Latest research in football - week 45 - 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 The Within-Subject Correlation Between Salivary IgA and Measures of Training Load in Elite Football Players
Reference: Int J Sports Physiol Perform. 2018 Nov 14:1-11. doi: 10.1123/ijspp.2018-0455. [Epub ahead of print]
Authors: Figueiredo P, Nassis GP, Brito J
Summary: The purpose was to quantify the association between salivary secretory immunoglobulin A (sIgA) and training load in elite football players. Data were obtained in four consecutive days during the preparation camp for the Rio 2016 Olympic Games. Saliva samples of 18 elite male football players were collected prior to breakfast. The session rating of perceived exertion (s-RPE) and external training load metrics from GPS were recorded. Within-subject correlation coefficients between training load and sIgA concentration, and magnitude of relationships were calculated. sIgA presented moderate to large negative correlations with s-RPE (r=-0.39), total distance covered (r=-0.55), accelerations (r=-0.52) and decelerations (r=-0.48). Trivial to small associations were detected between sIgA and distance covered per minute (r=0.01), high-speed distance (r=-0.23) and number of sprints (r=-0.18). sIgA displayed a likely moderate decrease from day 1 to day 2 (d=-0.7) but increased on day 3 (d=0.6). The training load variables had moderate to very large rises from day 1 to day 2 (d=0.7 to 3.2), but lowered from day 2 to day 3 (d=-5.0 to -0.4), except for distance per minute (d=0.8) and sprints (unclear). On day 3, all training load variables had small to large increments compared with day 1 (d=0.4 to1.5), with exception of accelerations (d=-0.8) and decelerations (unclear). In elite football sIgA might be more responsive to training volume rather than intensity. External load such as GPS-derived variables presented stronger association with sIgA compared with s-RPE. Salivary IgA can be used as an additional objective tool in monitoring football players.

#2 The Influence of Hamstring Muscle Peak Torque and Rate Of Torque Development for Sprinting Performance in Football Players: A Cross-Sectional Study
Reference: Int J Sports Physiol Perform. 2018 Nov 14:1-27. doi: 10.1123/ijspp.2018-0464. [Epub ahead of print]
Authors: Ishøi L, Aagaard P, Nielsen MF, Thornton KB, Krommes KK, Hölmich P, Thorborg K
Summary: This cross-sectional study aimed to investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development: RTD) versus sprint performance in elite youth football players. Thirty elite academy youth football players (16.75 ± 1.1 years, 176.9 ± 6.7 cm, 67.1 ± 6.9 kg) were included. Isometric peak torque (Nm/kg) and early (0-100 ms) and late (0-200 ms) phase RTD (RTD100, RTD200) (Nm/s/kg) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m sprint trial. Mechanical sprint variables (maximal horizontal force production (FH0) (N/kg); maximal theoretical velocity (V0) (m/s); maximal horizontal power output (Pmax) (W/kg)) and sprint split times (0-5 m; 0-15 m; 0-30 m; 15-30 m) (s) were derived as dependent variables. Subsequently, linear regression analysis was conducted for each pair of dependent and independent variables. Positive associations were observed between hamstring RTD100 and FH0 (r2=0.241, p=0.006) and Pmax (r2=0.227, p=0.008). Furthermore, negative associations were observed between hamstring RTD100 and 0-5 m (r2=0.206, p=0.012), 0-15 m (r2=0.217, p=0.009) and 0-30 m sprint time (r2=0.169, p=0.024). No other associations were observed. The present data indicate that early-phase (0-100 ms) rapid force capacity of the hamstring muscles plays an important role for the acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity. This indicates that strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.

#3 Circulation, Cell-free DNA for Monitoring Player Load in Professional Football
Reference: Int J Sports Physiol Perform. 2018 Nov 14:1-27. doi: 10.1123/ijspp.2018-0756. [Epub ahead of print]
Authors: Haller N, Ehlert T, Schmidt S, Ochmann D, Sterzing B, Grus F, Simon P
Authors: Player monitoring in elite sports settings is becoming increasingly important. Beside questionnaire based methods, biomarkers, such as circulating, cell-free DNA (cfDNA) are sug-gested for load monitoring. cfDNA concentrations were shown to increase dependent on total distance covered in football and was associated with overtraining in weightlifters. Thus, the objective of this study was to examine whether cfDNA is feasible as a monitoring tool in elite football players. We collected capillary blood samples from 22 male elite football players over 4 months of a regular season. Sampling was conducted the day before, one day after or several days after regular season games and/or training. In addition, each player filled in a Visual-Analogue-Scale questionnaire (VAS) including the items "general perceived exer-tion", "muscular fatigue" and "mental fatigue". Performance during training and games was tracked by the Catapult system (training) and with the OPTA system (games), respectively. cfDNA values were significantly elevated in players the day after regular season games (1.4-fold; p=0.0004) in line with the scores of the VAS. Both parameters showed sig-nificantly higher values during midweek game weeks. While cfDNA concentrations correlated with training data, the VAS was correlated with the tracking of the season games. However, cfDNA and VAS did not correlate with each other. Here we show that cfDNA concentrations at rest and VAS scores are influenced by previous load in professional football players. Future studies will reveal whether cfDNA might serve as a practically applicable marker for player load in football players.

#4 Towards the use of multidimensional performance indicators in football small-sided games: the effects of pitch orientation
Reference: J Sports Sci. 2018 Nov 14:1-8. doi: 10.1080/02640414.2018.1543834. [Epub ahead of print]
Authors: Folgado H, Bravo J, Pereira P, Sampaio J
Summary: This study aimed to compare youth football players' performance during two small-sided games with different pitch orientation: i) 40x30m and ii) 30x40m formats. Twenty under-15 players (age = 14.1 ± 0.5 years) participated in nine GK+4vs4+GK situations in each format, with the duration of six minutes each. Positional data were collected using individual GPS units, and computed for tactical and physical performance indicators. The SSG were video recorded, using notational analysis for collecting technical indicators. A novel method that incorporates time dependent notational information with spatiotemporal data was used to compute multidimensional parameters. Standardised effect sizes and non-clinical magnitude-based inferences were used to compare formats. Results showed that players covered more distance at higher intensities, presented more passes and dribbles and were more synchronised in the longitudinal axis while playing in the 40x30m pitch. In the 30x40m pitch, results showed a lower distance between team centroids, higher number of shots, more lateral passes and a wider team positioning. Multidimensional indicators, as players position and distance to the closest defender while shooting, revealed a more constant distance between attacker and defender in the 40x30m pitch. These results highlight the importance of integrating information from different indicators for a contextually valid information.

#5 Analysis of the PPARD Gene Expression Level Changes in Football Players in Response to the Training Cycle
Reference: Balkan J Med Genet. 2018 Oct 29;21(1):19-25. doi: 10.2478/bjmg-2018-0008. eCollection 2018 Jun.
Authors: Domańska-Senderowska D, Snochowska A, Szmigielska P, Jastrzębski Z, Jegier A, Kiszałkiewicz J, Dróbka K, Jastrzębska J, Pastuszak-Lewandoska D, Cięszczyk P, Maciejewska-Skrendo A, Zmijewski P, Brzeziańska-Lasota E
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Summary: The PPARD gene codes protein that belongs to the peroxisome proliferator-activated receptor (PPAR) family engaged in a variety of biological processes, including lipid metabolism in muscle cells. In this study, we assess the relationship between PPARD gene expression lipid metabolism parameters and the variation of the PPARD gene expression before (T1) and after 12 hours of training (T2) sessions in a group of football players. Peripheral blood lymphocytes were obtained from 22 football players (17.5±0.7 years, 178±0.7 cm, 68.05±9.18 kg). The PPARD gene expression, analyzed by quantitative polymerase chain reaction (qPCR), was significantly higher after T2 (p = 0.0006). Moreover, at the end of the training cycle, there was a significant decrease in relative fat tissue (FAT) (%) (p = 0.01) and absolute FAT (kg) (p = 0.01). A negative correlation was observed between absolute FAT (kg) and PPARD gene expression level in T2 (p = 0.03). The levels of cholesterol and triglyceride (TG) fractions were not significantly different (p >0.05) before and after training. No significant relationship between PPARD expression and cholesterol or TG levels was found. We found that physical training affects PPARD expression. Moreover, the negative correlation between PPARD expression and absolute FAT (kg) level may be indicative of the contribution of PPARD in metabolic adaptation to increased lipid uptake that can be used to control the body composition of athletes.

#5 Tattoos among elite football players during the 2018 FIFA World Cup Russia
Reference: J Eur Acad Dermatol Venereol. 2018 Nov 13. doi: 10.1111/jdv.15338. [Epub ahead of print]
Authors: Kluger N, Samimi M
Download link: J Eur Acad Dermatol Venereol. 2018 Nov 13. doi: 10.1111/jdv.15338. [Epub ahead of print]
Summary: Currently 10 to 30% of the general population has tattoos. Professional athletes harbor visible tattoos during sports events and advertisement. Motivations for tattoos may include body embellishment, expression of personal values or group affiliation. Tattoos may bolster ego, be the expression of physical strength and of traits of aggression and rebelliousness. We wondered whether being tattooed reflects players' performance and discipline. We investigated this hypothesis among elite football players during the 2018 FIFA World Cup.

#6 High incidence of hip and knee arthroplasty in former professional, male football players
Reference: J Sports Med Phys Fitness. 2018 Nov 8. doi: 10.23736/S0022-4707.18.08962-4. [Epub ahead of print]
Authors: Volpi P, Quaglia A, Carimati G, Petrillo S, Bisciotti GN
Summary: The purpose of this study was to estimate the incidence of hip and knee arthroplasty in Italian male professional football (soccer) players who have played for a minimum 10 years in the Italian major football leagues. The study group was formed by 104 male professional football players who were interviewed to evaluate the incidence of hip and knee arthroplasty. The data were collected through a questionnaire and the results collected were compared with a control group of 100 volunteers matched for age, weight and height, who did not present orthopaedic diseases but had never practiced sport. In the study group, 26 subjects (25 %) underwent hip and knee arthroplasty at an average mean age of 62.1 + 6 years. The frequency of arthroplasty was: 13.5% for the hip, 5.8% for the knee and 5.8% for both hip and knee. In the control group, the incidence of arthroplasty was 1% for the knee and no subjects presented hip arthroplasty. Italian male, former professional football players present a higher than normal incidence of hip and knee arthroplasty. Further studies are necessary to understand the pathological pathways underlying the ethiology of hip and knee osteoarthritis in male populations of former professional football players in order to develop effective preventive programmes to reduce the percentage of arthroplasties.

#7 Stepovers and Signal Detection: Response Sensitivity and Bias in the Differentiation of Genuine and Deceptive Football Actions
Reference: Front Psychol. 2018 Oct 29;9:2043. doi: 10.3389/fpsyg.2018.02043. eCollection 2018.
Authors: Jackson RC, Barton H, Ashford KJ, Abernethy B
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Summary: The ability to differentiate genuine and deceptive actions was examined using a combination of spatial and temporal occlusion to examine sensitivity to lower body, upper body, and full body sources of visual information. High-skilled and low-skilled association football players judged whether a player genuinely intended to take the ball to the participant's left or right or intended to step over the ball then take it in the other direction. Signal detection analysis was used to calculate measures of sensitivity (d') in differentiating genuine and deceptive actions and bias (c) toward judging an action to be genuine or deceptive. Analysis revealed that high-skilled players had higher sensitivity than low-skilled players and this was consistent across all spatial occlusion conditions. Low-skilled players were more biased toward judging actions to be genuine. Receiver Operating Characteristic (ROC) curves revealed that accuracy on deceptive trials in the lower body and full body conditions most accurately classified participants as high-skilled or low-skilled. The results highlight the value of using signal detection analysis in studies of deceptive actions. They suggest that information from the lower body or upper body was sufficient for differentiating genuine and deceptive actions and that global information concurrently derived from these sources was not necessary to support the expert advantage.

#8 Effectiveness of Field-Based Resistance Training Protocols on Hip Muscle Strength Among Young Elite Football Players
Reference: Clin J Sport Med. 2018 Oct 29. doi: 10.1097/JSM.0000000000000649. [Epub ahead of print]
Authors: Kohavi B, Beato M, Laver L, Freitas TT, Chung LH, Dello Iacono A
Summary: The objective of this study was to examine the effects of an 8-week progressive resistance training program on hip joint muscles' strength measures, using the Copenhagen adduction (CA) and the sliding hip (SH) exercises. Forty-two young male football athletes (age 17.5 ± 1.1 years; height 178.3 ± 3.2 cm; body mass 66.1 ± 8.6 kg) allocated to a CA, SH, and matched control (C) group participated in this study. Maximal eccentric strength test for the hip adductor (EHAD) and maximal eccentric strength test for the hip abductor (EHAB) muscles, and the relative EHAD/EHAB ratio assessed through a break test in the side-lying position. No significant differences between groups were found at baseline for any of the assessed variables (all P > 0.053). The CA group had a significant strength increase in the right and left leg (d = 2.11, d = 1.9, respectively). The SH group also had a significant strength increase in the right and left leg (d = 1.68 and d = 1.67, respectively). The CA group presented EHAD/EHAB improvements in the right and left leg (d = 0.84 and d = 1.14, respectively). The SH group also presented EHAD/EHAB improvements in the right and left leg (d = 1.34 and d = 1.44, respectively). Both exercises' protocols were effective in inducing significant increases on EHAD, EHAB, and EHAD/EHAB ratio when compared with the control group. Practitioners should be aware of the training effectiveness of both protocols.

#9 Recommendations for hamstring injury prevention in elite football: translating research into practice
Reference: Br J Sports Med. 2018 Nov 9. pii: bjsports-2018-099616. doi: 10.1136/bjsports-2018-099616. [Epub ahead of print]
Authors: Buckthorpe M, Wright S, Bruce-Low S, Nanni G, Sturdy T, Gross AS, Bowen L, Styles B, Della Villa S, Davison M, Gimpel M
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