Latest research in football - week 48 - 2014

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Somatotype of Competitive Youth Soccer Players From Brazil
Reference: J Hum Kinet. 2014 Oct 10;42:259-266. eCollection 2014.
Authors: Fidelix YL, Berria J, Ferrari EP, Ortiz JG, Cetolin T, Petroski EL
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Summary: The aim of this study was to identify the morphological configuration of youth athletes from professional soccer clubs and to verify their differences according to the tactical position on the field. Overall, 67 male players aged 15 to 17 years were evaluated. The examined anthropometric measurements included body mass, body height, skinfolds (triceps, subscapular, supraspinal and medial calf), girths (flexed and tensed arm and calf) and breadths (humerus and femur). For statistical purposes, analysis of variance and post hoc Bonferroni and Kruskal-Wallis tests were used. We concluded that goalkeepers were heavier and taller than center backs (p = 0.015 and p = 0.001), midfielders (p = 0.005 and p <0.001) and center forward players (p = 0.024 and p <0.001). The average somatotype for defense, forward and goalkeeper positions was a balanced mesomorph. Midfield players showed ectomorphic-mesomorph characteristics. It was concluded that goalkeepers were characterized as being taller and heavier and that somatotype features of athletes were similar between positions, except for midfield players.

#2 Changes in Muscle Strength in U19 Soccer Players During an Annual Training Cycle
Reference: J Hum Kinet. 2014 Oct 10;42:175-185. eCollection 2014.
Authors: Lehnert M, Xaverová Z, De Ste Croix M
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Summary: The aim of the study was to investigate the seasonal variation in isokinetic strength of the knee flexors and extensors, and conventional (H/QCONV) and functional (H/QFUNC) hamstring to quadriceps strength ratios in highly trained adolescent soccer players. The players (n=11; age 17.8±0.3) were measured at the end of the competitive season (autumn), at the beginning and the end of pre-season (winter) and during the sixth week of a new competitive season. Isokinetic peak torque (concentric and eccentric) was measured at 60°·s-1 in a sitting position with the hip flexed at 100°. The testing range of motion was set from 10 - 90° of knee flexion. The players performed a set of five maximum repetitions for both the dominant and non-dominant leg. Statistically significant differences (p<0.001) between the four seasonal measurements were noted for peak torque of the dominant leg knee flexors in concentric muscle action only. A post hoc analysis revealed a statistically significant increase in peak torque from the 1st to the 4th measurement (p<0.001; d=0.692) and from the 2nd to the 4th (p<0.01; d=0.564). The differences in the changes of peak torque of the knee flexors and extensors depending on type of muscle action and tendencies found in the H/Q ratios throughout the annual training cycle indicate that strength assessment of the knee flexors and extensors and their balance throughout the annual training cycle could be beneficial for elite male adolescent soccer players both in terms of performance and risk of injury.

#3 Tracking Changes in Maximal Oxygen Consumption with the Heart Rate Index in Female Collegiate Soccer Players
Reference: J Hum Kinet. 2014 Oct 10;42:103-111. eCollection 2014.
Authors: Esco MR, Snarr RL, Flatt A, Leatherwood M, Whittaker A
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Summary: The purpose of this study was to determine if the HRindex Method (VO2max = [6 x HRindex - 5] x 3.5, where HRindex = HRmax/HRrest) was accurate for tracking changes in VO2max following 8-weeks of endurance training among collegiate female soccer players. Predicted VO2max via the HRindex Method and observed VO2max from a maximal exercise test on a treadmill were determined for a group of female soccer athletes (n = 15) before and following an 8-week endurance training protocol. The predicted (pVO2max) and observed (aVO2max) values were compared at baseline and within 1-week post-training. Change values (i.e., the difference between pre to post) for each variable were also determined and compared. There was a significant difference between aVO2max before (43.2 ± 2.8 ml·kg·min-1) and following (46.2 ± 2.1 ml·kg·min-1) the 8-week training program (p < 0.05). However, pVO2max did not significantly change following training (pre = 43.4 ± 4.6 ml·kg·min-1, post = 42.9 ± 4.1 ml·kg·min-1, p = 0.53). Furthermore, the correlation between the change in aVO2max and the change in pVO2max was trivial and non-significant (r = 0.30, p = 0.28). The HRindex Method does not appear to be suitable for predicting changes in VO2max following 8-weeks of endurance training in female collegiate soccer players.

#4 Kinematic Analysis of the Instep Kick in Youth Soccer Players
Reference: J Hum Kinet. 2014 Oct 10;42:81-90. eCollection 2014.
Authors: Kapidžić A, Huremović T, Biberovic A.
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Summary: We attempted to establish which applied kinematic variables significantly contributed to the efficiency of the instep kick motion in soccer. The study sample comprised 13 boys (age: 13 ± 0.5 yrs; body mass: 41.50 ± 8.40 kg; body height: 151.46 ± 5.93 cm) from the FC Sloboda school of soccer. Each participant performed three kicks with maximum strength that were video recorded with two synchronized cameras (Casio Ex-F1) positioned 12 m away from the place of the kick. Data were collected by analyzing the video recordings of each kick. Data processing was performed using the APAS motion analysis system (Ariel Dynamics Inc., San Diego, CA). On the basis of the forward selection method of multiple regression analysis, we determined the correlations between the prediction variables and the selected criteria (speed of the ball; p = 0.01). On the basis of the regression coefficients, it was concluded that two variables significantly contributed to the speed of the ball: speed of the foot of the kicking leg at the time of contact with the ball (p = 0.01) and the distance between the angle support leg and center of the ball ("foot posterior displacement") (p = 0.01). In order to achieve the best possible technical performance and, therefore, a higher speed of the ball, soccer players must pay attention to two important elements during training. First, it is necessary to position the support leg as close to the ball as possible and, second, maximize the force used in the initial phases of the kick to achieve a high speed of the kicking foot.

#5 Effect of Leg Dominance on The Center-of-Mass Kinematics During an Inside-of-the-Foot Kick in Amateur Soccer Players
Reference: J Hum Kinet. 2014 Oct 10;42:51-61. eCollection 2014.
Authors: Zago M, Motta AF, Mapelli A, Annoni I, Galvani C, Sforza C
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Summary: Soccer kicking kinematics has received wide interest in literature. However, while the instep-kick has been broadly studied, only few researchers investigated the inside-of-the-foot kick, which is one of the most frequently performed techniques during games. In particular, little knowledge is available about differences in kinematics when kicking with the preferred and non-preferred leg. A motion analysis system recorded the three-dimensional coordinates of reflective markers placed upon the body of nine amateur soccer players (23.0 ± 2.1 years, BMI 22.2 ± 2.6 kg/m2), who performed 30 pass-kicks each, 15 with the preferred and 15 with the non-preferred leg. We investigated skill kinematics while maintaining a perspective on the complete picture of movement, looking for laterality related differences. The main focus was laid on: anatomical angles, contribution of upper limbs in kick biomechanics, kinematics of the body Center of Mass (CoM), which describes the whole body movement and is related to balance and stability. When kicking with the preferred leg, CoM displacement during the ground-support phase was 13% higher (p<0.001), normalized CoM height was 1.3% lower (p<0.001) and CoM velocity 10% higher (p<0.01); foot and shank velocities were about 5% higher (p<0.01); arms were more abducted (p<0.01); shoulders were rotated more towards the target (p<0.01, 6° mean orientation difference). We concluded that differences in motor control between preferred and non-preferred leg kicks exist, particularly in the movement velocity and upper body kinematics. Coaches can use these results to provide effective instructions to players in the learning process, moving their focus on kicking speed and upper body behavior.

#6 The Impact of the FIFA 11+ Training Program on Injury Prevention in Football Players: A Systematic Review
Reference: Int J Environ Res Public Health. 2014 Nov 19;11(11):11986-12000.
Authors: Barengo NC, Meneses-Echávez JF, Ramírez-Vélez R, Cohen DD, Tovar G, Bautista JE
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Summary: The FIFA 11+ is a simple, and easy to implement, sports injury prevention program comprising a warm up of 10 conditioning exercises. The aim of this systematic review was to evaluate the impact of the FIFA 11+ on injury incidence, compliance and cost effectiveness when implemented among football players. MEDLINE, EMBASE and Scopus databases were searched using the search terms "FIFA 11+", "football", "soccer", "injury prevention", and "The 11". The titles and abstracts were screened by two independent reviewers and the data were filtered by one reviewer using a standardized extraction form and thereafter checked by another one. The risk of bias and the methodological quality of the studies were evaluated through the PEDro score and Critical Appraisal Skills Programme (CASP). A total of 911 studies were identified, of which 12 met the inclusion criteria of the review. The FIFA 11+ has demonstrated how a simple exercise program completed as part of warm-up can decrease the incidence of injuries in amateur football players. In general, considerable reductions in the number of injured players, ranging between 30% and 70%, have been observed among the teams that implemented the FIFA 11+. In addition, players with high compliance to the FIFA 11+ program had an estimated risk reduction of all injuries by 35% and show significant improvements in components of neuromuscular and motor performance when participating in structured warm-up sessions at least 1.5 times/week. Most studies had high methodological quality and a low risk of bias. Given the large number of people who play football at amateur level and the detrimental impact of sports injuries on a personal and societal level, the FIFA 11+ can be considered as a fundamental tool to minimize the risks of participation in a sport with substantial health benefits.

#7 Effects of high-intensity running training on soccer-specific fitness in professional male players
Reference: Appl. Physiol. Nutr. Metab. 39: 763–769 (2014)
Authors: Wells C, Edwards A, Fysh M, Drust B
Summary: The purpose of this study was to investigate whether or not physiological and performance gains could be achieved with the addition of high-intensity running to an existing training programme in a group of well trained professional male soccer players. Sixteen professional male players (21.3 ± 2.1 years, stature 177.4 ± 4.2 cm, body mass 73.1 ± 8.1 kg) were randomised in training (TRA, n = 8) and control (CON, n = 8) groups. All players performed physiological assessments before and after a 6-week intervention. Outcome measures were: (i) V ̇ O2peak, (ii) V ̇ O2 kinetics during very heavy-intensity exercise, (iii) a maximal anaerobic running test, and (iv) Yo-Yo Intermittent Recovery Test level 2 (YIRT2). The only aerobic parameter to change after the intervention was the phase III time constant at exercise onset for CON, which lengthened (p = 0.012) to a value similar to that of the TRA group. However, TRA showed gains in anaerobic performance (p = 0.021), time to exhaustion (p = 0.019), and maximal running speed (p = 0.023). In the YIRT2, distance run increased for TRA over time (p = 0.015), and the TRA group were also capable of running further in the YIRT2 after the intervention compared with CON (p = 0.011). This study shows it is possible to improve the soccer-specific high-intensity running capacity of professional players when high-intensity intermittent training is added to the normal training load and that this effect is only detectable in anaerobic capabilities. The observed effects are meaningful to the training practices of elite athletes seeking a competitive edge in team sports when otherwise well matched.

#8 The effects of eccentric training on electromyographic activity and performance in soccer players
Reference: American Journal of Sports Science, 2014; 2(2): 23-29
Authors: Komsis S, Komsis G, Gissis I, Papadopoulos C, Patikas D, Mademli L, Papadopoulos P, Paschalis V, Vrabas IS
Summary: The purpose of the present study was to investigate the effects of eccentric training using a multi-joint dynamometer, on the electromyographic activity of rectus femoris, biceps femoris and medial gastrocnemius during counter movement jumps, drop jumps as well as during maximal eccentric actions. Sixteen amateur soccer players was divided into equal sized groups, the control group who participated in their regular training and the training group who performed 16 sessions (in 8 weeks) of eccentric exercise using a multi joint isokinetic dynamometer. The performance of counter movement and drop jumps were evaluated on a force plate. Additionally, maximal isometric, concentric and eccentric force were assessed on the isokinetic dynamometer. After the eccentric training, the electromyographic activity during the concentric phase of counter movement jumps was found to be increased in rectus femoris (p<0.05) and reduced in biceps femoris (p<0.05). During drop jumps, electromyographic activity of the experimental group found to be increased in the pre-activation phase of gastrocnemius (p<0.05). Additionally, during the takeoff phase of the drop jumps smaller angles for hip and ankle joints were observed (p<0.05). Finally, the electromyographic activity during eccentric strength evaluation were found to be elevated in rectus femoris (p<0.05) and decreased in gastrocnemius (p<0.05). The eccentric training which can cause neural adaptations, faster recruitment of motor units as well as changes in the architecture in muscle tendon system may also cause the alterations in electromyographic activity of leg muscles as observed in the present investigation.

#9 Psychophysiological Responses to Overloading and Tapering Phases in Elite Young Soccer Players
Reference: Pediatric Exercise Science, 2014, 26, 195-202
Authors: Freitas CG, Aoki MS, Franciscon CA, Arruda AFS, Carling C, Moreira A
Summary: This study investigated the effect of a 2-week overloading training phase followed by a 2-week tapering phase on internal training load (ITL), salivary cortisol, stress tolerance, and upper respiratory tract infections symptoms (URTI) in 11 male young soccer players (16.0 ± 0.5 yrs). Ratings of perceived exertion (session- RPE) were taken after each training session (N = 194) to determine ITL. Saliva sampling was conducted at the end of each week and cortisol concentration assessed by ELISA. DALDA and WURSS-21 questionnaires were administered every week to evaluate stress tolerance and severity of URTI respectively. The number of athletes reporting URTI symptoms was recorded. The overloading phase promoted greater ITL and a higher resting cortisol concentration than the tapering phase (P < .05). While no significant changes in stress toler- ance or URTI severity were observed, the number of athletes reporting URTI symptoms was higher during the overloading phase. A significant correlation was observed between symptoms of stress and severity of URTI (rs=-.71; P = .01). The results indicate that an integrated approach using psychological measures (session-RPE and DALDA), self-reports of URTI symptoms, and endocrine responses (cortisol) to training are pertinent for monitoring young soccer players.

#10 Evolution of match performance parameters for various playing positions in the English Premier League
Reference: Hum Mov Sci, 39C, 1-11. (2014).
Authors: Bush, M., Barnes, C., Archer, D. T., Hogg, B., & Bradley, P. S.
Summary: This study aimed to investigate position-specific evolution of physical and technical performance parameters in the English Premier League (EPL). Match performance observations (n=14700) were collected using a multiple-camera computerized tracking system across seven seasons (2006-07 to 2012-13). Data were analyzed relative to five playing positions: central defenders (n=3792), full backs (n=3420), central midfielders (n=3200), wide midfielders (n=2136) and attackers (n=2152). High-intensity running distance increased in the final season versus the first season in all playing positions (p<.05, ES: 0.9-1.3) with full backs displaying the greatest increase ( approximately 36% higher in 2012-13). Similar trends were observed for sprint distance with full backs demonstrating the most pronounced increase across the seven seasons (36-63%, p<.001, ES: 0.8-1.3). Central players (central defenders and midfielders) illustrated the most pronounced increases in total passes and pass success rate (p<.05, ES: 0.7-0.9) whilst wide players (full backs and wide midfielders) demonstrated only small-moderate increases in total passes and pass success rate (p<.05, ES: 0.6-0.8). The data demonstrates that evolving tactics in the EPL have impacted on the physical demands of wide players and the technical requirements of central players. These findings could be used for talent identification or position-specific physical and technical training.

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