Latest research in football - week 50 - 2019

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 Analysis of Physical Demands during Youth Soccer Match-play: Considerations of Sampling Method and Epoch Length
Reference: Res Q Exerc Sport. 2019 Nov 27:1-9. doi: 10.1080/02701367.2019.1669766. [Epub ahead of print]
Authors: Doncaster G, Page R, White P, Svenson R, Twist C
Summary: The purpose of this study was to examine the physical match profiles of professional soccer players using 3 and 5 min fixed and rolling averages as well as fixed 1 min averages, with considerations to training prescription. Twenty-nine professional U23 soccer outfield players competed across 17 competitive matches during the 2017/18 season, equating to a total of 130 separate physical match profiles. Match activities were recorded using global positioning system (GPS) devices with integrated micro-electrical mechanical systems (MEMS), recording total distance (TD), high-speed running (HSR), and metabolic power (MP). For each individual match profile and variable, 1, 3, and 5 min peak, post-peak, and average values were calculated using fixed-time epochs (FIXED) and rolling averages (ROLL). Linear mixed models were employed to examine the differences in the dependent variables as a function of the method of measurement. Results revealed significantly higher peak values, for relative TD, relative HSR and relative MP when employing the ROLL sampling method, in comparison to the FIXED method, for both 3 min and 5 min epoch lengths. Analysis of epoch length revealed significantly higher peak values, across all positions, for relative TD, relative HSR and MP for 1 min epochs, in comparison to 3 min and 5 min epochs. The data offers a novel insight into the appropriate identification of physical demands during youth soccer match-play. Researchers and practitioners should consider the sampling method and epoch length when assessing the physical demands of competitive match-play, as well as when designing and prescribing sport-specific conditioning drills.

#2 Maturity offset affects standing postural control in youth male soccer players
Reference: J Biomech. 2019 Nov 18:109523. doi: 10.1016/j.jbiomech.2019.109523. [Epub ahead of print]
Authors: Zago M, Moorhead AP, Bertozzi F, Sforza C, Tarabini M, Galli M
Summary: Quantifying the response of postural control in developmental athletes makes it possible to understand critical coordination and learning phases and to improve technical-physical interventions. However, the influence of maturation on postural control amongst young soccer players has neither been tested using quantitative methods, nor over a wide age range. In this study, we examined stabilometric parameters of 238 young male soccer players from 9 to 17 years old relative to maturity offset. Two 30-s tests (eyes open and eyes closed) were recorded on a baropodometric platform at 50 Hz. Participants were split into six groups according to their maturity offset, expressed as years from individual's peak height velocity. Dependent variables were: Sway Area, Center-of-Pressure velocity, standard deviation of the antero-posterior and medio-lateral Center-of-Pressure trajectory, Romberg Quotient. Sway Area was significantly higher in players with maturity offset <-1.5 than in groups with maturity offset > 0.5 years (p < 0.001, large effect). Center-of-Pressure velocity markedly dropped in players with maturity offset >-0.5 years (p < 0.001, very large effect). Antero-posterior standard deviation was higher before than after peak height velocity (p < 0.05, large effect) and significantly higher with closed eyes at some points. Medio-lateral standard deviation was higher in the youngest group of players (maturity offset <-2.5 years, large effect) than in those with maturity offset >-0.5 years. In sum, stabilometric parameters improved with age until zero maturity offset was achieved. Thereafter, variables describing postural control in developing soccer players were almost stable. No evidence of a changing role of vision in postural sway control during maturation was observed.

#3 Effect of pre-season training phase on anthropometric, hormonal and fitness parameters in young soccer players
Reference: PLoS One. 2019 Nov 25;14(11):e0225471. doi: 10.1371/journal.pone.0225471. eCollection 2019.
Authors: Perroni F, Fittipaldi S, Falcioni L, Ghizzoni L, Borrione P, Vetrano M, Del Vescovo R, Migliaccio S, Guidetti L, Baldari C
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Summary: The aims of the study were to investigate 1) the effect of 8 weeks of PSP training on anthropometrics, salivary hormones and fitness parameters in youth soccer players, 2) the correlations between fitness and hormonal parameters, and 3) the impact of the experience of the coach and his methodology of training on these parameters. Weight, height, BMI, pubertal development (PDS), salivary Cortisol (sC), salivary Testosterone (sT), salivary sDHEAS, intermittent tests (VO2max), and countermovement jump test (CMJ) modifications of 35 youth soccer players (age: 14±0 yrs; BMI: 20.8±1.8 k/m2) from two Italian clubs ("Lupa Frascati" -LF-; "Albalonga" -AL) were analysed. A significant (p<0.05) time by club effect was observed in sC (F(1,31) = 9.7, ES = 1.13), sT (F(1,31) = 4.2, ES = 0.74), CMJ (F(1,28) = 26.5, ES = 1.94), and VO2max (F(1,28) = 8.5, ES = 1.10). Statistical differences (p<0.05) in weight (F(1,32) = 25.5, ES = 0.11), sC (F(1,31) = 32.1, ES = 1.43), sT/sC ratio (F(1,31) = 10.1, ES = 0.97), sDHEAS/sC ratio (F(1,31) = 6.3, ES = 0.70), and VO2max (F(1,28) = 64.3, ES = 1.74) were found within time factor. Between clubs, differences (p<0.05) in sC (F(1,32) = 8.5, ES = 1.17), sT (F(1,31) = 4.2, ES = 0.74), CMJ (F(1,28) = 26.5, ES = 1.50), and VO2max (F(1,28) = 8.5, ES = 1.10) were found. CMJ was inversely correlated with sDHEAS (r = -0.38) before PSP, while Δ of CMJ showed significant correlations with Δ of sC (r = 0.43) and ΔVO2max was inversely correlated with ΔBMI (r = -0.54) and ΔsC (r = -0.37) in all subjects. Considering each single club, ΔVO2max showed correlations with ΔBMI (r = -0.45) in AL, while ΔCMJ showed correlations with ΔPDS (r = 0.72) in LF club. Since the PSP is often limited training time to simultaneously develop physical, technical and tactical qualities, an efficient method to distribute the training load is important in youth soccer players to increase the performance and to avoid injuries.

#4 Relationship Between Repeated Sprint Ability, Aerobic Capacity, Intermittent Endurance, and Heart Rate Recovery in Youth Soccer Players
Reference: J Strength Cond Res. 2019 Dec;33(12):3406-3413. doi: 10.1519/JSC.0000000000002193.
Authors: Rodríguez-Fernández A, Sanchez-Sanchez J, Ramirez-Campillo R, Nakamura FY, Rodríguez-Marroyo JA, Villa-Vicente JG
Summary: The purpose was to investigate the relationship between repeated sprint ability (RSA) and several aerobic and anaerobic-related soccer-performance indicators, 45 youth soccer players (age 16.8 ± 0.1 years) were classified into "high" (HAF) or "low" aerobic fitness (LAF) (VO2max ≥ or <60 ml·kg·min, respectively) and completed an RSA test measuring best (RSAbest), mean (RSAmean), total sprint time (RSAtotal), and percent sprint decrement (Sdec). A laboratory VO2max test (LabTest) together with anaerobic threshold (VT) and peak speed was measured (vLabTest). In addition, a 20-m multistage shuttle run test (MSRT) and a soccer-specific test (TIVRE-Soccer test-TST) were completed. Heart rate (HR) and HR recovery (HRR) were measured during all tests. High aerobic fitness presented greater (p ≤ 0.05) performance in LabTest, MSRT and TST, at maximal effort, at VT, as well as faster HRR. RSA was similar between HAF and LAF. Contrary to HAF, LAF showed negative correlation between vLabTest with RSAmean (r = -0.6, p = 0.000) and Sdec (r = -0.4, p = 0.044). Also, LAF showed negative correlation between TST end speed (vTST) and RSAmean (r = -0.5, p = 0.005) and Sdec (r = -0.5, p = 0.003). In LAF, RSA was strongly correlated with locomotor factors (e.g., vTST; VT) in both laboratory and field tests. Athletes with high total HRR (>12.5%) in TST presented better (p ≤ 0.05) Sdec in the RSA test. The multiple regression revealed that the LAF vLabTest explained 44.9, 40.0, and 13.5% of the variance in RSAbest, RSAmean, and Sdec, respectively. Practitioners may consider these findings to optimize youth athletes' assessment and preparation processes.

#5 Workload efficiency as a new tool to describe external and internal competitive match load of a professional soccer team: A descriptive study on the relationship between pre-game training loads and relative match load
Reference: Eur J Sport Sci. 2019 Nov 25:1-17. doi: 10.1080/17461391.2019.1697374. [Epub ahead of print]
Authors: Grünbichler J, Federolf P, Gatterer H
Summary: The current study introduces a new index for external and internal workload, "workload efficiency", and assesses in professional soccer the influence of pre-match training load on match workload efficiency. External and internal workloads were determined for 44 training sessions and 16 competitive matches using a 10-Hz global positioning system (GPS) and a 200-Hz accelerometer/heart rate monitor. Training loads were registered from day five (D-5) to day one (D-1) prior to each competitive match. Workload efficiency was calculated for each match as the ratio between overall external and internal load. A multiple stepwise regression analysis (including z-transformed variables) was used to determine training load variables that predict workload efficiency of the following matches. Training load variables of the previous days explained 26.6% of the variance in workload efficiency during the following matches. Long sprinting distance on D-3 and D-4 and total distance on D-1 positively influenced the players' workload efficiency, whereas long training durations and high training load on D-1 showed adverse effects. The present outcomes suggest that including sprint training (high sprinting distance) four and three days prior to a match, may provide a positive stimulus for the subsequent workload efficiency in matches. The negative impact of long training duration and high training load one day before the game highlights the importance of a diligent planning of the immediate competition preparation phase. This study shows that workload efficiency is a useful metric to assess match performance and that body-worn sensor technology can be useful for tailoring training loads.

#6 Contribution of lower body segment rotations in various height soccer volley kicking
Reference: Sports Biomech. 2019 Nov 25:1-16. doi: 10.1080/14763141.2019.1667422. [Epub ahead of print]
Authors: Sugi S, Nunome H, Tamura Y, Iga T, Lake M
Summary: We aimed to quantify the contribution of lower body segment rotations in producing foot velocity during the soccer volley kick. Fifteen male experienced university players kicked a soccer ball placed at four height conditions (0, 25, 50 and 75 cm). Their kicking motion was captured at 500 Hz. The effectiveness of lower body segment rotations in producing forward (Ffv) and upward (Fuv) foot velocity were computed and time integrated. Major contributors for Ffv were a) left hip linear velocity, b) knee extension and c) pelvis retroflexion (the pitch rotation). The contribution of a) become smaller as the ball height increased while those of b) and c) did not change significantly. Moreover, the pelvis clockwise rotation (the yaw rotation) showed apparent contribution only for volley kicking (except 0 cm height). Major contributors for Fuv were 1) knee flexion, 2) hip internal rotation, 3) pelvis clockwise rotation (the roll rotation) and 4) hip flexion. The contributions of 1) and 4) become consistently smaller as the ball height increased, while those of 2) and 3) become larger systematically. Soccer volley kicking was found to have unique adaptations of segmental contributions to achieve higher foot position while maintain foot forward velocity.

#8 Physical capacity, not skeletal maturity, distinguishes competitive levels in male Norwegian U14 soccer players
Reference: Scand J Med Sci Sports. 2019 Oct 12. doi: 10.1111/sms.13572. [Epub ahead of print]
Authors: Grendstad H, Nilsen AK, Rygh CB, Hafstad A, Kristoffersen M, Iversen VV, Nybakken T, Vestbøstad M, Algrøy EA, Sandbakk Ø, Gundersen H
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Summary: The main aim of the present study was to compare skeletal maturity level and physical capacities between male Norwegian soccer players playing at elite, sub-elite and non-elite level. Secondary, we aimed to investigate the association between skeletal maturity level and physical capacities. One hundred and two U14 soccer players (12.8-14.5 years old) recruited from four local clubs, and a regional team were tested for bone age and physical capacities. Bone age was estimated with x-ray of their left hand and used to indicate maturation of the skeleton. Players went through a comprehensive test battery to assess their physical capacities. Between-groups analysis revealed no difference in chronological age, skeletal maturity level, leg strength, body weight, or stature. However, elite players were superior to sub-elite and non-elite players on important functional characteristics as intermittent-endurance capacity (running distance: 1664 m ± 367 vs 1197 m ± 338 vs 693 m ± 235) and running speed (fastest 10 m split time: 1.27 seconds ± 0.06 vs 1.33 seconds ± 0.10 vs 1.39 seconds ± 0.11), in addition to maximal oxygen uptake ( VO2max ), standing long jump, and upper body strength (P < .05 for all comparisons). Medium-to-large correlations were found between skeletal maturity level and peak force (r = 695, P < .01), power (r = 684, P < .01), sprint (r = -.471, P<.001), and jump performance (r = .359, P < .01), but no correlation with upper body strength, VO2max , or intermittent-endurance capacity. These findings imply that skeletal maturity level does not bias the selection of players, although well-developed physical capacity clearly distinguishes competitive levels. The superior physical performance of the highest-ranked players seems related to an appropriate training environment.

#9 Incidence of injuries among professional football players in Spain during three consecutive seasons: A longitudinal, retrospective study
Reference: Phys Ther Sport. 2019 Nov 19;41:87-93. doi: 10.1016/j.ptsp.2019.11.008. [Epub ahead of print]
Authors: Torrontegui-Duarte M, Gijon-Nogueron G, Perez-Frias JC, Morales-Asencio JM, Luque-Suarez A
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Summary: The aim of the study was to determine risk factors that maybe be associated with a higher incidence of injuries in elite football players in the Spanish league during a three-year follow-up. Injury was defined as a musculoskeletal complaint (pain and/or discomfort) reported by players to the medical staff and receiving medical attention.  Seventy-one players from Malaga Football Club, who were in the first squad team for three consecutive seasons participated in this study. Incidence, location, severity of injuries were reported according to the Injury Consensus Group for football injuries. Three hundred and fifty six injuries were found, with the highest proportion (44%) being located in the thigh. We found 6.9 (SD 5.87) injuries per 1000 h of match time and 0.23 (SD 0.22) per 1000 h of training. Forwards presented the highest rates in both incidence and severity of injury. Exposure to training was inversely related to the total number of injuries, which means that the greater the exposure to training the lesser the number of injuries. This information can assist clinicians in the identification of risk factors and, thus, the elaboration of prevention programmes that reduce football injuries.

#10 An Extensive Comparative Analysis of Successful and Unsuccessful Football Teams in LaLiga
Reference: Front Psychol. 2019 Nov 8;10:2566. doi: 10.3389/fpsyg.2019.02566. eCollection 2019.
Authors: Brito de Souza D, López-Del Campo R, Blanco-Pita H, Resta R, Del Coso J
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Summary: The characterization of the in-game actions with the strongest influence on victory in football might be useful for designing playing styles that enhance teams' performance. The aim of this study was to analyze in-game match statistics on the top-3 and bottom-3 teams ranked in LaLiga. Accumulated offensive and defensive match statistics when playing at home and away were obtained from LaLiga for 8 consecutive seasons. Data extraction was performed by computerized video-analysis. The top-3 and bottom-3 teams were compared using independent t-test analysis and the magnitude of the difference was cataloged with effect sizes. Overall, the offensive variable with the greatest magnitude of difference in the top-3 vs. bottom-3 comparison was shooting accuracy (ES ± 90% confidence interval = 4.15 ± 0.52) followed by the number of offsides (2.25 ± 0.60) and corners (2.14 ± 0.61). However, when playing away, the offensive variable with the greatest magnitude of difference in the top-3 vs bottom-3 comparison was the number of shots (3.30 ± 0.44). The defensive variables that best differentiated top 3 - bottom 3 teams were the number of corners (2.16 ± 0.43) and shots conceded (2.04 ± 0.39). In conclusion, the match statistics that best discriminated successful from unsuccessful football teams were shooting accuracy while attacking and the number of shots conceded while defending.

#11 Submaximal field testing validity for aerobic fitness assessment in recreational football
Reference: Scand J Med Sci Sports. 2019 Nov 27. doi: 10.1111/sms.13606. [Epub ahead of print]
Authors: Cristina Araújo Póvoas S, Krustrup P, Castagna C
Summary: Submaximal field tests are especially recommended when repeated testing is warranted. This study aimed at assessing the validity of the submaximal versions of the Yo-Yo intermittent tests in male recreational football players in untrained and trained status. The participants' (n=66; age 39.3±5.8 years, VO2max 41.2±6.2 ml·kg-1 ·min-1 , body mass 81.9±10.8 kg, height 173.2±6.4 cm) heart rate after 2 min (HR2min ) during the level 1 (YYIE1HR2min ) and 2 (YYIE2HR2min ) versions of the Yo-Yo intermittent endurance test and the level 1 version of the Yo-Yo intermittent recovery test (YYIRHR2min ) was plotted against individual VO2max values. Thirty-two participants performed all the tests after a 12-week recreational football intervention for test responsiveness. Associations between VO2max and YYIE1HR2min were large to small (P=0.0001). Large to trivial associations were found between YYIE2HR2min , YYIR1HR2min and VO2max (P<0.01). Maximal Yo-Yo performances were large, significant and inversely related to HR2min (-0.68 to -0.49, P<0.0001). Pre-to-post-intervention ICC values were good for YYIE1HR2min and YYIE2HR2min , and excellent for YYIR1HR2min . Post-intervention associations between HR2min and Yo-Yo maximal performances were large to very large (-0.55 to -0.72; P<0.002, n=32). Training-induced changes in VO2max moderately correlated with YYR1HR2min (-0.48; P=0.007; n=32). HR2min lower than 89%, 98% and 91%HRmax for YYIE1HR2min , YYIE2HR2min and YYIR1HR2min , respectively, may be considered as signs of good to excellent VO2max levels. Since in the YYIE1HR2min , the participants attained 84%HRmax and test specificity increased for HR2min values <89%, this test may be the preferred choice when repeated assessment of aerobic fitness, using submaximal intermittent Yo-Yo tests, is considered in recreational football.

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