Latest research in football - week 12 - 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 Effect of an Inside Floater on Soccer Players Tactical Behaviour in Small Sided and Conditioned Games
Reference: J Hum Kinet. 2020 Jan 31;71:167-177. doi: 10.2478/hukin-2019-0080. eCollection 2020 Jan.
Authors: Moniz F, Scaglia A, Sarmento H, García-Calvo T, Teoldo I
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Summary: The aim of this study was to verify the effect of an inside floater on soccer players' tactical behaviour in small-sided and conditioned games (SSCGs). The sample comprised 54 Brazilian top-level academy players. The instrument used to assess players' tactical behaviour was the System of Tactical Assessment in Soccer (FUT-SAT). Tactical behaviour was analysed through the number of tactical actions and the percentage of correct actions regarding the core tactical principles of soccer. Repeated measures test was used to compare tactical behaviour between games (SSCGs) with and without an inside floater. Pearson's r was used to verify the effect size of the inside floater on tactical behaviour. As for tactical actions, SSCGs with an inside floater displayed significantly lower means for the tactical principles of penetration (2.76 ± 1.63; p < .001), delay (6.11 ± 2.68; p < .018), defensive coverage (1.64 ± 1.14; p < .001) and significantly higher means for the tactical principle of defensive unity (14.98 ± 4.57; p < .032). With respect to the percentage of correct actions, SSCGs with an inside floater displayed significantly lower means for all tactical principles, except for offensive coverage (90.5 ± 18.48; p < 1.000). It was concluded that the inside floater allowed players to modify their behaviour in such a way that they adapted to the constraints imposed by the presence of an inside floater. Furthermore, the inside floater provided more difficulty for players, and thus may be considered an important task constraint to be added in SSCGs.

#2 Eating Habits and Body Composition of International Elite Soccer Referees
Reference: J Hum Kinet. 2020 Jan 31;71:145-153. doi: 10.2478/hukin-2019-0078. eCollection 2020 Jan.
Authors: Mascherini G, Petri C, Ermini E, Pizzi A, Ventura A, Galanti G
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Summary: Soccer referees are a specific group of the athletes' population whose careers peak from 30 to 45 years old. An athlete's performance is not only determined by physical training but also by a lifestyle, e.g. eating habits. The purpose of this study was to verify current eating habits and resulting body composition of a group of elite international soccer referees. At an international FIFA seminar 60 elite international soccer referees (aged 39.2 ± 4.2 years) were enrolled. A body composition assessment was performed with skinfold thickness and bio impedance analysis, while eating habits were evaluated with a multi-pass 24-hour dietary recall. The body composition showed a normal weight condition with a fat content of 11.4 ± 2.5%. Macronutrients showed a low level of carbohydrates (43.6 ± 5.4%) and a high level of fat (40.0 ± 4.5%). Micronutrients showed a low level of calcium, potassium, zinc, magnesium, iodine, vitamin B12 and vitamin B9. Even though their body composition was within the normal range, the current eating habits of elite international soccer referees did not appear to follow the nutrition guidelines. Therefore, it would be advisable to provide knowledge on nutrition for this particular category of sports subjects, an individualized nutritional plan would be advisable, in order to achieve and maintain better performance and appropriate body composition for their role.

#3 A Longitudinal Investigation of Symptom Recovery following Concussion in Youth Soccer
Reference: J Pediatr. 2020 Mar 5. pii: S0022-3476(20)30141-4. doi: 10.1016/j.jpeds.2020.01.068. [Epub ahead of print]
Authors: Kirkwood MW, Crossland MM, Howell DR, Wilson JC, Peterson RL
Summary: The purpose was to prospectively evaluate symptom outcomes after youth soccer-related concussion. Using a prospective cohort design, we enrolled male and female competitive soccer players age 8-17 years into 3 groups: concussed (n = 23), matched control (n = 23), and orthopedic injury (n = 24). Postconcussive symptoms were monitored serially via both athlete and parent report at days 1-2, 4, 7, 10, 30, and 90. Repeated-measures analyses revealed a significant time by group interaction (F [12, 402] = 19.91, P < .001). In the initial days postinjury, the concussed group reported greater symptoms than the comparison groups, with more symptoms reported by athletes on average than parents. By 10 days, concussed athletes did not differ from the matched controls by either rater's report, but they did differ from the orthopedic injury group by parent report. At 30 days, no differences were apparent among groups. At 30 days, 100% of concussed youth and 91% of parents rated symptoms as back to preinjury levels using reliable change indices. At 30 days, 86% of athletes had been cleared to return to full game play. The natural clinical history of concussion symptoms in youth competitive soccer players was similar to that seen in older athletes, with resolution in days to a few weeks. Additional study will be required to investigate which factors best predict symptom outcomes for individual athletes and how symptom report relates to performance-based outcome measures and underlying neurophysiologic recovery.

#4 Football-specific validity of TRACAB's optical video tracking systems
Reference: PLoS One. 2020 Mar 10;15(3):e0230179. doi: 10.1371/journal.pone.0230179. eCollection 2020.
Authors: Linke D, Link D, Lames M
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Summary: The present study aimed to validate and compare the football-specific measurement accuracy of two optical tracking systems engineered by TRACAB. The "Gen4" system consists of two multi-camera units (a stereo pair) in two locations either side of the halfway line, whereas the distributed "Gen5" system combines two stereo pairs on each side of the field as well as two monocular systems behind the goal areas. Data were collected from 20 male football players in two different exercises (a football sport-specific running course and small-sided games) in a professional football stadium. For evaluating the accuracy of the systems, measures were compared against simultaneously recorded measures of a reference system (VICON motion capture system). Statistical analysis uses RMSE for kinematic variables (position, speed and acceleration) and the difference in percentages for performance indicators (e.g. distance covered, peak speed) per run compared to the reference system. Frames in which players were obviously not tracked were excluded. Gen5 had marginally better accuracy (0.08 m RMSE) for position measurements than Gen4 (0.09 m RMSE) compared to the reference. Accuracy difference in instantaneous speed (Gen4: 0.09 m⋅s-1 RMSE; Gen5: 0.08 m⋅s-1 RMSE) and acceleration (Gen4: 0.26 m⋅s-2 RMSE; Gen5: 0.21 m⋅s-2 RMSE) measurements were significant, but also trivial in terms of the effect size. For total distance travelled, both Gen4 (0.42 ± 0.60%) and Gen5 (0.27 ± 0.35%) showed only trivial deviations compared to the reference. Gen4 showed moderate differences in the low-speed distance travelled category (-19.41 ± 13.24%) and small differences in the high-speed distance travelled category (8.94 ± 9.49%). Differences in peak speed, acceleration and deceleration were trivial (<0.5%) for both Gen4 and Gen5. These findings suggest that Gen5's distributed camera architecture has minor benefits over Gen4's single-view camera architecture in terms of accuracy. We assume that the main benefit of the Gen5 towards Gen4 lies in increased robustness of the tracking when it comes to optical overlapping of players. Since differences towards the reference system were very low, both TRACAB's tracking systems can be considered as valid technologies for football-specific performance analyses in the settings tested as long as players are tracked correctly.

#5 The association between adolescent football participation and early adulthood depression
Reference: PLoS One. 2020 Mar 10;15(3):e0229978. doi: 10.1371/journal.pone.0229978. eCollection 2020.
Authors: Deshpande SK, Hasegawa RB, Weiss J, Small DS
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Summary: Concerned about potentially increased risk of neurodegenerative disease, several health professionals and policy makers have proposed limiting or banning youth participation in American-style tackle football. Given the large affected population (over 1 million boys play high school football annually), careful estimation of the long-term health effects of playing football is necessary for developing effective public health policy. Unfortunately, existing attempts to estimate these effects tend not to generalize to current participants because they either studied a much older cohort or, more seriously, failed to account for potential confounding. We leverage data from a nationally representative cohort of American men who were in grades 7-12 in the 1994-95 school year to estimate the effect of playing football in adolescent on depression in early adulthood. We control for several potential confounders related to subjects' health, behavior, educational experience, family background, and family health history through matching and regression adjustment. We found no evidence of even a small harmful effect of football participation on scores on a version of the Center for Epidemiological Studies Depression scale (CES-D) nor did we find evidence of adverse associations with several secondary outcomes including anxiety disorder diagnosis or alcohol dependence in early adulthood. For men who were in grades 7-12 in the 1994-95 school year, participating or intending to participate in school football does not appear to be a major risk factor for early adulthood depression.

#6 The relationship between training load and fitness indices over a pre-season in professional soccer players
Reference: J Sports Med Phys Fitness. 2020 Mar;60(3):329-337. doi: 10.23736/S0022-4707.20.10109-9.
Authors: Papadakis L, Tymvios C, Patras K
Summary: An association between training load and changes in aerobic fitness has been established but the effect of training load on changes in strength/power remains controversial. Internal (Banister's TRIMP) and external (total distance, high-speed running and sprint distance) training load was collected from sixteen professional soccer players during and aerobic fitness and strength/power variables were measured before and after a 9-week pre-season. Banister's TRIMP had a moderate correlation with changes in maximal oxygen uptake (r=0.46, 90% CI: 0.04; 0.74). Total distance had a large and a moderate correlation with changes in velocity at 2M (r=0.60, 90% CI: 0.23; 0.82) and changes in velocity at 4M (r=0.42, 90% CI: -0.01; 0.72). High-speed running had moderate correlations with changes in maximal oxygen uptake (r=0.45, 90% CI: 0.03; 0.74), velocity at 2M (r=0.45, 90% CI: 0.03; 0.74) and velocity at 4M (r=0.39, 90% CI: -0.00; 0.70). Sprint distance had a large and a moderate correlation with changes in maximal oxygen uptake (r=0.58, 90% CI: 0.20; 0.81) and velocity at 4M (r=0.46, 90% CI: 0.00; 0.74 respectively). High versus low total distance was associated with lower changes in squat jump and countermovement jump (ES=-0.90, 90% CI: -1.57; -0.24 and ES=-1.06, 90% CI: -1.89; -0.24) respectively. High versus low high-speed running was associated with higher changes in maximal oxygen uptake (ES=0.36, 90% CI: 0.02; 0.70) but lower changes in squat jump (ES=-0.58, 90% CI: -1.32; 0.15). External rather internal training load had more pronounced correlations with changes in aerobic fitness. Higher compared with lower volumes of total distance and high-speed running were associated with lower gains in strength/power indices. Establishing a "dose-response" association between external/internal training load and endurance as well as strength adaptations, may maximize endurance gains with the least possible interference on strength/power gains, thus better informing soccer training practice.

#7 Strength, Jumping, and Change of Direction Speed Asymmetries Are Not Associated With Athletic Performance in Elite Academy Soccer Players
Reference: Front Psychol. 2020 Mar 3;11:175. doi: 10.3389/fpsyg.2020.00175. eCollection 2020.
Authors: Raya-González J, Bishop C, Gómez-Piqueras P, Veiga S, Viejo-Romero D, Navandar A
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Summary: The aims of the present study were 2-fold: (1) to measure interlimb asymmetries from a battery of fitness tests in youth soccer players and (2) to determine the association between asymmetry and measures of athletic performance. Sixteen elite youth soccer players (14.7 ± 0.2 years) performed a single-leg Abalakov test (ABK), change of direction (COD) test over 10 m (5 + 5) and 20 m (10 + 10), and an iso-inertial power test. Subjects also performed 10-, 20-, and 30-m sprints and a bilateral countermovement jump, which were correlated with all ABK, COD, and iso-inertial asymmetry scores. A one-way repeated-measures analysis of variance showed significant differences between interlimb asymmetry scores across multiple tests (p < 0.05), with the iso-inertial power test presenting the greatest magnitude of asymmetry, whereas individual data highlighted substantially greater interindividual differences in each test. Pearson r correlations showed no significant relationships (p > 0.05) between the different interlimb asymmetry scores, and between asymmetry scores and athletic performance. These findings show the test-specific nature of asymmetries in youth soccer players, with the iso-inertial power test being the most sensitive in detecting asymmetry. Moreover, the results obtained suggest that inherent asymmetry in young soccer players did not negatively impact their performance.

#8 Influence of competition on performance factors in under-19 soccer players at national league level
Reference: PLoS One. 2020 Mar 19;15(3):e0230068. doi: 10.1371/journal.pone.0230068. eCollection 2020.
Authors: Izquierdo JM, De Benito AM, Araiz G, Guevara G, Redondo JC
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Summary: The aim of this study was to analyse and quantify the acute effects of competition on several performance factors in under-19 male soccer players. To this end, 198 national league players (17.56 ± 0.78 years) performed various tests to measure jump capacity, kicking velocity and sprint times immediately pre-match (T1), at half-time (T2) and post-match (T3). Tests included kicking the ball to measure ball velocity (KICK), sprinting for 40 meters, timing the first 30 meters (30mACCEL), the last 10 meters (10mACCEL) and the total distance (40mACCEL), and performing countermovement jumps (CMJ). For subsequent analysis, the sample was divided into 5 playing positions: goalkeepers (n = 24), defenders (n = 51), midfielders (n = 36), wingers (n = 54) and forwards (n = 33). For all positions, we found a significant decline in performance (p<0.05) for kicking velocity (2.91% - 6.51%) and sprinting (0.44%-5.85%). For the CMJ, all positions except defenders presented a significant decline in performance that ranged from 1.5% to 4.56%. These findings highlight the need to individualise fitness training, taking into account the match needs and demands of the different playing positions in order to minimise the effects of match fatigue and accelerate post-match recovery.

#9 Infrared Thermography Protocol on Reducing the Incidence of Soccer Injuries
Reference: J Sport Rehabil. 2020 Mar 17:1-6. doi: 10.1123/jsr.2019-0056. [Epub ahead of print]
Authors: Gómez-Carmona P, Fernández-Cuevas I, Sillero-Quintana M, Arnaiz-Lastras J, Navandar A.
Summary: Infrared thermography has been used to detect skeletal muscle overload and fatigue in athletes, but its use in injury prevention in professional soccer has not been studied to date. The purpose was to establish a novel injury prevention program based on infrared thermography and to determine its influence on the injury incidence in professional soccer players in the preseason. A cross-sectional, prospective study design was used to compare a conventional injury prevention program (CPP) applied over the first preseason and an infrared thermography injury prevention program (IRTPP) carried out in the following preseason. Twenty-four players belonging to a first division soccer team from Spain participated in this study.  Injury incidences of each player were recorded according to the Orchard Sports Injury Classification System (version 10.0) convention to determine the injury classification, location, and type were used as main outcome measures. The incidence of injuries decreased from 15 injuries in the CPP preseason (0.63 [0.77] injuries per player) to 6 injuries in the second preseason when the IRTPP was applied (0.25 [0.53] injuries per player). The days of absence due to injuries also decreased from the CPP preseason (156 d, 10.4 [11.0] d per injury) to the IRTPP preseason (14 d, 2.3 [2.8] d per injury). The injury severity also decreased from the first preseason to the second preseason, and fewer musculoskeletal injuries in the thigh, hip, and groin were reported. The implementation of an IRTPP can reduce the presence of injuries by identifying players potentially at risk and as a result, reducing the injury severity and days lost as a consequence.

#10 Influence of Maturation Status on Eccentric Hamstring Strength Improvements in Youth Male Soccer Players After the Nordic Hamstring Exercise
Reference: Int J Sports Physiol Perform. 2020 Mar 18:1-7. doi: 10.1123/ijspp.2019-0184. [Epub ahead of print]
Authors: Drury B, Green T, Ramirez-Campillo R, Moran J.
Summary: This study examined the effects of a 6-week Nordic hamstring exercise (NHE) program in youth male soccer players of less mature (pre-peak height velocity [PHV]) or more mature (mid/post-PHV) status. Forty-eight participants were separated into pre-PHV (11.0 [0.9] y) or mid/post-PHV (13.9 [1.1]) groups and further divided into experimental (EXP) and control groups with eccentric hamstring strength assessed (NordBord) both before and after the training program. Participants in the EXP groups completed a periodized NHE program performed once or twice weekly over a 6-week period. The NHE program resulted in moderate and small increases in relative eccentric hamstring strength (in newtons per kilogram) in the pre-PHV EXP (d = 0.83 [0.03-1.68]) and mid-PHV EXP (d = 0.53 [-0.06 to 1.12]) groups, respectively. Moderate increases in the same measure were also seen in the between-groups analyses in the pre-PHV (d = 1.03 [0.23-1.84]) and mid-PHV (d = 0.87 [0.22-1.51]) groups, with a greater effect observed in the former. The results from this study demonstrate that a 6-week NHE program can improve eccentric hamstring strength in male youth soccer players, with less-mature players achieving mostly greater benefits. The findings from this study can aid in the training prescription of NHE in youth male soccer players.

#11 Effect of acupuncture on heart rate variability during prolonged high-intensity training in soccer players
Reference: J Tradit Chin Med. 2017 Oct;37(5):636-642.
Authors: Lin S, Wichai E, Amonrat J, Somchai R
Summary: The purpose was to investigate the effects of acupuncture therapy compared with sham acupuncture on heart rate variability (HRV) in 24 elite soccer players during 4-week, high-intensity training sessions. The subjects were randomly divided into two groups: acupuncture group (AG) and sham acupuncture group (SG). In addition, AG had been implemented two times/week to stimulate Zusanli (ST 36), Hegu (LI 4), Shenshu (BL 23), and Chize (LU 5). While SG, had been applied to utilize a special ""placebo-needle"" technique on the same sites. What's more, the HRV parameters were calculated before and after interventions, respectively. First, stress index (SI) had a significantly increased in SG (P = 0.031) compare pre-test with post-test, however, no significantly difference in AG (P = 0.102). Secondly, standard deviation of N-N intervals (SNDD) have enormously significantly higher in AG when comparing baseline with post therapy (P = 0.001), while, declined in SG (P = 0.827). Meanwhile, the root mean square of successive differences (RMSSD) were significant differences in AG (P = 0.023). What's more, when the high-frequency (HF) were significantly higher in AG (P = 0.047) after receiving the acupuncture therapy, the lowe-frequency (LF) power were decreased but no significant in AG and SG. Comparing with pre-experiment, the ratio of LF/HF was lower in AG, but higher in SG. Furthermore, it was significant difference when compare the post-experiment parameters of AG with SG (P = 0.015). And HF parameters have significance (P = 0.005) compare between two groups during the post-experiment. Based on evidence, acupuncture therapy on special acupoints could strengthen the parasympathetic nervous activity and modulates the balance between parasympathetic and sympathetic activity in soccer players while they engage in high-intensity training.

#12 The influence of offside rule and pitch sizes on the youth soccer players' small-sided games external loads
Reference: Res Sports Med. 2020 Mar 18:1-15. doi: 10.1080/15438627.2020.1739687. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Manuel Clemente F, Yanci J
Summary: The aim was to analyse the influence of the offside rule and pitch sizes on the external loads encountered by young soccer players during small-sided games (SSGs). Twenty-four U12 soccer players belonged to the same Spanish Performance Soccer Academy participated in the study. Each player participated in six different SSGs attending to the offside rule (i.e., offside not applicable [NOS] and with offside [WOS]) and the pitch sizes (i.e., individual interaction space [IIS] of 25, 50 and 75 m2 per player). The obtained data included measures of external loads by global positioning systems. Players covered higher total distance and greater distances at jogging (8-12.9 km·h-1), cruising (13.0-16.0 km·h-1) and sprinting (>16.0 km·h-1) in NOS75 and WOS75 SSGs (p < 0.01; d = 0.65-6.60). Besides, in the NOS75 SSG, the total distance and the distance at cruising were higher in respect to WOS75 (p < 0.01; d = 0.63-0.82). In addition, players performed lower sprints (p < 0.01; d = 1.17-1.71) and achieved lower Vmax (p > 0.05; d = 1.10-1.88) during NOS25 and WOS25 SSGs. These findings could provide relevant information for coaches in order to apply different pitch sizes and the inclusion/absence of the offside rule throughout the microcycle.

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