Latest research in football - week 2 - 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 Biochemical, physical and tactical analysis of a simulated game in young soccer players
Reference: J Sports Med Phys Fitness. 2016 Jan 14. [Epub ahead of print]
Authors: Aquino RL, Goncalves L, Vieira LH, Oliveira LP, Alves GF, Santiago PR, Puggina EF
Summary: The objectives of this study were to describe and compare the displacement patterns and the tactical performance of the players in the first to the second game time and verify possible associations between indirect markers of muscle damage with displacement patterns in a 30 simulated game played by young soccer players. 18 young soccer players were submitted to a simulated game and two blood collections, one before and another 30 min post-game to analyze the behavior of creatine kinase and lactate dehydrogenase enzymes. The patterns of displacement and tactics variables were obtained through functions developed in Matlab environment (MathWorks, Inc., USA). It is observed a significant increase in average 35 speed (p = 0.05), number of sprints (p < 0.001), the percentage the total distance covered at high intensity (p <0.001) and tactical variables (team surface area - p = 0.002; spreading - p = 0.001) in the second period of the simulated game. In addition, there was significant reduction in the percentage of the total distance at low intensity (p ≤ 0.05) in the second period, and there was a strong association between the percentage of change delta of creatine kinase and lactate 40 dehydrogenase with the displacement patterns in the simulated game. The results show that indirect markers of muscle damage have great association with displacement patterns in game performed in training conditions for young soccer players, evidencing a need for reflection on the post-training recovery sessions strategies, contributing to better planning of sessions throughout the macrocycle.

#2 Timescales for exploratory tactical behaviour in football small-sided games
Reference: J Sports Sci. 2016 Jan 13:1-8. [Epub ahead of print]
Authors: Ric A, Hristovski R, Gonçalves B, Torres L, Sampaio J, Torrents C
Summary: The aim of this study was to identify the dynamics of tactical behaviour emerging on different timescales in football small-sided games and to quantify short- and long-term exploratory behaviour according to the number of opponents. Two teams of four professional male footballers played small-sided games against two different teams with a variable number of opponents (3, 5 and 7). Data were collected using a combination of systematic observation and a non-differential global positioning system (15 Hz). The temporal diversity and structural flexibility of the players were determined by calculating the dynamic overlap order parameter q, entropy and trapping strength. Analysis of the exploratory dynamics revealed two different timescales, forming a different metastable landscape of action for each constraint. Fast dynamics lasted on average a few seconds and consisted of changes in tactical patterns. The long timescale corresponded to the shared tasks of offence and defence lasting tens of seconds. The players' tactical diversity decreased with an increasing number of opponents, especially in defence. Manipulating numerical imbalance is likely to promote changes in the diversity, unpredictability and flexibility of tactical solutions. The fact that the temporally nested structure of constraints shaped the emergence of tactical behaviour provides a new rationale for practice task design. The manipulation of numerical imbalance on the timescale of a few tens of seconds, on which the exploratory behaviour of players saturates, may help coaches to optimise the exploratory efficiency of the small-sided games.

#3 Number of Players and Relative Pitch Area per Player: Comparing Their Influence on Heart Rate and Physical Demands in Under-12 and Under-13 Football Players
Reference: PLoS One. 2016 Jan 11;11(1):e0127505. doi: 10.1371/journal.pone.0127505. eCollection 2016.
Authors: Castellano J, Puente A, Echeazarra I, Usabiaga O, Casamichana D
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Summary: The aim of the present study is to analyse the influence of different large-sided games (LSGs) on the physical and physiological variables in under-12s (U12) and -13s (U13) soccer players. The effects of the combination of different number of players per team, 7, 9, and 11 (P7, P9, and P11, respectively) with three relative pitch areas, 100, 200, and 300 m2 (A100, A200, and A300, respectively), were analysed in this study. The variables analysed were: 1) global indicator such as total distance (TD); work:rest ratio (W:R); player-load (PL) and maximal speed (Vmax); 2) heart rate (HR) mean and time spent in different intensity zones of HR (<75%, 75-84%, 84-90% and >90%), and; 3) five absolute (<8, 8-13, 13-16 and >16 Km h-1) and three relative speed categories (<40%, 40-60% and >60% Vmax). The results support the theory that a change in format (player number and pitch dimensions) affects no similarly in the two players categories. Although it can seem that U13 players are more demanded in this kind of LSG, when the work load is assessed from a relative point of view, great pitch dimensions and/or high number of player per team are involved in the training task to the U12 players. The results of this study could alert to the coaches to avoid some types of LSGs for the U12 players such as: P11 played in A100, A200 or A300, P9 played in A200 or A300 and P7 played in A300 due to that U13>U12 in several physical and physiological variables (W:R, time spent in 84-90%HRmax, distance in 8-13 and 13-16 Km h-1 and time spent in 40-60%Vmax). These results may help youth soccer coaches to plan the progressive introduction of LSGs so that task demands are adapted to the physiological and physical development of participants.

#4 Impaired sleep and recovery after night matches in elite football players
Reference: J Sports Sci. 2016 Jan 11:1-7. [Epub ahead of print]
Authors: Fullagar HH, Skorski S, Duffield R, Julian R, Bartlett J, Meyer T
Summary: Despite the perceived importance of sleep for elite footballers, descriptions of the duration and quality of sleep, especially following match play, are limited. Moreover, recovery responses following sleep loss remain unclear. Accordingly, the present study examined the subjective sleep and recovery responses of elite footballers across training days (TD) and both day and night matches (DM and NM). Sixteen top division European players from three clubs completed a subjective online questionnaire twice a day for 21 days during the season. Subjective recall of sleep variables (duration, onset latency, time of wake/sleep, wake episode duration), a range of perceptual variables related to recovery, mood, performance and internal training loads and non-exercise stressors were collected. Players reported significantly reduced sleep durations for NM compared to DM (-157 min) and TD (-181 min). In addition, sleep restfulness (SR; arbitrary scale 1 = very restful, 5 = not at all restful) and perceived recovery (PR; acute recovery and stress scale 0 = not recovered at all, 6 = fully recovered) were significantly poorer following NM than both TD (SR: +2.0, PR: -2.6), and DM (SR: +1.5; PR: -1.5). These results suggest that reduced sleep quantity and quality and reduced PR are mainly evident following NM in elite players.

#5 The precision and torque production of common hip adductor squeeze tests used in elite football
Reference: J Sci Med Sport. 2015 Dec 12. pii: S1440-2440(15)00242-X. doi: 10.1016/j.jsams.2015.12.009. [Epub ahead of print]
Authors: Light N, Thorborg K
Summary: Decreased hip adductor strength is a known risk factor for groin injury in footballers, with clinicians testing adductor strength in various positions and using different protocols. Understanding how reliable and how much torque different adductor squeeze tests produce will facilitate choosing the most appropriate method for future testing. In this study, the reliability and torque production of three common adductor squeeze tests were investigated. Twenty elite level footballers (16-33 years) without previous or current groin pain were recruited. Relative and absolute test-retest reliability, and torque production of three adductor squeeze tests (long-lever in abduction, short-lever in adduction and short-lever in abduction/external rotation) were investigated. Each participant performed a series of isometric strength tests measured by hand-held dynamometry in each position, on two test days separated by two weeks. No systematic variation was seen for any of the tests when using the mean of three measures (ICC=0.84-0.97, MDC%=6.6-19.5). The smallest variation was observed when taking the mean of three repetitions in the long-lever position (ICC=0.97, MDC%=6.6). The long-lever test also yielded the highest mean torque values, which were 69% and 11% higher than the short-lever in adduction test and short-lever in abduction/external rotation test respectively (p<0.001). All three tests described in this study are reliable methods of measuring adductor squeeze strength. However, the test performed in the long-lever position seems the most promising as it displays high test-retest precision and the highest adductor torque production.

#6 Hamstring injuries have increased by 4% annually in men's professional football, since 2001: a 13-year longitudinal analysis of the UEFA Elite Club injury study
Reference: Br J Sports Med. 2016 Jan 8. pii: bjsports-2015-095359. doi: 10.1136/bjsports-2015-095359. [Epub ahead of print]
Authors: Ekstrand J, Waldén M, Hägglund M
Summary: There are limited data on hamstring injury rates over time in football. The purpose of the study was to analyse time trends in hamstring injury rates in male professional footballers over 13 consecutive seasons and to distinguish the relative contribution of training and match injuries. 36 clubs from 12 European countries were followed between 2001 and 2014. Team medical staff recorded individual player exposure and time-loss injuries. Injuries per 1000 h were compared as a rate ratio (RR) with 95% CI. Injury burden was the number of lay off days per 1000 h. Seasonal trend for injury was analysed using linear regression. A total of 1614 hamstring injuries were recorded; 22% of players sustained at least one hamstring injury during a season. The overall hamstring injury rate over the 13-year period was 1.20 injuries per 1000 h; the match injury rate (4.77) being 9 times higher than the training injury rate (0.51; RR 9.4; 95% CI 8.5 to 10.4). The time-trend analysis showed an annual average 2.3% year on year increase in the total hamstring injury rate over the 13-year period (R2=0.431, b=0.023, 95% CI 0.006 to 0.041, p=0.015). This increase over time was most pronounced for training injuries-these increased by 4.0% per year (R2=0.450, b=0.040, 95% CI 0.011 to 0.070, p=0.012). The average hamstring injury burden was 19.7 days per 1000 h (annual average increase 4.1%) (R2=0.437, b=0.041, 95% CI 0.010 to 0.072, p=0.014). Training-related hamstring injury rates have increased substantially since 2001 but match-related injury rates have remained stable. The challenge is for clubs to reduce training-related hamstring injury rates without impairing match performance.

#7 Effect of Combined Sensorimotor-Resistance Training on Strength, Balance, and Jumping Performance of Soccer Players
Reference: J Strength Cond Res. 2016 Jan;30(1):53-9. doi: 10.1519/JSC.0000000000001012.
Authors: Manolopoulos K, Gissis I, Galazoulas C, Manolopoulos E, Patikas D, Gollhofer A, Kotzamanidis C.
Summary: The purpose of the study was to investigate the effects of resistance training (RT) and sensorimotor training combined with RT (SM-RT) on balance, 1 repetition maximum (RM), rate of force development (RFD), and squat jump (SJ) height. Twenty amateur soccer players were equally divided into 2 groups assigned as SM-RT group (age: 22 ± 1.7 years, body mass: 79.9 ± 6.3 kg, body height: 1.81 ± 0.06 m) and RT group (age: 21.3 ± 1.3 years, body mass: 77.4 ± 9.3 kg, body height: 1.78 ± 0.04 m). Both groups were trained over a 6-week period with 2 session units per week. SM-RT group performed sensorimotor training (balance on balance board) followed by a high-intensity RT at 8-5RM leg press. The RT group performed the resistance program only. Both groups showed significantly increased 1RM leg press strength, RFD, SJ height, and balance abilities (p ≤ 0.05), whereas no significant between-group differences were observed in any of the outcome variables (p > 0.05). It was concluded that SM-RT was not superior compared with RT for both balance and strength enhancement. These findings have implications in time management during training for soccer players.

#8 Spontaneous Upper Extremity Venous Thrombosis in a Collegiate Soccer Player: A Case Report
Reference: Pediatr Emerg Care. 2016 Jan;32(1):25-8. doi: 10.1097/PEC.0000000000000667.
Authors: Fundora MP, Rudnick C, Barbur C.
Summary: Spontaneous effort-induced thrombosis is a rare but reported phenomena that was originally described over 100 years ago. The pathogenesis of this thrombosis arises from an abnormality of the thoracic outlet usually combined with a history of physical activity that includes repetitive arm motions, usually of the dominant hand. We present the case of an adolescent patient who presented to a pediatric emergency department with progressive pain, discoloration, and swelling of the shoulder of his nondominant hand. The pain became acutely worse with graying appearance of his arm. The patient was diagnosed with spontaneous thrombosis of the upper extremity extending from the left subclavian vein extending to the axillary vein. Treatment of this patient included aggressive anticoagulation, thrombolysis, and costectomy.

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