played, and a lower snap percentage, than uninjured controls. Defensive linemen, defensive backs, and linebackers were the 3 most affected positions. Players with a prior ACLR and combined meniscal-chondral pathology had significantly lower numbers of games started and games played in seasons 1 and 2 and a significantly lower season 2 snap percentage.

#12 Strategies to improve impact efficiency in football kicking
Reference: Sports Biomech. 2018 May 22:1-14. doi: 10.1080/14763141.2018.1452970. [Epub ahead of print]
Authors: Peacock JCA, Ball K
Summary: In football, kicking with high ball velocity can increase scoring opportunities and reduce the likelihood of interception. Efficient energy transfer from foot to ball during impact is important to attain a high ball velocity. It is considered impact efficiency can be increased by reducing the change in ankle plantarflexion during foot-ball impact. However, conflicting evidence exists, questioning its effectiveness as a coaching cue. The aim of the present study was to systematically analyse joint stiffness, foot velocity and impact location with a mechanical kicking machine to determine if change in ankle plantarflexion during foot-ball impact and ball velocity are influenced. Sagittal plane data of the shank, foot and ball were measured using high-speed video (4,000 Hz). Increasing joint stiffness reduced change in ankle plantarflexion and increased ball velocity from a greater effective mass. Increasing foot velocity increased change in ankle plantarflexion and increased ball velocity. Distal impact locations increased change in ankle plantarflexion and reduced ball velocity as coefficient of restitution decreased. These results identify that change in ankle plantarflexion is a dependent variable during foot-ball impact and does not directly influence ball velocity. Coaches can assess ankle motion during impact to provide feedback to athletes on their impact efficiency.

The Training Manager -