Latest research in football - week 50 - 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 Effects of the Nordic Hamstring exercise on sprint capacity in male football players: a randomized controlled trial
Reference: J Sports Sci. 2017 Dec 1:1-10. doi: 10.1080/02640414.2017.1409609. [Epub ahead of print]
Authors: Ishoi L, Holmich P, Aagaard P, Thorborg K, Bandholm T, Serner A
Summary: This assessor-blinded, randomized controlled superiority trial investigated the efficacy of the 10-week Nordic Hamstring exercise (NHE) protocol on sprint performance in football players. Thirty-five amateur male players (age: 17-26 years) were randomized to a do-as-usual control group (CG; n = 17) or to 10-weeks of supervised strength training using the NHE in-season (IG; n = 18). A repeated-sprint test, consisting of 4 × 6 10 m sprints, with 15 s recovery period between sprints and 180 s between sets, was conducted to evaluate total sprint time as the primary outcome. Secondary outcomes were best 10 m sprint time (10mST) and sprint time during the last sprint (L10mST). Additionally, peak eccentric hamstring strength (ECC-PHS) and eccentric hamstring strength capacity (ECC-CAPHS) were measured during the NHE. Ten players were lost to follow-up, thus 25 players were analyzed (CG n = 14; IG n = 11). Between-group differences in mean changes were observed in favor of the IG for sprint performance outcomes; TST (-0.649 s, p = 0.056, d = 0.38), 10mST (-0.047 s, p = 0.005, d = 0.64) and L10mST (-0.052 s, p = 0.094, d = 0.59), and for strength outcomes; ECC-PHS (62.3 N, p = 0.006, d = 0.92), and ECC-CAPHS (951 N, p = 0.005, d = 0.95). In conclusion, the NHE showed small-to-medium improvements in sprint performance and large increases in peak eccentric hamstring strength and capacity.

#2 Vertical and Horizontal Jump Capacity in International Cerebral Palsy Football Players
Reference: Int J Sports Physiol Perform. 2017 Nov 28:1-23. doi: 10.1123/ijspp.2017-0321. [Epub ahead of print]
Authors: Reina R, Iturricastillo A, Sabido R, Campayo-Piernas M, Yanci J
Summary: The aims of the present study were to evaluate the reliability and validity of vertical and horizontal jump tests in football players with cerebral palsy (FPCP), and to analyze the jump performance differences between current IFCPF functional classes (i.e. FT5-FT8). One hundred and thirty-two international para-footballers (25.8 ± 6.7 years; 70.0 ± 9.1 kg; 175.7 ± 7.3 cm; 22.8 ± 2.8 kg·m-2; 10.7 ± 7.5 years training experience) participated in the study. The participants were classified according to the IFCPF Classification Rules (i.e. FT5-FT8), and a group of 39 players without CP was included in the study as a control group (CG). Football players' vertical and horizontal jump performance was assessed. All the tests showed good to excellent relative intra-session reliability scores, both in FPCP and in the CG (ICC=.78-.97, SEM<10.5%). Significant between-group differences (p<.001) were obtained in the counter-movement jump (CMJ), standing broad jump (SBJ), four bounds for distance (4B), triple hop for distance dominant leg (THd) and non-dominant leg (THnd). The CG performed higher/farther jumps with regard to all the FPCP classes, obtaining significant differences and moderate to large effect sizes (.85< ES <5.54, p<.01). Players in FT8 class (less severe impairments) had significantly higher scores in all the jump tests compared to players in the lower classes (ES=moderate to large, p<.01). the vertical and horizontal jump tests performed in this study could be applied to the classification procedures and protocols for cerebral palsy football players.

#3 Prognostic factors for specific lower extremity and spinal musculoskeletal injuries identified through medical screening and training load monitoring in professional football (soccer): a systematic review
Reference: BMJ Open Sport Exerc Med. 2017 Sep 21;3(1):e000263. doi: 10.1136/bmjsem-2017-000263. eCollection 2017.
Authors: Hughes T, Sergeant JC, Parkes MJ, Callaghan MJ
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Summary: Medical screening and load monitoring procedures are commonly used in professional football to assess factors perceived to be associated with injury. The objectives were to identify prognostic factors (PFs) and models for lower extremity and spinal musculoskeletal injuries in professional/elite football players from medical screening and training load monitoring processes. The MEDLINE, AMED, EMBASE, CINAHL Plus, SPORTDiscus and PubMed electronic bibliographic databases were searched (from inception to January 2017). Prospective and retrospective cohort studies of lower extremity and spinal musculoskeletal injury incidence in professional/elite football players aged between 16 and 40 years were included. The Quality in Prognostic Studies appraisal tool and the modified Grading of Recommendations Assessment, Development and Evaluation synthesis approach was used to assess the quality of the evidence. Fourteen studies were included. 16 specific lower extremity injury outcomes were identified. No spinal injury outcomes were identified. Meta-analysis was not possible due to heterogeneity and study quality. All evidence related to PFs and specific lower extremity injury outcomes was of very low to low quality. On the few occasions where multiple studies could be used to compare PFs and outcomes, only two factors demonstrated consensus. A history of previous hamstring injuries (HSI) and increasing age may be prognostic for future HSI in male players. The assumed ability of medical screening tests to predict specific musculoskeletal injuries is not supported by the current evidence. Screening procedures should currently be considered as benchmarks of function or performance only. The prognostic value of load monitoring modalities is unknown.

#4 Data concerning the effect of plyometric training on jump performance in soccer players: A meta-analysis
Reference: Data Brief. 2017 Sep 30;15:324-334. doi: 10.1016/j.dib.2017.09.054. eCollection 2017 Dec.
Authors: Slimani M, Paravlic A, Bragazzi NL
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Summary: Plyometric training (PT) enhances soccer performance, particularly vertical jump. However, the effectiveness of PT depends on various factors. A systematic search of the research literature was conducted for randomized controlled trials (RCTs) studying the effects of PT on countermovement jump (CMJ) height in soccer players. Ten studies were obtained through manual and electronic journal searches (up to April 2017). Significant differences were observed when compared: (1) PT group vs. control group (ES=0.85; 95% CI 0.47-1.23; I2=68.71%; p<0.001), (2) male vs. female soccer players (Q=4.52; p=0.033), (3) amateur vs. high-level players (Q=6.56; p=0.010), (4) single session volume (<120 jumps vs. ≥120 jumps; Q=6.12, p=0.013), (5) rest between repetitions (5 s vs. 10 s vs. 15 s vs. 30 s; Q=19.10, p<0.001), (6) rest between sets (30 s vs. 60 s vs. 90 s vs. 120 s vs. 240 s; Q=19.83, p=0.001) and (7) and overall training volume (low: <1600 jumps vs. high: ≥1600 jumps; Q=5.08, p=0.024). PT is an effective form of training to improve vertical jump performance (i.e., CMJ) in soccer players. The benefits of PT on CMJ performance are greater for interventions of longer rest interval between repetitions (30 s) and sets (240 s) with higher volume of more than 120 jumps per session and 1600 jumps in total. Gender and competitive level differences should be considered when planning PT programs in soccer players.

#5 Soccer (Football Association) and chronic traumatic encephalopathy: A short review and recommendation
Reference: Dement Neuropsychol. 2017 Jul-Sep;11(3):218-220. doi: 10.1590/1980-57642016dn11-030002 in English, Portuguese
Authors: Nitrini R
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Summary: Chronic traumatic encephalopathy (CTE) was initially described in boxers, but in recent years it has been reported in other settings, particularly in contact sports and military personnel. Soccer (football association) had previously been (and still is) considered relatively safe when compared to other sports, such as American football. However, a few cases of professional soccer players with CTE have been reported in the last few years. It is still unknown how frequent this condition is in soccer players, and the role played by heading the ball remains elusive. Other traumas to the head, face and neck caused by contact with another player's head, arm or other body parts are among the most frequent in soccer. In spite of the lack of more in-depth knowledge, there is reasonable evidence for recommending severe punishment (red card and suspension for several matches) for players causing avoidable trauma to another player's head.

#6 The Reliability and Validity of A Submaximal Warm-Up Test for Monitoring Training Status in Professional Soccer Players
Reference: J Strength Cond Res. 2017 Nov 27. doi: 10.1519/JSC.0000000000002335. [Epub ahead of print]
Authors: Rabbani A, Kargarfard M, Twist C
Summary: Two studies were conducted to assess the reliability and validity of a submaximal warm-up test (SWT) in professional soccer players. For the reliability study, 12 male players performed SWT over three trials, with one week between trials. For the validity study, 14 players of the same team performed SWT and 30-15 Intermittent Fitness Test (30-15IFT) 7 days apart. Week-to-week reliability in selected heart rate (HR) responses [exercise HR (HRex), HR recovery (HRR) expressed as the number of beats recovered within 1 min (HRR60s) and expressed as the mean HR during 1 min (HRpost1)], were determined using intraclass correlation coefficient (ICC) and typical error of measurement expressed as coefficient of variation (CV). The relationships between HR measures derived from SWT and the maximal speed reached at the 30-15IFT (VIFT) were used to assess validity. The range for ICC and CV values were 0.83 to 0.95 and 1.4 to 7.0% in all HR measures, respectively, with the HRex as the most reliable HR measure of SWT. Inverse large (r = -0.50, 90% confidence limits, CL (-0.78; -0.06)) and very large (r = -0.76, CL, -0.90; -0.45) relationships were observed between HRex and HRpost1 with VIFT in relative (expressed as the % of maximal HR) measures, respectively. SWT is a reliable and valid submaximal test to monitor high-intensity intermittent running fitness in professional soccer players. In addition, the test's short duration (5-min) and simplicity mean that it can be used regularly to assess training status in high-level soccer players.

#7 The FIFA 11+ injury prevention program for soccer players: a systematic review
Reference: BMC Sports Sci Med Rehabil. 2017 Nov 28;9:18. doi: 10.1186/s13102-017-0083-z. eCollection 2017.
Authors: Sadigursky D, Braid JA, De Lira DNL, Machado BAB, Carneiro RJF, Colavolpe PO
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Summary: Soccer is one of the most widely played sports in the world. However, soccer players have an increased risk of lower limb injury. These injuries may be caused by both modifiable and non-modifiable factors, justifying the adoption of an injury prevention program such as the Fédération Internationale de Football Association (FIFA) 11+. The purpose of this study was to evaluate the efficacy of the FIFA 11+ injury prevention program for soccer players. This meta-analysis was based on the PRISMA 2015 protocol. A search using the keywords "FIFA," "injury prevention," and "football" found 183 articles in the PubMed, MEDLINE, LILACS, SciELO, and ScienceDirect databases. Of these, 6 studies were selected, all of which were randomized clinical trials. The sample consisted of 6,344 players, comprising 3,307 (52%) in the intervention group and 3,037 (48%) in the control group. The FIFA 11+ program reduced injuries in soccer players by 30%, with an estimated relative risk of 0.70 (95% confidence interval, 0.52-0.93, p = 0.01). In the intervention group, 779 (24%) players had injuries, while in the control group, 1,219 (40%) players had injuries. However, this pattern was not homogeneous throughout the studies because of clinical and methodological differences in the samples. This study showed no publication bias. The FIFA 11+ warm-up program reduced the risk of injury in soccer players by 30%.

#8 Sprint and jump performance in elite male soccer players following a 10-week Nordic Hamstring exercise Protocol: a randomised pilot study
Reference: BMC Res Notes. 2017 Dec 4;10(1):669. doi: 10.1186/s13104-017-2986-x.
Authors: Krommes K, Petersen J, Nielsen MB, Aagaard P, Holmich P, Thorborg K
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Summary: The preseason Nordic Hamstring Protocol (NHP) reduces hamstring strain injuries in football players. Despite persisting injury rates, elite clubs are reluctant to apply the NHP often over concerns of negative impacts on performance. This pilot study investigated if sprint or jump-performance outcomes tended to increase or decrease following implementation of the NHP in elite male soccer-players. Nineteen male soccer players from the Danish 1st division were randomised to perform NHP (27 sessions) during pre-season, or to control group (CG). Sprint performance (30 m with 5 and 10 m split times) and countermovement jump (CMJ height) was measured before the mid-seasonal break and again after 10 weeks of performing the NHP at the end of pre-season. Dropouts were due to transfers and injuries unrelated to performing NHP (NHP = 0, CG = 5). Sprint performance on the short split distances improved for most players in the NHP (6 out of 9 improved, median changes for 5 m split: - 0.068 s; 10 m split: - 0.078 s), but not CG (2 out of 5 improved, median changes for 5 m split: + 0.1 s; 10 m split: CG: + 0.11 s), but both groups had small declines at 30 m sprint (NHP: 7 out of 9 declined, median changes: + 0.116 s; CG: 4 out of 5 declined, median changes: + 0.159 s). CMJ height mostly improved in both groups (NHP: 6 out of 9 improved, median changes: + 2.1 cm; CG: 4 out of 8 improved, median changes: + 0.55 cm). Performing the NHP in elite soccer players did therefore not seem to negatively affect sprint and vertical jump performance outcomes in the present study, while in fact showing some promise for the more explosive characteristics such as the short 5 and 10 m split-times and maximal CMJ height, which all are highly relevant performance parameters in elite football.

#9 Analysis of the acceleration profile according to initial speed and positional role in elite professional male soccer players
Reference: J Sports Med Phys Fitness. 2017 Dec 1. doi: 10.23736/S0022-4707.17.08003-3. [Epub ahead of print]
Authors: de Hoyo M, Sanudo B, Suarez-Arrones L, Carrasco L, Joel T, Dominguez-Cobo S, Nunez FJ
Summary: The aim of the current study was to analyse the acceleration profile in elite professional soccer players according to their initial speed but also considering players' position. Players' accelerations profiles were analysed using a relative acceleration profile according to the initial speed (S1, from 0 to 7 km/h; S2, from 7.1 to 14.3 km/h; and S3, ≥14.4 km/h) and the maximum acceleration. Within-group analyses showed that Center Backs (CB) performed more high intensity accelerations (likely) when they started in S1 than S2 (ES: 0.50). Strikers (S) and Wide Midfielders (W-MD) achieved more accelerations (likely to almost certain) starting in S3 than S1 (ES: 0.80 and 0.59, respectively) and S2 (ES: 0.67 and 1.09, respectively). Full Backs (FB) completed more accelerations (almost certain) starting in S1 and S3 than S2 (ES: 1.39 and 1.36, respectively). Finally, Midfielders (MD) executed a greater number of high intensity accelerations (likely to almost certain) when they started in S1 than S2 (ES: 0.83) and S3 (ES: 0.66), and in S3 than S2 (ES: 4.72). Between-group analyses showed that S, W-MD, and FB performed a greater total number of high intensity accelerations (very likely to almost certain) than CB (ES: 1.94, 1.57, and 1.51, respectively) and MD (ES: 1.23, 0.92; and 0.81, respectively). Furthermore, MD performed substantially greater total number of high intensity accelerations (likely) than CB (ES: 0.56). Results suggest that CB achieved more high-intensity accelerations starting in low and moderate speed, S and W-MD in high speed, and FB combined low and high speed.

#10 Anthropometric and physiological characteristics of male Soccer players according to their competitive level, playing position and age group: a systematic review
Reference: J Sports Med Phys Fitness. 2017 Dec 1. doi: 10.23736/S0022-4707.17.07950-6. [Epub ahead of print]
Authors: Slimani M, Nikolaidis PT
Summary: The aim of the present systematic review was to profile soccer players' anthropometric, physiological, and physical attributes relative to different competitive levels, playing positions and age groups. The systematic search was conducted using different databases and according to the Population/Intervention or Exposure/Comparison/Outcome(s) [PICO] criteria. The present review shows that the somatotype characteristics, percentage (%) of body fat, maximal oxygen uptake (VO2max), repeatedsprint ability (RSA), running speed, strength, and muscular power of the lower limbs were the most powerful discriminators between male soccer players of different competitive levels, playing positions, and age groups. Specifically, higher VO2max, muscle strength, muscular power (vertical jump height), running speed (1030 m) and agility, and lower % of body fat were identified in elite soccer players (higherlevel) compared to all other competitive levels (i.e., lowerlevel: subelite, amateur, recreational). As for the competitive level differences, higher VO2max, mean anaerobic power, RSA and sprint performances (5 to 20 m), and lower % of body fat and lower limbs' explosive capabilities (countermovement jump (CMJ) and squat jump (SJ)) were found in outfielders (forwards, midfielders, and defenders) as compared to goalkeepers, from a very youth age (8 years old). Concerning age related performance, it appears that physical performance increased significantly with age. These data, together with the fact that each position, age category, and playing level has a different physiological background in male soccer players, demonstrate that training programs should be individualized to each position, playing level and age category, as is already done with goalkeepers.

American Football
#1 Characterization of American Football Injuries in Children and Adolescents
Reference: J Pediatr Orthop. 2017 Nov 16. doi: 10.1097/BPO.0000000000001101. [Epub ahead of print]
Authors: Smith PJ, Hollins AM, Sawyer JR, Spence DD, Outlaw S, Kelly DM
Summary: As a collision sport, football carries a significant risk of injury, as indicated by the large number of pediatric football-related injuries seen in emergency departments. There is little information in the medical literature focusing on the age-related injury patterns of this sport. Our purpose was to evaluate the types of football-related injuries that occur in children and adolescents and assess which patient characteristics, if any, affect injury pattern. Retrospective chart review was performed of football-related injuries treated at a level 1 pediatric referral hospital emergency department and surrounding urgent care clinics between January 2010 and January 2014. Patients with e-codes for tackle football selected from the electronic medical record were divided into 4 age groups: younger than 8 years old, 8 to 11, 12 to 14, and 15 to 18 years. Data collected included diagnosis codes, procedure codes, and hospital admission status. Review identified 1494 patients with 1664 football-related injuries, including 596 appendicular skeleton fractures, 310 sprains, 335 contusions, 170 closed head injuries, 62 dislocations, 9 spinal cord injuries, and 14 solid organ injuries. There were 646 (43.2%) athletes with upper extremity injuries and 487 (32.6%) with injuries to the lower extremity. Hospital admissions were required in 109 (7.3%) patients. Fracture was the most common injury in all four patient age groups, but occurred at a lower rate in the 15 to 18 years old age group. The rate of soft tissue injury was higher in the 15 to 18 years old age group. The rate of closed head injury, which included concussions, was highest in the younger than 8 years old age group. Age does influence the rates of certain football-related injuries in children and adolescents. Fractures decrease with increasing age, while the rate of soft tissue trauma increases with increasing age. Younger patients (younger than 8 y old) trended toward higher rates of closed head injury compared with other age groups. Awareness of these variations in injury patterns based on age could result in age-specific changes in equipment, training, and safety rules.

#2 Positional Differences in Running and Non-Running Activities During Elite American Football Training
Reference: J Strength Cond Res. 2017 Nov 22. doi: 10.1519/JSC.0000000000002294. [Epub ahead of print]
Authors: Ward PA, Ramsden S, Coutts AJ, Hulton AT, Drust B
Summary: The aim of this investigation was to describe differences in training loads between position groups within professional American football. Integrated micro technology data was collected on 63 NFL football players during an American football training camp. Five key metrics (total distance, high speed distance, Player Load, Player Load per Minute, and Total Inertial Movement Analysis (IMA)) served to quantify both running and non-running activities. Players were classified into position groups (DB, DL, LB, OL, QB, RB, TE, and WR). Training sessions were identified by their relationship to the upcoming match (e.g., -4, -3, -2). Running and non-running activities varied between position groups relative to the training day. Differences in total distance were between DB and WR were observed to be unclear between the three training days (Game Day (GD) -4: 74 ± 392 m; GD -3: -122 ± 348; GD - 2: -222 ± 371 m). However, moderate to large differences were observed between these two positions and the other positional groups. A similar relationship was observed in Player Load and Player Load per Minute, with the DB and WR groups performing greater amounts of load compared to other positional groups. Differences in High Speed Distance varied across positional groups, indicating different outputs based on ergonomic demands. The OL and DL groups ran less but engaged in a higher amount of non-running activities (Total IMA) with differences ranging from moderate to large across the three training days. Total IMA differences between offensive and defensive linemen were unclear on GD -4 (-4 ± 9) and GD -2 (-2 ± 8) and likely moderate on GD -3 (-9 ± 9). Positional differences with regard to running and non-running activities highlight the existence of position specific training within a training micro-cycle. Additionally, Total IMA provides a useful metric for quantifying sport specific movements within the game of American football.

#3 Motion-preserving, 2-stage transoral and posterior treatment of an unstable Jefferson fracture in a professional football player
Reference: J Neurosurg Spine. 2017 Dec 1:1-5. doi: 10.3171/2017.6.SPINE17274. [Epub ahead of print]
Authors: Rodts GE Jr, Baum GR, Stewart FG, Heller JG
Summary: The authors report the case of a patient who suffered a Jefferson fracture during a professional football game. The C-1 (atlas) fracture was widely displaced anteriorly, but the transverse ligament was intact. In an effort to enable a return to play and avoid intersegmental (C1-2) fusion, the patient underwent a transoral approach for open reduction and internal fixation of the fracture. The associated posterior ring fracture displacement widened after this procedure, and a subsequent posterior arthrodesis and fixation of the fracture site was performed 6 months later when the fracture failed to heal with rigid collar immobilization. The approach maintained the normal range of motion at the atlantoaxial and atlantooccipital joints, which would have been sacrificed by an atlantoaxial or occipitocervical fusion, as is traditionally performed. Ultimately, the patient decided not to return to the football field, but this approach could avoid the more significant loss of motion associated with atlantoaxial or occipitocervical fusion for unstable Jefferson fractures.

Australian Football
#1 How do professional Australian Football League (AFL) players utilise social media during periods of injury? A mixed methods analysis
Reference: J Sci Med Sport. 2017 Nov 7. pii: S1440-2440(17)31747-4. doi: 10.1016/j.jsams.2017.10.034. [Epub ahead of print]
Authors: Nankervis B, Ferguson L, Gosling C, Storr M, Ilic D, Young M, Maloney S
Summary: The objective of this study was to explore how social media is used by a population of injured professional athletes, by comparing the content and frequency of posts on social media, pre and post-injury. Professional Australian Football League (AFL) players, injured during the 2015 season, were included in the study. Publicly accessible social media profiles for these players were identified on Twitter and Instagram. All posts published on verified profiles, from four weeks prior to injury until return to play, were extracted. Thematic analysis was used to investigate the content of these posts, while univariate and multivariate linear regression was used to investigate the frequency of posts during this time period. Two reoccurring themes were identified exclusively post-injury; 'supporting team from the sideline' and 'sharing information about injury and rehabilitation'. The frequency of total posts did not differ significantly pre and post-injury, but the frequency of injury related posts increased in the immediate post-injury phase, then decreased between 4-8 weeks and 8-12 weeks post-injury. The frequency of injury related posts was higher with more severe injuries. The findings of this study suggest that injured players use social media to seek social support from their followers, especially in the immediate post-injury period and after sustaining a severe injury. The role of social media in injury rehabilitation may warrant further investigation, to determine if it could be used to facilitate return to play.

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