Latest research in football - week 35 - 2018

#1 The Relative Age Effect in the 10 Best Leagues of Male Professional Football of the Union of European Football Associations (UEFA)
Reference: J Sports Sci Med. 2018 Aug 14;17(3):409-416. eCollection 2018 Sep.
Authors: Yagüe JM, de la Rubia A, Sánchez-Molina J, Maroto-Izquierdo S, Molinero O
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6090398/pdf/jssm-17-409.pdf
Summary: The aim of the present research was to observe the relative age effect on professional soccer players of the ten best leagues of the Union of European Football Associations (UEFA), according to the IFFHS (International Federation of Football History and Statistics). The sample consisted of 5201 professional players who participated in the professional leagues during the 2016-2017 season. The birth date of each player was classified in four quartiles (Q1, Q2, Q3 and Q4). The frequencies (fr) and percentages (%) of the birth quartiles were analyzed. The chi square test (X2) and degrees of freedom (gl) were performed to check the differences in the intergroup distribution. Likewise, odd ratios were calculated for the different quartiles, where Q4 was the reference group according to the different leagues studied, playing positions (goalkeeper, defender, midfielder and forward) and classification (first four places, half-of the table and four last places). To calculate the size of the effect on the nominal variables, the Cramer V test was carried out. The results confirmed a greater representation of players born in Q1 and Q2, indicating statistically significant values (p < 0.05) for all the leagues studied, except in the Eerste Klasse A (Belgium). This significance was repeated for the demarcation variables in the field, with a greater effect in the case of the midfielders. Finally, the RAE also affected the three groups according to teams´ classification. The conclusions confirm the effect of the RAE in the sample studied, which would require a review of the talent selection processes in football in order to balance the chances of success of players born at the end of the year.


#2 Is Plantar Loading Altered During Repeated Sprints on Artificial Turf in International Football Players?
Reference: J Sports Sci Med. 2018 Aug 14;17(3):359-365. eCollection 2018 Sep.
Authors: Girard O, Millet GP, Thomson A, Brocherie F
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6090389/pdf/jssm-17-359.pdf
Summary: We compared fatigue-induced changes in plantar loading during the repeated anaerobic sprint test over two distinct distance intervals. Twelve international male football outfield players (Qatar Football Association) completed 6 × 35-m sprints (10 s of active recovery) on artificial turf with their football boots. Insole plantar pressure distribution was continuously recorded and values (whole foot and under 9 foot zones) subsequently averaged and compared over two distinct distance intervals (0-17.5 m vs. 17.5-35 m). Sprint times increased (p <0.001) from the first (4.87 ± 0.13 s) to the last (5.63 ± 0.31 s) repetition, independently of the distance interval. Contact area (150 ± 23 vs. 158 ± 19 cm2; -5.8 ± 9.1%; p = 0.032), maximum force (1910 ± 559 vs. 2211 ± 613 N; -16.9 ± 18.2%; p = 0.005) and mean pressure (154 ± 41 vs. 172 ± 37 kPa; -13.9 ± 19.0%; p = 0.033) for the whole foot were lower at 0-17.5 m vs. 17.5-35 m, irrespectively of sprint number. There were no main effects of sprint number or any significant interactions for any plantar variables of the whole foot. The distance interval × sprint number × foot region interaction on relative loads was not significant. Neither distance interval nor fatigue modified plantar pressure distribution patterns. Fatigue led to a decrement in sprint time but no significant change in plantar pressure distribution patterns across sprint repetitions.


#3 Time-use and environmental determinants of dropout from organized youth football and tennis
Reference: BMC Public Health. 2018 Aug 16;18(1):1022. doi: 10.1186/s12889-018-5919-2.
Authors: Deelen I, Ettema D, Kamphuis CBM
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6097310/pdf/12889_2018_Article_5919.pdf
Summary: Many adolescents drop out of organized sports. Lack of motivation and competing priorities are known as important reasons for dropout. However, time use factors as well as environmental determinants have been largely neglected in the current literature on dropout from youth sports. The aim of this study is to investigate how (changes in) time use and characteristics of the physical environment determine dropout from football and tennis among adolescents. Data on time use and background characteristics were collected through online surveys in 2015 and 2016 among adolescents aged 13-21 (N = 2555), including both the dropped outs and those who still continued membership of their football or tennis clubs. Physical environmental determinants (travel distance to the sports club, and neighbourhood density) were measured objectively. Binary logistic regression analyses were carried out for football and tennis separately to examine the associations between time use (time spent on various activities and changes related to the school and job situation), and environmental factors on the probability of dropping out from sports. Time spent on sports outside the context of the sports club, and time spent on social or voluntary activities at the sports club was positively associated with continuing being football and tennis members. Tennis players who changed schools or participated in two sports at the same time had a higher probability of dropping out, whereas tennis players who travelled greater distances from home to the tennis club were less likely to drop out. Determinants of dropout differed between football and tennis. However, time use variables were important predictors of dropout from football as well as tennis, whereas environmental determinants hardly contributed to the prediction of dropout. To keep youths involved in organized sports, this study recommends that sports professionals should: 1) offer flexibility in training and competition schedules, 2) stimulate participation in social activities and voluntary work at the sports club, 3) pay special attention to their needs and preferences, and 4) encourage possibilities to practice and play sports outside of regular training hours, for instance at the sports club or at playgrounds or parks in the neighbourhood.


#4 The effect of playing status, maturity status, and playing position on the development of match skills in elite youth football players aged 11-18 years: A mixed-longitudinal study
Reference: Eur J Sport Sci. 2018 Aug 17:1-12. doi: 10.1080/17461391.2018.1508502. [Epub ahead of print]
Authors: Saward C, Morris JG, Nevill ME, Sunderland C
Summary: This mixed-longitudinal study examined the development of match skills in elite male youth footballers (aged 11-18 years), while considering the effect of playing status, maturity status, and playing position. Across two seasons, 126 elite male youth footballers were assessed in 1-10 competitive matches (401 player-matches). For each match, the on-the-ball actions of each player were recorded using a notation system. The match skills observed were frequencies of successful passes, on-target shots, dribbles, crosses, clearances, and tackles/blocks/interceptions. Multilevel Poisson analysis was used to model the development of players, with regard to each match skill. Modelling revealed significant (p < .05) age-related changes in the frequency of several match skills. That is, dribbles increased, on-target shots, crosses and tackles/blocks/interceptions decreased, whereas changes in successful passes were position-specific. Players retained by an academy performed more dribbles compared to released players (p < .05) (e.g. retained vs. released 18-year-old centre forward = 4.1 vs. 2.0 dribbles per hour), and retained defenders performed more tackles/blocks/interceptions than released defenders (p < .05) (e.g. retained vs. released 18-year-old, on-time maturing centre back = 12.5 vs. 10.2 tackles/blocks/interceptions per hour). Moreover, compared to on-time maturing players, early maturing players performed more tackles/blocks/interceptions (p < .05) (e.g. on-time vs. early maturing retained 18-year-old centre back = 12.5 vs. 15.2 tackles/blocks/interceptions per hour). Playing position affected all match skills (p < .05). The developmental profiles of match skills presented here may support experts in identifying and developing talented footballers across a wide age range, while considering the influence of maturity status and playing position.


#5 Evaluation of Muscle Injuries in Professional Football Players: Does Coach Replacement Affect the Injury Rate?
Reference: Clin J Sport Med. 2018 Aug 15. doi: 10.1097/JSM.0000000000000640. [Epub ahead of print]
Authors: Dönmez G, Kudaş S, Yörübulut M, Yıldırım M, Babayeva N, Torgutalp ŞŞ
Summary: The objective was to assess the incidence and characteristics of muscle injuries in professional football players and to assess if coach dismissal may be related with muscle injuries within 1-month period from the dismissal. One hundred eighteen male football players from the Turkis first league participated in this study. Data on time-loss muscle injuries confirmed using magnetic resonance imaging were recorded, including type, body part, duration, and lay-off time, and training session and match exposure times. The muscle injury rate was evaluated at 2 weeks and 30 days after coach dismissal. In total, 124 muscle injuries were recorded, with injury incidences of 2.3 muscle injuries per 1000 hours of exposure overall, 1.2 in training sessions, and 13.6 in matches. Injury time loss ranged from 3 to 67 days (median, 13 days). Eighteen percent of the injuries (n = 23) were recurrent; no association was found between recurrence rate and the player's age or position (P = 0.15, P = 0.27, respectively). Recurrent injuries caused more severe injuries (26.1%, P = 0.02) and longer median lay-off time (P = 0.01). During the study, teams A and B replaced 7 and 3 coaches, respectively. The injury incidence increased to 5.3 per 1000 hours of exposure in the 2 weeks after the coach dismissal, and decreased to 4.5 within 1 month of coach dismissal. Given the link between coach dismissal and increased rates of muscle strain injuries, increased attentiveness to preventing muscle injuries during coaching transitions and to the impact of new training regimens is required by trainers and medical teams.


#6 Overuse injuries are prevalent in children's competitive football: a prospective study using the OSTRC Overuse Injury Questionnaire
Reference: Br J Sports Med. 2018 Aug 14. pii: bjsports-2018-099218. doi: 10.1136/bjsports-2018-099218. [Epub ahead of print]
Authors: Leppänen M, Pasanen K, Clarsen B, Kannus P, Bahr R, Parkkari J, Haapasalo H, Vasankari T
Summary: The purpose was to investigate the prevalence and burden of overuse injuries in children's football as well as player characteristics and their association with overuse injury risk. This investigation is based on the control arm (10 clubs) of a randomised controlled trial investigating prevention of injuries in youth football. We conducted a prospective 20-week follow-up study on overuse injuries among Finnish football players (n=733, aged 9-14 years). Each week, we sent a text message to players' parents to ask if the player had sustained any injury during the past week. Players with overuse problem were interviewed over the phone using an overuse injury questionnaire. The main outcome measures were prevalence of all overuse injuries and substantial overuse injuries (those leading to moderate or severe reductions in participation or performance) and injury severity. The average response rate was 95%. In total, 343 players (46.8%) reported an overuse problem while in the study. The average weekly prevalence of all overuse problems and substantial overuse problems was 12.8% and 6.0%, respectively. Injuries affecting the knee had the highest weekly prevalence (5.7% and 2.4% for all and substantial knee problems, respectively). Girls had a higher likelihood of knee problems (OR 2.70; 95% CI 1.69 to 4.17), whereas boys had a higher likelihood of heel problems (OR 2.82; 95% CI 1.07 to 7.44). The likelihood of reporting an overuse problem increased with age (OR 1.21; 95% CI 1.00 to 1.47). Overuse injuries are prevalent in children's competitive football. Knee overuse injuries represent the greatest burden on participation and performance.


#7 Communication quality between the medical team and the head coach/manager is associated with injury burden and player availability in elite football clubs
Reference: Br J Sports Med. 2018 Aug 13. pii: bjsports-2018-099411. doi: 10.1136/bjsports-2018-099411. [Epub ahead of print]
Authors: Ekstrand J, Lundqvist D, Davison M, D'Hooghe M, Pensgaard AM
Download link: https://bjsm.bmj.com/content/bjsports/early/2018/08/21/bjsports-2018-099411.full.pdf
Summary: We investigated medical staff interpretations and descriptions of internal communication quality in elite football teams to determine whether internal communication was correlated with injuries and/or player availability at training and matches. Medical staff from 36 elite football clubs across 17 European countries produced 77 reports at four postseason meetings to provide their perceptions of internal communications in their teams. They also recorded data on individual players' exposure to football and time-loss injuries. The injury burden and incidence of severe injuries were significantly higher in teams with low quality of communication between the head coach/manager and the medical team (scores of 1-2 on a 5-point Likert scale) compared with teams with moderate or high-quality scores (scores of 3-5; p=0.008 for both). Teams with low scores had 4%-5% lower training attendance (76% vs 83%, p=0.001) and less availability at matches (82% vs 88%, p=0.004) compared with teams with moderate or high communication quality scores. The quality of internal communication within a team was correlated with injury rates, training attendance and match availability.


#8 An Augmented Perceptual-Cognitive Intervention Using a Pattern Recall Paradigm With Junior Soccer Players
Reference: Front Psychol. 2018 Aug 23;9:1260. doi: 10.3389/fpsyg.2018.01260. eCollection 2018.
Authors: Schorer J, Schapschröer M, Fischer L, Habben J, Baker J
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6115512/pdf/fpsyg-09-01260.pdf
Summary: In sport, perceptual skill training software is intended to assist tactical training in the field. The aim of this field study was to test whether "laboratory-based" pattern recall training would augment tactical skill training performed on the field. Twenty-six soccer players between 14 and 16 years of age from a single team participated in this study and were divided into three groups. The first received field training on a specific tactical skill plus cognitive training sessions on the pattern recall task. The second performed only the field training while the third group served as a control group and had field training on other topics. The task on the pre-, post-, and retention-tests was to recall specific soccer patterns displayed on a computer screen. Results showed significant changes between pre- and post-test performance. There was no significant interaction between groups and tests but the effect size was large. From pre- to retention-test, there was a significant difference between tests and an interaction between groups and tests, but no main effect difference between groups. On the basis of significance testing only retention was affected by the additional training, however, descriptive results and effect sizes from pre- to post-test were as expected and suggested there were learning benefits. Together these results indicate that augmented perceptual-cognitive training might be beneficial, but some limitations in our study design (e.g., missing field test, missing placebo group, etc.) need to be improved in future work.


#9 Effect of a 6-week supervised detraining period on bone metabolism markers and their association with ergometrics and components of the hypothalamic-pituitary-gonadal (HPG) axis in professional male soccer players
Reference: J Bone Miner Metab. 2018 Sep 5. doi: 10.1007/s00774-018-0947-7. [Epub ahead of print]
Authors: Koundourakis NE, Androulakis N, Dermitzaki E, Venihaki M, Margioris AN
Summary: The aim of this study was to examine the effect of a supervised 6-week detraining period on bone metabolism markers, and their association with ergometrics, and components of the hypothalamic-pituitary-gonadal (HPG) axis in elite male professional soccer players. Sixty-seven soccer players (mean age ± SD 23.4 ± 5.2 years) that were following a supervised training program participated in this study. Players were tested twice: immediately after the conclusion of the competition period, and following the detraining period, for the determination of bone-turnover rates, ergometrics, and components of the HPG-axis. The detraining period resulted in significant reduction in osteocalcin [OC] (p < 0.001), C-terminal propeptide of collagen type-I [CICP] (p = 0.002), and bone-alkaline-phosphatase [b-ALP] (p < 0.001) values, while C-terminal telopeptide [CTX] was increased (p < 0.001). No significant relationships were apparent between bone biomarkers and body weight, body-fat %, total testosterone, free testosterone, estradiol, follicle-stimulating hormone, and luteinizing hormone in both experimental sessions (p > 0.05). Similarly, despite the deterioration in ergometrics after detraining (all p < 0.001), no significant correlations were evident (p > 0.05) between bone biomarkers and maximal oxygen consumption, squat jump, countermovement jump, and 20 m sprint performance, and also between % change of bone biomarkers and ergometrics, apart from a weak relationship (p = 0.041) between OC and VO2max of questionable value. Our results suggest that the 6-week soccer off-season detraining period in our study negatively affected bone physiology as reflected by the suppression of bone-formation rate and a parallel induction of bone resorption. The cause of this acute alteration of bone-turnover rates is not related to the examined components of the HPG-axis, although parallels is not associated with the changes in ergometrics.


#10 Epidemiology of Upper Extremity Soccer Injuries Among High School- and College-Aged Players in the United States: An Analysis of the 1999-2016 NEISS Database
Reference: Sports Health. 2018 Sep 5:1941738118795483. doi: 10.1177/1941738118795483. [Epub ahead of print]
Authors: Durand WM, Goodman AD, Giglio P, Etzel C, Owens BD
Summary: Although lower extremity injuries are more common than upper extremity injuries in high school- and college-aged soccer players, upper extremity injuries may be equally severe. The epidemiology of upper extremity injuries is poorly characterized in this population.  The authors hypothesis that upper extremity injuries are an important contributor to soccer-related morbidity among high school- and college-aged players. The National Electronic Injury Surveillance System (NEISS) is a nationally representative sample of 100 hospital emergency departments (EDs). Each record contains demographic and injury information. Records from 1999 to 2016 were analyzed, including patients between the ages of 14 and 23 years with a soccer-related injury sustained at school or during an athletic event. A total of 1,299,008 high school- or college-aged patients presented to the ED for a soccer-related injury from 1999 to 2016, of which 20.4% were in the upper extremity. Patients were predominantly male (58.0%) and high school-aged (81.4%). Males constituted a greater proportion of upper extremity injuries when compared with other injury locations (63.5% male for upper extremity). Upper extremity injuries were more likely to be fractures (43.7% vs 13.9%) and dislocations (7.1% vs 3.4%) and less likely to be strains/sprains (27.8% vs 56.6%). Males suffered more shoulder dislocations (81.8% males among patients with shoulder dislocation vs 57.8% among those with other injuries), finger dislocations (72.0% vs 58.0%), upper arm fractures (74.9% vs 57.6%), and forearm fractures (68.3% vs 57.3%). Upper extremity injuries are frequent in high school- and college-aged soccer players presenting to the ED. Efforts to reduce soccer-related injuries should include strategies targeting the upper extremity, perhaps reducing the incidence of high-energy falls. Efforts to reduce soccer-related injuries should include strategies targeting upper extremity injuries, particularly among males and college-aged players.


#11 Pathogenic Factors Associated With Osgood-Schlatter Disease in Adolescent Male Soccer Players: A Prospective Cohort Study
Reference: Orthop J Sports Med. 2018 Aug 28;6(8):2325967118792192. doi: 10.1177/2325967118792192. eCollection 2018 Aug.
Authors: Watanabe H, Fujii M, Yoshimoto M, Abe H, Toda N, Higashiyama R, Takahira N
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6113738/pdf/10.1177_2325967118792192.pdf
Summary: A previous cross-sectional study reported that pathogenic factors associated with Osgood-Schlatter disease (OSD) in adolescent athletes include increased quadriceps muscle tightness, lower leg malalignment, and development of apophysitis in the tibial tuberosity. The purpose was to confirm these pathogenic factors associated with OSD in a longitudinal study with regard to physical function and performance. In this study, 37 boys (mean age, 10.2 ± 0.4 years) were recruited from 2 soccer teams at an elementary school. This cohort study was conducted over an observation period of 1 year, with measurements recorded at baseline, followed by screening for OSD every 6 months. Variables evaluated at baseline included physical function (morphometry, joint flexibility, and lower extremity alignment), presence of Sever disease, and kicking motion. Pathogenic factors associated with OSD in the support leg of adolescent male soccer players included height, weight, body mass index, quadriceps femoris muscle tightness in the kicking and support legs, and gastrocnemius muscle tightness, soleus muscle tightness, and medial longitudinal arch in the support leg. Additional factors included a diagnosis of Sever disease and distance from the lateral malleolus of the support leg's fibula to the center of gravity during kicking. The onset of OSD was found to be affected by many factors, including developmental stage, physical attributes, and pre-existing apophysitis. In particular, a diagnosis of Sever disease and backward shifting of the center of gravity during kicking increased the risk of the subsequent onset of OSD, suggesting that these factors are very important as a possible focus for interventions.


#12 Inter-individual Variability in Responses to 7 Weeks of Plyometric Jump Training in Male Youth Soccer Players
Reference: Front Physiol. 2018 Aug 20;9:1156. doi: 10.3389/fphys.2018.01156. eCollection 2018.
Authors: Ramirez-Campillo R, Alvarez C, Gentil P, Moran J, García-Pinillos F, Alonso-Martínez AM, Izquierdo M
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6109752/pdf/fphys-09-01156.pdf
Summary: The purpose of this study was to compare the inter-individual variability in the effects of plyometric jump training (PJT) on measures of physical fitness (sprint time, change of direction speed, countermovement jump, 20- and 40-cm drop jump reactive strength index, multiple five bounds distance, maximal kicking distance, and 2.4-km time trial) in youth soccer players who completed a PJT program versus players who completed soccer training only. In a single-blinded study, participants aged between 10 and 16 years were randomly divided into a PJT group (n = 38) and a control group (n = 38). The experimental group participated in a PJT program twice weekly for 7 weeks, whereas the control group continued with their regular soccer training sessions. Between-group differences were examined using a Mann-Whitney U test. Nonresponders where defined as individuals who failed to demonstrate any beneficial change that was greater than two times the typical error of measurement from zero. The results indicated that the mean group improvement for all physical fitness measures was greater (p < 0.05) in the PJT group (Δ = 0.4 to 23.3%; ES = 0.04 to 0.58) than in the control group (Δ = 0.1 to 3.8%; ES = 0.02 to 0.35). In addition, a significantly greater (p < 0.05) number of responders across all dependent variables was observed in the PJT group (from 4 up to 33 responders) than in the control group (from 0 up to 9 responders). In conclusion, compared to soccer training only, PJT induced greater physical fitness improvements in youth soccer players, with a greater number of responders for all the physical fitness tests related to jumping, speed, change of direction speed, endurance, and kicking technical ability.


#13 Heart Rate and Perceived Experience Differ Markedly for Children in Same- versus Mixed-Gender Soccer Played as Small- and Large-Sided Games
Reference: Biomed Res Int. 2018 Aug 5;2018:7804642. doi: 10.1155/2018/7804642. eCollection 2018.
Authors: Póvoas S, Randers MB, Krustrup P, Larsen MN, Pereira R, Castagna C
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6098911/pdf/BMRI2018-7804642.pdf
Summary: This study examines heart rate (HR) and perceived experience during same- versus mixed-gender soccer played as small- (SSG) and large-sided (LSG) games. HR, rating of perceived exertion (RPE), and fun scores were determined in 134 pupils (50 girls, 84 boys) randomly assigned to same- and mixed-genders formats playing 2x15-min of SSG (2v2, 4v4) and LSG (12v12) in a random order (~50 m2/player). HR was lower (p≤0.03) for girls when playing together with boys than when playing alone (71±10 versus 77±7%HRmax), while being similar for boys playing mixed- or same-gender games (74±7 versus 77±4%HRmax). Boys perceived less fun when playing together with girls than when playing alone (4.4±2.3 versus 6.3±2.3, p<0.001). Irrespective of gender, higher (p<0.001) HRmean, %time>80%HRmax, and RPE were observed during 2v2 (78±9%HRmax, 43±33%, 5.5±2.5) and 4v4 (76±9%HRmax, 39±32%, 5.5±2.7) than during 12v12 (70±10%HRmax, 23±27%, 3.8±2.9). Cardiovascular strain was lower for girls when playing together with boys than when playing alone in LSG. SSG were more intense than LSG when girls played mixed-gender games and when boys played mixed- and same-gender games. When boys played mixed-gender games, SSG were considered more fun than LSG. Physical education teachers and coaches should consider gender and game format differences when using soccer.