Latest research in football - week 50 - 2014

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

#1 Acute and Overuse Injuries in Soccer - What about the Evidence Level?
Reference: Sportverletz Sportschaden. 2014 Nov 25. [Epub ahead of print]
 [Article in German]
Authors: Kelm J, Ludwig O, Ahlhelm F, Andre B, Hopp S
Summary: Over the last years, several studies on harmful events (h. e.) in soccer have been published. The aim was to develop a ranking of these studies according to their evidence, and to analyse the data with respect to the number of study participants, athletes' status, gender distribution, and genesis of harmful events in soccer. Between 1976 and 2011, the data bases MEDLINE, EBMR, and SPOTLIT were scanned by the keywords/combinations: soccer, acute injuries, overuse injuries, training, and match. In doing so, 644 initially potential relevant articles were found. On the basis of the QUORUM standard, 78 potentially relevant articles were filtered out, and an The results were rated according to importance and shown descriptively, because the heterogeneity of the study inhibited meta-analytical evaluation. 23 % of the publications could be assigned to EBL 2a - 2c, 27 % to EBL 3a and 3b, and 50 % to EBL 4 and 5. The studies comprised altogether 22 294 male and 2375 female athletes; 87 % of the male and 29 % of the female were professional athletes. 7 usable publications with a total of 8011 h. e. in men and 6 publications with 1055 h. e. in women dealt with contact/non-contact genesis of h. e.. 46 % male (72 % female) athletes suffered from h. e. caused by contact events, and 54 % male (28 % female) athletes suffered from h. e. caused by non-contact events. The distribution of acute and overuse injuries was analysed in 9969 h. e. in men (11 publications), and in 624 h. e. in women (5 publications). On average, the number of acute injuries (90 % male, 86 % female) was much higher than that of overuse injuries. The prevalence of h. e. with respect to training or match playing was analysed in 11 studies with 10 078 h. e. in men, and in 4 studies with 546 harmful events in women. 35 % of men's h. e. occurred during training and 65 % during matches, whereas 60 % of the women's h. e. occurred during training and 40 % during matches. The number of athletes included in the studies is quite low in relation to the number of active athletes. Studies of professional athletes are over-represented. Independent of gender, there are more acute injuries than overuse injuries, whereas the distribution of harmful events with respect to genesis and occurrence during training and match is gender-specific. The studies' evidence level is quite low in relation to the socio-economic significance of this kind of sport; the studies' evidence is higher for women.

#2 Sudden cardiac death in the soccer field: a retrospective study in young soccer players from 2000 to 2013
Reference: Phys Sportsmed. 2014 Nov;42(4):20-9. doi: 10.3810/psm.2014.11.2088.
Authors: Davogustto G, Higgins J.
Summary: Soccer is the most popular sport in the world, with over 200 million active players. Sudden cardiac death (SCD) represents the most striking as well as the most common cause of death in the soccer field. Underlying cardiovascular pathologies predispose to life threatening ventricular arrhythmias and SCD in soccer players. Up to thousands to hundred thousands players might have an underlying condition that predisposes them for SCD. After several media striking SCD events in soccer players the Fédération Internationale de Football Association (FIFA) has made screening recommendations that are more thorough than the ones recommended for the American Heart Association and the European Society of Cardiology. We present a retrospective search through Internet databases that resulted in 54 soccer players with SCD events from 2000 until 2013. In this article, we will describe and discuss the conditions of those cases of SCD in order to provide more knowledge of the factors that may precipitate SCD in young soccer players.

#3 Hamstrings strength imbalance in professional football (soccer) players in Australia
Reference: J Strength Cond Res. 2014 Nov 25. [Epub ahead of print]
Authors: Ardern CL, Pizzari T, Wollin M, Webster KE.
Summary: The aim of this study was to describe the isokinetic thigh muscle strength profile of professional male football players in Australia. Concentric (60° and 240°/second) and eccentric (30° and 120°/second) hamstrings and quadriceps isokinetic strength was measured with a HUMAC NORM dynamometer. The primary variables were bilateral concentric and eccentric hamstring and quadriceps peak torque ratios, concentric hamstring-quadriceps peak torque ratios, and mixed ratios (eccentric hamstring 30°/second ÷ concentric quadriceps 240°/second). Hamstring strength imbalance was defined as deficits in any two of: bilateral concentric hamstring peak torque ratio < 0.86, bilateral eccentric hamstring peak torque ratio < 0.86, concentric hamstring-quadriceps ratio < 0.47, mixed ratio < 0.80. Fifty-five strength tests involving 42 players were conducted. Ten players (24%) were identified as having hamstring strength imbalance. Athletes with strength imbalance had significantly reduced concentric and eccentric bilateral hamstring peak torque ratios at all angular velocities tested; and reduced eccentric quadriceps peak torque (30°/second) in their stance leg, compared to those without strength imbalance. Approximately one in four players had preseason hamstring strength imbalance; and all strength deficits were observed in the stance leg. Concentric and eccentric hamstrings strength imbalance may impact in-season football performance, and could have implications for the future risk of injury.

#4 Relationships Between RPE- and HR-derived Measures of Internal Training Load in Professional Soccer Players: A Comparison of On-field Integrated Training Sessions
Reference: Int J Sports Physiol Perform. 2014 Dec 4. [Epub ahead of print]
Authors: Campos-Vazquez MA, Mendez-Villanueva A, Gonzalez-Jurado JA, León-Prados JA, Santalla A, Suarez-Arrones L.
Summary: Describe the internal training load (ITL) of common training sessions performed during a typical week and to determine the relationships between different indicators of ITL commonly employed in professional football. Session-RPE TL (sRPE-TL) and HR-derived measurements of ITL as Edward's-TL and Stagno training impulses (TRIMPMOD) were used in nine players during three periods of the season. The relationships between them were analyzed in different training sessions during a typical week: Skill Drills/Circuit Training+Small-Sided Games (SCT+SSGs), Ball-Possession Games+Technical-Tactical Exercises (BPG+TTE), Tactical-Training (TT) and Pre-Match activation (PMa). HR values obtained during SCT+SSGs and BPG+TTE were substantially greater than the other two sessions, all the ITL markers and session duration were substantially greater in SCT+SSGs than in any other session, and all ITL measures in BPG+TTE were substantially greater than in TT and PMa sessions. Large relationships were found between HR>80% HRmax- and HR>90% HRmax - sRPR-TL during BPG+TTE and TT sessions (r = 0.61 to 0.68). Very large relationships were founded between Edward's TL - sRPE-TL and between TRIMPMOD - sRPE-TL in sessions with BPG+TTE and TT (r = 0.73 to 0.87). Correlations between the different HR-based methods were always extremely large (r = 0.92 to 0.98), and unclear correlations were observed for other relationships between variables. Session-RPE provided variable magnitude within-individual correlations with HR-derived measures of training intensity and load during different types of training sessions typically performed during a week in professional soccer. Caution should be applied when using RPE- or HR-derived measures of exercise intensity/load in soccer training interchangeably.

#5 Changes in acceleration and deceleration capacity throughout professional soccer match-play
Reference: J Strength Cond Res. 2014 Dec 2. [Epub ahead of print]
Authors: Russell M, Sparkes W, Northeast J, Cook CJ, Love TD, Bracken RM, Kilduff LP.
Summary: As the acceleration and deceleration demands of soccer are currently not well understood, this study aimed to profile markers of acceleration and deceleration capacity during professional soccer match-play. This within-player observational study required reserve team players from a Premier League club to wear 10 Hz Global Positioning System units throughout competitive matches played in the 2013/2014 competitive season. Data is presented for players who completed four or more games during the season (n = 11) and variables are presented according to six 15 min intervals (I1-6: 00:00-14:59 min, 15:00-29:59 min, 30:00-44:59 min, 45:00-59:59 min, 60:00-74:59 min, 75:00-89:59 min). During I6, the distance covered (total, per minute, and at high intensity), number of sprints, accelerations (total and high intensity), decelerations (total and high intensity), and impacts were reduced compared to I1 (all P ≤ 0.05). The number of high intensity impacts remained unchanged throughout match-play (P > 0.05). These findings indicate that high intensity actions and markers of acceleration and deceleration capacity are reduced in the last 15 min of the normal duration of match-play. Such information can be used to increase the specificity of training programmes designed for soccer players while also giving further insight in to the effects of 90 min of soccer-specific exercise. Interventions that seek to maintain the acceleration and deceleration capacity of players throughout the full duration of a soccer match warrant investigation.

#6 Effect of unilateral, bilateral and combined plyometric training on explosive and endurance performance of young soccer players
Reference: J Strength Cond Res. 2014 Dec 2. [Epub ahead of print]
Authors: Ramírez-Campillo R, Burgos C, Henríquez-Olguín C, Andrade DC, Martínez C, Alvarez C, Castro-Sepúlveda M, Marques MC, Izquierdo M.
Summary: The aim of the study was to compare the effects of bilateral, unilateral, or combined bilateral and unilateral plyometric training (PT) on muscle power output, endurance and balance performance adaptations in young soccer players. Four groups of young soccer players (age 11.4 ± 2.2 y) were divided into: control (CG; n = 14), bilateral group (BG; n = 12), unilateral group (UG; n = 16), and bilateral + unilateral group (B+UG; n = 12). Players were measured in unilateral and bilateral countermovement jump with arms (CMJA), 5 multiple bounds test (MB5), 20 cm drop jump reactive strength index (RSI20), maximal kicking velocity (MKV), sprint and agility test time, endurance and balance performance. The PT was applied during 6 weeks, 2 sessions per week, for a total of 2160 jumps. After intervention, all PT groups showed a statistically significant (p<0.05) change in all performance measures, with no statistically significant differences between treatments. Among the 21 performance measures, the B+UG showed a significantly (p<0.05) higher performance change in 13 of them vs. the CG, while the UG and BG showed only 6 and 3, respectively. The current study showed that bilateral, unilateral and combined bilateral and unilateral PT ensured significant improvement in several muscular power and endurance performance measures in young soccer players. However, the combination of unilateral and bilateral drills seems more advantageous to induce superior performance improvements.

#7 Influence of the number of players and the relative pitch area per player on heart rate and physical demands in youth soccer

Reference: J Strength Cond Res. 2014 Dec 2. [Epub ahead of print]
Authors: Julen C, Asier P, Ibon E, David C.
Summary: The aim of the present study was to analyze the influence of different large-sided games on the physical and physiological variables in under-13s soccer players. The effects on heart rate (HR) and physical demands of different number of players (7, 9, and 11) together with the relative pitch area (100, 200, and 300 m) during two 12 min repetitions were analyzed in this study. The variables analyzed were: mean, maximum and different intensity zones of HR; total distance (TD); work:rest ratio (W:R); player-load (PL); five absolute and three relative speed categories. The results support the theory that a change in pitch dimensions affects locomotor activity more than the number of players does, but also refutes the hypothesis that the change in the number of players has a greater effect on HR. To be more specific, an increase in the relative pitch area per player (300/200/100 m) was associated with higher values of the following variables: TD (2250-2314/2003-2148/1766-1845 m), W:R (0.5-0.6/0.4-0.5/0.3 AU), PL (271-306/246-285/229-267 UA), %HRmean (85-88/85-89/81-83 %), %HRmax (95-100/97-100/95-98 %), and affected the percentage of time spent in both absolute (above 8 km·h) and relative speed (above 40% of Vmax) categories (p<0.05, effect size: 0.31-0.85). These results may help youth soccer coaches to plan the progressive introduction of large-sided games so that task demands are adapted to the physiological and physical development of participants.

#8 A retrospective study on anthropometrical, physical fitness and motor coordination characteristics that influence drop out, contract status and first-team playing time in high-level soccer players, aged 8 to 18 years
Reference: J Strength Cond Res. 2014 Dec 2. [Epub ahead of print]
Authors: Deprez D, Fransen J, Lenoir M, Philippaerts RM, Vaeyens R.
Summary: The goal of this manuscript was twofold and a two-study approach was conducted. The first study aimed to expose the anthropometrical, physical performance and motor coordination characteristics that influence drop out from a high-level soccer training program in players aged 8-16 years. The mixed-longitudinal sample included 388 Belgian youth soccer players who were assigned to either a 'club group' or a 'drop out group'. In the second study, cross-sectional data of anthropometry, physical performance and motor coordination were retrospectively explored to investigate which characteristics influence future contract status (contract vs. no contract group) and first-team playing time for 72 high-level youth soccer players (mean age=16.2 y).Generally, club players outperformed their drop out peers for motor coordination, soccer-specific aerobic endurance and speed. Anthropometry and estimated maturity status did not discriminate between club and drop out players. Contract players jumped further (p=0.011) and had faster times for a 5m sprint (p=0.041) than no contract players. The following prediction equation explains 16.7% of the variance in future playing minutes in adolescent youth male soccer players: -2869.3 + 14.6 * standing broad jump.Practitioners should include the evaluation of motor coordination, aerobic endurance and speed performances to distinguish high-level soccer players further succeeding a talent development program and future drop out players, between 8 and 16 years. From the age of 16 years, measures of explosivity are supportive when selecting players into a future professional soccer career.

#9 Relationships between repeated sprint ability, mechanical parameters and blood metabolites in professional soccer players
Reference: J Strength Cond Res. 2014 Dec 1. [Epub ahead of print]
Authors: Morcillo JA, Cuadrado V, Jiménez-Reyes P, Ortega-Becerra M, Lozano E, Párraga J.
Summary: This study analysed the acute metabolic and mechanical responses to a specific Repeated Sprint Ability (RSA) test. Eighteen male professional soccer players from a team of the First Division of Spanish National League participated. A 12x30m RSA test with 30 s recovery together with countermovement jump test (CMJ) pre a post RSA test was performed. Mechanical responses (i.e. height performance in CMJ and speed loss) and metabolic responses (i.e. blood lactate, and ammonia concentrations) were measured pre-exercise and post-exercise. A related samples t-test was used to analyse CMJ height pre-post changes as well as to compare pre- and post-exercise lactate and ammonia levels. CMJ height loss pre-post session (8%) was significant, and fatigue, measured as CMJ height loss, was strongly correlated to lactate (r = 0.97; p<0.001) and ammonia (r = 0.92; p<0.001) for all players. The relationships between the variables studied were determined by calculating the Pearson correlation coefficients. The metabolic stress developed during the effort can be estimated by controlling CMJ because of the high correlation between CMJ and blood lactate and ammonia concentrations. The high correlations found between mechanical (speed and CMJ height losses) and metabolic (lactate and ammonia) measures of fatigue highlight the utility and validity of using CMJ to monitor training load and quantify objectively neuromuscular fatigue during RSA.

#10 Posterior Tibial Labrum Injury in a Professional Soccer Player: A Case Report
Reference: J Foot Ankle Surg. 2014 Nov 21. pii: S1067-2516(14)00497-9. doi: 10.1053/j.jfas.2014.09.047. [Epub ahead of print]
Authors: Batista JP, Del Vecchio JJ, Maestu R
Summary: Ankle ligament injuries are one of the most frequent lesions identified in professional soccer players. In most cases, the ligaments involved are the anterior talofibular ligament and the calcaneal fibular ligament. In the present report, we describe a professional soccer player who sustained an ankle sprain that did not respond to initial therapy. The findings from radiographic and magnetic resonance images were inconclusive. Ultimately, rupture of the posterior, transverse ligament with avulsion of the tibial labrum was identified as the cause of his ongoing ankle pain. Confirmation of the pathologic findings and successful treatment were performed arthroscopically.

#11 Does SAQ training improve the speed and flexibility of young soccer players? A randomized controlled trial
Reference: Hum Mov Sci. 2014 Dec;38:197-208. doi: 10.1016/j.humov.2014.09.005. Epub 2014 Nov 9.
Authors: Milanović Z, Sporiš G, Trajković N, Sekulić D, James N, Vučković G
Summary: The aim of this study was to determine the effects of a 12week speed, agility and quickness (SAQ) training program on speed and flexibility in young soccer players. One hundred and thirty-two soccer players were randomly assigned to experimental (EG; n=66, mean±SD: age: 18.5±0.4years (range 17-19years); body mass: 71.30±5.93kg; stature: 177.2±6.5cm) and control groups (CG; n=66, mean±SD: age: 18.6±0.6years (range 17-19years); body mass: 70.63±4.87kg; stature: 175.9±5.7cm). The experimental group performed SAQ training whilst the control group undertook straight-line sprint training matched for volume and duration. Sprint performance was assessed using 5 and 10m sprints and a further test including maximal speed, a 20m sprint. Flexibility was assessed using sit and reach, V-sit and reach, leg lift from supine position and lateral leg lift while lying on the side tests. Sprints over 5, 10 and 20m did not differ between groups at baseline, but by week 12, the 5m sprint had significantly improved (P<.05) in the SAQ training group compared to the control group (1.40±0.13 vs. 1.46±0.12s, respectively) although this improvement had a trivial effect size (ES=0.15). The 10m sprint time had improved by 3.3% (P<.01) in the SAQ group with a moderate effect size (ES=0.66). No significant differences (P>.05) for all flexibility tests were found between experimental and control group at baseline and after the training programs. Consequently SAQ training was found to be an effective way of improving sprint time for short distances over 5 and 10m but not over 20m (where maximum speed was achieved) or flexibility. These results indicate that SAQ training may be more effective for improving sprint performance for some soccer players but more research is required to determine ideal training methods for improving acceleration and flexibility in young soccer players.

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