Latest research in football - week 24 - 2016

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 Epidemiology of soccer players traumatic injuries during the 2015 America Cup
Reference: Muscles Ligaments Tendons J. 2016 May 19;6(1):124-30. doi: 10.11138/mltj/2016.6.1.124.
Authors: Pangrazio O, Forriol F
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Summary: The aim of the study was to provide an overview of the traumatic injuries sustained by players in the 2015 America Cup. We collected the medical reports on all the matches held during the 2015 America Cup, in Chile, in 2015. Twelve American teams took part in the championship, consisted of 26 matches with a total of 276 players. The physician for each team sent a request form of the traumatic injuries sustained, including the time at which the injury was produced, the location and diagnosis, its severity and the circumstances (contact injury, sanction, treatment required). The mean number of minutes played was 233 (SD: 147) (5-570) minutes. An injury occurred every 58 minutes, which means that there were 17.25 injuries per 1,000 minutes of match time. We found 44 injuries in 30 players. There were 14 non-contact injuries, and 30 contact injuries, of which 13 were declared fouls and resulted in cards being given. Five teams had one injured player, two had 2, two had 4, and one had 25 injuries. The most frequent injuries were those to the lower limbs. The muscles strains happened in the second part of the second half of the match, the ACL rupture at the end of the first half, and the other sprains and strains in the second half. The contusions occurred at all times throughout the match, although they seemed to be concentrated towards the end of the first half, while the cases of tendinitis were caused in the first part of the second half. Football injuries are very common, and even though serious injuries are rare, it is increasingly necessary to set protocols for action which ensure good medical attention at all levels to address the problems that arise, both during training and in competitions, and to be prepared to treat serious injuries if these occur.

#2 Prediction of hamstring injury in professional soccer players by isokinetic measurements
Reference: Muscles Ligaments Tendons J. 2016 May 19;6(1):116-23. doi: 10.11138/mltj/2016.6.1.116.
Authors: Dauty M, Menu P, Fouasson-Chailloux A, Ferréol S, Dubois C
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Summary: Previous studies investigating the ability of isokinetic strength ratios to predict hamstring injuries in soccer players have reported conflicting results. We hypothesized if isokinetic ratios are able to predict hamstring injury occurring during the season in professional soccer players. From 2001 to 2011, 350 isokinetic tests were performed in 136 professional soccer players at the beginning of the soccer season. Fifty-seven players suffered hamstring injury during the season that followed the isokinetic tests. These players were compared with the 79 uninjured players. The bilateral concentric ratio (hamstring-to-hamstring), ipsilateral concentric ratio (hamstring-to-quadriceps), and mixed ratio (eccentric/concentric hamstring-to-quadriceps) were studied. The predictive ability of each ratio was established based on the likelihood ratio and post-test probability. The mixed ratio (30 eccentric/240 concentric hamstring-to-quadriceps) <0.8, ipsilateral ratio (180 concentric hamstring-to-quadriceps) <0.47, and bilateral ratio (60 concentric hamstring-to-hamstring) <0.85 were the most predictive of hamstring injury. The ipsilateral ratio <0.47 allowed prediction of the severity of the hamstring injury, and was also influenced by the length of time since administration of the isokinetic tests. Isokinetic ratios are useful for predicting the likelihood of hamstring injury in professional soccer players during the competitive season.

#3 Combined active and passive heat exposure induced heat acclimation in a soccer referee before 2014 FIFA World Cup
Reference: Springerplus. 2016 May 13;5:617. doi: 10.1186/s40064-016-2298-y. eCollection 2016.
Authors: Ruddock AD, Thompson SW, Hudson SA, James CA, Gibson OR, Mee JA
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Summary: The 2014 FIFA World Cup was held in Brazil, where the climatic conditions presented a significant thermoregulatory and perceptual challenge to those unfamiliar with the heat and humidity. This case report documents the adaptation induced by a novel mixed methods (isothermic and passive) heat acclimation (HA) regime for a northern European professional soccer match official prior to the tournament. The intervention involved 13 HA sessions over an 18 day period comprising five isothermic HA sessions whereby intermittent running was used to target and maintain tympanic temperature (Tytemp) at 38 °C for 90 min, and seven passive HA sessions of 48 °C water bathing for 30 min. The athlete performed a heat stress test (HST) (35 min running at four incremental intensities in 30 °C) and a repeated high-intensity running test (as many 30 s self-paced efforts as possible, to a maximum of 20, with 30 s passive recovery) before and after the intervention. The mixed methods HA regime increased plasma volume (+7.1 %), and sweat loss (+0.9 L h(-1)), reduced exercising Tytemp (-0.6 °C), and mean body temperature (-0.5 °C). High-intensity running performance improved after HA (+29 %), as did the perception of thermal comfort during exercise (-0.3 units). This data evidences the effectiveness of a practical, mixed methods HA strategy, remotely implemented around training and competition, at inducing the heat acclimation phenotype in a high-level soccer match official.

#4 Physical characteristics that predict involvement with the ball in recreational youth soccer
Reference: J Sports Sci. 2016 Sep;34(18):1716-22. doi: 10.1080/02640414.2015.1136067. Epub 2016 Jan 11.
Authors: Ré AH, Cattuzzo MT, Henrique Rdos S, Stodden DF
Summary: This study examined the relative contribution of age, stage of puberty, anthropometric characteristics, health-related fitness, soccer-specific tests and match-related technical performance to variance in involvements with the ball during recreational 5-a-side small-sided (32 × 15 m) soccer matches. Using a cross-sectional design, 80 healthy male students (14.6 ± 0.5 years of age; range 13.6-15.4) who played soccer recreationally were randomly divided into 10 teams and played against each other. Measurements included height, body mass, pubertal status, health-related fitness (12-min walk/run test, standing long jump, 15-m sprint and sit-ups in 30 s), soccer-specific tests (kicking for speed, passing for accuracy and agility run with and without a ball), match-related technical performance (kicks, passes and dribbles) and involvements with the ball during matches. Forward multiple regression analysis revealed that cardiorespiratory fitness (12-min walk/run test) accounted for 36% of the variance in involvements with the ball. When agility with the ball (zigzag running) and power (standing long jump) were included among the predictors, the total explained variance increased to 62%. In conclusion, recreational adolescent players, regardless of their soccer-specific skills, may increase participation in soccer matches most through physical activities that promote improvement in cardiorespiratory fitness, muscle power and agility.

#5 Muscle injuries of the dominant or non-dominant leg in male football players at elite level
Reference: Knee Surg Sports Traumatol Arthrosc. 2016 Jun 23. [Epub ahead of print]
Authors: Svensson K, Eckerman M, Alricsson M, Magounakis T, Werner S
Summary: The aim was to study possible differences of muscle injuries regarding type, localization and the extent of injury between the dominant and non-dominant leg in elite male football players. Another aim was to study the injury incidence of muscle injuries of the lower extremity during match and training. Data were consecutively collected between 2007 and 2013 in a prospective cohort study based on 54 football players from one team of the Swedish first league. The injury incidence was calculated for both match and training, injuries to the hip adductors, quadriceps, hamstrings and triceps surae were diagnosed and evaluated with ultrasonography, and their length, depth and width were measured to determine the extent of structural muscle injuries. Fifty-four players suffered totally 105 of the studied muscle injuries. Out of these 105 injuries, the dominant leg was affected in 53 % (n = 56) of the cases. A significantly greater extent of the injury was found in the dominant leg when compared with the non-dominant leg with regard to structural injuries of the hamstrings. No other significant differences were found. Structural hamstring muscle injuries were found to be of greater extent in the dominant leg when compared with the non-dominant leg. This new finding should be taken into consideration when allowing the football player to return to play after leg muscle injuries.

#6 A serious game for improving the decision making skills and knowledge levels of Turkish football referees according to the laws of the game
Reference: Springerplus. 2016 May 14;5:622. doi: 10.1186/s40064-016-2227-0. eCollection 2016.
Authors: Gulec U, Yilmaz M
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Summary: Digital game-based learning environments provide emerging opportunities to overcome learning barriers by combining newly developed technologies and traditional game design. This study proposes a quantitative research approach supported by expert validation interviews to designing a game-based learning framework. The goal is to improve the learning experience and decision-making skills of soccer referees in Turkey. A serious game was developed and tested on a group of referees (N = 54). The assessment results of these referees were compared with two sample t-test and the Wilcoxon signed-ranked test for both the experimental group and the control group. The findings of the current study confirmed that a game-based learning environment has greater merit over the paper-based alternatives.

#7 Small-sided football in schools and leisure-time sport clubs improves physical fitness, health profile, well-being and learning in children
Reference: Br J Sports Med. 2016 Jun 20. pii: bjsports-2016-096266. doi: 10.1136/bjsports-2016-096266. [Epub ahead of print]
Authors: Krustrup P, Dvorak J, Bangsbo J
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#8 Change of direction ability in young elite soccer players: determining factors vary with angle variation
Reference: J Sports Med Phys Fitness. 2016 Jul 8. [Epub ahead of print]
Authors: Rouissi M, Chtara M, Owen A, Burnett A, Chamari K.
Summary: The ability to change direction is considered of paramount importance in team sports. Currently there is a lack of consensus regarding the most important physical factors that determine change of direction (COD) ability. Therefore, the aim of this study was to examine the relationship strength and explosive power. 31 young elite soccer players (mean±SD, age=17.4±0.6year, height=177±0.5cm; leg length=96.9±3.3cm, body-mass=69.0±6.2kg) were recruited. A total of eight COD tasks consisting of; a 5m sprint then a COD of 45°, 90°, 135° or 180° followed by another 5m sprint were performed using dominant (DL) and non-dominant legs (NDL). Physical tests including a 10 m straight-line sprint test (10m SS), 12 lower limb isometric strength tests, and jumping tests including i) five alternate leg jump-test (5JT) ii) triple hop distance (3HD) (DL and NDL) and iii) standing broad jump-test (SBJ) were performed. Stepwise multiple regression analysis showed that the physical attributes explained between 30% and 74% of the variance of the COD performance. Furthermore, these physical attributes were dependent upon COD angle and direction. The affecting variables of the COD performance differ according to the angle of between COD ability and targeted selected physical attributes of sprinting, isometric COD and the leg used to turn. Moreover, isometric strength of the lower-limb muscles represented a major determinant factor of the COD-ability. Consequently, physical fitness coaches should include isometric muscle strengthening exercises in addition to traditional dynamic muscle strength exercises. Moreover, they should implement specific lower limb strength exercises depending on players' deficit in each COD's angles.

#9 Effect of a congested match schedule on immune-endocrine responses, technical performance and session-RPE in elite youth soccer players
Reference: J Sports Sci. 2016 Jul 8:1-7. [Epub ahead of print]
Authors: Moreira A, Bradley P, Carling C, Arruda AF, Spigolon LM, Franciscon C, Aoki MS
Summary: This study investigated the effects of a congested match schedule (7 matches played in 7 days) on steroid hormone concentrations, mucosal immunity, session rating of perceived exertion (S-RPE) and technical performance in 16 elite youth soccer players (14.8 ± 0.4 years; 170.6 ± 9.4 cm; 64.9 ± 7 kg). No change was observed for salivary cortisol concentration across match time points (P = 0.33; effect size [ES] = 0.13-0.48). In contrast, there was a decrease in salivary testosterone and salivary IgA (SIgA) concentrations from the 1st compared with the last time point (P = 0.01 and 0.001, ES = 0.42 and 0.67, respectively). The SIgA concentration varied across time points (P < 0.001) with the highest value observed at the 3rd time point (rest day) (3rd vs all time point; ES = 0.47-0.73). No changes were observed for S-RPE across time points (P > 0.05). A higher number of tackles and interceptions were observed during the 4th match vs 1st and 7th matches (P < 0.001; ES = 2.25 and 1.90, respectively). The present data demonstrate that accumulated fatigue related to participation in a congested match schedule might induce a decrease in testosterone concentration in youth players and negatively affect their mucosal immunity and capacity to perform certain technical actions.

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