Latest research in football - week 45 - 2017

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 Prospective evaluation of injuries occurred during a professional soccer championship in 206 in Sao Paulo
Reference: BrazilActa Ortop Bras. 2017 Sep-Oct;25(5):212-215. doi: 10.1590/1413-785220172505167238.
Authors: Arliani GG, Lara PHS, Astur DC, Pedrinelli A, Pagura JR, Cohen M
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Summary: The aim of the study was to identify the incidence of injuries, their main characteristics, and the way they were managed throughout 2016 in two major series of a professional soccer championship in São Paulo, Brazil. This prospective study used an electronic questionnaire previously developed by the Medical Committee of the Paulista Soccer Federation which was sent to the team doctors after each match. Two hundred and fifty-nine injuries occurred during 361 matches, and the incidence of injury per 1000 hours of game play was 21.32. Strikers were the most affected by injury; the most frequent diagnosis was muscle injury and the legs were predominantly affected. Most of the injuries occurred in the last 15 minutes of the first half and only 7.7% required surgical treatment. Muscle injuries were the most frequent, with most occurring in forwards and in the legs. Approximately half of the injuries occurred after contact and the vast majority was treated without surgery. MRI was the most requested exam and most injuries were classified as moderate (8 to 28 lost play days).

#2 Does decrease in hip range of motion interfere in frontal plane leg alignment in teenage soccer players?
Reference: Eur J Orthop Surg Traumatol. 2017 Oct 27. doi: 10.1007/s00590-017-2066-x. [Epub ahead of print]
Authors: Scaramussa K, de Castro JV, Ellera Gomes JL
Summary: This study determines cross-sectional changes in transverse plane hip range of motion (ROM) in teenager soccer athletes and non-athletes and correlates these measures with changes in frontal plane leg alignment (varus-valgus alignment). Participants were recruited from a major professional soccer club and two local state-run schools in southern Brazil. A total of 396 male participants aged 9-18 years were assessed, 183 soccer players (athlete group; mean age, 13.3 ± 2.7 years) and 213 students (non-athlete group; mean age 14.4 ± 2.5 years). Hip internal rotation (IR) and external rotation (ER) and frontal plane leg alignment were measured in all participants. Changes in transverse plane hip ROM and frontal plane leg alignment were determined. Mean IR was 20.7° ± 5.8° in athletes versus 32.8° ± 2.9° in non-athletes, and mean ER was 36.5° ± 7.4° in athletes versus 46.7° ± 4.8° in non-athletes. Overall, IR was decreased in the athlete group compared to the non-athlete group (P < 0.001). Mean IR and ER were significantly lower in older athletes (P < 0.001), while only ER was significantly lower in older non-athletes (P < 0.001). Varus leg alignment was prevalent at all ages in the athlete group (71.0%, P = 0.153). In the non-athlete group, the occurrence of varus leg alignment was higher in older participants (P = 0.001). Lower mean IR was correlated with more severe varus leg alignment in the athlete group (rs = 0.19; P = 0.009). We found a lower hip ROM, particularly in IR, in teenager soccer players according to the enhancement age group from the sample. But varus alignment of the leg was also prevalent in this group and comes before hip abnormalities started to be detected.

#3 Examination of the external and internal load indicators' association with overuse injuries in professional soccer players
Reference: J Sci Med Sport. 2017 Oct 13. pii: S1440-2440(17)31655-9. doi: 10.1016/j.jsams.2017.10.005. [Epub ahead of print]
Authors: Jaspers A, Kuyvenhoven JP, Staes F, Frencken WGP, Helsen WF, Brink MS
Summary: Research in professional soccer focusing on the relevance of external and internal load indicators for injury prevention is scarce. This study examined the relationship between load indicators and overuse injuries. Data were collected from 35 professional male soccer players over two seasons. Following load indicators were examined: total distance covered (TD), distance covered at high speed (THSR; >20kmh-1), number of accelerations (ACCeff; >1ms-2), number of decelerations (DECeff; <-1ms-2), and rating of perceived exertion (RPE) multiplied by duration. Cumulative 1-, 2-, 3-, 4-weekly loads and acute:chronic workload ratios (ACWR) were calculated and split into low, medium and high groups. Only overuse injuries were included in the analysis to focus on their specific relationship with the load indicators. Generalized estimating equations were applied to analyse the relationship between load indicators and overuse injuries in the subsequent week. In total, 64 overuse injuries were registered. For cumulative loads, results indicated an increased injury risk for higher 2- to 4-weekly loads as indicated by TD, DECeff, and RPE multiplied by duration. For ACWR, a high ratio for THSR (>1.18) resulted in a higher injury risk. In contrast, a lower injury risk was found when comparing medium ratios for ACCeff (0.87-1.12), DECeff (0.86-1.12), and RPE x duration (0.85-1.12) to low ratios. Findings demonstrate that mainly external load indicators are associated with increased or decreased injury risk. The monitoring of various load indicators is recommended for injury prevention in professional soccer.

#4 Individualisation of speed thresholds does not enhance the dose-response determination in football training
Reference: J Sports Sci. 2017 Nov 3:1-10. doi: 10.1080/02640414.2017.1398894. [Epub ahead of print]
Authors: Scott D, Lovell R
Summary: This study examined the utility of a range of approaches used to develop player-dependent speed zones in time-motion analysis (TMA), in determining the dose-response (internal load) of daily football training. Daily external (10 Hz GPS) and internal load (heart rate metrics, ratings of perceived exertion [RPE], wellness ratings) measures were tracked for 22 International women's football players during a 21-day training camp. High-speed (HSR) and very high speed running (VHSR) were determined according to arbitrary speed thresholds, as well as using a range of different individualization approaches that included the velocities corresponding to the heart rate deflection point, maximal aerobic speed, YYIR1 performance, and maximal sprint speed (MSS). Within-player correlations between the TMA approaches versus internal load measures quantified the dose-response to training. Correlations between HSR and VHSR vs. RPE were large (r = 0.53-0.67), with the exception of VHSR for the MSS technique (moderate; r = 0.44). HSR was very-largely associated with heart rate indices (r = 0.72-0.78), again with the exception of MSS (large; r = 0.60-0.67). Using a range of different fitness characteristics to individualise speed thresholds did not enhance the dose-response determination to daily fluctuations in external load, and was worsened with MSS per se.

#5 Comprehensive profile of hip, knee and ankle ranges of motion in professional football players
Reference: J Sports Med Phys Fitness. 2017 Oct 31. doi: 10.23736/S0022-4707.17.07910-5. [Epub ahead of print]
Authors: Lopez-Valenciano A, Ayala F, Vera-Garcia FJ, de Ste Croix M, Hernández-Sanchez S, Ruiz-Perez I, Cejudo A, Santonja F
Summary: Limited ranges of motion (ROM) have been considered as a primary risk factor for some football injuries, but only a few studies have analysed differences in lower extremity joints. The main purposes were (a) to describe the lower extremity ROM profile in professional football players; and (b) to examine differences between goalkeepers and outfield players. 82 professional male football players from 4 teams were measured in the 2013 pre-season. Measures of passive hip (flexion with knee flexed [PHFKF] and extended [PHFKE], extension [PHE], abduction [PHA], external [PHER] and internal [PHIR] rotation), knee (flexion [PKF]) and ankle (dorsiflexion with knee flexed [ADFKF] and extended [ADFKE]) ROMs were taken. Magnitude-based inferences exploring differences between player position and limb were made. 46% of all participants showed restricted PHFKE and/or around 30% showed restricted ADFKF ROM values. Contrarily, most players reported normal PHFKF, PHE, PHIR and PHER as well as PKF ROM scores with percentage values close to 100%. Bilateral meaningful differences for PHA, PHIR and PHER were found in approximately 30% of outfield players and goalkeepers. Statistical analysis found trivial differences between players for PHFKE, PHE, PHIR, PHER, ADFKE and ADFKF. However, moderate differences between players were found for PHFKF, PHA and PKF, with goalkeepers demonstrating higher values than outfield players. The findings of this study reinforce the necessity of prescribing exercises aimed at improving PHFKE and ADFKF ROM within everyday football training routines. In addition, as some bilateral deficits were observed, unilateral training should be considered where appropriate.

#6 An evaluation of the impact of FIFA World Cup on soccer emergency department injuries among Montreal adolescents
Reference: J Paediatr Child Health. 2017 Nov 10. doi: 10.1111/jpc.13784. [Epub ahead of print]
Authors: Keays G, Friedman D, Beaudin M, Gagnon I
Summary: The 'trickle-down effect', or how major sports events have a positive impact on sports participation, has been the subject of many studies, but none produced conclusive results. We took a different approach and rather than look at sports participation, we used injuries as a proxy and see if injuries increased, or remained the same, after the International Federation of Association Football World Cup. Using a retrospective cohort design, we looked at the injuries suffered by males and females (13-16 years old) while playing team sports in Montreal, that occurred in May to July, from 1999 to 2014. Information reported by the Canadian Hospitals Injury Reporting Prevention Program (CHIRPP) was limited to the two CHIRPP centres in Montreal: the Montreal Children's Hospital and Hopital Sainte-Justine. In females, no significant trends were noticed. In males who played non-organised soccer, the percent changes between FIFA World Cup (WC) (June) and pre-FIFA WC (May) was always highest during FIFA WC years: 17.2% more injuries in years when FIFA WC was held compared to 1.3% less injuries during non-FIFA WC years. In non-organised soccer, male players suffered less strains/sprains (11.9% vs. 30.1%; P = 0.015), suffered more severe injuries (59.7% vs. 43.1%; P = 0.049) and more of their injuries were the results of direct contact with another player (26.8% vs. 13.3%; P = 0.028) during FIFA WC. FIFA WC seems to have an impact on the injuries of teenage boys when playing non-organised soccer. The impact was short-lived, only lasting during the FIFA WC event.

#7 A soccer player with an unstable knee
Reference: Ned Tijdschr Geneeskd. 2017;161(0):D1524. [Article in Dutch]
Authors: Janssen D, Koc B, Jansen E
Summary: A 19-year-old soccer player presented with instability of his left knee after a rotation trauma. Congenital absence of the anterior cruciate ligament was suspected because of leg length discrepancy and specific MRI findings. He regained stability after an anterior cruciate reconstruction.

#8 An audit of injuries in six english professional soccer academies
Reference: J Sports Sci. 2017 Nov 10:1-7. doi: 10.1080/02640414.2017.1402535. [Epub ahead of print]
Authors: Read PJ, Oliver JL, De Ste Croix MBA, Myer GD, Lloyd RS
Summary: Regulations now state that professional academies in the United Kingdom are required to substantially increase the volume of soccer training. This study assessed the current injury occurrence, providing an update to reports published prior to the introduction of the Elite Player Performance Plan (EPPP). 608 soccer players aged 11-18 years from six professional soccer clubs were prospectively monitored, recording injuries during the 2014-2015 season. An injury rate of 1.32 injuries per player/season was indicated with a mean time loss of 21.9 days per injury. The greatest time loss per injury was in the U14s-U15s, and the highest rate of severe injuries in the U15s. Strains and sprains were the most common injury type, with the knee and ankle the most frequently injured anatomical sites. Seasonal variation indicated two peaks in injury incidence, occurring in September and January. In comparison to a published audit prior to the inception of the EPPP, this study indicates that academy soccer players are three-times more likely to experience an injury. Given that time loss and injury severity also increased during periods that typically follow rapid growth, these players should be considered an important group for training load monitoring and injury prevention strategies.

#9 Match-derived relative pitch area changes the physical and team tactical performance of elite soccer players in small-sided soccer games
Reference: J Sports Sci. 2017 Nov 10:1-7. doi: 10.1080/02640414.2017.1403412. [Epub ahead of print]
Authors: Olthof SBH, Frencken WGP, Lemmink KAPM
Summary: Small-sided games (SSGs) are used in training sessions to prepare for full-sized matches. For the same number of players, smaller pitch sizes result in decreased physical performance and shorter interpersonal distances. A relative pitch area derived from the full-sized match results in larger pitch sizes and this may increase the fit between SSGs and full-sized matches. This study aimed to investigate SSGs with a traditional small pitch and a match-derived relative pitch area in youth elite soccer players. Four age categories (under-13, under-15, under-17 and under-19) played 4 vs. 4 plus goalkeepers on a small (40x30m, 120m2 relative pitch area) and large pitch (68x47m, 320m2 relative pitch area). The number of games per age category ranged 15-30. Positional data (LPM-system) were collected to determine physical (total distance covered, high intensity distance and number of sprints) and team tactical (inter-team distance, LPW-ratio, surface area, stretch indices, goalkeeper-defender distance) performance measures and tactical variability. On a large pitch, physical performance significantly increased, inter-team and intra-team distances were significantly larger and tactical variability of intra-team distance measures significantly increased. The match-derived relative pitch area is an important training manipulation and leads to changes in physical and tactical performance 4 vs. 4 plus goalkeepers.

#10 Etiology and Recovery of Neuromuscular Fatigue following Competitive Soccer Match-Play
Reference: Front Physiol. 2017 Oct 25;8:831. doi: 10.3389/fphys.2017.00831. eCollection 2017.
Authors: Brownstein CG, Dent JP, Parker P, Hicks KM, Howatson G, Goodall S, Thomas K
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Summary: Previous research into the etiology of neuromuscular fatigue following competitive soccer match-play has primarily focused on peripheral perturbations, with limited research assessing central nervous system function in the days post-match. The aim of the present study was to examine the contribution and time-course of recovery of central and peripheral factors toward neuromuscular fatigue following competitive soccer match-play. Sixteen male semi-professional soccer players completed a 90-min soccer match. Pre-, post- and at 24, 48, and 72 h participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and transcranial magnetic stimulation (TMS) of the motor cortex during isometric knee-extension and at rest were measured to assess central nervous system (voluntary activation, VA) and muscle contractile (potentiated twitch force, Qtw, pot) function. Electromyography responses of the rectus femoris to single- and paired-pulse TMS were used to assess corticospinal excitability and short-interval intracortical inhibition (SICI), respectively. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump (countermovement jump height and reactive strength index) and sprint performance. Competitive match-play elicited significant post-match declines in MVC force (-14%, P < 0.001) that persisted for 48 h (-4%, P = 0.01), before recovering by 72 h post-exercise. VA (motor point stimulation) was reduced immediately post-match (-8%, P < 0.001), and remained depressed at 24 h (-5%, P = 0.01) before recovering by 48 h post-exercise. Qtw,pot was reduced post-match (-14%, P < 0.001), remained depressed at 24 h (-6%, P = 0.01), before recovering by 48 h post-exercise. No changes were evident in corticospinal excitability or SICI. Jump performance took 48 h to recover, while perceptions of fatigue persisted at 72 h. Conclusion: Competitive soccer match-play elicits substantial impairments in central nervous system and muscle function, requiring up to 48 h to resolve. The results of the study could have important implications for fixture scheduling, the optimal management of the training process, squad rotation during congested competitive schedules, and the implementation of appropriate recovery interventions.

American Football
#1 Effects of Career Duration, Concussion History, and Playing Position on White Matter Microstructure and Functional Neural Recruitment in Former College and Professional Football Athletes
Reference: Radiology. 2017 Oct 31:170539. doi: 10.1148/radiol.2017170539. [Epub ahead of print]
Authors: Clark MD, Varangis EML, Champagne AA, Giovanello KS, Shi F, Kerr ZY, Smith JK, Guskiewicz KM
Summary: The purpose was to better understand the relationship between exposure to concussive and subconcussive head impacts, white matter integrity, and functional task-related neural activity in former U.S. football athletes. Materials and Methods Between 2011 and 2013, 61 cognitively unimpaired former collegiate and professional football players (age range, 52-65 years) provided informed consent to participate in this cross-sectional study. Participants were stratified across three crossed factors: career duration, concussion history, and primary playing position. Fractional anisotropy (FA) and blood oxygen level-dependent (BOLD) percent signal change (PSC) were measured with diffusion-weighted and task-related functional magnetic resonance imaging, respectively. Analyses of variance of FA and BOLD PSC were used to determine main or interaction effects of the three factors. Results A significant interaction between career duration and concussion history was observed; former college players with more than three concussions had lower FA in a broadly distributed area of white matter compared with those with zero to one concussion (t29 = 2.774; adjusted P = .037), and the opposite was observed for former professional players (t29 = 3.883; adjusted P = .001). A separate interaction between concussion history and position was observed: Nonspeed players with more than three concussions had lower FA in frontal white matter compared with those with zero to one concussion (t25 = 3.861; adjusted P = .002). Analysis of working memory-task BOLD PSC revealed a similar interaction between concussion history and position (all adjusted P < .004). Overall, former players with lower FA tended to have lower BOLD PSC across three levels of a working memory task. Conclusion Career duration and primary playing position seem to modify the effects of concussion history on white matter structure and neural recruitment. The differences in brain structure and function were observed in the absence of clinical impairment, which suggested that multimodal imaging may provide early markers of onset of traumatic neurodegenerative disease. © RSNA, 2017 Online supplemental material is available for this article.

#2 White matter alterations over the course of two consecutive high-school football seasons and the effect of a jugular compression collar: A preliminary longitudinal diffusion tensor imaging study
Reference: Hum Brain Mapp. 2017 Oct 28. doi: 10.1002/hbm.23859. [Epub ahead of print]
Authors: Yuan W, Barber Foss KD, Thomas S, DiCesare CA, Dudley JA, Kitchen K, Gadd B, Leach JL, Smith D, Altaye M, Gubanich P, Galloway RT, McCrory P, Bailes JE, Mannix R, Meehan WP 3rd, Myer GD
Summary: The cumulative effects of repetitive subclinical head impacts during sports may result in chronic white matter (WM) changes and possibly, neurodegenerative sequelae. In this pilot study, we investigated the longitudinal WM changes over the course of two consecutive high-school football seasons and explored the long-term effects of a jugular vein compression collar on these WM alterations. Diffusion tensor imaging data were prospectively collected both pre- and postseason in the two consecutive seasons. Participants were assigned into either collar or noncollar groups. Tract-based spatial statistics (TBSS) approach and region of interest-based approach were used to quantify changes in WM diffusion properties. Despite comparable exposure to repetitive head impacts, significant reductions in mean, axial, and/or radial diffusivity were identified in Season 1 in multiple WM regions in the noncollar group but not in the collar group. After an 8- to 9-month long off-season, these changes observed in the noncollar group partially and significantly reversed but also remained significantly different from the baseline. In Season 2, trend level WM alterations in the noncollar group were found but located in spatially different regions than Season 1. Last, the WM integrity in the collar group remained unchanged throughout the four time points. In conclusion, we quantitatively assessed the WM structural changes and partial reversal over the course of two consecutive high-school football seasons. In addition, the mitigated WM alterations in athletes in the collar group might indicate potential effect of the collar in ameliorating the changes against repetitive head impacts.

#3 Postural Control and Head Impact Exposure in Youth Football Players: Comparison of the Balance Error Scoring System and a Force Plate Protocol
Reference: J Appl Biomech. 2017 Nov 1:1-25. doi: 10.1123/jab.2017-0066. [Epub ahead of print]
Authors: Campolettano ET, Brolinson G, Rowson S
Summary: Postural control testing is often used by clinicians and athletic trainers to assess the health of athletes during recovery from a concussion. Characterization of postural control as a clinical tool for use with youth athletes is limited though. The objective of this study was to compare performance on the Balance Error Scoring System (BESS) and a force plate protocol at the beginning and end of a season of football within a cohort of 34 healthy youth football players (average age of 9.9 ± 0.6 years). A secondary aim was to investigate if changes in measures of balance from the postseason to the preseason were correlated with head impact exposure. Players completed testing at the beginning and end of the youth football season. There were no significant differences between BESS scores before the season and after the season (p = 0.54). Performance on the BESS was not associated with any of the center of pressure (COP) metrics considered in this study. No correlation was observed between measures of balance and head impact exposure for the season. Further research is required to determine the viability of postural control testing with this population.

Australian Football
#1 Brief Education Intervention Increases Nutrition Knowledge and Confidence of Coaches of Junior Australian Football Teams
Reference: Int J Sport Nutr Exerc Metab. 2017 Nov 1:1-21. doi: 10.1123/ijsnem.2017-0170. [Epub ahead of print]
Authors: Belski R, Donaldson A, Staley K, Skiadopoulos A, Randle E, O'Halloran P, Kappelides P, Teakel S, Stanley S, Nicholson M
Summary: This study evaluated the impact of a brief (20-minute) nutrition education intervention embedded in an existing mandatory coach education course for coaches of junior (8-12 year old) Australian football teams. Two hundred and eighty-four coaches (68% of 415 coaching course participants) completed a pre-session questionnaire and 110 (27% of coaching course participants) completed an identical post-session questionnaire. The responses to the pre- and post-session surveys were matched for 78 coaches. Coaches' ratings of their own understanding of the nutritional needs of young athletes (6.81, 8.95, p<0.001), the importance of young athletes adhering to a healthy diet (9.09, 9.67, p=001), their confidence in their own nutrition knowledge (7.24, 8.64, p<0.001) and their confidence in advising young athletes on nutrition and hydration practices (6.85, 8.62, p<0.001), all improved significantly following the education session. Nearly all coaches (>95%) provided a correct response to six of the 15 nutrition and hydration knowledge questions included in the pre-session questionnaire. Even with this high level of pre-session knowledge, there was a significant improvement in the coaches' nutrition and hydration knowledge after the education session across five of the 15 items, compared to before the education session. The results of this study suggest that a simple, short nutrition education intervention, embedded in an existing coach education course, can positively influence the nutrition knowledge and self-efficacy of community-level, volunteer coaches of junior sports participants.

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