Latest research in football - week 1 - 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 Physiological and Physical Responses According to the Game Surface in a Soccer Simulation Protocol
Reference: Int J Sports Physiol Perform. 2017 Dec 28:1-22. doi: 10.1123/ijspp.2017-0570. [Epub ahead of print]
Authors: Lopez-Fernandez J, Sanchez-Sanchez J, Garcia-Unanue J, Felipe JL, Colino-Acevedo E, Gallardo L
Summary: Recent studies have shown that soccer player's responses are similar on natural grass (NG) and artificial turf (AT), but they did not control the mechanical properties of these surfaces. This work aimed to analyse the influence of the game surface on amateur soccer player's physical and physiological responses using a soccer simulation protocol (SSP). Sixteen amateur players performed three bouts of the SSP on AT and NG. The mechanical properties of both surfaces were recorded. The order of surfaces was randomly established for each participant. Physiological responses of players were assessed before and after the six-repeated sprints test existing at the midpoint of each bout. Fatigue (% Best; % Diff) and general variables (total time; best time, mean time; maximum speed) for both the repeated sprint test and the agility tests (nonlinear actions at maximum speed) incorporated into the SSP were also analysed. The two surfaces displayed different mechanical properties. Physical responses were found similar for both surfaces (p>0.05) before and after the repeated sprint test. There were no surface differences in sprint times or fatigue variables for the repeated sprint test (p>0.05). The agility test was faster on AT than on NG in bout 1 (average speed [+1.17 Km/h; p=0.037]; agility test cut time [-0.31 s; p=0.027] and best time [-0.52 s; p=0.042]). The differences in the mechanical properties of the two surfaces are not sufficient to cause differences in the physiological and physical responses of soccer players, although they may affect turns and cuts.

#2 Investigating the influence of intra-individual changes in perceived stress symptoms on injury risk in soccer
Reference: Scand J Med Sci Sports. 2017 Dec 28. doi: 10.1111/sms.13048. [Epub ahead of print]
Authors: Clement D, Ivarsson A, Tranaeus U, Johnson U, Stenling A
Summary: Research has shown that high levels of stress and stress responsivity can increase the risk of injuries. However, most of the research that has supported this notion has focused on between-person relationships, ignoring the relationships at the within-person level. As a result, the objective of this study was to investigate if within-person changes in perceived stress symptoms over a one-month time period could predict injury rates during the subsequent three months. A prospective design with two measurement points (Time 1 - at the beginning of the season and Time 2 - one month into the season) was utilized. A total of 121 competitive soccer players (85 males and 36 females; Mage = 18.39, SD = 3.08) from Sweden and the United States completed the Kessler Psychological Distress Scale (KPDS) and a demographic sheet at Time 1. The KPDS was also completed at Time 2 and all acute injuries that occurred during the subsequent three-month period were recorded. A Bayesian latent change scores model was used to determine if within-person changes in stress symptoms could predict the risk of injury. Results revealed that there was a credible positive effect of changes in stress symptoms on injury rates, indicating that an increase in reported stress symptoms was related to an increased risk for injury. This finding highlights the importance of creating caring and supportive sporting environments and relationships and teaching stress management techniques, especially during the earlier portion of competitive seasons, to possibly reduce the occurrence of injuries.

#3 Soccer helps build strong bones during growth: a systematic review and meta-analysis
Reference: Eur J Pediatr. 2017 Dec 28. doi: 10.1007/s00431-017-3060-3. [Epub ahead of print]
Authors: Lozano-Berges G, Matute-Llorente A, Gonzalez-Aguero A, Gomez-Bruton A, Gomez-Cabello A, Vicente-Rodriguez G, Casajus JA
Summary: The aim of this study was to analyze the effects of soccer practice on bone in male and female children and adolescents. MEDLINE, PubMed, SPORTDiscus and Web of Science databases were searched for scientific articles published up to and including October 2016. Twenty-seven studies were included in this systematic review (13 in the meta-analysis). The meta-analysis was performed by using OpenMeta[Analyst] software. It is well documented that soccer practice during childhood provides positive effects on bone mineral content (BMC) and density (BMD) compared to sedentary behaviors and other sports, such as tennis, weightlifting, or swimming. Furthermore, soccer players present higher BMC and BMD in most weight-bearing sites such as the whole body, lumbar spine, hip, and legs. Moreover, bone differences were minimized between groups during prepuberty. Therefore, the maturity status should be considered when evaluating bone. According to meta-analysis results, soccer practice was positively associated with whole-body BMD either in males (mean difference 0.061; 95%CI, 0.042-0.079) or in females (mean difference 0.063; 95%CI, 0.026-0.099). Soccer may be considered a sport that positively affects bone mass during growth. Pubertal soccer players presented increased bone mass compared to controls or other athletes; however, these bone differences are minimized during the prepubertal stage. What is known: • It has been described that childhood and adolescence are important periods for bone mass and structure. • Previous studies have demonstrated that soccer participation improves bone mass in male and female children and adolescents. What is new: • The differences between soccer players and controls are more marked during puberty than prepuberty. • Weight-bearing sites such as lumbar spine, hip, femoral neck, trochanter, intertrochanteric region and both legs are particularly sensitive to soccer actions.

#4 Assessing Differences in Cardiorespiratory Fitness With Respect to Maturity Status in Highly Trained Youth Soccer Players
Reference: Pediatr Exerc Sci. 2017 Dec 23:1-13. doi: 10.1123/pes.2017-0185. [Epub ahead of print]
Authors: Doncaster G, Iga J, Unnithan V
Summary: The purpose of the study was to examine differences in measures of cardiorespiratory fitness and determinants of running economy with respect to maturity status in a group of highly trained youth soccer players. A total of 21 highly trained youth soccer players participated in this study. On separate visits, players' peak oxygen uptake (VO2peak), running economy at 3 different speeds [8 km·h-1, 80% gaseous exchange threshold (GET), and 95% GET], and pulmonary oxygen uptake (VO2) kinetics were determined. Players also performed a Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1). Players were categorized as either "pre-PHV" (peak height velocity) or "mid-PHV" group using the measure of maturity offset. Independent t tests and Cohen's d effect sizes were then used to assess differences between groups. The mid-PHV group was significantly taller, heavier, and advanced in maturity status. Absolute measures of VO2peak were greater in the mid-PHV group; however, when expressed relative to body mass, fat-free mass, and theoretically derived exponents, VO2peak values were similar between groups. Pre-PHV group presented a significantly reduced VO2 response, during relative submaximal running speeds, when theoretically derived exponents were used, or expressed as %VO2peak. VO2 kinetics (tau) were faster during a low (standing) to moderate (95% GET) transition in the pre-PHV group. Yo-Yo IR1 performance was similar between groups. Although measures of VO2peak and Yo-Yo IR1 performance are shown to be similar between groups, those categorized as pre-PHV group display a superior running economy at relative submaximal running speeds and faster taus during a low to moderate exercise transition than their more mature counterparts.

#5 Reliability, Validity and Sensitivity of a Novel Smartphone-Based Eccentric Hamstring Strength Test in Professional Football Players
Reference: Int J Sports Physiol Perform. 2017 Dec 28:1-19. doi: 10.1123/ijspp.2017-0336. [Epub ahead of print]
Authors: Lee JWY, Cai MJ, Yung PSH, Chan KM
Summary: This study aims to evaluate the test-retest reliability, sensitivity and concurrent validity of a smartphone-based method for assessing eccentric hamstring strength among male professional football players. Twenty-five healthy male professional football players have performed CUHK Nordic break-point test, hamstring fatigue protocol and isokinetic hamstring strength test. CUHK Nordic break-point test is based on a Nordic hamstring exercise. The Nordic break-point angle was defined as the maximum point where the participants could no longer support the weight of their body against gravity. The criterion for the sensitivity test was the pre-sprinting and post-sprinting difference of the Nordic break-point angle with a hamstring fatigue protocol. The hamstring fatigue protocol consists of 12 repetitions of the 30m sprint with 30 seconds recovery between each sprint. Hamstring peak torque of the isokinetic hamstring strength test was used as the criterion for validity. A high test-retest reliability (ICC = 0.94, 95% CI = 0.82 - 0.98) was found in the Nordic break-point angle measurements. The Nordic break-point angle significantly correlated with isokinetic hamstring peak torques at eccentric action of 30 °/s (r = 0.88, r2 = 0.77, p < 0.001). The minimal detectable difference was 8.03 °. The sensitivity of the measure was good enough that a significance difference (ES = 0.70, p < 0.001) was found between pre-sprinting and post-sprinting value. The CUHK Nordic break-point test is a simple, portable, quick smartphone based method to provide reliable and accurate eccentric hamstring strength measures among male professional football players.

#6 Electrocardiographic patterns and long-term training-induced time changes in 2484 elite football players
Reference: Arch Cardiovasc Dis. 2017 Dec 21. pii: S1875-2136(17)30233-4. doi: 10.1016/j.acvd.2017.10.005. [Epub ahead of print]
Authors: Huttin O, Selton-Suty C, Venner C, Vilain JB, Rochecongar P, Aliot E
Summary: High-level physical training induces cardiac structural and functional changes, including 12-lead electrocardiogram modifications. The purpose of this cross-sectional longitudinal study was to establish a quantitative electrocardiographic profile in highly trained football players. Initial and serial annual electrocardiogram monitoring over subsequent years allowed us to investigate the long-term effects of exercise on cardiac conduction and electrophysiological remodelling. Between 2005 and 2015, serial evaluations, including 12-lead electrocardiograms, were performed in 2484 elite male football players from the French Professional Football League. A total of 6247 electrocardiograms were performed (mean 2.5±1.8 electrocardiograms/player). Heart rate (beats/min), atrioventricular delay (PR, ms), intraventricular conduction delay (QRS, ms), corrected QT delay (QTc) and electrical left ventricular hypertrophy (LVH) (Sokolow-Lyon index, mm) were measured, and the fixed effect of time was evaluated using panel data analysis (β [95% confidence interval] change between two visits). According to European Society of Cardiology and Seattle criteria, 15% of the electrocardiogram intervals were considered abnormal. We observed 17% sinus bradycardia<50 beats/min (mean heart rate 60±11 beats/min), 8% first-degree atrioventricular block>200ms (mean PR 170±27ms), 1.5% QRS>120ms (mean QRS 87±19ms) and 3% prolonged QT interval (mean QTc using Bazett's formula [QTcB] 395±42ms). Electrical LVH (mean Sokolow-Lyon index 34±10mm) was noted in 37% of players. Over time, electrocardiogram changes were noted, with a significant remodelling trend in terms of decreased heart rate (-0.41 [-0.55 to -0.26] beats/min), QRS duration (-2.4 [-2.7 to -2.1] ms) and QTcB delay (-1.2 [-1.9 to -0.5] ms) (all P<0.001). This study describes usual electrocardiographic training-induced changes in a large series of football players over the follow-up timeframe. The most frequent outliers were electrical LVH and sinus bradycardia. These results have important implications for optimizing electrocardiogram interval measurements in initial screening and during follow-up of football players, with potential cost-effective implications.

#7 A Multinational Cluster Randomised Controlled Trial to Assess the Efficacy of '11+ Kids': A Warm-Up Programme to Prevent Injuries in Children's Football
Reference: Sports Med. 2017 Dec 22. doi: 10.1007/s40279-017-0834-8. [Epub ahead of print]
Authors: Rossler R, Junge A, Bizzini M, Verhagen E, Chomiak J, Aus der Funten K, Meyer T, Dvorak J, Lichtenstein E, Beaudouin F, Faude O
Summary: The objective of this study was to assess the efficacy of a newly developed warm-up programme ('11+ Kids') regarding its potential to reduce injuries in children's football. Children's football teams (under 9 years, under 11 years, and under 13 years age groups) from Switzerland, Germany, the Czech Republic and the Netherlands were invited. Clubs were randomised to an intervention group and a control group, and followed for one season. The intervention group replaced their usual warm-up by '11+ Kids', while the control group warmed up as usual. The primary outcome was the overall risk of football-related injuries. Secondary outcomes were the risks of severe and lower extremity injuries. We calculated hazard ratios using extended Cox models, and performed a compliance analysis. In total, 292,749 h of football exposure of 3895 players were recorded. The mean age of players was 10.8 (standard deviation 1.4) years. During the study period, 374 (intervention group = 139; control group = 235) injuries occurred. The overall injury rate in the intervention group was reduced by 48% compared with the control group (hazard ratio 0.52; 95% confidence interval 0.32-0.86). Severe (74% reduction, hazard ratio 0.26; 95% confidence interval 0.10-0.64) and lower extremity injuries (55% reduction, hazard ratio 0.45; 95% confidence interval 0.24-0.84) were also reduced. Injury incidence decreased with increasing compliance. '11+ Kids' is efficacious in reducing injuries in children's football. We observed considerable effects for overall, severe and lower extremity injuries. The programme should be performed at least once per week to profit from an injury preventive effect. However, two sessions per week can be recommended to further increase the protective benefit.

#8 Crowd medical services in the English Football League: remodelling the team for the 21st century using a realist approach
Reference: BMJ Open. 2017 Dec 21;7(12):e018619. doi: 10.1136/bmjopen-2017-018619.
Authors: Leary A, Kemp A, Greenwood P, Hart N, Agnew J, Barrett J, Punshon G
Summary: The objective was to evaluate the new model of providing care based on demand. This included reconfiguration of the workforce to manage workforce supply challenges and meet demand without compromising the quality of care. Currently the Sports Ground Safety Authority recommends the provision of crowd medical cover at English Football League stadia. The guidance on provision of services has focused on extreme circumstances such as the Hillsborough disaster in 1989, while the majority of demand on present-day services is from patients with minor injuries, exacerbations of injuries and pre-existing conditions. A new model of care was introduced in the 2009/2010 season to better meet demand. A realist approach was taken. Data on each episode of care were collected over 14 consecutive football league seasons at Millwall FC divided into two periods, preimplementation of changes and postimplementation of changes. Data on workforce retention and volunteer satisfaction were also collected. The data were obtained from one professional football league team (Millwall FC) located in London, UK. The primary outcome was to examine the demand for crowd medical services. The secondary outcome was to remodel the service to meet these demands. In total, 981 episodes of care were recorded over the evaluation period of 14 years. The groups presenting, demographic and type of presentation did not change over the evaluation. First aiders were involved in 87.7% of episodes of care, nurses in 44.4% and doctors 17.8%. There was a downward trend in referrals to hospital. Workforce feedback was positive. The new workforce model has met increased service demands while reducing the number of referrals to acute care. It involves the first aid workforce in more complex care and key decision-making and provides a flexible registered healthcare professional team to optimise the skill mix of the team.

Australian Football
#1 The Quantification of Within Week Session Intensity, Duration and Intensity Distribution Across a Season in Australian Football Using the Session RPE Method
Reference: Int J Sports Physiol Perform. 2017 Dec 28:1-21. doi: 10.1123/ijspp.2017-0626. [Epub ahead of print]
Authors: Juhari F, Ritchie DM, O'Connor F, Pitchford N, Weston M, Thornton HR, Bartlett JDB
Summary: Team-sports training requires the daily manipulation of intensity, duration and frequency with pre-season focusing on meeting the demands of in-season competition and in-season on maintaining fitness. To provide information about daily training in Australian Football (AF), this study aimed to quantify session intensity, duration, and intensity distribution across different stages of an entire season. Intensity (session Ratings of Perceived Exertion [s-RPE]; CR-10 scale) and duration were collected from forty-five professional male AF for every training session and game. Each s-RPE was categorized into the corresponding intensity zone; Low (<4.0 AU), Moderate (≥4.0 and <7.0), and High (≥7.0) to categorize session intensity. Linear mixed models were constructed to estimate session duration, intensity and distribution between the 3 pre-season and 4 in-season periods. Effects were assessed using linear mixed models, and magnitude-based inferences. The distribution of the mean session intensity across the season was 29% low-, 57% moderate- and 14% high-intensity. While 96% of games were high-intensity, 44% and 49% of skills training sessions were low- and moderate-intensity, respectively. Running had the highest proportion of high-intensity training sessions (27%). Pre-season displayed higher training session intensity (ES = 0.29-0.91) and duration (ES = 0.33-1.44), while in-season game intensity (ES = 0.31-0.51) and duration (ES = 0.51-0.82) were higher. By using a cost-effective monitoring tool, this study provides information about the intensity, duration and intensity distribution of all training types across different phases of a season, thus allowing a greater understanding of the training and competition demands of Australian Footballers.

American Football
#1 Catastrophic Eye Injury in a Football Player
Reference: Phys Sportsmed. 1982 Oct;10(10):71-72. doi: 10.1080/00913847.1982.11947341.
Authors: Heinrichs EH, Willcockson JR
Summary: In brief Although catastrophic eye injuries are rare in collegiate football, this varsity defensive tackle sustained a giant inferior retinal tear with a partially detached retina when another player's thumb went through his face mask. The retina was surgically repaired, and the player's vision in that eye is 20/20 with a contact lens. He continues to play football as an offensive tackle.

#2 Fatalities and Catastrophic Injuries in Football
Reference: Phys Sportsmed. 1982 Oct;10(10):135-140. doi: 10.1080/00913847.1982.11947346.
Authors: Mueller FO, Blyth CS
Summary: In brief Football fatality and catastrophic injury data for 1976 through 1981 are compared with earlier data. The purpose is to analyze the data in regard to rule and equipment changes that have taken place in football since 1976 and to demonstrate the reduction in fatalities and catastrophic injuries. Fatality data for 1981 show five high school and two college fatalities. In 1981 there were five permanent spinal cord injuries in high schools and one in college.

#3 Mouth Protectors in Junior Football Players
Reference: Phys Sportsmed. 1982 Sep;10(9):41-48. doi: 10.1080/00913847.1982.11947318.
Authors: Godwin WC, Craig RG, Koran A, Lang BR, Powers JM
Summary: In brief This study tested Sta-Guard and Proform mouth protectors that were worn by 280 football players aged 9 to 12 years. Laboratory studies were also conducted to test tensile and tear strength, dynamic modulus and resilience, and hardness. The players received new mouth guards every two weeks for 12 weeks and reported any problems with gagging, taste, speech, feel, and durability. Ninety percent of the boys preferred the Sta-Guard mouth protector, stating that it was softer, more resilient, and more comfortable than the Proform mouth guard.

#4 The Association of Vitamin D Status in Lower Extremity Muscle Strains and Core Muscle Injuries at the National Football League Combine
Reference: Arthroscopy. 2017 Dec 19. pii: S0749-8063(17)31282-3. doi: 10.1016/j.arthro.2017.10.005. [Epub ahead of print]
Authors: Rebolledo BJ, Bernard JA, Werner BC, Finlay AK, Nwachukwu BU, Dare DM, Warren RF, Rodeo SA
Summary: The purpose of the study was to evaluate the association between serum vitamin D level and the prevalence of lower extremity muscle strains and core muscle injuries in elite level athletes at the National Football League (NFL) combine. During the 2015 NFL combine, all athletes with available serum vitamin D levels were included for study. Baseline data were collected, including age, race, body mass index, position, injury history specific to lower extremity muscle strain or core muscle injury, and Functional Movement Screen scores. Serum 25-hydroxyvitamin D was collected and defined as normal (≥32 ng/mL), insufficient (20-31 ng/mL), and deficient (<20 ng/mL). Univariate regression analysis was used to examine the association of vitamin D level and injury history. Subsequent multivariate regression analysis was used to examine this relation with adjustment for collected baseline data variables. The study population included 214 athletes, including 78% African American athletes and 51% skilled position players. Inadequate vitamin D was present in 59%, including 10% with deficient levels. Lower extremity muscle strain or core muscle injury was present in 50% of athletes, which was associated with lower vitamin D levels (P = .03). Athletes with a positive injury history also showed significantly lower vitamin D levels as compared with uninjured athletes (P = .03). African American/black race (P < .001) and injury history (P < .001) was associated with lower vitamin D. Vitamin D groups showed no differences in age (P = .9), body mass index (P = .9), or Functional Movement Screen testing (P = .2). Univariate analysis of inadequate vitamin D levels showed a 1.86 higher odds of lower extremity strain or core muscle injury (P = .03), and 3.61 higher odds of hamstring injury (P < .001). Multivariate analysis did not reach an independent association of low vitamin D with injury history (P = .07). Inadequate vitamin D levels are a widespread finding in athletes at the NFL combine. Players with a history of lower extremity muscle strain and core muscle injury had a higher prevalence of inadequate vitamin D.

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