Latest research in football - week 33 - 2018

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 Speed synchronization, physical workload and match-to-match performance variation of elite football players
Reference: PLoS One. 2018 Jul 24;13(7):e0200019. doi: 10.1371/journal.pone.0200019. eCollection 2018.
Authors: Gonçalves B, Coutinho D, Travassos B, Folgado H, Caixinha P, Sampaio J
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Summary: This study aimed to: (i) examine whether the speed synchronization and physical performance of an elite football team changed between the first and the second half, using match time blocks of 15-min, and (ii) explore the match-to-match variation of players' speed synchronization performance. Twenty-eight outfield elite footballers participated in 51 official matches. Positional data were gathered and used to calculate the total distance covered as a physical workload indicator. For all the outfield teammate dyad combinations (45 pairs), it was processed the percentage of time that players' speed was synchronized during walking, jogging and running using relative phase (Hilbert Transform). Also, the match-to-match variation of the players' speed synchronization, expressed in coefficient of variation was computed. The differences in the total distance covered from all players within the different match's time block periods revealed a moderate decrease in the distance covered in the last 15-min of the match compared to the first 15-min (-6.5; ±1.07%, most likely: change in means with 95% confidence limits). However, when compared the last minutes from both halves a small increase was observed (2.7; ±1.2%, likely) from first to second half. The synchronization of the players' speed displacements revealed small to moderate decreases in the % of synchronization in the second half periods for the jogging and running speed, while the opposite was found for the walking speed (~13 to 24% more, most likely). The playing position analysis for the walking zone showed similar trends between the groups, with small to moderate higher values in the second half, with the exception of [30'-45'] vs [75'-90'] in the midfielder's dyads and in [15'-30'] vs [60'-75'] match periods for forwards. Similar trend was found during the running speed, in which small to moderate higher synchronization was found during the first half periods, with the exception of [15'-30'] vs [60'-75'] and [30'-45'] vs [75'-90'] in midfielder's dyads. Regarding to the match-to-match variation of the players' speed synchronization, overall results showed small to moderate increases in coefficient of variation during jogging and running displacements from the beginning to the end of the match (32.1; ±13.2% increase in jogging and 26.2; ±10.5% in running, both comparisons most likely). The higher distance covered during most of the first half periods and the higher dyadic synchronization at high speeds might have limited players' performance in the second half. In addition, the decrease trend in speed synchronization during the second half periods might have resulted from accumulated muscular and mental fatigue towards the match. Within, the match-to-match variation in tactical-related variables increased across the match duration, with especial focus in the midfielder dyads. Dyadic speed synchronization might provide relevant information concerning the individual and collective performance.

#2 Kinematic and kinetic analysis of the goalkeeper's diving save in football
Reference: J Sports Sci. 2018 Jul 23:1-9. doi: 10.1080/02640414.2018.1499413. [Epub ahead of print]
Authors: Ibrahim R, Kingma I, de Boode VA, Faber GS, van Dieën JH
Summary: Kinetics and full body kinematics were measured in ten elite goalkeepers diving to save high and low balls at both sides of the goal, aiming to investigate their starting position, linear and angular momentum, and legs' contribution to end-performance. Our results showed that goalkeepers adopted a starting position with a stance width of 33 ± 1% of leg length, knee flexion angle of 62 ± 18° and hip flexion angle of 63 ± 18°. The contralateral leg contributed more than the ipsilateral leg to COM velocity (p < 0.01), both for the horizontal (2.7 ± 0.1 m·s-1 versus 1.2 ± 0.1 m·s-1) and for the vertical component (3.1 ± 0.3 m·s-1 versus 0.4 ± 0.2 m·s-1). Peak horizontal and peak angular momenta were significantly larger (p < 0.01) for low dives than for high dives with a mean difference of 55 kg·m·s-1 and 9 kg·m2·s-1, respectively. In addition, peak vertical momentum was significantly larger (p < 0.01) for high dives with a mean difference between dive heights of 113 kg·m·s-1. Coaches need to highlight horizontal lateral skills and exercises (e.g. sideward push-off, sideward jumps), with emphasis on pushing-off with the contralateral leg, when training and assessing goalkeeper's physical performance.

#3 High knee loading in male adolescent pre-professional football players: Effects of a targeted training programme
Reference: J Sci Med Sport. 2018 Jul 5. pii: S1440-2440(18)30320-7. doi: 10.1016/j.jsams.2018.06.016. [Epub ahead of print]
Authors: Lagas IF, Meuffels DE, Visser E, Groot FP, Reijman M, Verhaar JAN, de Vos RJ
Summary: The objective was to assess whether targeted neuromuscular exercises can decrease knee loading of adolescent pre-professional footballers with high knee loading as identified with the field-based Drop Vertical Jump Test (DVJT). We undertook a prospective controlled trial, conducted between August and November 2016 at Erasmus Medical Centre, The Netherlands. Pre-professional football players (aged 14-21years) were evaluated at baseline and after 12weeks follow-up with the field-based DVJT. The field-based DVJT is a standardised test in which a player drops from a box and jumps up immediately after landing; knee load is calculated based on five parameters. Players with high knee load (probability≥0.75) from one club performed regular training(control group), and players with high knee load from another other club performed targeted neuromuscular exercises for 12weeks (intervention group). The difference of change in knee load between both groups after 12weeks was the primary outcome measure. Of 107 eligible players, 75 had a high knee loading. Knee loading decreased in both groups after 12weeks of training, but change in probability of high knee load was not significantly different between both groups (95% Confidence Interval [-0.012-0.082], p=0.139). Targeted neuromuscular exercises had no additional effect in decreasing knee loading of adolescent male pre-professional football players compared to regular training.

#4 Implicit learning increases shot accuracy of football players when making strategic decisions during penalty kicking
Reference: Hum Mov Sci. 2018 Jul 18;61:72-80. doi: 10.1016/j.humov.2018.07.004. [Epub ahead of print]
Authors: Navarro M, van der Kamp J, Schor P, Savelsbergh GJP
Summary: Implicit learning has been proposed to improve athletes' performance in dual-task situations. Yet, only a few studies tested this with a sports-relevant dual-task. Hence, the current study aimed to compare the effects of implicit and explicit training methods on penalty kicking performance. Twenty skilled football players were divided in two training groups and took part in a practice phase to improve kicking accuracy (i.e., without a goalkeeper) and in a post-test in order to check penalty kick performance (i.e., accuracy including a decision to kick to the side opposite the goalkeeper's dive). Results found that the implicit and explicit training method resulted in similar levels of decision-making, but after implicit training this was achieved with higher kicking accuracy. Additionally, applications for football players and coaches are discussed.

#5 Osteogenic impact of football training in 55- to 70-year-old women and men with prediabetes
Reference: Scand J Med Sci Sports. 2018 Jul 26. doi: 10.1111/sms.13252. [Epub ahead of print]
Authors: Skoradal MB, Helge EW, Jørgensen NR, Mortensen J, Weihe P, Krustrup P, Mohr M
Summary: The effects of football training on bone health were examined in 55- to 70-year-old sedentary women and men with prediabetes. Patients (n = 50) with prediabetes (age; 61 ± 9 years, BMI 29.7 ± 0.6 kg/m2 , body fat content; 37 ± 1%, VO2max ; 22.7 ± 0.8 mL/min/kg and mean arterial pressure; 104 ± 3 mm Hg) were randomized into a football training group (FTG; n = 27, 14 women) and a control group (CON; n = 23, 11 women). At baseline, 73% and 24% were diagnosed with femur osteopenia and osteoporosis, respectively. FTG performed football training twice weekly 30-60-minute sessions in 16 weeks, and both FTG and CON received professional dietary advice. Pre- and post-intervention whole-body and regional bone mineral content (BMC) and density (BMD) were determined with DXA-scans, and venous blood samples were drawn and analyzed for plasma bone turnover markers. Change scores were greater (P < 0.05) in FTG compared to CON in leg BMD (0.023 ± 0.005 vs -0.004 ± 0.001 g/cm2 ) and in leg BMC (32 ± 8 vs -4 ± 6 g). Between-group changes in favor of FTG (P < 0.05) also occurred in the femur neck BMD (3.2%) and femur shaft BMD (2.5%). Whole-body BMC and BMD were unchanged in both groups during the intervention. In FTG, resting plasma osteocalcin, P1NP, and CTX-1 rose (P < 0.05) by 23 ± 8, 52 ± 9 and 38 ± 7%, with greater change scores (P < 0.05) than in CON. Finally, P1NP (formation)/CTX-1 (resorption) ratio increased (P < 0.05) in FTG (127 ± 15 vs 150 ± 11) from pre- to post-intervention, with no change in CON (124 ± 12 and 123 ± 12). In conclusion, football training provides a powerful osteogenic stimulus and improves bone health in 55- to 70-year-old women and men diagnosed with prediabetes.

#6 Comparison of the lumbopelvic rhythm among adolescent soccer players with and without low back pain
Reference: Int J Sports Phys Ther. 2018 Apr;13(2):171-176.
Authors: Tojima M, Torii S
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Summary: Hip-spine incoordination can cause low back pain (LBP) in adolescents. Hip-spine coordination, including the lumbopelvic rhythm (LPR) and the lumbar-hip ratio (LHR), can be used to assess lower limb and spine function. However, there are no reports of the values of LPR or LHR in adolescent soccer players with and without LBP. The purpose of this study was to clarify the effect of LBP on LPR and LHR during trunk extension among adolescent soccer players. One hundred and nine adolescent soccer players were recruited and divided into two groups, one with and one without LBP. Using three-dimensional motion analysis, participants range of motion (ROM) of the lumbar spine (LS) and hip during trunk and hip extension was measured to calculate the LPR and LHR. Paired, two-tailed t-tests were used to compare the LS and hip ROM between the non-LBP and LBP groups, two-way repeated measures analysis of variance was used to compare time with the non-LBP and LBP groups for LHR, and linear prediction was used to describe the LPR. The maximum LS ROM in the LBP group was significantly less than that in the non-LBP group by 6.6 ° (p = .005). There was no difference in the maximum hip ROM between the groups (p = .376). The LHR did not change during trunk extension (F [4, 428] = 1.840, p = .120), the mean LHR was 4.6 in the non-LBP group and 3.7 in the LBP group, and there was no difference between the groups (p = .320). The linear function of the LPR indicated, that when the hip joint was extended by 1 °, the LS extended by 3.2 ° in the non-LBP group (R2 = .997, p < .001) and 2.8 ° in the LBP group (R2 = .999, p < .001). LBP inhibited lumbar motion relative to hip extension as LPR was smaller in the LBP group than in the non-LBP group. However, there was no difference between the groups in LHR because inter-individual variability affected the LHR.

#7 Foot and Soccer Referees': A Pilot Study Searching "Performance" Throughout Prevention
Reference: Front Physiol. 2018 Jul 25;9:1009. doi: 10.3389/fphys.2018.01009. eCollection 2018.
Authors: Gianturco L, Bodini BD, Gianturco V, Pregliasco FE, Cascio M, Serafin A, Turiel M
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Summary: Soccer refereeing is a "not-conventional" sport in which aerobic workload is prevalent. Along the years, several studies have attempted to define best markers of referees' performance. Many studies focused their attention on field tests and their relationship with aerobic power. Instead, in this study, starting by a medical assessment satisfying the FIFA 11+ criteria for injuries prevention, we have investigated the foot of soccer referees and we have also wanted to find possible and/or unexpected improvements in performance. As performance marker, we have used the referral field test for soccer referees that is internationally validated and known as Yo-Yo test (YYiR1). While standardized foot posture index (FPI) questionnaire was used for screening foot referees conditions (40 young, all men by sex, with mean age 23.47 ± 4.36). Analyzing collected data, we have demonstrated by means of Read-Cressie Chi square test that neutral FPI is an important favor item affecting YYiR1 results. Further studies will be necessary in order to confirm our pilot investigation.

#8 Outcomes of Cardiac Screening in Adolescent Soccer Players
Reference: N Engl J Med. 2018 Aug 9;379(6):524-534. doi: 10.1056/NEJMoa1714719.
Authors: Malhotra A, Dhutia H, Finocchiaro G, Gati S, Beasley I, Clift P, Cowie C, Kenny A, Mayet J, Oxborough D, Patel K, Pieles G, Rakhit D, Ramsdale D, Shapiro L, Somauroo J, Stuart G, Varnava A, Walsh J, Yousef Z, Tome M, Papadakis M, Sharma S
Summary: Reports on the incidence and causes of sudden cardiac death among young athletes have relied largely on estimated rates of participation and varied methods of reporting. We sought to investigate the incidence and causes of sudden cardiac death among adolescent soccer players in the United Kingdom. From 1996 through 2016, we screened 11,168 adolescent athletes with a mean (±SD) age of 16.4±1.2 years (95% of whom were male) in the English Football Association (FA) cardiac screening program, which consisted of a health questionnaire, physical examination, electrocardiography, and echocardiography. The FA registry was interrogated to identify sudden cardiac deaths, which were confirmed with autopsy reports. During screening, 42 athletes (0.38%) were found to have cardiac disorders that are associated with sudden cardiac death. A further 225 athletes (2%) with congenital or valvular abnormalities were identified. After screening, there were 23 deaths from any cause, of which 8 (35%) were sudden deaths attributed to cardiac disease. Cardiomyopathy accounted for 7 of 8 sudden cardiac deaths (88%). Six athletes (75%) with sudden cardiac death had had normal cardiac screening results. The mean time between screening and sudden cardiac death was 6.8 years. On the basis of a total of 118,351 person-years, the incidence of sudden cardiac death among previously screened adolescent soccer players was 1 per 14,794 person-years (6.8 per 100,000 athletes). Diseases that are associated with sudden cardiac death were identified in 0.38% of adolescent soccer players in a cohort that underwent cardiovascular screening. The incidence of sudden cardiac death was 1 per 14,794 person-years, or 6.8 per 100,000 athletes; most of these deaths were due to cardiomyopathies that had not been detected on screening. (Funded by the English Football Association and others.).

#9 Nesfatin-1 and irisin levels in response to the soccer matches performed in morning, afternoon and at night in young trained male subjects
Reference: Cell Mol Biol (Noisy-le-grand). 2018 Jul 30;64(10):130-133.
Authors: Ozcelik O, Algul S, Yilmaz B
Summary: This study aimed to investigate the potential effects of acute soccer matches performed in morning, afternoon and at night on both nesfatin-1 and irisin levels in trained subjects. Total of 20 male subjects performed in soccer matches at three different times of day: morning, afternoon, and night. Pre- and post-match venous blood samples were taken, and levels of both nesfatin-1 and irisin were analysed using the enzyme-linked immunosorbent assay (ELISA). Following all matches, the subjects' irisin levels increased significantly in all subjects (p &lt; 0.0001). Nesfatin-1 levels were also increased after the matches; however, the increase was statistically significant for morning (P=0.01) and night-time (p=0.009). The subjects' nesfatin-1 levels did not increase in all subjects and decrease of nesfatin-1 levels observed in some subjects after matches. This study finds that soccer matches performed different workout times have strong stimulatory effects on irisin levels in all subjects but nesfatin-1 response varied among the subjects and it did not change significantly in afternoon match.

#10 Are soccer matches dangerous for patients with heart disease? The HeartAtaque trial - a prospective pilot study
Reference: Rev Port Cardiol. 2018 Aug;37(8):645-653. doi: 10.1016/j.repc.2017.09.024. Epub 2018 May 22.
Authors: Martins JL, Adrega T, Santos L, Afreixo V, Viana J, Santos J
Summary: Behavioral and emotional factors are triggers of cardiovascular events (CVEs). It is uncertain whether soccer fans, particularly individuals with coronary artery disease (CAD), are at increased risk for CVEs. The purpose was to assess the effect of watching soccer matches in patients with known CAD on the incidence of CVEs according to the match result. We prospectively assessed 82 male soccer fans with a history of acute coronary syndrome during 23 matches of the 2015/2016 season. Each individual was assessed by Holter monitoring on the day of their team's match and on the control day. The primary endpoint was the composite of death, stroke, reinfarction, angina or sustained arrhythmia. Secondary endpoints assessed were episodes of non-sustained supraventricular or ventricular arrhythmia and mean heart rate (HR). Participants' mean age was 61±10 years. Compared with the control day, despite a significant increase in HR (p<0.001) that was independent of the result (p>0.97), the number of CVEs did not differ according to the result (p>0.05). Moreover, the number of non-sustained episodes of supraventricular and ventricular arrhythmia did not differ when stratified according to the match result (p>0.05). The match result was not associated with a difference in incidence of CVEs in patients with a past history of CAD, with ischemic and arrhythmic substrate, who watched soccer matches on television.

#11 Longevity and cardiovascular mortality of Polish elite football players
Reference: Kardiol Pol. 2018 Aug 9. doi: 10.5603/KP.a2018.0173. [Epub ahead of print]
Authors: Gajda J, Śmigielski W, Śmigielski J, Pakos E, Drygas W
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Summary: Despite the wide popularity of football, there is a paucity of scientific evidence explaining the relationship between being a competitive footballer and life expectancy AIM: The study analyses and compares cause-specific mortality between Polish elite footballers (men) and the general male population. A retrospective method of analysis is employed to study a sample of 455 elite footballers who died between 1990 and 2015. The cause of death was established based on the official statistics of Polish Central Statistical Office. The comparative sample consists of men in the general male population in Poland who died in the sampled period being at least 25 years of age at the time of death. The mean age at death turned out to be higher for footballers than controls (70.2 vs 67.4 years). Cardiovascular diseases were a more common cause of death among footballers than in the general male population in both the under 65-group and the above- 65-group (46.9% to 32.3% and 61.3% to 53.3%, respectively). A closer analysis of cause-specific cardiovascular mortality revealed that acute myocardial infarction caused more deaths (OR=1.31; CI 95%: [1.02-1.68]) and hypertensive disease less deaths (OR=0.20; CI 95%: [0.05-0.79]) among athletes than in the general male population. The study results point to excess cardiovascular mortality among Polish elite footballers. A trend analysis has shown, however, that its level is falling.

#12 The Use of Microtechnology to Quantify the Peak Match Demands of the Football Codes: A Systematic Review
Reference: Sports Med. 2018 Aug 7. doi: 10.1007/s40279-018-0965-6. [Epub ahead of print]
Authors: Whitehead S, Till K, Weaving D, Jones B
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Summary: Quantifying the peak match demands within the football codes is useful for the appropriate prescription of external training load. Wearable microtechnology devices can be used to identify the peak match demands, although various methodologies exist at present. This systematic review aimed to identify the methodologies and microtechnology-derived variables used to determine the peak match demands, and to summarise current data on the peak match demands in the football codes. A systematic search of electronic databases was performed from earliest record to May 2018; keywords relating to microtechnology, peak match demands and football codes were used. Twenty-seven studies met the eligibility criteria. Six football codes were reported: rugby league (n = 7), rugby union (n = 5), rugby sevens (n = 4), soccer (n = 6), Australian Football (n = 2) and Gaelic Football (n = 3). Three methodologies were identified: moving averages, segmental and 'ball in play'. The moving averages is the most commonly used (63%) and superior method, identifying higher peak demands than other methods. The most commonly used variables were relative distance covered (63%) and external load in specified speed zones (57%). This systematic review has identified moving averages to be the most appropriate method for identifying the peak match demands in the football codes. Practitioners and researchers should choose the most relevant duration-specific period and microtechnology-derived variable for their specific needs. The code specific peak match demands revealed can be used for the prescription of conditioning drills and training intensity.

#13 Different neuromuscular parameters influence dynamic balance in male and female football players
Reference: Knee Surg Sports Traumatol Arthrosc. 2018 Aug 7. doi: 10.1007/s00167-018-5088-y. [Epub ahead of print]
Authors: López-Valenciano A, Ayala F, De Ste Croix M, Barbado D, Vera-Garcia FJ
Summary: The purpose of the study was to analyse the relationship between several parameters of neuromuscular performance with unilateral dynamic balance measured through the Y-Balance test, as well as to determine the possible sex-related differences. The Y-Balance test, isokinetic (concentric and eccentric) knee flexion and extension strength, isometric hip abduction and adduction strength, lower extremity joint range of motion (ROM) (hip, knee and ankle) and core stability were assessed in male (n = 88) and female (n = 44) professional football players. A stepwise multivariate linear least square regression with backward elimination analysis was carried out to identify a group of factors that were independently associated with balance performance in both sexes. Passive hip flexion and ankle dorsiflexion with knee flexed ROM were the main factors that retained a significant association to dominant (R2 = 23.1) and non-dominant (R2  = 33.5) balance scores for males. For females, core stability, hip abduction isometric peak torque, passive hip abduction and ankle dorsiflexion with knee flexed ROM variables retained a significant association with balance scores for both, dominant (R2 = 38.2) and non-dominant (R2 = 46.9) legs. Training interventions aimed at improving or maintaining unilateral dynamic balance in male football players should include, among other things, stretching exercises for the posterior chain of the lower extremity. However, females should also include exercises for strength and mobility of the hip abductors and core stability (especially in the frontal plane). This knowledge would allow clinicians and sport practitioners to develop more effective and tailored unilateral dynamic balance training interventions in male and female football players, possibly improving performance and reducing the risk of injury.

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