Latest research in football - week 28 - 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 Prone Hip Extension Muscle Recruitment is Associated with Hamstring Injury Risk in Amateur Soccer
Reference: Int J Sports Med. 2017 Jul 13. doi: 10.1055/s-0043-103016. [Epub ahead of print]
Authors: Schuermans J, Van Tiggelen D, Witvrouw E
Summary: 'Core stability' is considered essential in rehabilitation and prevention. Particularly with respect to hamstring injury prevention, assessment and training of lumbo-pelvic control is thought to be key. However, supporting scientific evidence is lacking. To explore the importance of proximal neuromuscular function with regard to hamstring injury susceptibility, this study investigated the association between the Prone Hip Extension (PHE) muscle activation pattern and hamstring injury incidence in amateur soccer players. 60 healthy male soccer players underwent a comprehensive clinical examination, comprising a range of motion assessments and the investigation of the posterior chain muscle activation pattern during PHE. Subsequently, hamstring injury incidence was recorded prospectively throughout a 1.5-season monitoring period. Players who were injured presented a PHE activation pattern that differed significantly from those who did not. Contrary to the controls, hamstring activity onset was significantly delayed (p=0.018), resulting in a shifted activation sequence. Players were 8 times more likely to get injured if the hamstring muscles were activated after the lumbar erector spinae instead of vice versa (p=0.009). Assessment of muscle recruitment during PHE demonstrated to be useful in injury prediction, suggesting that neuromuscular coordination in the posterior chain influences hamstring injury vulnerability.

#2 Effects of a Tapering Period on Physical Condition in Soccer Players
Reference: J Strength Cond Res. 2017 Jul 12. doi: 10.1519/JSC.0000000000002138. [Epub ahead of print]
Authors: Beltran-Valls MR, Camarero-Lopez G, Beltran-Garrido JV, Cecilia-Gallego P
Summary: The aim of this research was to analyze the effects of a two-week step tapering period on lower-limb muscle power, change of direction (COD) and acceleration capacities, and on the stress-recovery state in an amateur soccer team. Twenty-two male players were included in the study. Following a six-week progressive training, the sample was divided into: experimental group (n = 11), who did a two-week period of taper in which training volume was 50% reduced (intensity was kept high) and control group (n = 11), which kept on with the training. Muscle power (countermovement jump test), acceleration (10m sprint test), COD (Illinois test) and stress and recovery perceptions (RESTQ questionnaire) were evaluated before training, at the end of it (pre-tapering, PRE-TP) and after the tapering period (post-tapering, POST-TP). Following the taper, the experimental group in comparison to the control group showed significantly improved power (1029.71 ± 108.51 W/kg vs. 1084.21 ± 110.87 W/kg; p < 0.01), acceleration (1.72 ± 0.09 s vs. 1.67 ± 0.07 s; p < 0.05), and lower stress levels (1.9±0.5 vs. 1.6±0.5; p < 0.01) (PRE-TP vs. POST-TP, respectively). COD did not show significant changes. In conclusion, a two-week step tapering program was found to be an effective periodization strategy to increase muscle power and acceleration, and to reduce stress perception in soccer amateur players.

#3 Between-game variation of physical soccer performance measures in highly trained youth soccer players
Reference: J Strength Cond Res. 2017 Jul 12. doi: 10.1519/JSC.0000000000002132. [Epub ahead of print]
Authors: Doncaster G, Unnithan V
Summary: The purpose was to assess the between-game variation in measures of physical performance during 11 v 11 soccer match-play, over a short period of time, in highly trained youth soccer players. A single cohort observational study design was employed. Physical match performance data were collected from 17 male, highly trained youth soccer players (age: 13.3 ± 0.4 y) over three, 2 x 20min, 11 v 11 matches. Using 10 Hz GPS, the variables selected for analyses were total distance (TD), high-speed running (HSR), very high-speed running (VHSR), number of high-speed running efforts (HSReff) and number of very high-speed running efforts (VHSReff). Match data was also separated into cumulative 5 min epochs, to identify the peak 5 min epoch and the mean of the cumulative 5 min epochs for each match. Variability was quantified using the coefficient of variation (CV), Standard error of measurement (SEM) and intra-class correlation coefficient (ICC). Between- and within-player smallest worthwhile changes (SWC) were also calculated for each variable to aid in the interpretation of the data. Analysis of the variance between games reported a low CV for TD (3.8%) but larger CVs for HSR (33.3%), HSReff (35.4%) and VHSR and VHSReff (59.6 and 57.4 %, respectively). Analysis of 5 min epochs (peak and average) found an increase in the CVs beyond that of the values reported for the whole match. Between-player SWC in high intensity physical performance data ranged from 24.7 - 42.4 %, whereas within-player SWC ranged from 1.2 - 79.9%. The between-game variability of high and very high intensity activities in youth soccer players, across three soccer matches over a short period of time (2 weeks), is relatively 'large' and specific to the individual, thus highlighting the need for caution when interpreting physical performance data between games and players.

#4 Fatigue In U12 Soccer-7 Players During Repeated One-Day Tournament Games - A Pilot Study
Reference: J Strength Cond Res. 2017 Jul 12. doi: 10.1519/JSC.0000000000002141. [Epub ahead of print]
Authors: Sanchez-Sanchez J, Sanchez M, Hernandez D, Ramirez-Campillo R, Martinez C, Nakamura FY
Summary: The aim of this study was to describe and compare the distances and displacement speeds of U12 Soccer-7 athletes during four tournament Soccer-7 games (TG) played in less than 24-h (experimental condition) with those recorded during two league Soccer-7 games (LG) with 24-h of rest prior to the match (control condition). Ten participants (age = 10.3 ± 0.5 years) were recruited for the study. Main data analyzed during games included distance completed relative to match duration (Drel), maximal velocity and distance completed at different running speeds (including acceleration, deceleration, standing, walking, jogging, medium-intensity running, high-intensity running and sprinting). For data collection during games, athletes wore a GPS unit. Different (p<0.05) mean playing time was recorded during TG and LG (15.1 and 31.8 minutes/match, respectively). Drel during the four TG was maintained between 85.7 ± 8.5 m/min and 87.5 ± 8.5 m/min (P>0.05) and during the two LG between 84.2 ± 10.9 m/min and 87.5 ± 9.9 m/min (P>0.05). Moreover, similar Drel was recorded during TG and LG (86.8 m/min and 85.9 m/min, respectively). Compared to LG, during TG maximal velocity was lower (23.0 km/h and 21.3 km/h, respectively; P<0.05). In addition, compared to the last game of the tournament, in the preceding games the distance covered at low speeds (3.1-8.0 km/h) was lower (37.7% and 32.4%, respectively; P<0.05) and at high speeds (≥18.1 km/h) tend to be higher (2.5% and 3.3%, respectively). Therefore, compared with the control condition, accumulated Soccer-7 games with less than 24-h of inter-day rest negatively affects displacement speeds distribution (but not overall relative distances) in U12 Soccer-7 athletes. These results may help to better plan training and competition schedules to youth players.

#5 Effect of a professional soccer match in skin temperature of the lower limbs: a case study
Reference: J Exerc Rehabil. 2017 Jun 30;13(3):330-334. doi: 10.12965/jer.1734934.467. eCollection 2017 Jun.
Authors: de Andrade Fernandes A, Pimenta EM, Moreira DG, Sillero-Quintana M, Marins JCB, Morandi RF, Kanope T, Garcia ES
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Summary: The purpose of this study is to analyze the relationship between lower limbs skin temperature (Tsk) recorded by infrared thermography and creatine kinase (CK) response following an official soccer game. A professional soccer player, from the first division Brazilian League, defender, 27 years and 183 cm of height was analyzed. Measures of Tsk with a thermal camera and blood CK concentrations were obtained 24 hr before (24H-PRE), 24 (24H-POST) and 48 hr (48H-POST) after an official match. The results showed that CK values were 193 U/L 24 hr before, rising to 1,083 U/L 24 hr after the game and 414 U/L 48 hr after the game. Anterior thigh Tsk was 31.5°C, 33.8°C, and 31.8°C in the moments 24H-PRE, 24H-POST, and 48H-POST, respectively. Similarly, anterior leg presented temperature of 31.2°C, 33.3°C, and 31.5°C at the same moments. Qualitative analysis of the thermograms showed that whole lower limbs are much warmer 24 hr after the match and certain areas as the right anterior thigh, the left anterior leg, both anterior ankles, and both posterior thighs have not fully recovered their initial Tsk 48 hr after the match. The results of this study indicate that participation in a professional soccer match can lead to significant increases in Tsk values measured by IRT 24 hr after the match. Considering this variable as an indicator of muscular damage, it could help in the process of training control, being part of an injury prevention program in professional soccer clubs.

#6 Quantifying changes in squat jump height across a season of men's collegiate soccer
Reference: J Strength Cond Res. 2017 Jul 8. doi: 10.1519/JSC.0000000000002118. [Epub ahead of print]
Authors: Sams ML, Sato K, DeWeese BH, Sayers AL, Stone MH
Summary: The purposes of this study were to examine the effectiveness of an athlete monitoring program in managing athlete neuromuscular fatigue across a men's collegiate soccer season as measured by changes in squat jump (SJ) height and to compare possible changes with session rating of perceived exertion (sRPE) training load (TL). Eighteen outfield Division I men's college soccer players performed SJ testing prior to each game of the fall season in addition to a baseline measurement at the start of pre-season. The athletes provided sRPE values after all training sessions, weight training, and games. Linear mixed modeling was used to compare changes in SJ height across the season with the baseline, and a correlation coefficient and single-lag cross-correlation coefficient were calculated between TL and changes in SJ height. No statistically significant decreases in SJ height occurred across the season, although a moderate practical decline occurred following the pre-season (-1.6 cm, ES = -0.70). The correlation between TL and changes in SJ height was statistically non-significant, while the cross-correlation was significant (r = 0.18, p = .48 and r = 0.55, p = 0.02, respectively). The athlete monitoring program was successful in managing the athletes' neuromuscular fatigue across the season as evidenced by the maintenance of SJ height and positive relationship between TL and changes in SJ height. Thus, SJ monitoring may serve as a useful fatigue monitoring tool for collegiate soccer athletes. Future study is needed relating changes in vertical jump performance to other markers of athlete preparedness and performance.

#7 Position specific acceleration and deceleration profiles in elite youth and senior soccer players
Reference: J Strength Cond Res. 2017 Apr 4. doi: 10.1519/JSC.0000000000001918. [Epub ahead of print]
Authors: Vigh-Larsen JF, Dalgas U, Andersen TB
Summary: The purpose of the study was to characterize and compare the position specific activity profiles of young and senior elite soccer players with special emphasis put on accelerations and decelerations. Eight professional senior matches were tracked using the ZXY tracking system and analyzed for number of accelerations and decelerations and running distances within different speed zones. Likewise, four U19- and five U17 matches were analyzed for comparison between youth and senior players. In senior players the total distance (TD) was 10776±107 m with 668±28 and 143±10 m being high-intensity running (HIR) and sprinting, respectively. Number of accelerations and decelerations were 81±2 and 84±3, with central defenders performing the lowest- and wide players the highest number. Declines were found between first and second halves for accelerations and decelerations (11±3 %), HIR (6±4 %) and TD (5±1 %), whereas sprinting distance did not differ. U19 players performed a higher number of accelerations, decelerations and TD compared to senior players. In conclusion, differences in number and distribution of accelerations and decelerations appeared between player positions, which is of importance when monitoring training and match loads and when prescribing specific training exercises. Further, youth players performed as much high-intensity activities as senior players indicating that this is not a discriminating physiological parameter between these players.

#8 Severe musculoskeletal time-loss injuries and symptoms of common mental disorders in professional soccer: a longitudinal analysis of 12-month follow-up data
Reference: Knee Surg Sports Traumatol Arthrosc. 2017 Jul 11. doi: 10.1007/s00167-017-4644-1. [Epub ahead of print]
Authors: Kiliç O, Aoki H, Goedhart E, Hagglund M, Kerkhoffs GMMJ, Kuijer PPFM, Walden M, Gouttebarge V
Summary: Psychological factors have shown to be predictors of injury in professional football. However, it seems that this is a two-way relationship, as severe musculoskeletal time-loss injuries have shown to be associated with the onset of symptoms of common mental disorders (CMD). There is no longitudinal study performed exploring this interaction between symptoms of CMD and injuries. The purpose of this study was to explore the interaction between severe musculoskeletal time-loss injuries and symptoms of CMD in professional football players over a 12-month period. Players were recruited by their national players' unions in five European countries. Symptoms of CMD included in the study were related to distress, anxiety/depression, sleep disturbance and adverse alcohol use. A total of 384 professional football players were enrolled in the study, of whom 262 (68%) completed the 12-month follow-up period. The mean age of the participants at baseline was 27 ± 5 years, and they had played professional football for 8 ± 5 years on average. Symptoms of CMD at baseline were not associated with the onset of severe musculoskeletal time-loss injuries during the follow-up period with relative risks (and 95% CI) ranging from 0.6 (0.3-1.0) to 1.0 (0.5-2.2). In contrast, severe musculoskeletal time-loss injuries reported at baseline were associated with the onset of symptoms of CMD during the follow-up period with relative risks ranging from 1.8 (0.8-3.7) to 6.9 (4.0-11.9). No relationship was found between symptoms of CMD and the onset of severe musculoskeletal time-loss injuries. However, professional football players who suffered from severe musculoskeletal time-loss injuries are likely to develop subsequent symptoms of CMD. This study emphasizes the need for an interdisciplinary medical approach, which not only focuses on the physical but also on the mental health of professional football players. An early identification of players at risk of symptoms of CMD, such as those suffering from severe musculoskeletal injuries, creates the opportunity for an interdisciplinary clinical medical team to treat the players timely and adequately.

#9 Individual ball possession in soccer
Reference: PLoS One. 2017 Jul 10;12(7):e0179953. doi: 10.1371/journal.pone.0179953. eCollection 2017.
Authors: Link D, Hoernig M
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Summary: This paper describes models for detecting individual and team ball possession in soccer based on position data. The types of ball possession are classified as Individual Ball Possession (IBC), Individual Ball Action (IBA), Individual Ball Control (IBC), Team Ball Possession (TBP), Team Ball Control (TBC) und Team Playmaking (TPM) according to different starting points and endpoints and the type of ball control involved. The machine learning approach used is able to determine how long the ball spends in the sphere of influence of a player based on the distance between the players and the ball together with their direction of motion, speed and the acceleration of the ball. The degree of ball control exhibited during this phase is classified based on the spatio-temporal configuration of the player controlling the ball, the ball itself and opposing players using a Bayesian network. The evaluation and application of this approach uses data from 60 matches in the German Bundesliga season of 2013/14, including 69,667 IBA intervals. The identification rate was F = .88 for IBA and F = .83 for IBP, and the classification rate for IBC was κ = .67. Match analysis showed the following mean values per match: TBP 56:04 ± 5:12 min, TPM 50:01 ± 7:05 min and TBC 17:49 ± 8:13 min. There were 836 ± 424 IBC intervals per match and their number was significantly reduced by -5.1% from the 1st to 2nd half. The analysis of ball possession at the player level indicates shortest accumulated IBC times for the central forwards (0:49 ± 0:43 min) and the longest for goalkeepers (1:38 ± 0:58 min), central defenders (1:38 ± 1:09 min) and central midfielders (1:27 ± 1:08 min). The results could improve performance analysis in soccer, help to detect match events automatically, and allow discernment of higher value tactical structures, which is based on individual ball possession.

#10 A shower before bedtime may improve the sleep onset latency of youth soccer players
Reference: Eur J Sport Sci. 2017 Jul 9:1-10. doi: 10.1080/17461391.2017.1346147. [Epub ahead of print]
Authors: Whitworth-Turner C, Di Michele R, Muir I, Gregson W, Drust B
Summary: During the competitive season, soccer players are likely exposed to numerous factors that may disrupt the process of sleep. The current investigation looked to evaluate a practical sleep hygiene strategy (10-min showering at ∼40°C before lights out), within a group of 11 youth soccer players in comparison to normal sleeping conditions (control). Each condition consisted of three days within a randomised crossover trial design. Sleep information was collected using a commercial wireless bedside sleep monitor. Measures of skin temperature were evaluated using iButton skin thermistors to establish both distal and proximal skin temperatures and distal to proximal gradient. The shower intervention elevated distal skin temperature by 1.1°C (95% CI: 0.1-2.1°C, p = .04) on average prior to lights out. The elevation in distal temperature was also present during the first 30-min following lights out (1.0°C, 95% CI: 0.4-1.6°C, p < .01). The distal to proximal gradient also showed a significant effect between the conditions within the first 30-min after lights out (0.7°C, 95% CI: 0.3-1.2°C, p < .01). On average the sleep latency of the youth soccer players was -7-min lower (95% CI: -13 to -2 min, p < .01) and sleep efficiency +2% higher (95% CI: 1-3%; p < .01) in the shower condition. These findings demonstrate that a warm shower performed before lights out may offer a practical strategy to promote thermoregulatory changes that may advance sleep onset latency and improve sleep efficiency in athletes.

#11 Dynamics of tactical behaviour in association football when manipulating players' space of interaction
Reference: PLoS One. 2017 Jul 14;12(7):e0180773. doi: 10.1371/journal.pone.0180773. eCollection 2017.
Authors: Ric A, Torrents C, Goncalves B, Torres-Ronda L, Sampaio J, Hristovski R
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Summary: The analysis of positional data in association football allows the spatial distribution of players during matches to be described in order to improve the understanding of tactical-related constraints on the behavioural dynamics of players. The aim of this study was to identify how players' spatial restrictions affected the exploratory tactical behaviour and constrained the perceptual-motor workspace of players in possession of the ball, as well as inter-player passing interactions. Nineteen professional outfield male players were divided into two teams of 10 and 9 players, respectively. The game was played under three spatial constraints: a) players were not allowed to move out of their allocated zones, except for the player in possession of the ball; b) players were allowed to move to an adjacent zone, and; c) non-specific spatial constraints. Positional data was captured using a 5 Hz interpolated GPS tracking system and used to define the configuration states of players for each second in time. The configuration state comprised 37 categories derived from tactical actions, distance from the nearest opponent, distance from the target and movement speed. Notational analysis of players in possession of the ball allowed the mean time of ball possession and the probabilities of passing the ball between players to be calculated. The results revealed that the players' long-term exploratory behaviour decreased and their short-term exploration increased when restricting their space of interaction. Relaxing players' positional constraints seemed to increase the speed of ball flow dynamics. Allowing players to move to an adjacent sub-area increased the probabilities of interaction with the full-back during play build-up. The instability of the coordinative state defined by being free from opponents when players had the ball possession was an invariant feature under all three task constraints. By allowing players to move to adjacent sub-areas, the coordinative state became highly unstable when the distance from the target decreased. Ball location relative to the scoring zone and interpersonal distance constitute key environmental information that constrains the players' coordinative behaviour. Based on our results, dynamic overlap is presented as a good option to capture tactical performance. Moreover, the selected collective (i.e. relational) variables would allow coaches to identify the effects of training drills on teams and players' behaviour. More research is needed considering these type variables to understand how the manipulation of constraints induce a more stable or flexible dynamical structure of tactical behaviour.

American Football
#1 Alcohol and violence in 2017 National Football League Super Bowl commercials
Reference: Health Promot Perspect. 2017 Jun 14;7(3):163-167. doi: 10.15171/hpp.2017.29. eCollection 2017.
Authors: MacLean SA, Basch CH, Garcia P
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Summary: The National Football League (NFL) Super Bowl is a widely-viewed sports event and the commercials are especially popular among viewers. Previous research has demonstrated risky health behaviors in advertisements aired during sporting events. The purpose of this study was to analyze the content of the advertisements aired during the 2017 NFL Super Bowl. This cross-sectional study involved examining the content of all commercials, with an emphasis on health-compromising behaviors. The themes and highlights of the advertisements were analyzed based on whether there was a reference to alcohol or violence. A total of 103 unique commercials were analyzed. The most common themes were humor (n=43), happiness (n=25), innovation (n=25), and enjoyment or relaxation (n=25).Alcohol was referenced in 13 (12.6%, 95% CI 7.5%, 20.4%) of the commercials. Advertisements with alcohol references were more likely to contain the themes of partying (odds ratio [OR]:16.2, 95% CI 1.4-193.4, P=0.041) and enjoyment or relaxation (OR: 4.7, 95% CI 1.4-15.6,P=0.014). There were 24 commercials with references to violence and these were more likely tobe promoting a movie (OR: 5.4, 95% CI 3.5-8.2, P<0.001) or television program (OR: 8.9,95% CI 2.6-30.26, P<0.001). Parents should consider whether it is appropriate for their children to watch a concentrated number of intense images containing references to alcohol and violence during this popular sporting event.

Australian Football
#1 The influence of contextual factors on running performance in female Australian Football match-play
Reference: J Strength Cond Res. 2017 Jul 12. doi: 10.1519/JSC.0000000000002142. [Epub ahead of print]
Authors: Black GM, Gabbett TJ Naughton G, Cole MH, Johnston RD, Dawson B
Summary: Given the recent growth of the professional status among multiple female football codes, the aim of this study is to investigate the effects of contextual factors on activity profiles and pacing strategies in female Australian football players. Thirty-five female Australian football players participated in this study. Global positioning system analysis was completed over one competitive season. Matches were separated into eight 10-minute periods. Greater distances were covered during the first half irrespective of playing position (ES = 0.39-0.50, Likelihood ≥90%). Throughout a number of periods half-backs (defensive players) covered greater distances during losses (ES ≥0.74, Likelihood ≥92%) and against Top 3 opponents (ES ≥1.0, Likelihood ≥ 97%). Midfielders and half-backs covered greater distances (ES ≥ 0.49, Likelihood ≥89%) in the final match period in winning compared with losing matches. A reduction in player work-rate is evident during the second half of matches. The influence of contextual factors varied across positional groups. However, it is clear coaches could use player rotation both early in the match in an attempt to delay the effect of fatigue and more frequently during the second half to increase running intensity.

#2 Radio Gaga? Intra-team communication of Australian Rules Football Umpires - Effect of radio communication on content, structure and frequency
Reference: Ergonomics. 2017 Jul 12:1-43. doi: 10.1080/00140139.2017.1353140. [Epub ahead of print]
Authors: Neville TJ, Salmon PM, Read GJM
Summary: Intra-team communication plays an important role in team effectiveness in various domains including sport. As such, it is a key consideration when introducing new tools within systems that utilise teams. The difference in intra-team communication of Australian Rules Football (AFL) umpiring teams was studied when umpiring with or without radio communications technology. A cross-sectional observational study was conducted to analyse the verbal communication of seven umpiring teams (20 participants) grouped according to their experience with radio communication. The results identified that radio communication technology increased the frequency and altered the structure of intra-team communication. Examination of the content of the intra-team communication identified impacts on the 'Big Five' teamwork behaviours and associated coordinating mechanisms. Analysis revealed that the communications utilised did not align with the closed-loop form of communication described in the Big Five model. Implications for teamwork models, coaching and training of AFL umpires are discussed.  Practitioner statement Assessing the impact of technology on performance is of interest to ergonomics practitioners. The impact of radio communications on teamwork is explored in the highly dynamic domain of AFL umpiring. When given radio technology, intra-team communication increased which supported teamwork behaviours such as backup behaviour and mutual performance monitoring.

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