Latest research in football - week 19 - 2019

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 Acute and chronic effects of competition on ankle dorsiflexion ROM in professional football players
Reference: Eur J Sport Sci. 2019 May 9:1-10. doi: 10.1080/17461391.2019.1611930. [Epub ahead of print]
Authors: Moreno-Pérez V, Soler A, Ansa A, López-Samanes Á, Madruga-Parera M, Beato M, Romero-Rodríguez D
Summary: The aim of this study was to investigate the acute (a football match) and chronic (a whole season) effects of competition on ankle dorsiflexion ROM in professional football players. Forty football players participated in this study. Ankle dorsiflexion ROM was recorded to examine acute (pre-match, immediately post-match and 48 h post-match) and chronic (pre-season, mid-season and post-season) effects of competitive football. In addition, it was found that players had restricted mobility measures on ankle dorsiflexion as >2 cm change between baseline measures (pre-match and pre-season). The training load of all played matches was estimated using a global positioning system (GPS) and RPE. Pre-season ankle dorsiflexion ROM was greater compared to mid-season (8.1% in the dominant, and 9.6% in the non-dominant leg) and post-season (13.8% in the dominant, and 12.5% in the non-dominant leg). In addition, around 30% of all players showed restricted ankle dorsiflexion ROM values in post-season compared with pre-season. Related to acute effects, ankle dorsiflexion ROM increased after a match (5.8%) in the dominant ankle, and this value decreased (2.65%) 48 h post-match when post-match measurements in both dominant and non-dominant ankles were compared. The progressive decrease in ankle dorsiflexion ROM throughout a season can be an indicator of increased risk of injury and may be reinforce the need of prevention actions such as stretching exercises and eccentric strength training in professional football players. In addition, these findings suggest to implement specific recovery strategies aiming at minimizing alteration in ankle dorsiflexion ROM 48 h post-match.

#2 The effect of compression shorts on pain and performance in male football players with groin pain - A double blinded randomized controlled trial
Reference: Phys Ther Sport. 2019 Apr 25;38:87-95. doi: 10.1016/j.ptsp.2019.04.013. [Epub ahead of print]
Authors: Otten R, Stam S, Langhout R, Weir A, Tak I
Summary: The purpose was to investigate the effects of compression shorts on pain and performance in football players with groin pain. Thirty-four male football players with groin pain participated in this study. The effect of wearing zoned high compression shorts (ZHC-shorts), non-zoned low compression shorts (NZLC-shorts), and normal sports clothes on pain measured with the Numeric Pain Rating Scale (NPRS) and performance during the Copenhagen 5-s squeeze test (CS), the Illinois Agility test (IAT), and maximum shooting (ST). The effects of wearing ZHC versus NZLC shorts on symptoms were measured using the Hip and groin outcome score (HAGOS) during actual football activities. Wearing ZHC-shorts reduced pain during the IAT (1.4, ES = 0.58, p= <0.01) and ST (1.2, ES = 0.47, p= <0.01) compared to wearing normal sports clothes, but did not negatively affect performance. Compared to the baseline HAGOS scores a clinically significant improvement in the symptoms (9.7, ES = 0.63, p= <0.01) and sport/recreation (13.2, ES = 0.68, p = 0.01) subscales was found when wearing the ZHC-short during football activities. Wearing zoned high compression shorts could be useful in reducing groin pain in football players during their football activities.

#3 Jump height as performance indicator for the selection of youth football players to national teams
Reference: J Sports Med Phys Fitness. 2019 May 2. doi: 10.23736/S0022-4707.19.09739-1. [Epub ahead of print]
Authors: Ryman Augustsson S, Arvidsson J, Haglund E
Summary: Different jump tests such as the Countermovement Jump (CMJ), Abalakov Jump (AJ) and Standing Long Jump (SLJ) are often used in practice to evaluate muscular power and functional performance in football. These tests are also used in different selection processes and talent identification, but the significance of the tests for the selection of youth players to national teams are relatively unknown. The aim of this study was to compare jump ability between youth football players selected or not selected for the national team. In this cross-sectional study, 22 players (aged 17±2 years), 11 national players (NP) and 11 non- national players (NNP) were evaluated in three different jump tests; CMJ, AJ and SLJ. Mean scores for the tests were analysed and compared. Significant differences were found between the groups regarding jump height in favour of the NP group in both the CMJ (NP 39.9±5.0 cm vs NNP 34.2±4.9 cm, p=0.013) and the AJ (NP 47.1±5.4 vs NNP 40.9±4.7, p=0.010). No group difference was found regarding jump length in SLJ (NP 246.2±17.9 vs NNP 232.9±16.5, p=0.084). The results suggest that tests, measuring jump height, could be used as a performance indicator and part of the selection process of youth football players to national teams, whereas the use of jump length could be questioned.

#4 Anterior cruciate ligament injury risk factors in football: a narrative review
Reference: J Sports Med Phys Fitness. 2019 Apr 30. doi: 10.23736/S0022-4707.19.09563-X. [Epub ahead of print]
Authors: Bisciotti GN, Chamari K, Cena E, Bisciotti A, Bisciotti A, Corsini A, Volpi P
Summary: Anterior cruciate ligament (ACL) lesion represents one of the most dramatic injuries in a football (soccer) player's career. There are many injury risk factors related to intrinsic (non-modifiable) and/or extrinsic (modifiable) factors of ACL-injury. To date, evidence from the literature suggests that the risk of ACL-injury is multifactorial and involves biomechanical, anatomical, hormonal, and neuromuscular factors. Despite this relative complexity, the mechanisms of injury are well known and rationally classified into two categories: mechanisms of injury based on contact or on non- contact with another player, with the non-contact injury mechanisms clearly prevailing over the mechanisms of contact injury. One of the most frequent biomechanical risk factors, associated with ACL non-contact injury, is represented by the valgus knee in the pivoting and cutting movements and in the landing phase after jumping. Gender related risk factors show female populations to have a higher predisposition to ACL-injury than males However, there are still some theoretical and practical aspects that need further investigation such as; genetic risks together with the role of oestrogen and progesterone receptors in female populations, and the in vivo interaction shoe- playing surface. In particular, the genetic risk factors of ACL lesion seem to be an interesting and promising field of investigation, where considerable progress has still to be made. This narrative review provides an insight into the risk factors of ACL-injury that could be used by practitioners for preventing injury in football (soccer).

#5 Misbehavior During Penalty Kicks and Goalkeepers Holding the Ball Too Long as Trivial Offenses in Football
Reference: Front Psychol. 2019 Apr 18;10:844. doi: 10.3389/fpsyg.2019.00844. eCollection 2019.
Authors: Kolbinger O, Stöckl M
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Summary: Rule violations occur in every sport and the respective book of rules prescribes how match officials need to sanction them. However, there are some rule violations that are nearly never penalized, even if they are perceived by the match officials. A phenomenon that has been neglected in the scientific community so far, for which we want to introduce the term trivial offenses. This research focuses on two potential trivial offenses in football: rule violations regarding the six-seconds rule, the time a goalkeeper is allowed to control the ball with his hands, and rule violations during the performance of penalty kicks. The aim is to provide empirical proof of the existence of those trivial offenses and describe the respective patterns. For this purpose, two observation systems were constructed; one to investigate 45 games from the German Bundesliga with respect to the six-seconds rule and one to study rule violations during 618 penalty kicks from four European football leagues and one cup event. The following variables were collected: Goalkeeper, MatchLocation, Minute (representing the minute of the game), PreviousAction, CurrentScore, Time (representing the time the goalkeeper controlled the ball with his hands), and Penalization for the six-seconds study; Responsibility for infringement, Decision of the referee, and Outcome for the penalty study. Reliability tests showed almost perfect agreement for the data of both samples. On average, goalkeepers control the ball 6.0 s (SD:4.54) with their hands and the six-second rule was violated in 38.4% of the situations, none of which was penalized. This duration was significantly influenced by CurrentScore (p < 0.001), which indicates a tactical abuse of this situation. None of the investigated penalty kicks was conducted without a rule violation either. In most incidents (96.3%) outfield players from both teams as well as the goalkeeper commit offenses. The umpire only judges 2.8% of these incidents correctly, most of them by approving the scored goal. In total, this research proves the existence of trivial offenses in football and shows how methods and tools of performance analysis can serve to investigate and even solve this issue.

#6 The ball kicking speed: A new, efficient performance indicator in youth soccer
Reference: PLoS One. 2019 May 17;14(5):e0217101. doi: 10.1371/journal.pone.0217101. eCollection 2019.
Authors: Rađa A, Kuvačić G, De Giorgio A, Sellami M, Ardigò LP, Bragazzi NL, Padulo J
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Summary: Success in different soccer skills like kicking depends on motor abilities achieved. Kicking is a soccer fundamental, which depends on many different and complex factors (technique, foot-ball interaction, ball flight, etc.). Therefore, it is important to identify players that are able to perform faster kicks using both dominant and non-dominant leg. The current study investigated some basic variables of different soccer kicking speed and their relevance to success in youth soccer academy. 119 players from the first and the second division participated to this study. They were randomly divided into age groups (U-15, U-17, and U19) and team status (first team, reserves). The diagnostic ability of the different ball kicking speed tests in capturing differences between first team players and reserves among different age categories were computed using the receiver operating characteristics analysis. Results demonstrated that first team players achieved better results when comparing to reserves in each category. In addition, differences were greater in the U-15 and the U-17 than in the U-19 age group. In conclusion, ball kicking speed could be one of the possible identification tools to evaluate players' success in youth soccer.

#7 Hamstring rate of torque development is more affected than maximal voluntary contraction after a professional soccer match
Reference: Eur J Sport Sci. 2019 May 17:1-16. doi: 10.1080/17461391.2019.1620863. [Epub ahead of print]
Authors: Grazioli R, Lopez P, Andersen LL, Machado CLF, Pinto MD, Cadore EL, Pinto RS
Summary: Match-induced fatigue of knee muscle strength and agonist-antagonist strength-ratios may affect both performance and risk of injury in soccer players. Once explosive tasks are imperative in soccer as well as hamstring strain injuries occur during high-velocity moments, rapid force capacity of this muscle group is especially important. This study evaluated the effect of match-induced fatigue on knee muscle strength and strength-ratio parameters after a single professional soccer match. Male professional soccer players (n = 16; 24.2 ± 3.9 years) were tested before and after a soccer match (56.2 ± 22.6 minutes of playing) for knee flexors (hamstring) and extensors (quadriceps) isometric peak torque (MVC) and rate of torque development (RTD) - as well as the hamstring-to-quadriceps ratio (H:Q) - at 30° of knee flexion. Knee injuries often occur at this joint angle, which is common in sprinting, pivoting, sidecutting, and jumping. Match-induced fatigue caused a left shift in the knee extensors torque-time curve with no significant change in both early (i.e. 0 to 50 ms) and late (i.e. 0 to 200 ms) RTD, and a right shift in the knee flexors torque-time curve with a decrease in early RTD (∼16%, P = 0.029) and late RTD (∼11%, P = 0.011). Knee extensors and knee flexors peak torque remained unchanged (P > 0.05). Early RTD H:Q decreased by∼24% (P = 0.027), while late RTD H:Q and MVC H:Q remained unchanged (P > 0.05). In conclusion, match-induced fatigue impaired the ability to rapidly produce force at an angle where injuries are most susceptible to occur. Important information is missed if only the traditional H:Q is considered.

#8 Age-related physical and technical match performance changes in elite soccer players
Reference: Scand J Med Sci Sports. 2019 May 17. doi: 10.1111/sms.13463. [Epub ahead of print]
Authors: Sal de Rellán-Guerra A, Rey E, Kalén A, Lago-Peñas C
Summary: The age of peak performance is likely to vary between sports and competitions, affected by the specific skills and attributes needed to succeed in the particular competition. However, no studies using modern tracking techniques have examined on the effects of age on competitive match play performance. Thus, the purpose of this study was to evaluate the effects of age on match physical and technical performance using a large-scale analysis of match performance in professional soccer players. A total of 14,546 individual match observations were undertaken in the first German league (Bundesliga) during the 2012-13, 2013-14, and 2014-15 seasons using a computerized tracking system (VISTRACK, by Impire Corp., Germany). Differences on physical and technical match performance of soccer players were analysed for the following variables: total distance covered, number of fast runs, number of sprints and percentage of successful passes. Professional soccer players aged >30 years showed a significant lower performance in the total distance covered, the number of fast runs, and the number of sprints compared with younger players (≤30 years). Conversely, the player's ability to make successful passes increased with age. These effects were observed in all positional roles except wide midfielders. These findings may help coaches and managers to better understand the effects of age on match-related physical and technical performance and may have the potential to assist in decisions such as, for example, when a new contract would be signed, the duration of the contract, the salary or when to replace or transfer a player depending on their age.

#9 Effects of Taping and Balance Exercises on Knee and Lower Extremity Function in Amateur Soccer Players: A Randomized Controlled Trial
Reference: J Sport Rehabil. 2019 May 16:1-25. doi: 10.1123/jsr.2018-0452. [Epub ahead of print]
Authors: Espí-López GV, Serra-Añó P, Cobo-Pascual D, Zarzoso M, Suso-Martí L, Cuenca-Martínez F, Inglés M
Summary: Knee injury prevention is a critical aspect in sport rehabilitation sciences and taping is a widely used technique in this field. Nevertheless, the role and effectiveness of a long-term application of Kinesio Taping on knee function, disability and injury prevention remains unclear. The objective was to determine the effect of Kinesio Taping, alone or in combination with balance exercises, on dynamic and static knee balance and flexibility. 48 male amateur soccer players were assigned to three groups: Sham KT (sKT) + BE; KT + BE; and KT in isolation. The intervention period lasted 4 weeks. Three evaluations were performed: at baseline (pre), at two weeks (mid) and at four weeks post-treatment (post). Y-Balance Test (YBT), Unipedal Stance Test (UST), the Toe Touch Test (TTT) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) were utilized as main outcome measures.  Both sKT + BE and KT + BE groups achieved significant pre-post improvements in SEBT, UST and TTT. The KT group only showed significant intra-group differences in the left and right UST variable (p<0.05, d=0.76, d=0.62 respectively). The sham KT group obtained the strongest results in all physical variables. Regarding the KOOS, pre-post significant changes were found in the sham group (p<0.05, d=0.28). Both sham and real KT in combination with BE achieved significant improvements on all physical variables, and these differences were significantly greater compared to those found in the KT in isolation group, suggesting that benefits in knee function are due to the BE.

#10 Effects of Plyometric vs Optimum Power Training on Components of Physical Fitness in Young Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 May 16:1-27. doi: 10.1123/ijspp.2019-0039. [Epub ahead of print]
Authors: Ribeiro J, Teixeira L, Lemos R, Teixeira AS, Moreira V, Silva P, Nakamura FY
Summary: The current study aimed to compare the effects of plyometric (PT) vs. optimum power load (OPL) training on physical performance of young high-level soccer players. Athletes were randomly divided into PT (horizontal and vertical drills) and OPL (squat+hip thrust exercises at the load of maximum power output) interventions, applied over 7 weeks during the in-season period. Squat (SJ) and countermovement (CMJ) jumps, maximal sprint (10 and 30 m) and change of direction (COD; agility T test) were the pre-and post-training measured performance variables. Magnitude-based inference was used for within-and between-group comparisons. OPL training induced moderate improvements in vertical SJ (ES:0.97; 90%CI:0.32-1.61) and CMJ (ES:1.02; 90%CI:0.46-1.57), 30 m sprint speed (ES:1.02; 90%CI:0.09-1.95) and COD performance (ES:0.93; 90%CI:0.50-1.36). After PT training method, vertical SJ (ES:1.08; 90%CI:0.66-1.51) and CMJ (ES:0.62; 90%CI:0.18-1.06) were moderately increased, while small enhancements were noticed for 30 m sprint speed (ES:0.21; 90%CI:-0.02-0.45) and COD performance (ES:0.53; 90%CI:0.24-0.81). The 10 m sprint speed possibly increased after PT intervention (small ES: 0.25; 90%CI:-0.05-0.54), but no substantial change (small ES:0.36; 90%CI:-0.40-1.13) was noticed in OPL. For between-group analyses, the COD ability and 30 m sprint performances were possibly (small ES:0.30; 90%CI:-0.20-0.81; Δ=+1.88%) and likely (moderate ES:0.81; 90%CI:-0.16-1.78; Δ=+2.38%) more improved in the OPL than in the PT intervention, respectively. The two different training programs improved physical performance outcomes during the in-season period. However, the combination of vertically-and horizontally-based training exercises (squat+hip thrust) at optimum power zone led to superior gains in COD and 30 m linear sprint performances.

#11 Dynamic Warm-up With a Weighted Vest: Improvement of Repeated Change-of-Direction Performance in Young Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 May 16:1-28. doi: 10.1123/ijspp.2018-0800. [Epub ahead of print]
Authors: Turki O, Dhahbi W, Gueid S, Hmaied S, Souaifi M, Khalifa R
Summary: This study aims to explore the effect of 4 different warm-up strategies using weighted vests, and to determine the specific optimal recovery duration required to optimize the repeated change of direction (RCOD) performance in young soccer players. Nineteen male soccer players (age: 18±0.88 years, body-mass: 69.85±7.68 kg, body-height: 1.75±0.07 m, body-mass-index: 22.87±2.23 kg·m-2 and body-fat-percentage: 12.53±2.59 %), completed the following loaded warm-up protocols in a randomized, counterbalanced cross-over, within participants order and on separate days: weighted-vest with a loading of 5% (WUV5%), 10% (WUV10%), 15% (WUV15%) body-mass, and an unloaded condition (control). RCOD performance (total time, peak time and fatigue index) was collected during the pre-intervention phase (5 min after the dynamic stretching sequence) for baseline values and immediately (at 15ths), at the 4th and 8th min post-warm-up intervention. For each post-warm-up tested, recovery-times (i.e., 15-s, 4-min, and 8-min), both total, and peak times were faster following WUV5%, WUV10%, and WUV15%, compared to the unloaded condition (P [<0.001-0.031], d [1.28-2.31] [large]). There were no significant differences (P [0.09-1.00], d [0.03-0.72] [trivial-moderate]) in-between recovery times in both total and peak times following WUV5%, WUV10% and WUV15%. However, baseline fatigue index score was significantly worse than all other scores (P [<0.001-0.002], d [1.35-2.46] [large]) following the loaded conditions. The findings demonstrated that a dynamic loaded warm-up increases an athlete's initial RCOD performance up to the 8th min post-warm-up intervention. Therefore, strength coaches need to consider using weighted-vests during the warm-up for trained athletes in order to acutely optimize RCODs.

#12 The Increased Effectiveness of Loaded Versus Unloaded Plyometric-Jump Training in Improving Muscle Power, Speed, Change-of-Direction, and Kicking-Distance Performance in Prepubertal Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 May 16:1-25. doi: 10.1123/ijspp.2018-0866. [Epub ahead of print]
Authors: Negra Y, Chaabene H, Sammoud S, Prieske O, Moran J, Ramirez-Campillo R, Nejmaoui A, Granacher U
Summary: This study examined the effects of loaded (LPJT) and unloaded (UPJT) plyometric jump training programmes on measures of muscle power, speed, change-of-direction and kicking-distance performance in prepubertal male soccer players. Participants (N=29) were randomly assigned to a LPJT group (n=13; age=13.0±0.7 years) using weighted vests or UPJT group (n=16; age=13.0±0.5 years) using body mass only. Before and after the intervention, tests for the assessment of proxies of muscle power (i.e., countermovement-jump [CMJ], standing-long-jump [SLJ]), speed (i.e., 5-m, 10-m, and 20-m sprint), change-of-direction (i.e., Illinois change-of-direction test [ICoDT], modified 505 agility test), and kicking-distance test were conducted. Data were analysed using magnitude-based inferences. Within-group analyses for the LPJT group showed large and very large improvements for 10-m sprint-time (effect size [ES]=2.00) and modified 505 CoD (ES=2.83) tests, respectively. For the same group, moderate improvements were observed in ICoDT (ES=0.61), 5- and 20-m sprint-time (ES=1.00 for both tests), CMJ (ES=1.00) and MKD (ES=0.90). Small enhancements in the SLJ (ES=0.50) test were apparent. Regarding the UPJT group, small improvements were observed for all tests (ES=0.33 to 0.57) except 5-m and 10-m sprint-time (ES=1.00 and 0.63, respectively). Between-group analyses favored the LPJT group for the modified 505 CoD (ES=0.61), SLJ (ES=0.50), and MKD (ES=0.57) tests, but not for 5-m sprint-time (ES=1.00). Only trivial between-group differences were shown for the remaining tests (ES=0.00 to 0.09). Overall, LPJT appears to be more effective than UPJT in improving measures of muscle power, speed, change-of-direction and kicking-distance performance in prepubertal male soccer players.

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