Latest research in football - week 18 - 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 Effect of increasing maximal aerobic exercise on serum gonadal hormones and alpha-fetoprotein in the luteal phase of professional female soccer players
Reference: J Phys Ther Sci. 2016 Mar;28(3):807-10. doi: 10.1589/jpts.28.807. Epub 2016 Mar 31.
Authors: Otağ A, Hazar M, Otağ İ, Beyleroğlu M
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Summary: The performance of female athletes during their menstrual period has attracted the attention of researchers for many years. It is known that the menstrual period changes with exercise. Alpha-fetoprotein (AFP) is an oncofetal protein. In this study, the effect of maximal aerobic exercise in the luteal phase on some hormones and AFP in female athletes was researched. [Subjects and Methods] Twelve volunteers and healthy female footballers with normal menstrual cycles volunteered for this study as subjects. All the participants performed a shuttle run test. Blood samples were taken before, after, and one hour after exercise. Serum AFP, estrogen, progesterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) values were measured using an auto analyzer and original kits. Heart rate measurements were performed before and after the exercise. [Results] AFP activity had significantly decreased after 1 h of recovery from the exercise in the female soccer players, and estrogen and LH activity had significantly increased immediately after the exercise. Progesterone activity had significantly decreased immediately after the exercise. FSH values had significantly increased immediately after the exercise. [Conclusion] The results of the present study show there were significant decreases in the values of AFP, which is a cancer parameter, 1 hour after the exercise. This result may be valuable in future physiotherapy studies on the relationship between exercise and cancer.

#2 Surgical treatment of the adductor longus muscle's distal tendon total rupture in a soccer player
Reference: Orthop Traumatol Surg Res. 2016 Apr 25. pii: S1877-0568(16)30014-7. doi: 10.1016/j.otsr.2016.03.011. [Epub ahead of print]
Authors: Masionis P, Popov K, Kurtinaitis J, Uvarovas V, Porvaneckas N
Summary: Only a few cases of adductor longus tendon ruptures have been reported in the literature and - there are no clear criteria for conservative or surgical treatment. A case of traumatic rupture of the right distal adductor longus tendon is presented in an elite soccer player, which was surgically repaired. The condition was managed conservatively primarily. However, after 2 months, a palpable mass remained on the medial side of the thigh, and the patient had pain after moderate everyday load and insufficient strength of the right leg during physical exercise. It was decided to explore ruptured tendon surgically and reattach to the femur. Full function of the right leg was achieved at 3 months after surgical repair. At 6 months postoperatively, the patient had returned to soccer at the same level.

#3 Prognostic relevance of motor talent predictors in early adolescence: A group- and individual-based evaluation considering different levels of achievement in youth football
Reference: J Sports Sci. 2016 May 5:1-10. [Epub ahead of print]
Authors: Höner O, Votteler A
Summary: In the debate about the usefulness of motor diagnostics in the talent identification process, the prognostic validity for tests conducted in early adolescence is of critical interest. Using a group- and individual-based statistical approach, this prospective cohort study evaluated a nationwide assessment of speed abilities and technical skills regarding its relevance for future achievement levels. The sample consisted of 22,843 U12-players belonging to the top 4% in German football. The U12-results in five tests served as predictors for players' selection levels in U16-U19 (youth national team, regional association, youth academy, not selected). Group-mean differences proved the prognostic relevance for all predictors. Low individual selection probabilities demonstrated limited predictive values, while excellent test results proved their particular prognostic relevance. Players scoring percentile ranks (PRs) ≥ 99 had a 12 times higher chance to become youth national team players than players scoring PR < 99. Simulating increasing score cut-off values not only enhanced specificity (correctly identified non-talents) but also led to lower sensitivity (loss of talents). Extending the current research, these different approaches revealed the ambiguity of the diagnostics' prognostic relevance, representing both the usefulness and several pitfalls of nationwide diagnostics. Therefore, the present diagnostics can support but not substitute for coaches' subjective decisions for talent identification, and multidisciplinary designs are required.

#4 The ARCANE Project: How an Ecological Dynamics Framework Can Enhance Performance Assessment and Prediction in Football
Reference: Sports Med. 2016 May 3. [Epub ahead of print]
Authors: Couceiro MS, Dias G, Araújo D, Davids K
Summary: This paper discusses how an ecological dynamics framework can be implemented to interpret data, design practice tasks and interpret athletic performance in collective sports, exemplified here by research ideas within the Augmented peRCeption ANalysis framEwork for Football (ARCANE) project promoting an augmented perception of football teams for scientists and practitioners. An ecological dynamics rationale can provide an interpretation of athletes' positional and physiological data during performance, using new methods to assess athletes' behaviours in real-time and, to some extent, predict health and performance outcomes. The proposed approach signals practical applications for coaches, sports analysts, exercise physiologists and practitioners through merging a large volume of data into a smaller set of variables, resulting in a deeper analysis than typical measures of performance outcomes of competitive games.

#5 Age-related effects of practice experience on collective behaviours of football players in small-sided games
Reference: Hum Mov Sci. 2016 Apr 28;48:74-81. doi: 10.1016/j.humov.2016.04.007. [Epub ahead of print]
Authors: Barnabé L, Volossovitch A, Duarte R, Ferreira AP, Davids K
Summary: The purpose of this study was to examine whether offensive and defensive collective behaviours emerging in six-a-side football games (GK+5 vs. 5+GK) varied according to age-related practice experience of young, male players (U16, U17 and U19yrs). Players' were not instructed to implement specific tactical plans and their movement trajectories (2D analyses) were recorded using 10 GPS units. Four common measures of team dispersion investigated in previous research (surface area, stretch index, length and width of a team) were used to analyse team performance behaviours. After recording these collective variables, we used sample entropy (SampEn) and cross-sample entropy (Cross-SampEn) measures to assess the regularity and synchronization of participant actions in teams. Results demonstrated clear age-related variations in effects on the collective performance measures analysed. In attacking phases, older and more experienced players occupied a greater surface area and displayed higher values of team width and stretch index. In defensive phases, significant differences were observed in team length and stretch index. Cross-SampEn analysis demonstrated a greater synchronization between offensive and defensive surface areas and team width in older age groups (U17 and U19yrs). Data suggest how coaches can manipulate practice task constraints to enhance development of team tactical performance behaviours in developing footballers between 16 and 19yrs of age.

#6 Inflammatory Biomarkers' Response to Two Different Intensities of a Single Bout Exercise Among Soccer Players
Reference: Iran Red Crescent Med J. 2016 Jan 1;18(2):e21498. doi: 10.5812/ircmj.21498. eCollection 2016.
Authors: Ghafourian M, Ashtary-Larky D, Chinipardaz R, Eskandary N, Mehavaran M
Summary: There is a strong relationship between physical inactivity and low-grade inflammation and its adverse health outcomes, particularly cardiovascular disease. The level of anti-inflammatory and pro-inflammatory cytokines may be changed by exercise. The aim of the present study was to determine the response of certain inflammatory biomarkers to exercise with differences in maximal oxygen consumption (VO2max). These biomarkers were IL-1β, TNF-α, hs-CRP, IL-6, sICAM-1, IL-10, and ratios of TNF-α/IL-10 and IL-6/IL-in circulating peripheral blood (PB). In a semi-experimental study, twenty male students who performed regular football exercise at least three days a week, for two years, were selected by easy sampling at Shahid Chamran university of Iran. Subjects were then randomly assigned to two groups: the protocol of the first group was 30 minutes of running at a speed of 65% of VO2max, and the second group performed six periodic repetitions with three minutes at a speed of 85% of VO2max with a 90-second rest between the repetitions. Blood samples were taken at baseline, immediately after the exercise and at rest. Cytokine levels were quantified by the Sandwich enzyme-linked immunosorbent assay (ELISA) method. The first protocol resulted in a decrease of serum IL-1β to 3.77 ± 0.28 pg/mL at rest, from 4.33 ± 0.28 at baseline and 4.32 ± 0.34 immediately after exercise (P = 0.008 and P = 0.013, respectively). There was also a decrease in the level of sICAM-1 to 260.11±15.64 ng/mL at rest, from 329.58 ± 20.82 at baseline and 302.7 ± 20.49 post exercise (P = 0.013 and P = 0.038, respectively). On the other hand, IL-6 and ratio of IL-6/IL-10 increased to 6.55±0.84 pg/mL and 2.12 ± 0.37 immediately after exercise from baseline (2.73 ± 0.58 and 1.16 ± 0.33) and rest (2.49 ± 0.45 and 0.95 ± 0.19) in the second protocol (P = 0.001 and P = 0.001, respectively for IL-6, and P = 0.047 and P = 0.024, respectively for IL-6/IL-10). The data of the present study demonstrated that a single bout of exercise with higher-intensity induces a transient increase in some proinflammatory markers, and lower-intensity can reduce these biomarkers.

#7 Traditional vs. sport-specific vertical jump tests: reliability, validity and relationship with the legs strength and sprint performance in adult and teen soccer and basketball players
Reference: J Strength Cond Res. 2016 May 9. [Epub ahead of print]
Authors: Rodriguez-Rosell D, Mora-Custodio R, Franco-Márquez F, Yáñez-García JM, González-Badillo JJ.
Summary: The vertical jump is considered an essential motor skill in many team sports. Many protocols have been used to assess vertical jump ability. However, controversy regarding test selection still exists based upon the reliability and specificity of the tests. The main aim of this study was to analyze the reliability and validity of two standardized [Countermovement jump (CMJ) and Abalakov jump (AJ)] and two sport-specific [run-up with two (2-LEGS) or one leg (1-LEG) take-off jump] vertical jump tests, and their usefulness as predictors of sprint and strength performance for soccer (n = 127) and basketball (n = 59) players in three different categories (Under-15, Under-18 and Adults). Three attempts for each of the four jump tests were recorded. Twenty-meter sprint time and estimated one-repetition maximum in full squat were also evaluated. All jump tests showed high intraclass correlation coefficients (0.969-0.995) and low coefficients of variation (1.54-4.82%), although 1-LEG was the jump test with the lowest absolute and relative reliability. All selected jump tests were significantly correlated (r = 0.580-0.983). Factor analysis resulted in the extraction of one principal component, which explained 82.90%-95.79% of the variance of all jump tests. The 1-LEG test showed the lowest associations with sprint and strength performance. The results of this study suggest that CMJ and AJ are the most reliable tests for the estimation of explosive force in soccer and basketball players in different age categories.

#8 Peak torque and muscle balance in the knees of young U-15 and U-17 soccer athletes playing various tactical positions
Reference: J Sports Med Phys Fitness. 2016 May 11. [Epub ahead of print]
Authors: Bona CC, Tourinho Filho H, Izquierdo M, Pires Ferraz RM, Marques M.
Summary: Soccer is a sport that is practiced worldwide and has been investigated in its various aspects, particularly muscle strength, which is an essential motor skill for sports performance. The objective of this study was to investigate the peak torque and muscle balance on the knee extensor and flexor of young (U-15 and U-17) soccer players in the tactical positions of goalkeeper, defender, full back, midfielder, defensive midfielder and striker, as well as to determine which field position has the highest peak torque. Forty-nine male players were recruited and divided into two categories during the preparatory period of the season (mean ± SD: in the U-15 category (n=23), age 14.7±0.5 yr, body mass 58.2 ± 10.5 kg and body height 168.5 ± 7.6 cm; and U-17 (n=26), age 16.8±0.4 yr, body mass 69.2±7.9 kg and body height 176.2±6.6 cm). The Under-17 athletes presented a higher peak torque in all the movements of flexion and extension in the two angular velocities (i.e. 60 and 300 ° / s), but only the dominant knee extensor at 300 ° / s was significant different between the two categories as well as the percentage change in peak torque compared between U-15 and U-17 was always above 20%. The peak torque variation in the U-17 category (i.e. mostly above 20%) highlights a higher peak torque compared to U-15 athletes. The muscular deficit of the two categories presented a low average of 10-15%, indicating a good muscle balance between knee extensors and flexors. Finally, goalkeepers and defenders achieved the highest peak torque amongst the field positions.

#9 The Influence of Referee Bias on Extra Time in Elite Soccer Matches
Reference: Percept Mot Skills. 2016 Apr;122(2):666-77. doi: 10.1177/0031512516633342. Epub 2016 Feb 25.
Authors: Lago-Peñas C, Gómez-López M
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Summary: Referees have discretion over the addition of extra time at the end of the soccer game to compensate for lost time due to unusual stoppages. This study assesses if referees favor big teams by shortening close games where the big team is ahead and lengthening close games where the big team is behind. The sample comprises all 380 matches in the Spanish La Liga during the 2014-2015 season. The dependent variable was the extra time the referee decides to add to the second half. The independent variables were the score difference, opponent team's level of play, yellow cards, red cards, player substitutions, average attendance, and fouls committed. Linear regression analysis suggested that the greater the score difference between teams, the less extra time was added by the referee. However, in close games, referees tended to add more time for a higher level team when they were behind and add less time when they were ahead. Red cards and the number of fouls committed increased the extra time.

#9 The Importance of Vitaminsfor Soccer Players
Reference: Int J Vitam Nutr Res. 2016 May 10:1-21. [Epub ahead of print]
Authors: Eskici G
Summary: Soccer is one of the most widely played and complex sports in the world, where success depends on technical, tactical and physical skills of the players. Studies to improve performance in soccer have often focused on technique and tactics. However, nutrition is one of the most important factors influencing athletic performance of the players. The duration of matches is long and the training is intense. This leads to increased requirements for energy and nutrients, as well as increased reactive oxygen radicals and hence increased muscle damage. Vitamins are micronutrients that a living organism requires in trace quantities for health. As these assume crucial functions in the body, the performance of the player is negatively affected particularly during long-term deficiency. Beta-carotene, C and E vitamins are antioxidants that protect against oxygen radicals. In case of their deficiency, oxidative stress and muscle fatigue increases. Vitamin D is involved in maintaining mineral balance, and it increases absorption of dietary calcium and phosphorus. In case of vitamin D deficiency, injuries resulting from the musculoskeletal system might increase. B Vitamins (B1, B2, niacin, B6, B12, biotin, folic acid and pantothenic acid) perform duties such as energy production, absorption and transport of iron and blood cell production. Athletes who follow an energy-restricted and imbalanced diet might develop vitamin deficiency. In such a case, supplements can be used as recommended by the doctor/dietician. It is further reported that supplement use by athletes who have an adequate and balanced nutrition does not increase performance.

#10 Injury profile among elite male youth soccer players in a Swedish first league
Reference: J Exerc Rehabil. 2016 Apr 26;12(2):83-9. doi: 10.12965/jer.1632548.274. eCollection 2016.
Authors: Nilsson T, Östenberg AH, Alricsson M
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Summary: This study investigated the injury profile among elite male youth soccer players in a Swedish first league during two seasons. The present cohort study is based on data collected during the 2013-2014 seasons. In total, 43 young elite male soccer players, aged 15 to 19 yr, were prospectively followed regarding injuries, time of exposure, injury location, type of injury, and injury severity. The overall incidence of injury in the present study was estimated to 6.8 injuries per 1,000 exposure hours and 15.5 and 5.6 injuries per 1,000 hr for matches and training, respectively. The single most common injury subtype was muscle strain (53%). The hip and groin were the most common locations for injuries. Thirty-one percent of the injuries were classified as severe injury and caused >28 days absence from training and match play. Both the injury incidence and the number of serious injury seems to be relatively high in youth elite players according to this study. Although the injury incidence seems to be slightly lower than in adult elite players the injuries seem to be more traumatic in youth elite players.

#11 Compression and texture in socks enhance football kicking performance
Reference: Hum Mov Sci. 2016 May 5;48:102-111. doi: 10.1016/j.humov.2016.04.008. [Epub ahead of print]
Authors: Hasan H, Davids K, Chow JY, Kerr G
Summary: The purpose of this study was to observe effects of wearing textured insoles and clinical compression socks on organisation of lower limb interceptive actions in developing athletes of different skill levels in association football. Six advanced learners and six completely novice football players (15.4±0.9years) performed 20 instep kicks with maximum velocity, in four randomly organised insoles and socks conditions, (a) Smooth Socks with Smooth Insoles (SSSI); (b) Smooth Socks with Textured Insoles (SSTI); (c) Compression Socks with Smooth Insoles (CSSI) and (d), Compression Socks with Textured Insoles (CSTI). Reflective markers were placed on key anatomical locations and the ball to facilitate three-dimensional (3D) movement recording and analysis. Data on 3D kinematic variables and initial ball velocity were analysed using one-way mixed model ANOVAs. Results revealed that wearing textured and compression materials enhanced performance in key variables, such as the maximum velocity of the instep kick and increased initial ball velocity, among advanced learners compared to the use of non-textured and compression materials. Adding texture to football boot insoles appeared to interact with compression materials to improve kicking performance, captured by these important measures. This improvement in kicking performance is likely to have occurred through enhanced somatosensory system feedback utilised for foot placement and movement organisation of the lower limbs. Data suggested that advanced learners were better at harnessing the augmented feedback information from compression and texture to regulate emerging movement patterns compared to novices.

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