Latest research in football - week 30 - 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 Are acceleration and cardiovascular capacities related to perceived load in professional soccer players?
Reference: Res Sports Med. 2019 Jul 21:1-15. doi: 10.1080/15438627.2019.1644642. [Epub ahead of print]
Authors: Azcárate U, Los Arcos A, Jiménez-Reyes P, Yanci J
Summary: This study aims at assessing physical fitness performance and its relationship with the differential ratings of perceived exertion of training load (dRPE TL) and match load (dRPE ML) in a Spanish professional soccer team at the beginning of several in-season periods: 1-4 weeks, 5-8 weeks and 1-8 weeks. Performance and mechanical variables over the acceleration phase, as well as cardiovascular performance variables were evaluated in 20 male professional soccer players of a team competing in the Spanish Second Division League. Moreover, dRPE TL and dRPE ML were quantified. The dRPE TL showed negative and large associations between both maximal aerobic speed (MAS) and maximal oxygen consumption (VO2max) (from r = -0.53; ± 0.06 to r = -0.53; ± 0.05 95% CL, p = 0.035 to 0.036) and RPEres TL values throughout the 5-8 and 1-8 week periods. Furthermore, dRPE ML positive and large associations were found between players initial MAS or VO2max (from r = 0.50; ± 0.17 to r = 0.56; ± 0.11 95% CL, p = 0.026 to 0.049) and RPEmus ML in 1-4 and 1-8 week periods. The current study suggests that a better cardiovascular capacity could be connected with a lower RPEres TL and higher RPEmus ML.

#2 Injury burden differs considerably between single teams from German professional male football (soccer): surveillance of three consecutive seasons
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Jul 19. doi: 10.1007/s00167-019-05623-y. [Epub ahead of print]
Authors: Klein C, Luig P, Henke T, Platen P
Summary: The purpose of this study was to analyse unique injury data of the national statutory accident insurance for the two highest divisions in German male football (Bundesliga and 2. Bundesliga) over three consecutive seasons regarding inter-season, inter-division and inter-team differences. This was a prospective observational open cohort study over the seasons 2014/2015, 2015/2016 and 2016/2017. Every acute injury that was registered by clubs or physicians with the German statutory accident insurance for professional athletes (VBG) as part of occupational accident reporting and that led to time loss and/or to medical attention, was included. The complete sample consisted of 1449 players. The study covered 2663.5 player seasons with an observed match exposure of 69,058 h and a projected training exposure of 529,136 h. In total, 7493 injuries were included. The overall incidence rate was 12.5 (± 0.28) injuries per 1000 exposure hours, which translated into match and training rates of 47.0 (± 1.62) and 8.02 (± 0.24) injuries per 1000 h, respectively. Findings of 2.7 injuries per player and season underline the need of effective preventive approaches. Higher injury incidences in seasons after international tournaments suggest an increasing risk of injury with increasing number of matches. However, large differences between the single teams from the same division indicate that a reduction in the injury burden is generally possible. Continuing the presented injury surveillance might be helpful to identify injury trends in the future and to evaluate the effectiveness of preventive approaches under real-life conditions.

#3 An Approach to the Fatigue in Young Soccer Players Resulting from Sided Games
Reference: Sports (Basel). 2019 Jul 18;7(7). pii: E174. doi: 10.3390/sports7070174.
Authors: Castillo D, Yanci J, Sánchez-Díaz S, Raya-González J
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Summary: It is crucial to understand the fatigue associated with sided games (SGs) of soccer in the training context, in order to establish the appropriate intervals between training sessions. Thus, the aim of this study was to investigate the effects of different SGs on internal load, measured by the session rating of perceived exertion (sRPE), and on sprint performance. Ten outfield players (age: 14.5 ± 0.5 years, height: 169 ± 6 cm, body mass: 59.7 ± 6.4 kg) belonging to U15 age category participated in this study. The participants played four SG formats with modifications in the pitch size and in the bout duration, but with the same total duration for the SGs (SG1, SG2, SG3, and SG4). All the players performed a 10 and a 30 m sprint test before and after the SGs. The internal load was measured by the sRPE. The results showed no significant differences (p > 0.05) in the sRPE registered by the soccer players for the different SGs, but worse sprint performances over the 10 m (p < 0.05; ES: 0.74-1.38, large) and 30 m (p < 0.05; ES: 0.70-2.10, moderate to large) distances after completion of the SGs, except the 10 m sprint after SG2 and SG3 (p > 0.05; ES: 0.43-0.55, moderate). In addition, no correlation (p > 0.05) was reported between the sprint performances for the 10 and 30 m distances and the sRPE registered during the SGs. These results could be useful for technical staff wishing to design the playing area and bout duration of their training tasks effectively.

#4 A Genome-Wide Association Study of Sprint Performance in Elite Youth Football Players
Reference: J Strength Cond Res. 2019 Jul 22. doi: 10.1519/JSC.0000000000003259. [Epub ahead of print]
Authors: Pickering C, Suraci B, Semenova EA, Boulygina EA, Kostryukova ES, Kulemin NA, Borisov OV, Khabibova SA, Larin AK, Pavlenko AV, Lyubaeva EV, Popov DV, Lysenko EA, `Vepkhvadze TF, Lednev EM, Leońska-Duniec A, Pająk B, Chycki J, Moska W, Lulińska-Kuklik E, Dornowski M, Maszczyk A, Bradley B, Kana-Ah A, Cięszczyk P, Generozov EV, Ahmetov II
Summary: Sprint speed is an important component of football performance, with teams often placing a high value on sprint and acceleration ability. The aim of this study was to undertake the first genome-wide association study to identify genetic variants associated with sprint test performance in elite youth football players and to further validate the obtained results in additional studies. Using micro-array data (600 K-1.14 M single nucleotide polymorphisms [SNPs]) of 1,206 subjects, we identified 12 SNPs with suggestive significance after passing replication criteria. The polymorphism rs55743914 located in the PTPRK gene was found as the most significant for 5-m sprint test (p = 7.7 × 10). Seven of the discovered SNPs were also associated with sprint test performance in a cohort of 126 Polish women, and 4 were associated with power athlete status in a cohort of 399 elite Russian athletes. Six SNPs were associated with muscle fiber type in a cohort of 96 Russian subjects. We also examined genotype distributions and possible associations for 16 SNPs previously linked with sprint performance. Four SNPs (AGT rs699, HSD17B14 rs7247312, IGF2 rs680, and IL6 rs1800795) were associated with sprint test performance in this cohort. In addition, the G alleles of 2 SNPs in ADRB2 (rs1042713 & rs1042714) were significantly over-represented in these players compared with British and European controls. These results suggest that there is a genetic influence on sprint test performance in footballers, and identifies some of the genetic variants that help explain this influence.

#5 Kinematic Profile of Visually Impaired Football Players During Specific Sports Actions
Reference: Sci Rep. 2019 Jul 23;9(1):10660. doi: 10.1038/s41598-019-47162-z.
Authors: Finocchietti S, Gori M, Souza Oliveira A
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Summary: Blind football, or Football 5-a-side, is a very popular sport amongst visually impaired individuals (VI) worldwide. However, little is known regarding the movement patterns these players perform in sports actions. Therefore, the aim of this study was to determine whether visually impaired players present changes in their movement patterns in specific functional tasks compared with sighted amateur football players. Six VI and eight sighted amateur football players performed two functional tasks: (1) 5 m shuttle test and (2) 60 s ball passing against a wall. The sighted players performed the tests while fully sighted (SIG) as well as blindfolded (BFO). During both tasks, full-body kinematics was recorded using an inertial motion capture system. The maximal center-of-mass speed and turning center-of-mass speed were computed during the 5 m shuttle test. Foot resultant speed, bilateral arm speed, and trunk flexion were measured during the 60 s ball passing test. The results showed that VI players achieved lower maximal and turning speed compared to SIG players (p < 0.05), but BFO were slower than the VI players. The VI players presented similar foot contact speed during passes when compared to SIG, but they presented greater arm movement speed (p < 0.05) compared to both SIG and BFO. In addition, VI players presented greater trunk flexion angles while passing when compared to both SIG and BFO (p < 0.05). It is concluded that VI players present slower speed while running and turning, and they adopt specific adaptations from arm movements and trunk flexion to perform passes.

#6 Interpersonal Dynamics in 2-vs-1 Contexts of Football: The Effects of Field Location and Player Roles
Reference: Front Psychol. 2019 Jul 3;10:1407. doi: 10.3389/fpsyg.2019.01407. eCollection 2019.
Authors: Laakso T, Davids K, Liukkonen J, Travassos B
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Summary: This study analyzed the spatial-temporal interactions that sustained 2-vs-1 contexts in football at different field locations near the goal. Fifteen male players (under 15 years, age 13.2 ± 1.03 years, years of practice 4.2 ± 1.10 years), 5 defenders, 7 midfielders, and 3 attackers, participated in the study. Each participant performed a game to simulate a 2-vs-1 sub-phase as a ball carrier, second attacker, and defender at three different field locations, resulting in a total number of 142 trials. The movements of participants in each trial were recorded and digitized with TACTO software. Values of interpersonal distance between the ball carrier and defender and interpersonal angles between players and between the goal target, defender, and ball carrier were calculated. The results revealed a general main effect of field location. Generally, the middle zone revealed the lowest values of interpersonal distance and angle between players and the right zone and the highest values of interpersonal distance between players and interpersonal angle between players and the goal. Related with participants' roles, defenders revealed subtle differences as attackers on interpersonal distances and relative angles compared with midfielders and attackers. Findings supported that field location is a key constraint of players' performance and that players' role constraint performance effectiveness in football.

#7 Characteristics of potential concussive events in three elite football tournaments
Reference: Inj Prev. 2019 Jul 22. pii: injuryprev-2019-043242. doi: 10.1136/injuryprev-2019-043242. [Epub ahead of print]
Authors: Armstrong N, Rotundo M, Aubrey J, Tarzi C, Cusimano MD
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Summary: Identify patterns in the nature and characteristics of potential concussive events (PCEs) in football. This study analysed the incidence and characteristics of PCEs that occurred during the 2014 and 2018 Fédération Internationale de Football Association World Cups, and the 2016 UEFA Euro Cup. PCEs were defined as direct head collision incidents resulting in the athlete being unable to immediately resume play for at least 5 sec following impact. A total of 218 incidents were identified in 179 matches (1.22 per match, 36.91 per 1000 hours of exposure). The most common mechanism of PCE was elbow-to-head (28.7%, n=68). The frontal region was the most frequently affected location of impact with 22.8% (n=54). Our study defined the identification, prevalence and nature of PCEs in professional international soccer tournaments. Our findings indicate the different contexts and mechanisms of head contact and contact to different regions of the head can be associated with varying signs of concussion. The results highlight targets for future injury prevention strategies.

#8 Neuromuscular changes in football players with previous hamstring injury
Reference: Clin Biomech (Bristol, Avon). 2019 Jul 13;69:115-119. doi: 10.1016/j.clinbiomech.2019.07.010. [Epub ahead of print]
Authors: Areia C, Barreira P, Montanha T, Oliveira J, Ribeiro F
Summary: Impact of prior injury on myoelectrical activity of the hamstrings during isokinetic eccentric contractions has received increased literature attention. This cross-sectional study aimed to assess neuromuscular adaptations, namely proprioception, core stability, muscle strength, extensibility and activity, in football players with history of hamstring strain injury. Seventeen players, 10 with history of hamstring injury and 7 without prior injury underwent isokinetic strength testing, eccentric knee extension at 30 and 120°/s. Myoelectrical activity of bicep femoris and medial hamstrings was calculated at 30, 50 and 100 ms after onset of contraction. Functional tests included core stability, muscle strength, and knee proprioception tests. Differences were observed between Hamstring Group injured and uninjured and Control Group dominant limbs in the bicep femoris activity at almost all times in both velocities (p < 0.05). Joint position sense error was higher in the injured side compared to uninjured and control dominant limb; additionally there were also differences between injured and uninjured limb in the triple-hop test. Previously injured side showed deficits in bicep femoris myoelectrical activity after onset of contraction during eccentric testing, proprioceptive deficits, and functional asymmetry.

#9 Effects of Different Training Interventions on the Recovery of Physical and Neuromuscular Performance After a Soccer Match
Reference: J Strength Cond Res. 2019 Jul 31. doi: 10.1519/JSC.0000000000003269. [Epub ahead of print]
Authors: Trecroci A, Porcelli S, Perri E, Pedrali M, Rasica L, Alberti G, Longo S, Iaia FM
Summary:  In competitive soccer, players are frequently required to play in periods with congested fixtures in which they have limited time to recover between matches (3-4 days). Thus, finding the most appropriate intervention strategy to limit players' neuromuscular (muscle function of lower limbs) and physical (running performance) impairments in this short period becomes crucial. The aim of the study was to examine how muscle function of knee extensors and flexors and sprint performance recovered +72 hours after match in relation to different field-based training sessions. Using a crossover design, 9 subelite players (age 17.6 ± 0.5 years, height 1.77 ± 0.02 m, body mass 66.4 ± 5.8 kg) underwent a soccer-specific training (SST) session or an active recovery regime (AR) on the second day after a match. Immediately after (0 hour) and +72 hours after match, 30-m sprint and repeated sprint ability (RSA) were assessed. Maximum isometric voluntary force (MVF) of knee extensors and flexors was determined at 120° and 90° (with 180° being full extension), respectively. SST and AR promoted similar effects on the recovery kinetics of sprint, RSA, and MVF of knee extensors (p > 0.05). However, compared with SST, AR promoted a significantly better restoration of MVF of knee flexors (p < 0.05) after +72 hours from the match. Because muscle fatigue has been related with increased hamstring injury risk, a training based on AR can be a valid intervention to promote the recovery of muscle force production of knee flexors and reduce hamstring injury risk in the postmatch period.

#10 Anterior Cruciate Ligament Repair in a Professional Soccer Player Using Internal Brace Ligament Augmentation: A Case Report Focusing on Rehabilitation
Reference: Surg Technol Int. 2019 Aug 1;35. pii: sti35/1162. [Epub ahead of print]
Authors: McIntyre V, Hopper GP, Mackay GM
Summary: Anterior cruciate ligament (ACL) reconstruction with hamstring or patellar tendon autograft has been the gold standard for the operative treatment of an ACL rupture for many years. Repair with Internal Brace Ligament Augmentation (IBLA) is a new technique that uses ultra-high strength tape (FiberTape, Arthrex, Naples, FL, USA) to bridge the ligament. This technique reinforces the ligament as a secondary stabiliser, encouraging natural healing of the ligament by protecting it during the healing phase and supporting early mobilisation. This retrospective case report focuses on the rehabilitation of a 21-year-old male professional soccer player who ruptured his ACL in a contact injury whilst playing a competitive game. He underwent ACL repair with IBLA two weeks following injury. The six-month rehabilitation programme consisted of gradual progressions for mobility, proprioception, strengthening, cardiovascular maintenance and running in conjunction with physiotherapy to assist with the maintenance of soft tissue quality, pain management and control of oedema. After completing the rehabilitation programme, the patient returned to unrestricted sporting activity within six months. At 18-month follow-up, the patient continues to play at the same competitive level without any issues. This rehabilitation programme after ACL repair with IBLA successfully enabled a professional soccer player to return to his pre-injury playing level.

#11 Posture correctness of young female soccer players
Reference: Sci Rep. 2019 Aug 1;9(1):11179. doi: 10.1038/s41598-019-47619-1.
Authors: Żuk B, Sutkowski M, Paśko S, Grudniewski T
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Summary: The objectives of the study were to evaluate the correctness of the body posture of female soccer players in the frontal plane from the back based on selected body points in two static positions (habitual and actively corrected) using a non-contact optical measurement method. Forty-two young women (aged 16-20) playing soccer in a sports club in Poland were examined and compared with controls. The spatial coordinates (x, y, z) of the selected body points were determined. Four points (OcL, OcR, PvL and PvR) were extracted and used to calculate vectors [Formula: see text] and [Formula: see text] for analysis. The results show that median of the pelvic line angle was positive (PvR was lower than PvL) in both groups. For the habitual posture, the absolute value of the difference between the 25th and 75th percentiles in the pelvic line was almost three times greater among the soccer players than the controls (ratio between soccer players and controls: 2.93). Static postural imbalances in female soccer players require diagnosis of the sacroiliac joints with analysis of lumbar-pelvic system support and inhibition in the context of myofascial connection integration. Exercises can be implemented to stabilize the lumbar-pelvis complex as prophylaxis for spinal overload during the training cycle.

#12 Comparison of Complex Versus Contrast Training on Steroid Hormones and Sports Performance in Male Soccer Players
Reference: J Chiropr Med. 2019 Jun;18(2):131-138. doi: 10.1016/j.jcm.2018.12.001. Epub 2019 Jun 26.
Authors: Ali K, Verma S, Ahmad I, Singla D, Saleem M, Hussain ME
Summary: The purpose of this study was to compare the effects of a complex versus a contrast training regimen with steroid hormones and the performance of soccer players. Thirty-six professional male soccer players were randomly divided into 3 equal groups: complex training (n = 12; body mass index [BMI], 22.95 ± 1.76 kg/m2), contrast training (n = 12; BMI, 22.05 ± 2.03 kg/m2), and control (n = 12; BMI, 22.27 ± 1.44 kg/m2). Players from the complex and contrast groups were trained for 6 weeks (3 d/wk). The complex group performed 4 different exercises, each composed of strength (80% of 1 repetition maximum [RM]) and power components alternately. The contrast group performed the same strengthening exercises alternately at different intensities (40% and 80% of 1 RM). All players were tested for free testosterone, cortisol, vertical jump, 20-m sprint, and agility T-test at the baseline and after 6 weeks of training. A 3 × 2 mixed analysis of variance revealed a significant difference in time effect (P ≤ .05), whereas a nonsignificant difference was found in the group effect for all outcome variables. group × time interaction was significant in all the variables (P < .01) except cortisol (P = .28). Complex training showed greater improvement in physical performance and free testosterone concentration compared with contrast training, whereas both types of training decreased cortisol concentration in a similar fashion.

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