Latest research in football - week 2 - 2020

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 Groin Injuries in Soccer: Investigating the Effect of Age on Adductor Muscle Forces
Reference: Med Sci Sports Exerc. 2019 Dec 31. doi: 10.1249/MSS.0000000000002243. [Epub ahead of print]
Authors: Dupré T, Lysdal FG, Funken J, Mortensen KRL, Müller R, Mayer J, Krahl H, Potthast W
Summary: The sudden rise in the injury incidence during adolescence, is also evident in soccer related injuries to the groin. Submaximal passing applies high stress on the adductor muscles and pubic symphysis and is therefore likely to be connected to the occurrence of groin injuries. Therefore, the purpose of the study was to compare hip joint kinematics and adductor muscle forces of different adolescent age groups during submaximal soccer passing. Sixty participants, in four groups, below 12, 15, 16 and 23 years (U12, U15, U16, U23), were analyzed. A Footbonaut, equipped with a 3D motion capture system consisting of 16 cameras, was used to capture kinematic data of short passes. Inverse dynamic analysis was performed to calculate muscle forces of ten passes of each subject. The U15 group showed reduced angular velocities. A rise in hip adductor muscle forces was evident from the youngest group up to the oldest groups. The largest increase (49%) was found between U12 and U15. Lower limb mass was identified as the best predictor for the increasing adductor force. The reduced angular velocities of the U15 and the increase in muscle forces between all age groups was attributed to the increasing segment masses and length. This increases the moments of inertia of the leg segments thereby demanding higher forces to accelerate the segments. Most likely, the stress put upon the adductors apophyses increases during adolescence, as tendons are known to adapt slower than muscles, increasing the risk for overuse injuries. Coaches could use lower limb mass as an indicator for fast increases in the force demand to identify players who would benefit from a reduced training volume.

#2 Pathoanatomy of the Jones Fracture in Male University Soccer Players
Reference: Am J Sports Med. 2019 Dec 30:363546519893365. doi: 10.1177/0363546519893365. [Epub ahead of print]
Authors: Fujitaka K, Tanaka Y, Taniguchi A, Ogawa M, Isomoto S, Otuki S, Okubo M
Summary: Jones fractures are relatively common in soccer players and require an extended recovery period because this type of fracture has a high incidence of delayed union, nonunion, and refracture. There has been some previous research on risk factors for Jones fracture, but no study has yet investigated the effect of the length of the fifth metatarsal bone and the positional relationship of the articular surface of the fifth metatarsal bones and the tarsal bones. Clarification of the characteristics of the foot structure that predispose soccer players to Jones fracture may aid in the prevention of this injury. The purpose was to investigate the association between Jones fracture and foot structure as assessed with a mapping system on weightbearing dorsoplantar and lateral foot radiographs. We used a mapping system to evaluate the radiographs of 60 feet from 30 university soccer players with Jones fractures and a control group of 60 feet from 60 male university soccer players without Jones fracture. The groups were compared regarding the length of the fifth metatarsal and the positions of the metatarsal and tarsal bones. Analysis of weightbearing dorsoplantar foot radiographs showed that the fifth metatarsal was significantly longer and that its proximal tip was positioned more proximally in the Jones fracture group as compared with the control group. Analysis of weightbearing lateral foot radiographs showed that the reference points for the medial arch were significantly higher in the Jones fracture group than in the control group. This study indicated that the proximally longer fifth metatarsal may cause greater stress at the base of the fifth metatarsal bone because the lever arm becomes long. In addition, high medial longitudinal arch may contribute to increased load on the lateral side of the foot. Thus, these anatomic features may be useful to identify soccer players at high risk of Jones fracture at medical checkup.

#3 Multidirectional Plyometric Training: Very Efficient Way to Improve Vertical Jump Performance, Change of Direction Performance and Dynamic Postural Control in Young Soccer Players
Reference: Front Physiol. 2019 Dec 9;10:1462. doi: 10.3389/fphys.2019.01462. eCollection 2019.
Authors: Jlid MC, Racil G, Coquart J, Paillard T, Bisciotti GN, Chamari K
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Summary: The aim of the study was to assess the effects of multidirectional plyometric training (MPT) on vertical jump height, change of direction performance (CODP), and dynamic postural control (DPC) in young soccer players. Twenty-eight young male soccer players were randomly assigned to an experimental group (EG, n = 14; age: 11.8 ± 0.4 years) and a control group (CG, n = 14; age: 11.6 ± 0.5 years). The EG introduced 8-week MPT, two days per week into their in-season training, while CG continued training without change. Measurements of vertical jump height, CODP, and DPC were completed at the beginning and end of the 8-week MPT. A significant group × time interaction was observed for Squat-Jump (p < 0.05), for Counter-Movement Jump (p < 0.05), and for CODP test (p < 0.05). In addition, a significant group × time interaction was observed for DPC in seven axes for the dominant- (anterior, lateral, postero-lateral, posterior, postero-medial, medial, and antero-medial; p < 0.05 for all) and in seven axes for the non-dominant- (anterior, antero-lateral, lateral, posterior, postero-medial, medial and antero-medial; p < 0.05 for all) legs. The rest of the axes of both legs did not show any significant group × time interaction (p > 0.05). In conclusion, incorporating MPT into the in-season regimen of young male soccer players improved performance of various indices related to soccer activity (i.e., vertical jump height, CODP, and DPC). MPT has the potential to be appealing to coaches, as it requires little time while yielding valuable results in the physical preparation of young soccer players.

#4 Predictive modelling of the physical demands during training and competition in professional soccer players
Reference: J Sci Med Sport. 2019 Dec 17. pii: S1440-2440(19)31238-1. doi: 10.1016/j.jsams.2019.12.008. [Epub ahead of print]
Authors: Giménez JV, Jiménez-Linares L, Leicht AS, Gómez MA
Summary: The present study aimed to predict the cut-off point-values that best differentiate the physical demands of training and competition tasks including friendly matches (FM), small sided games (SSG), large sided games (LSG), mini-goal games (MG) and ball circuit-training (CT) in professional soccer players. Fourteen professional players participated in all tasks with the CT, SSG and MG consisting of 8 repetitions of 4-min game play, interspersed by 2-min of active recovery. The training data were compared to the first 32-min of the LSG and two competitive FM per player. All movement patterns from walking to sprint running were recorded using 10Hz GPS devices while player perception of exertion was recorded via a visual analogue scale, post-task. Decision tree induction was applied to the dataset to assess the cut-off point-values from four training drills (SSG, LSG, MG, and CT) and FM for every parameter combination. Distance covered during jogging (2.3-3.3m/s; >436m), number of decelerations (≤730.5) and accelerations (≤663), and maximum velocity reached (>5.48m/s) characterized the physical demands during competition (FM) with great variability amongst training drills. The use of these novel, cut-off points may aid coaches in the design and use of training drills to accurately prepare athletes for soccer competition.

#5 Technical-Tactical Analysis of the Players of the Left and Right Wing in Elite Soccer
Reference: J Hum Kinet. 2019 Nov 30;70:233-244. doi: 10.2478/hukin-2019-0045. eCollection 2019 Nov.
Authors: Amatria M, Dios RM, Pérez-Turpin JA, Gomis-Gomis MJ, Elvira-Aranda C, Suárez-Llorca C
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Summary: In today's soccer, teams are increasingly better trained both physically and tactically, hence different game styles can be identified and differences between them reduced. However, without an exhaustive analysis of reality, the view can lead to the extraction of erroneous conclusions, and what seems to be a team with a marked offensive profile is a mere illusion, resulting to be a team that develops a perfectly balanced game. In this paper, an analysis of technical-tactical performance of players who occupied both wings in an elite team was made, taking as reference the Spanish national soccer team as the model of international game to imitate in the last decade. The development of this paper was located within the observational methodology, using the polar coordinates technique for the analysis of the obtained data. The results showed how, despite identifying offensive profiles within technical-tactical performance of players that occupied the outer wings or lanes of the playing field, their tactical means and orientations diverged from each other. The results showed a more offensive profile and with higher technical complexity of players that occupied the left wing, while players that held the right wing showed a more defensive and recuperative profile, indicating a less vertical and complex style of play at a technical level with the forward as an offensive reference.

#6 External Load Variations Between Medium- and Large-Sided Soccer Games: Ball Possession Games Vs Regular Games with Small Goals
Reference: J Hum Kinet. 2019 Nov 30;70:191-198. doi: 10.2478/hukin-2019-0031. eCollection 2019 Nov.
Authors: Clemente FM, Praça GM, Bredt SDGT, van der Linden CMI, Serra-Olivares J
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Summary: This study compared external load variations between 5 vs 5 and 10 vs 10 sided game formats played under two conditions: (i) a ball possession game with two floaters, and (ii) a regular game with goalkeepers and small goals. Twenty-two professional soccer players participated in this study: four central defenders, four wide defenders, nine central midfielders, three wide forwards, and three strikers. Total distance (TD), running distance (RD), sprinting distance (SD), number of sprints (NS), and player's training load (PL) were recorded by GPS units. Within-format analyses revealed very likely large increases in TD (20.0%, [9.2; 31.9]; effect size (ES): 1.48, [0.71; 2.25]) and RD (130.9%, [20.2; 343.7]; ES: 1.32, [0.29; 2.35]) during the regular game when compared to the ball possession game in the 5 vs 5 format. In the 10 vs 10 format, large increases in TD (27.9%, [17.7; 39.1]; ES: 3.54, [2.34; 4.74]) and PL (27.4%, [12.6; 44.1]; ES: 2.46, [1.20; 3.72]) were observed in the regular condition when compared to the ball possession condition. Between-formats analyses revealed that, in the 10 vs 10 format, when compared to the 5 vs 5 format, RD was very likely larger (123.5%, [33.7; 273.7]), as was SD (195.8%, [20.5; 626.2]). However, very likely large decreases in PL were observed in the 10 vs 10 format (-19.6%; [-29.4; -8.3]) in the ball possession condition. Unclear differences were revealed based on variations in external load variables between formats in the regular condition. Smaller formats reduce the area available for running and sprinting and, thus, may be more adequate for increasing player's training load (based on accelerometer data).

#7 Short-Term Repeated-Sprint Training (Straight Sprint Vs. Changes of Direction) in Soccer Players
Reference: J Hum Kinet. 2019 Nov 30;70:183-190. doi: 10.2478/hukin-2019-0040. eCollection 2019 Nov.
Authors: Beato M, Coratella G, Bianchi M, Costa E, Merlini M
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Summary: Repeated-sprint training (RST) is considered a critical training method in team sports. It is well known that RST effects may depend on several variables such as the duration of the protocol and repeated-sprint methodology. Few studies have evaluated very short-term protocols and compared different RST modalities. The aim of this study was to compare the effectiveness of 2 week RST including straight sprints or changes of direction (CODs) on physical performance in a sample of soccer players. This study used a randomised pre-post parallel group trial design. The participants were assigned to either an RST group using straight sprints (RST-SS = 18 players) or an RST group using CODs (RST-COD = 18 players). The protocols were: 3 sets of 7 x 30 m sprints for the RST-SS and 7 x 20 + 20 m (one COD of 180°) for the RST-COD, with 20 s and 4 min recovery between sprints and sets, respectively. The following evaluations were performed: 10 and 20 m sprint, agility test, repeated sprint test (RSTbest and RSTmean), and Yo-Yo Recovery Level 1. After the training period, the RST-SS did not report any performance variation, while the RST-COD showed improvements in the 10 m sprint and RSTbest (effect size = 0.70 and 0.65, respectively). The between-group analysis did not report any statistical difference between the RST-SS and the RST-COD. In conclusion, this study did not support the utilisation of a very short-term RST protocol with soccer players, however, the RST-COD presented some additional benefits in sprint performance compared to the RST-SS.

#8 Analysis of Match Dynamics of Different Soccer Competition Levels Based on the Player Dyads
Reference: J Hum Kinet. 2019 Nov 30;70:173-182. doi: 10.2478/hukin-2019-0030. eCollection 2019 Nov.
Authors: Caetano FG, da Silva VP, Torres RDS, Anido RO, Cunha SA, Moura FA
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Summary: The purpose of this study was to analyse the dynamics of play based on dyads during soccer matches, according to the competition level, period of the matches, and playing positions. We recorded eight Brazilian soccer matches (four of the national and four of the regional level), using up to six digital cameras (30 Hz). The position information of the 204 players in the eight matches was obtained using an automatic tracking system. The Euclidean distance between the nearest opponents was calculated over time to define the dyads. The interaction between the components of dyads was assessed by the distances between players and was compared among the different positions (defender, full-back, defensive midfielder, midfielder, and forward), match periods (15, 30, 45, 60, 75, and 90 min), and competition levels. Results showed smaller distances for the national level dyads, compared to the regional matches. Greater distances between the players were found in the last 15 minutes of the matches, compared to the other periods. The full-backs were more distant from opposing players compared to players from other playing positions. Thus, coaches should consider the characteristics of each playing position and the greater proximity between opponents' players in top-level competition for the development of tactical proficiency of the players.

#9 Different Cleat Models Do Not Influence Side Hop Test Performance of Soccer Players with and Without Chronic Ankle Instability
Reference: J Hum Kinet. 2019 Nov 30;70:156-164. doi: 10.2478/hukin-2019-0029. eCollection 2019 Nov.
Authors: Silva DCF, Santos R, Vilas-Boas JP, Macedo R, Montes AM, Sousa ASP
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Summary: The lateral ankle sprain is one of the most common sport injury, representing 10-30% of all musculoskeletal disorders. The lateral ankle sprain is induced by sport gestures involving changes of direction and landing manoeuvres and constitutes a risk factor for the occurrence of chronic ankle instability. Although cleat models and performance have been already explored, no study has evaluated this relationship in athletes with chronic ankle instability. Therefore, the purpose of the study was to analyse the influence of different soccer cleat models on Side Hop Test performance of athletes with and without chronic ankle instability. Thirty-nine athletes were divided into two groups, a chronic ankle instability group (n = 20) and a healthy group (n = 19). Each participant performed the Side Hop Test, executing 10 consecutive jumps on dry artificial grass with 4 cleat models. The Qualisys System and two force platforms were used to analyse the test runtime, the distance travelled and the mean velocity. No statistically significant interaction was observed between the group and the cleat model for all variables evaluated. In addition, no differences were observed between models or groups. In this specific test, performance does not seem to be influenced by different cleat models on dry artificial grass in athletes with and without chronic ankle instability.

#10 Assessment of Lower Body and Abdominal Strength in Professional Soccer Players
Reference: J Hum Kinet. 2019 Nov 30;70:15-23. doi: 10.2478/hukin-2019-0035. eCollection 2019 Nov.
Authors: Michaelides MA, Parpa KM, Zacharia AI
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Summary: The purpose of this study was to evaluate abdominal strength in professional soccer players and compare the findings to their lower body strength. An observational design was used to examine abdominal and lower body strength using two functional performance tests (a lower body isokinetic test and an isometric abdominal test, respectively). One hundred and thirty-two professional male soccer players from Cyprus's first and second divisions participated in this study. Testing included three and twenty-five maximal concentric flexion and extension repetitions at angle speeds of 60°/s (degrees/second) and 300°/s, respectively. On a separate occasion, participants completed two trials on an isometric device (ABTEST Gen. 3 system) for evaluation of abdominal strength. At both isokinetic speeds of 300°/s and 60°/s, abdominal strength had low to moderate significant correlations (p < .05) with quadriceps and hamstring strength. Coefficients of determination (R2) demonstrated that the variability in isokinetic variables accounted for only 14-16% of the variability of abdominal strength. Abdominal strength appears to be high in professional soccer players, but is not dependent on the sports level and/or a playing position. The results of this study demonstrate that abdominal strength and knee joint strength need to be evaluated separately.

#11 Effects of fatigue induced by repeated-sprint on kicking accuracy and velocity in female soccer players
Reference: PLoS One. 2020 Jan 7;15(1):e0227214. doi: 10.1371/journal.pone.0227214. eCollection 2020.
Authors: Torreblanca-Martínez V, Nevado-Garrosa F, Otero-Saborido FM, Gonzalez-Jurado JA
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Summary: The aim of this study was to investigate the effects of fatigue induced by repeated sprint in the kicking accuracy and velocity in female soccer players. Eighteen Under-23 female soccer players from a Spanish professional club were subjected to a fatigue protocol based on a repeated-sprint ability (RSA) test. Measurements of the kicking velocity (maximal ball velocity) and accuracy (Loughborough Soccer Shooting Test) were taken before and after fatigue induction. Correlations between the change in the maximal ball velocity/accuracy and the heart rate (HR), the fatigue index (FI), the sprint decrement (Sdec) and the rating of perceived exertion (RPE) were made. There was a significant difference between maximal ball velocity under fatigue conditions with respect to non-fatigue conditions (p = 0.001; ES = 0.89). However, despite a lower kicking accuracy punctuation with fatigue, this was not statistically significant (p = 0.433; ES = 0.22). Significant correlations were found between the maximal kicking velocity and the FI (r = 0.632, p < 0.01) and the Sdec (r = -0.554, p < 0.05) and between the kicking accuracy and the RPE (r = -0.506, p < 0.05). In conclusion, there was a significant reduction in the maximal kicking velocity, but not in the kicking accuracy, under fatigued conditions. The RSA-related FI and Sdec were the best predictors of the maximal kicking velocity and the RPE for the kicking accuracy.

#12 Agility Testing in Youth Football (Soccer)Players; Evaluating Reliability, Validity, and Correlates of Newly Developed Testing Protocols
Reference: Int J Environ Res Public Health. 2020 Jan 1;17(1). pii: E294. doi: 10.3390/ijerph17010294.
Authors: Krolo A, Gilic B, Foretic N, Pojskic H, Hammami R, Spasic M, Uljevic O, Versic S, Sekulic D
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Summary: Reactive agility (RAG) and change of direction speed (CODS) are important determinants of success in football (soccer), but there is an evident lack of information on reliable and valid football-specific testing procedures which will be applicable in defining sport-specific RAG and CODS in youth players. This study evaluated reliability and construct validity of newly developed tests of football-specific RAG (FS_RAG) and CODS (FS_CODS), which involved the ball kicking football technique. Additionally, factors associated with FS_RAG and FS_CODS were evaluated. The participants were youth football players (n = 59; age: 13.40 ± 1.25 years) divided according to their age into U13 (11-12 years of age; n = 29), and U15 (13-14 years of age; n = 30) categories. Additionally, performance levels (starters [first-team] vs. non-starters [substitutes]) were observed in each age category. The dependent variables were newly developed FS_RAG and FS_CODS tests. The independent variables were sprinting capacities over 10 and 20 meters (S10M, S20M), countermovement jump (CMJ), the reactive strength index (RSI), and a generic CODS test of 20 yards (20Y). The newly developed FS_CODS and FS_RAG were observed as dependent variables. Results showed appropriate intra-testing and inter-testing reliability of the FS_RAG and FS_CODS, with somewhat better reliability of the FS_CODS (ICC=0.82 and 0.79, respectively). Additionally, better reliability was evidenced in U15 than in U13 (ICC: 0.82-0.85, and 0.78-0.80 for U15 and U13, respectively). Independent samples t-test indicated significant differences between U13 and U15 in S10 (t-test: 3.57, p < 0.001), S20M (t-test: 3.13, p < 0.001), 20Y (t-test: 4.89, p < 0.001), FS_RAG (t-test: 3.96, p < 0.001), and FS_CODS (t-test: 6.42, p < 0.001), with better performance in U15. Starters outperformed non-starters in most capacities among U13, but only in FS_RAG among U15 (t-test: 1.56, p < 0.05). Multiple regression calculations indicated nonsignificant association between independent and dependent variables in U13 (FS_CODS: 19%, FS_RAG: 21% of the explained variance, both p > 0.05), but independent variables explained significant proportion of both dependent variables in U15 (FS_CODS: 35%, FS_RAG: 33% explained variance, both p < 0.05). The study confirmed the applicability of newly developed tests in distinguishing studied age categories of players. Results indicate that superiority in all studied fitness capacities is translated into performance level in U13. Meanwhile, FS_RAG seems to be important determinant of quality in U15.

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