Latest research in football - week 7 - 2017

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 Effects of light-load maximal lifting velocity weight training vs. combined weight training and plyometrics on sprint, vertical jump and strength performance in adult soccer players
Reference: J Sci Med Sport. 2017 Jan 24. pii: S1440-2440(17)30241-4. doi: 10.1016/j.jsams.2016.11.010. [Epub ahead of print]
Authors: Rodriguez-Rosell D, Torres-Torrelo J, Franco-Marquez F, Gonzalez-Suarez JM, Gonzalez-Badillo JJ
Summary: The purpose of this study was to compare the effects of combined light-load maximal lifting velocity weight training (WT) and plyometric training (PT) with WT alone on strength, jump and sprint performance in semiprofessional soccer players. Thirty adult soccer players were randomly assigned into three groups: WT alone (FSG, n=10), WT combined to jump and sprint exercises (COM, n=10) and control group (CG, n=10). WT consisted of full squat with low load (∼45-60% 1RM) and low volume (4-6 repetitions). Training program was performed twice a week for 6 weeks of competitive season in addition to 4 soccer sessions a week. Sprint time in 10 and 20m, jump height (CMJ), estimated one-repetition maximum (1RMest) and velocity developed against different absolute loads in full squat were measured before and after training period. Both experimental groups showed significant improvements in 1RMest (17.4-13.4%; p<0.001), CMJ (7.1-5.2%; p<0.001), sprint time (3.6-0.7%; p<0.05-0.001) and force-velocity relationships (16.9-6.1%; p<0.05-0.001), whereas no significant gains were found in CG. No significant differences were found between FSG and COM. Despite FSG resulted of greater increases in strength variables than COM, this may not translate into superior improvements in the sport-related performance. In fact, COM showed higher efficacy of transfer of strength gains to sprint ability. Therefore, these findings suggest that a combined WT and PT program could represent a more efficient method for improving activities which involve acceleration, deceleration and jumps compared to WT alone.

#2 Between-Session Reliability Of Isometric Mid-Thigh Pull Kinetics And Maximal Power Clean Performance In Male Youth Soccer Players
Reference: J Strength Cond Res. 2017 Feb 1. doi: 10.1519/JSC.0000000000001830. [Epub ahead of print]
Authors: Dos'Santos T, Thomas C, Comfort P, McMahon JJ, Jones PA, Oakley NP, Young AL
Summary: The aim of the study was to determine the between-session reliability of isometric mid-thigh pull (IMTP) kinetics and maximal weight lifted during the power clean (PC) in male youth soccer players, and to identify the smallest detectable differences between sessions. Thirteen male youth soccer players (age: 16.7 ± 0.5 years, height: 1.80 ± 0.08 m, mass: 70.5 ± 9.4 kg) performed three IMTP trials, while only ten soccer players performed maximal power cleans. These were performed twice, separated by 48 hours to examine the between-session reliability. Intraclass correlation coefficients (ICC) and coefficient of variation (CV) demonstrated high levels of within-session (ICC = 0.84-0.98, CV = 4.05-10.00%) and between-session reliability (ICC = 0.86-0.96, CV = 3.76-7.87%) for IMTP kinetics (peak force and time-specific force values 30-250 ms) and maximal PC (ICC = 0.96, CV = 3.23%), all meeting minimum acceptable reliability criteria. No significant differences (p>0.05, effect size ≤0.22) were revealed between sessions for IMTP kinetics and maximal PC performance. Strength and conditioning coaches and practitioners should consider changes of >6.04% in maximal PC and changes in IMTP kinetics of >14.31% in force at 30 ms, > 14.73% in force at 50 ms, >12.36% in force at 90 ms, >12.37% in force at 100 ms, >14.51% in force at 150 ms, >11.71% in force at 200 ms, >7.23% in force at 250 ms and >8.50% in absolute peak force as meaningful improvements in male youth soccer players. Decrements in the IMTP kinetics greater than aforementioned values could possibly be used as an indicator of neuromuscular fatigue and preparedness for training or competition.

#3 Coach-led preventive training program in youth soccer players improves movement technique
Reference: J Sci Med Sport. 2017 Jan 24. pii: S1440-2440(17)30265-7. doi: 10.1016/j.jsams.2017.01.235. [Epub ahead of print]
Authors: Pryor JL, Root HJ, Vandermark LW, Pryor RR, Martinez JC, Trojian TH, Denegar CR, DiStefano LJ
Summary: Long-term implementation of preventive training programs (PTP) in youth sport requires coach involvement. However, the optimal training of coaches to effectively implement a PTP remains unknown. It is also unknown if the benefits of PTP can be enhanced with multiple sport seasons of exposure. The objective of the study was to evaluate the influence of prior PTP exposure on movement technique in youth soccer players after completing a coach-led PTP. Twelve youth soccer teams (n=89; age range 8-14 years) were divided into groups with (Experience (EXP); 6 teams [n=18 females, n=25 males]) and without (Novice (NOV); 6 teams [n=30 females, n=16 males]) previous professional-led PTP experience. The coaches and players of the EXP teams were exposed to an eight-week professional-led PTP before the coach-led PTP. EXP and NOV coaches attended the educational workshop prior to implementing the coach-led PTP. The Landing Error Scoring System (LESS) was used to evaluate movement technique. Both groups improved LESS scores over time (mean difference±SD [post-pre]=-0.8±0.2, 95%CI [-1.2, -0.4], p=0.0001). Of the 64 participants classified as high risk for injury (LESS ≥5) prior to PTP implementation, a greater proportion of EXP (n=14) compared to NOV (n=7) participants changed risk classification from high to low (LESSΔ≥1 and LESS <5; p=0.03). Our PTP enhanced movement technique regardless of PTP experience, but the benefits of the PTP impacted a proportionally greater number of players with previous PTP experience supporting continued PTP implementation. Coaches effectively implemented an exercise-based PTP after attending a training workshop regardless of previous PTP experience.

#4 Injury mechanism of midfacial fractures in football causes in over 40% typical neurological symptoms of minor brain injuries
Reference: Knee Surg Sports Traumatol Arthrosc. 2017 Feb 8. doi: 10.1007/s00167-017-4431-z. [Epub ahead of print]
Authors: Krutsch V, Gesslein M, Loose O, Weber J, Nerlich M, Gaensslen A, Bonkowsky V, Krutsch W
Summary: The injury mechanisms of midfacial fractures may be typical causes of concussion, but hardly any scientific data on midfacial injuries sustained in football are available. Head and brain trauma represent frequent injuries in athletes of different sports that require appropriate treatment by sports and trauma physicians. This study investigated the management of midfacial fractures in football and the association of such fractures with concomitant brain injury. In a prospective cohort study lasting 24 months (2012 to 2013), midfacial injuries of football players were analysed with regard to the injury mechanisms, first aid procedures on the field, treatment and return-to-play. To analyse concomitant and potentially overlooked minor brain injuries due to the trauma, we retrospectively investigated the neurological symptoms of the study population. The study included 132 football players (37 semi-professionals and 95 amateurs) with midfacial fractures. The main injury mechanisms were head-to-head and head-to-elbow trauma. The mean period of return-to-play after trauma was 33.5 days, which was significantly shortened if a protective face mask was worn (mean 10.4 days earlier, p = 0.0006). Semi-professional football players returned to play earlier (p = 0.009) and more often used protective face masks (p = 0.001). 55 players (41.6%) had neurological symptoms immediately after trauma as a possible sign of concomitant minor brain injury. 5 of 132 players with concussion had been hospitalised for 24 h, but no persistent neurological symptoms were detected. In football, midfacial fractures represent moderate-to-severe injuries with time away from sports of more than 4 weeks. Over 40% of athletes with a midfacial fracture showed concomitant neurological symptoms as a sign of minor brain injury. Therefore, sports physicians and other staff supervising athletes in daily practice should be aware of the presence of neurological symptoms.

#5 Visual search behaviors of association football referees during assessment of foul play situations
Reference: Cogn Res Princ Implic. 2016;1(1):12. doi: 10.1186/s41235-016-0013-8. Epub 2016 Oct 31
Authors: Spitz J, Put K, Wagemans J, Williams AM, Helsen WF
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Summary: It is well reported that expert athletes have refined perceptual-cognitive skills and fixate on more informative areas during representative tasks. These perceptual-cognitive skills are also crucial to performance within the domain of sports officials. We examined the visual scan patterns of elite and sub-elite association football referees while assessing foul play situations. These foul play situations (open play and corner kick situations) were presented on a Tobii T120 Eye Tracking monitor. The elite referees made more accurate decisions and differences in their visual search behaviors were observed. For the open play situations, referees in the elite group spent significantly more time fixating the most informative area of the attacking player (contact zone) and less time fixating the body part that was not involved in the infringement (non-contact zone). Furthermore, the average total fixation time in the contact zone and non-contact zone tended to differ between the elite and sub-elite referees in corner kick situations. In conclusion, elite level referees have learned to discern relevant from less-relevant information in the same way as expert athletes. Findings have implications for the development of perceptual training programs for sport officials.

#6 The acceleration and deceleration profiles of elite female soccer players during competitive matches
Reference: J Sci Med Sport. 2017 Jan 24. pii: S1440-2440(17)30268-2. doi: 10.1016/j.jsams.2016.12.078. [Epub ahead of print]
Authors: Mara JK, Thompson KG, Pumpa KL, Morgan S
Summary: The aim of this study was to determine the acceleration (≥2ms-2) and deceleration (≤-2ms-2) profiles of elite female soccer players during competitive matches. An Optical Player Tracking system was used to determine acceleration (≥2ms-2) and deceleration (≤-2ms-2) variables for twelve elite female players across seven competitive matches. In total, players performed 423 (±126) accelerations and 430 (±125) decelerations per match. It was shown that the number of accelerations (p=0.003-0.034, partial η2=0.229-321) and decelerations (p=0.012-0.031, partial η2=0.233-275) at different intensities (based on the start and final velocity) varied according to player position. Mean and maximum distance per effort was 1-4m and 2-8m, respectively, and differed between each intensity category (p<0.001, partial η2=0.753-0.908). The mean time between efforts was 14s for both accelerations (±5s) and decelerations (±4s) and fluctuated between 15min time periods (p<0.001, partial η2=0.148-0.206). The acceleration and deceleration profiles varied according to player position and time period of the match. The results of this study can be used to design match-specific acceleration and deceleration drills to enhance change of speed ability.

#7 The influence of genetic polymorphisms on performance, cardiac and hemodynamic parameters among Brazilian soccer players
Reference: Appl Physiol Nutr Metab. 2017 Jan 24. doi: 10.1139/apnm-2016-0608. [Epub ahead of print]
Authors: Dionisio TJ, Thiengo CR, Brozoski DT, Dionisio EJ, Talamoni GA, Silva RB, Garlet GP, Santos CF, Amaral SL
Summary: This study investigated whether ACTN3 R577X, AMPD1 C34T, I/D ACE and M235T AGT polymorphisms can affect performance tests such as jumping, sprinting and endurance in 220 young male athletes from professional minor league soccer team from São Paulo Futebol Clube, Brazil. I/D ACE and M235T AGT polymorphisms were also analyzed according to cardiac and hemodynamic parameters. Athletes were grouped or not by age. DNA from saliva and Taqman® assays were used for genotyping 220 athletes and the results were associated with performance tests. Ventricle mass, ventricle end-diastolic diameter, end diastolic volume and ejection fraction were assessed by echocardiogram. Arterial pressure, heart rate and oximetry were assessed by a cardioscope. The main results of this study were that athletes who carried RR/RX (ACTN3) and DD (ACE) genotypes presented better performance during jump and sprint tests. On the other hand, athletes with ID/II genotype presented better results during endurance test, while AGT genotypes did not seem to favor the athletes during the evaluated physical tests. CC genotype (AMPD1) only favored the athletes during 10-m sprint test. Although there are environmental interactions influencing performance, the present results suggest that RR/RX ACTN3 and ACE DD genotypes may benefit athletes in activities that require strength and speed, while II ACE genotype may benefit athletes in endurance activities. This information could help coaches to plan the training session in order to improve the athletes' performance.

#8 Free-sugar, total-sugar, fibre and micronutrient intake within elite youth British soccer players: a nutritional transition from schoolboy to fulltime soccer player
Reference: Appl Physiol Nutr Metab. 2017 Jan 10. doi: 10.1139/apnm-2016-0459. [Epub ahead of print]
Authors: Naughton RJ, Drust B, O'Boyle A, Abayomi J, Mahon E, Morton JP, Davies IG
Summary: It is recommended that soccer players consume a high carbohydrate (CHO) diet to augment performance. However, growing evidence suggests that there is a link between high free-sugar (FS) intake (>5% total energy intake; TEI) and metabolic diseases. Furthermore, foods that are often high in sugar, such as processed foods, are typically lacking in nutrient quality. We therefore analysed total- and FS, dietary fibre and micronutrient intake of players from an English Premier League academy under(U) 18 (n=13); U15/16 (n=25); U13/14 (n=21) using a 7-day food diary. Data was compared to current UK dietary reference value (DRV) for free-sugar via a t-test. The U13/14s (1018 %) and U15/16s (1130 %) both consumed higher amounts of free-sugar in comparison to the UK DRV of 5% TEI 5% (P<0.01), conversely, the U18s did not exceed the DRV (513 %). Furthermore, FS intake of the U18s was significantly lower than the U13/14s and U15/16s (P<0.01). Dietary fibre was below the DRV (25g/d for U13/14 & U15/16s; 30g/d for U18s) for all squads (19.04.7; 19.68.3; 17.14.2 g/d, respectively), but not different between squads. Additionally, micronutrient reference intakes were generally met. In conclusion, we provide novel data on dietary sugar, fibre and micronutrient intake within elite youth soccer players. We report an apparent 'nutritional transition' from schoolboy to fulltime soccer player, with U18s showing a significantly lower intake of sugar in comparison to younger squads, and a similar intake of FS to the UK DRVs. Practitioners should target improving player education around sugar and fibre consumption.

#9 Core executive functions are associated with success in young elite soccer players
Reference: PLoS One. 2017 Feb 8;12(2):e0170845. doi: 10.1371/journal.pone.0170845. eCollection 2017.
Authors: Vestberg T, Reinebo G, Maurex L, Ingvar M, Petrovic P
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Summary: Physical capacity and coordination cannot alone predict success in team sports such as soccer. Instead, more focus has been directed towards the importance of cognitive abilities, and it has been suggested that executive functions (EF) are fundamentally important for success in soccer. However, executive functions are going through a steep development from adolescence to adulthood. Moreover, more complex EF involving manipulation of information (higher level EF) develop later than simple executive functions such as those linked to simple working memory capacity (Core EF). The link between EF and success in young soccer players is therefore not obvious. In the present study we investigated whether EF are associated with success in soccer in young elite soccer players. We performed tests measuring core EF (a demanding working memory task involving a variable n-back task; dWM) and higher level EF (Design Fluency test; DF). Color-Word Interference Test and Trail Making Test were performed on an exploratory level as they contain a linguistic element. The lower level EF test (dWM) was taken from CogStateSport computerized concussion testing and the higher level EF test (DF) was from Delis-Kaplan Executive Function System test battery (D-KEFS). In a group of young elite soccer players (n = 30; aged 12-19 years) we show that they perform better than the norm in both the dWM (+0.49 SD) and DF (+0.86 SD). Moreover, we could show that both dWM and DF correlate with the number of goals the players perform during the season. The effect was more prominent for dWM (r = 0.437) than for DF (r = 0.349), but strongest for a combined measurement (r = 0.550). The effect was still present when we controlled for intelligence, length and age in a partial correlation analysis. Thus, our study suggests that both core and higher level EF may predict success in soccer also in young players.

#10 Commentary: "How Much is that Player in the Window? The One with the Early Birthday?" Relative Age Influences the Value of the Best Soccer Players, but Not the Best Businesspeople
Reference: Front Psychol. 2017 Jan 25;8:58. doi: 10.3389/fpsyg.2017.00058. eCollection 2017.
Authors: Fumarco L, Gibbs BG
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#11 The Effect of Plyometric Training Volume in Prepubertal Male Soccer Players' Athletic Performance
Reference: Int J Sports Physiol Perform. 2017 Feb 9:1-22. doi: 10.1123/ijspp.2016-0372. [Epub ahead of print]
Authors: Chaabene H, Negra Y
Summary: The aim of this study was to assess and to compare the effects of 8-weeks in-season (2 sessions per-week) low and high-volume plyometric training (PT) on measures of physical fitness in prepubertal male soccer players. A total of twenty-five soccer players were randomly assigned to low-volume plyometric training group (LPT; n=13; age = 12.68 ± 0.23 years; age at peak height velocity (APHV) = 14.25 ± 0.29 years, maturity-offset = -1.57 ± 0.29 years) and high-volume plyometric training group (HPT; n=12; age = 12.72 ± 0.27 years; APHV = 14.33 ± 0.77 years, maturity-offset = -1.61 ± 0.76 years). Linear sprint test (5-m, 10-m, 20-m, and 30-m), change of direction test (T-test), vertical (squat-jump [SJ] and counter-movement-jump [CMJ]), and horizontal (standing-long-jump [SLJ]) jump ability were carried out pre and post 8-weeks of PT. A significant main effect of time for sprint outcomes (5-m: p=0.005, ES=0.86; 10-m: p=0.006, ES=0.85; 20-m: p=0.03, ES=0.64, and 30-m: p=0.05, ES=0.57), change of direction (p = 0.002, ES=0.96), vertical (SJ: p=0.008, ES= 0.81); CMJ: p=0.01, ES= 0.73), and horizontal jump ability (SLJ: p = 0.007, ES = 0.83). There were no significant training group × time interactions in all the measured outcomes. Following 8-weeks of training, results showed similar performance improvement on measures of sprint time, change of direction, and jumping ability between LPT and HPT groups. From a time efficiency perspective, it is recommended to use LPT in prepubertal male soccer players so as to improve their proxies of athletic performance.

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