Latest research in football - week 17 - 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 Daily Distribution of Carbohydrate, Protein and Fat Intake in Elite Youth Academy Soccer Players Over a 7-day Training Period.
Reference: Int J Sport Nutr Exerc Metab. 2016 Apr 20. [Epub ahead of print]
Authors: Naughton RJ, Drust B, O'Boyle A, Morgans R, Abayomi J, Davies IG, Morton JP, Mahon E.
Summary: While traditional approaches to dietary analysis in athletes have focused on total daily energy and macronutrient intake, it is now thought that daily distribution of these parameters can also influence training adaptations. Using seven-day food diaries, we quantified the total daily macronutrient intake and distribution in elite youth soccer players from the English Premier League in U18 (n=13), U15/16 (n=25) and U13/14 squads (n=21). Total energy (43.1±10.3, 32.6±7.9, 28.1±6.8 kcal·kg-1·day-1), CHO (6±1.2, 4.7±1.4, 3.2±1.3 g·kg-1·day-1) and fat (1.3±0.5, 0.9±0.3, 0.9±0.3 g·kg-1·day-1) intake exhibited hierarchical differences (P<0.05) such that U13/14>U15/16>U18. Additionally, CHO intake in U18s was lower (P<0.05) at breakfast, dinner and snacks when compared with both squads but no differences were apparent at lunch. Furthermore, the U15/16s reported lower relative daily protein intake than the U13/14s and U18s (1.6±0.3 vs. 2.2±0.5, 2.0±0.3 g·kg-1). A skewed distribution (P<0.05) of daily protein intake was observed in all squads, with a hierarchical order of dinner (~0.6 g·kg-1) > lunch (~0.5 g·kg-1) > breakfast (~0.3 g·kg-1). We conclude elite youth soccer players do not meet current CHO guidelines. Although daily protein targets are achieved, we report a skewed daily distribution in all ages such that dinner>lunch>breakfast. Our data suggest that dietary advice for elite youth players should focus on both total daily macronutrient intake and optimal daily distribution patterns.

#2 Prevalence of Articular Cartilage Lesions and Surgical Clinical Outcomes in Football (Soccer) Players' Knees: A Systematic Review
Reference: Arthroscopy. 2016 Apr 16. pii: S0749-8063(16)00106-7. doi: 10.1016/j.arthro.2016.01.055. [Epub ahead of print]
Authors: Andrade R, Vasta S, Papalia R, Pereira H, Oliveira JM, Reis RL, Espregueira-Mendes J
Summary: The purpose of the study was to systematize the available scientific literature on the prevalence of articular cartilage and/or osteochondral lesions in football (soccer) players' knees, and overview the surgical procedures and functional outcomes and return to sports. A comprehensive search using Pubmed, Cochrane Library, SPORTDiscus, and CINAHL databases was carried out until September 30, 2015. All English language studies that assessed the outcomes of a surgical technique for the treatment of articular cartilage lesions in football players' knees, with a minimum follow-up of 12 months, were included. The reference list of the most relevant papers was screened. The main outcomes of interest were the clinical, arthroscopy or imaging primary outcomes and the return to sports rate. The methodological and reporting qualities were assessed according to Coleman methodology score. The search provided 485 titles and abstracts. Five studies were eligible for inclusion (mean Coleman score of 37.2 points), comprising a total of 183 football players with a mean age of 25.7 years. A total of 217 articular cartilage and/or osteochondral lesions were reported, where the medial and lateral femoral condyles were the most common sites of lesion. The surgical procedures investigated were mosaicplasty, microfracture, autologous chondrocyte implantation, and chondral debridement. No definitive conclusion could be made in respect to the best current surgical technique for articular cartilage and osteochondral lesions. Microfracture and mosaicplasty can provide a faster return to competition and faster clinical and functional results, whereas autologous chondrocyte implantation and/or matrix-induced autologous chondrocytes implantation procedures can enhance longstanding clinical and functional results.

#3 Genetic biomarkers in non-contact muscle injuries in elite soccer players
Reference: Knee Surg Sports Traumatol Arthrosc. 2016 Apr 16. [Epub ahead of print]
Authors: Pruna R, Artells R, Lundblad M, Maffulli N
Summary: Damage to skeletal muscle necessitates regeneration to maintain proper muscle form and function. Interindividual differences in injury severity, recovery time, and injury rate could be explained by the presence of single nucleotide polymorphisms (SNPs) in genes involved in the reparation and regeneration of connective tissue . We wished to identify new genetic biomarkers that could help to prevent or minimize the risk of non-contact muscle injuries and are associated with a predisposition to developing muscle injuries. Using allelic discrimination techniques, we analysed 12 SNPs in selected genes from the genomic DNA of 74 elite soccer players. SNPs in the hepatocyte growth factor (HGF) gene showed evidence of a statistically significant association with injury incidence, severity, and recovery time. SNPs in the SOX15 gene showed evidence of a statistically significant association with injury incidence. SNPs in the GEFT and LIF genes showed evidence of a statistically significant association with recovery time. Genetic profile could explain why some elite soccer players are predisposed to suffer more injuries than others and why they need more time to recover from a particular injury. SNPs in HGF genes have an important role as biomarkers of biological processes fragility within muscle injuries related to injury rate, severity, and long recovery time.

#4 Risk Factors of Tendo-Achilles Injury in Football, Cricket and Badminton Players at Dhaka, Bangladesh.
Reference: Bangladesh Med Res Counc Bull. 2015 Apr;41(1):19-23.
Authors: Khan MJ, Giasuddin AS, Khalil MI.
Summary: Achilles tendon is the tendon connecting the heel with the calf muscles. Tendo-achilles injury (TAI) in players is common in games. The frequency of TAI is unknown and aetiology is controversial: The present descriptive cross-sectional study was done to determine the prevalence of TAI and associated factors contributing to it in football, cricket and badminton. From January to June 2012, male players (n = 131), age -17-35 years, were selected by purposive sampling technique from renowned sporting clubs at Dhaka, Bangladesh. TAI was diagnosed through structured questionnaire and interviewing the respondents. The analysis by Statistical Package for Social Sciences (SPSS) programme revealed that 11.5% players suffered from TAI, i.e. prevalence was 115 per 1000 respondents. Most injuries (70/131; 53.4%) occurred in the playground and (59/131; 45.3%) happened in practice field. Injuries among the players of third division were higher, i.e. about 36% (p = 0.000). TAI was significantly dependent on occupation (p = 0.046), BMI (p = 0.008), divisional status (p = 0.023), game type (p = 0.043), ground condition (p = 0.05) and injury severity (p = 0.000). The injured players referred for treatment to the physiotherapist was highest (9/15, i.e. 60%) followed by the physicians (5/15, i.e. 33%) (p = 0.000). The associations of TAI with various factors were discussed suggesting effective measures be taken and treatment, particularly physiotherapy, be given to injured players. However, there is a need of team work with sports medicine specialist also to enable the injured players to continue their professional games.

#5 MRI findings and return to play in football: a prospective analysis of 255 hamstring injuries in the UEFA Elite Club Injury Study.
Reference: Br J Sports Med. 2016 Apr 15. pii: bjsports-2016-095974. doi: 10.1136/bjsports-2016-095974. [Epub ahead of print]
Authors: Ekstrand J, Lee JC, Healy JC
Summary: The present study evaluated whether the MRI parameters of hamstring injuries in male professional football players correlate with time to return to play (RTP). 46 elite European football teams were followed prospectively for hamstring injuries between 2007 and 2014. Club medical staff recorded individual player exposure and time-loss after hamstring injury. MRI parameters were evaluated by two independent radiologists and correlated with the RTP data. A total of 255 grade 1 and 2 injuries were evaluated in this study. RTP was longer for grade 2 than grade 1 injuries (24±13, 95% CI 21 to 26 days vs 18±15, 95% CI 16 to 20 days; mean difference: 6, 95% CI 2 to 9 days, p=0.004, d=0.39). 84% of injuries affected the biceps femoris (BF) muscle, whereas 12% and 4% affected the semimembranosus (SM) and semitendinosus (ST), respectively. No difference in lay-off time was found for injuries to the three different muscles (BF 20±15 days, SM 18±11 days, ST 23±14 days; p=0.83). The recurrence rate was higher for BF injuries than for SM and ST injuries combined (18% vs 2%, p=0.009). The size of the oedema weakly correlated with time to RTP (r2=6-12%). No correlation was found between location of injury and time to RTP. The majority of the intramuscular injuries affected the MT junction (56% in grade 1 and 2 injuries), but no difference in lay-off time was found between the different types of injuries. The radiological grade and size of the oedema correlate with time to RTP for both, grade 1 and 2 injuries. No correlations were found between time to RTP and the location and type of injury

#6 Sequencing effects of balance and plyometric training on physical performance in youth soccer athletes
Reference: J Strength Cond Res. 2016 Mar 17. [Epub ahead of print]
Authors: Hammami R, Granacher U, Makhlouf I, Behm DG, Chaouachi A.
Summary: Balance training may have a preconditioning effect on subsequent power training with youth. There are no studies examining whether the sequencing of balance and plyometric training has additional training benefits. The objective was to examine the effect of sequencing balance and plyometric training on the performance of 12-13 years old athletes. Twenty-four young elite soccer players trained twice per week for eight weeks either with an initial four weeks of balance training followed by four weeks of plyometric training (BPT) or four weeks of plyometric training proceeded by four weeks of balance training (PBT). Testing was conducted pre- and post-training and included medicine ball throw, horizontal and vertical jumps, reactive strength, and leg stiffness, agility, 10, 20, 30-m sprints, Standing Stork balance test and Y-Balance Test. Results indicated that BPT provided significantly greater improvements with reactive strength index, absolute and relative leg stiffness, triple hop test (THT) and a trend for the Y balance test (p=0.054) compared to PBT. While all other measures had similar changes for both groups, the average relative improvement for the BPT was 22.4% (d= 1.5) versus 15.0% (d= 1.1) for the PBT. BPT effect sizes were greater with 8 of 13 measures. In conclusion, while either sequence of BPT or PBT improved jumping, hopping, sprint acceleration, and Standing Stork and Y balance; BPT initiated greater training improvements in reactive strength index, absolute and relative leg stiffness, THT and the Y balance test. BPT may provide either similar or superior performance enhancements compared to PBT.

#7 Match-to-match variability in high-speed running activity in a professional soccer team
Reference: J Sports Sci. 2016 May 4:1-9. [Epub ahead of print]
Authors: Carling C, Bradley P, McCall A, Dupont G
Summary: This study investigated variability in competitive high-speed running performance in an elite soccer team. A semi-automated tracking system quantified running performance in 12 players over a season (median 17 matches per player, 207 observations). Variability [coefficient of variation (CV)] was compared for total sprint distance (TSD, >25.2 km/h), high-speed running (HSR, 19.8-25.2 km/h), total high-speed running (THSR, ≥19.8 km/h); THSR when the team was in and out of ball possession, in individual ball possession, in the peak 5 min activity period; and distance run according to individual maximal aerobic speed (MAS). Variability for % declines in THSR and distance covered at ≥80% MAS across halves, at the end of play (final 15 min vs. mean for all 15 min periods) and transiently (5 min period following peak 5 min activity period), was analysed. Collectively, variability was higher for TSD versus HSR and THSR and lowest for distance run at ≥80% MAS (CVs: 37.1%, 18.1%, 19.8% and 11.8%). THSR CVs when the team was in/out of ball possession, in individual ball possession and during the peak 5 min period were 31.5%, 26.1%, 60.1% and 23.9%. Variability in THSR declines across halves, at the end of play and transiently, ranged from 37.1% to 142.6%, while lower CVs were observed in these metrics for running at ≥80% MAS (20.9-53.3%).These results cast doubt on the appropriateness of general measures of high-speed activity for determining variability in an elite soccer team, although individualisation of HSR thresholds according to fitness characteristics might provide more stable indicators of running performance and fatigue occurrence.

#8 Minimizing Head Acceleration in Soccer: A Review of the Literature.
Reference: Sports Med. 2016 May 3. [Epub ahead of print]
Authors: Caccese JB, Kaminski TW
Summary: Physicians and healthcare professionals are often asked for recommendations on how to keep athletes safe during contact sports such as soccer. With an increase in concussion awareness and concern about repetitive subconcussion, many parents and athletes are interested in mitigating head acceleration in soccer, so we conducted a literature review on factors that affect head acceleration in soccer. We searched electronic databases and reference lists to find studies using the keywords 'soccer' OR 'football' AND 'head acceleration'. Because of a lack of current research in soccer heading biomechanics, this review was limited to 18 original research studies. Low head-neck segment mass predisposes athletes to high head acceleration, but head-neck-torso alignment during heading and follow-through after contact can be used to decrease head acceleration. Additionally, improvements in symmetric neck flexor and extensor strength and neuromuscular neck stiffness can decrease head acceleration. Head-to-head impacts and unanticipated ball contacts result in the highest head acceleration. Ball contacts at high velocity may also be dangerous. The risk of concussive impacts may be lessened through the use of headgear, but headgear may also cause athletes to play more recklessly because they feel a sense of increased security. Young, but physically capable, athletes should be taught proper heading technique in a controlled setting, using a carefully planned progression of the skill.

#9 Maturational effect on Functional Movement Screen™ score in adolescent soccer players
Reference: J Sci Med Sport. 2015 Dec 12. pii: S1440-2440(15)00234-0. doi: 10.1016/j.jsams.2015.12.001. [Epub ahead of print]
Authors: Portas MD, Parkin G, Roberts J, Batterham AM
Summary: The effect of maturity on Functional Movement Screen (FMS) scores in elite, adolescent soccer players was examined. A cross-sectional observational study was completed. Participants were 1163 male English Football League soccer players (age 8-18 years). Players were mid-foundation phase (MF) (U9); late foundation phase (LF) (U10 and U11); early youth development phase (EYD) (U12 and U13); mid-youth development (MYD) phase (U14-U15); Late Youth Development Phase (LYD) (U16) and early professional development phase (EPD) (U18). Age from peak height velocity was estimated and players were categorized as pre- or post-peak height velocity (PHV). To analyse where differences in FMStotal score existed we separated the screen into FMSmove (3 movement tests); FMSflex (2 mobility tests) and FMSstab (2 stability tests). FMStotal median score ranged from 11 at MF to 14 for EPD. There was a substantial increase (10%) in those able to achieve a score of ≥14 on FMStotal in those who were post-PHV compared to pre-PHV. This was explained by a substantial increase in those achieving a score of ≥4 on FMSstab (21%). There was a substantial increase in the proportion of players who achieved the FMStotal threshold of ≥14 with an increase of 47.5 (41.4-53.6)% from the MF phase to the EPD phase due to improvements in FMSmove and FMSstab. PHV and maturity have substantial effects on FMS performance. FMS assessment appears to be invalid for very young players. Findings are relevant to those analyzing movement in soccer players.

#10 Effects of an in-season plyometric training program on repeated change of direction and sprint performance in the junior soccer player.
Reference: J Strength Cond Res. 2016 Apr 21. [Epub ahead of print]
Authors: Hammami M, Negra Y, Aouadi R, Shephard RJ, Chelly MS.
Summary: We aimed to determine the gains in explosive movements of male junior soccer players induced by incorporating an 8-week plyometric training program (PTP) into a standard soccer conditioning regimen 5 months after the beginning of the competitive season. Our hypothesis was that PTP would enhance explosive movements, and thus sprint running, repeated shuttle sprint ability (RSSA), agility and the ability to make repeated changes of direction (RCOD). A group of junior soccer players were randomly divided into two groups: an experimental group (E, n=15, age 15.7 ± 0.2 years) and a control group (C, n=13, age 15.8 ± 0.2 years). E and C performed training exercises and matches together, but for an 8-week period in the latter part of the season the experimental group replaced a part of the normal regimen (the tactical session) by a bi-weekly course of PTP (hurdle and drop jumps). Two familiarizations sessions were held 2 weeks before definitive testing. The ability of the players was assessed by 3 agility tests (a sprint test with 180° turns, a 9-3-6-3-9 m sprint with backward and forward running and a four 5 m sprint test with turns); two repeated sprint tests (RSSA and RCOD); and running times over 5m, 10m, 20m, 30 and 40m distances. E showed gains relative to C in sprint times (p≤0.05 for 5m, 10m and 20m), and 2 of 3 the RCOD parameters (RCOD best, p≤0.001; RCOD total, p≤0.05). However, with the pattern of plyometric training that we adopted, and perhaps because participants were in good initial physical condition, the agility and RSSA test scores remained unchanged. Nevertheless, we conclude that our PTP can be commended to junior soccer players as a means of improving important components of their physical performance.

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