Latest research in football - week 18 - 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 Relationship of Pre-season Training Load With In-Season Biochemical Markers, Injuries and Performance in Professional Soccer Players
Reference: Front Physiol. 2019 Apr 12;10:409. doi: 10.3389/fphys.2019.00409. eCollection 2019.
Authors: Coppalle S, Rave G, Ben Abderrahman A, Ali A, Salhi I, Zouita S, Zouita A, Brughelli M, Granacher U, Zouhal H
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Summary: There is controversy in the literature in regards of the link between training load and injury rate. Thus, the aims of this non-interventional study were to evaluate relationships between pre-season training load with biochemical markers, injury incidence and performance during the first month of the competitive period in professional soccer players. Healthy professional soccer players were enrolled in this study over two pre-season periods. Data sets were available from 26 players during the first season (2014-2015) and 24 players during the second season (2015-2016) who completed two pre-season periods (6 weeks each). External training load was assessed from all athletes during training using Global Positioning System (GPS). Internal training load was monitored after each training session using rate of perceived exertion (RPE). Before and after each pre-season, blood samples were taken to determine plasma lactate dehydrogenase (LDH), creatine kinase (CK) and C-reactive protein (CRP). Injury incidence and overall performance (ranking of the team after the first five official games of the championship) were recorded for both seasons separately. There was no statistically significant difference in mean RPE values of the two-preparation periods (2737 ± 452 and 2629 ± 786 AU, p = 0.492). The correlational analysis did not reveal significant associations between internal and external training load (RPE and GPS data) and biological markers. There was a significant positive correlation between RPE and LDH during the 2015/2016 season (r = 0.974, p = 0.001). In addition, a significant negative correlation was found between total distance >20 km/h and CRP during the 2015-2016 season (r = -0.863, p = 0.027). The injury rates for the two seasons were 1.76 and 1.06 per 1000 h exposure for the 2014-2015 and 2015-2016 seasons, respectively (p = 0.127). Our study showed that pre-season training load is not associated with overall team performance. This association is most likely multifactorial and other factors (e.g., technical and tactical level of the team, opponents, environment) may play an important role for the collective team performance. Our findings may help coaches to better prepare their athletes during pre-season.

#2 Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football
Reference: PLoS One. 2019 Apr 30;14(4):e0216364. doi: 10.1371/journal.pone.0216364. eCollection 2019.
Authors: Thomson A, Whiteley R, Wilson M, Bleakley C
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Summary: An optimal range of shoe-surface traction (grip) exists to improve performance and minimise injury risk. Little information exists regarding the magnitude of traction forces at shoe-surface interface across a full season of elite football (soccer) using common football shoes. The objective was to assess variation in shoe-surface traction of six different football shoe models throughout a full playing season in Qatar encompassing climatic and grass species variations. Football shoes were loaded onto a portable shoe-surface traction testing machine at five individual testing time points to collect traction data (rotational and translational) on a soccer playing surface across one season. Surface mechanical properties (surface hardness, soil moisture) and climate data (temperature and humidity) were collected at each testing time point. Peak rotational traction was significantly different across shoe models (F = 218, df = 5, p <0.0001), shoe outsole groups (F = 316.2, df = 2, p < .0001), and grass species (F = 202.8, df = 4, p < 0.0001). No main effect for shoe model was found for translational traction (F = 2.392, p = 0.07). The rotational (but not translational) traction varied substantially across different shoe types, outsole groups, and grass species. Highest rotational traction values were seen with soft ground outsole (screw-in metal studs) shoes tested on warm season grass. This objective data allows more informed footwear choices for football played in warm/hot climates on sand-based elite football playing surfaces. Further research is required to confirm if these findings extend across other football shoe brands.

#3 When Better Seems Bigger: Perceived Performance of Adult Professional Football Players Is Positively Associated With Perceptions of Their Body Size
Reference: Evol Psychol. 2019 Apr-Jun;17(2):1474704919841914. doi: 10.1177/1474704919841914.
Authors: Knapen JEP, Pollet TV, van Vugt M
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Summary: Research has shown a positive association between cues of physical formidability and perceptions of status, supporting a generic "bigger-is-better" heuristic. However, does better also lead to appraisals as bigger? Recent research suggests that the perceptual association between body size and social status can also be explained in terms of prestige. To test whether perceptions of prestige lead to higher appraisals of body size, we examined whether people apply a "better is bigger bias" (BBB) in football, where performance and body size tend to be uncorrelated. In two studies, we examined real coalitional sports groups on a national (Study 1) and team level (Study 2), and we manipulated target performance in an experimental third study. Results suggest that perceived performance significantly predicted both the perceived height (Studies 2 and 3) and perceived weight (Studies 1 and 2) of professional football players, supporting the BBB. Support for the team had a positive effect on body size estimations of the players; however, we did not find any support for winner or loser effects. We discuss these results in light of individual versus team performance and coalitional affiliation.

#4 Efficacy of using non-linear pedagogy to support attacking players' individual learning objectives in elite-youth football: A randomised cross-over trial
Reference: J Sports Sci. 2019 Apr 27:1-11. doi: 10.1080/02640414.2019.1609894. [Epub ahead of print]
Authors: Roberts SJ, Rudd JR, Reeves MJ
Summary: The present study examined the efficacy of a coaching curriculum, based on non-linear pedagogy, on improving attacking players' individual learning objectives (ILOs) in elite-youth football. Participants included 22 attacking players (i.e., centre-forwards, wide-players and attacking midfield players) from a professional football academy in England. The players were randomly appointed to both control (CON) and intervention (INT) periods following baseline measures. The INT (non-linear) and CON (linear) periods were both designed to support the ILOs provided to each player as part of the elite player performance plan. The study adopted a randomised cross-over design and ILOs considered important for attacking players (i.e., strong foot finishing, weak foot finishing, 1-v-1 and decision-making) were evaluated using the Loughborough Shooting Skill Test. The results showed significant differences for INT in 1-v-1 (P< 0.02) and decision-making (P< 0.01). However, there were no significant differences for strong foot finishing, weak foot finishing or time taken. These results support non-linear pedagogy in developing 1-v-1 game play and decision-making but not for technical shooting proficiency.

#5 Injury Prevention in Amateur Soccer: A Nation-Wide Study on Implementation and Associations with Injury Incidence
Reference: Int J Environ Res Public Health. 2019 May 7;16(9). pii: E1593. doi: 10.3390/ijerph16091593.
Authors: Gebert A, Gerber M, Pühse U, Stamm H, Lamprecht M
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Summary: Prevention programmes can reduce injury risk in amateur soccer. Hence, we examined the implementation of injury prevention in the real-world context of Swiss amateur soccer. In 2004 (n = 1029), 2008 (n = 705) and 2015 (n = 1008), a representative sample of Swiss amateur soccer coaches was interviewed by telephone about the frequency of injuries in their teams, the implementation of preventive measures and the use of injury prevention programmes. In the 2015 survey, 86.1% of amateur coaches stated that injury prevention is important and 85.3% of amateur coaches reported that they would implement some kind of preventive measures. The proportion of teams which performed a prevention programme according to minimal standards remained unchanged between 2008 (21.7%) and 2015 (21.9%), although a second prevention programme was made available in 2011. Only 8.6% of the 30+/40+ league teams, which are composed as a function of age, implemented a programme. Overall, the level of implementation of prevention programmes in this real-world context is still unsatisfactory. Offering an additional programme did not lead to a higher willingness to implement such programmes among the coaches. Concerted efforts are needed to remove barriers that hinder the use of such programmes, particularly among coaches of 30+/40+ league teams.

#6 Validity and reliability of a 6-a-side small-sided game as an indicator of match-related physical performance in elite youth Brazilian soccer players
Reference: J Sports Sci. 2019 May 7:1-6. doi: 10.1080/02640414.2019.1608895. [Epub ahead of print]
Authors: Aquino R, Melli-Neto B, Ferrari JVS, Bedo BLS, Vieira LHP, Santiago PRP, Gonçalves LGC, Oliveira LP, Puggina EF
Summary: The aims of this study were: (i) to compare the external and internal load during a 6-a-side small-sided game (6v6-SSG) according to age-group; (ii) to relate these parameters between the 6v6-SSG and official matches; and (iii) to test the reliability of the 6v6-SSG. A total of 51 Brazilian youth soccer players participated in this study (U11 [n = 16]; U13 [n = 10]; U15 [n = 9]; U17 [n = 8]; U20 [n = 8]). Three experiments were conducted. Experiment A: fifty-one U11 to U20 players were submitted to 6v6-SSGs (n = 10 games; two for each age-group). Experiment B: thirty-two players were randomized to also play official matches (n = 6 matches). Experiment C: thirty-five youth players played the 6v6-SSG twice for test and retest reliability analysis. External load was obtained using Global Positioning Systems and the internal load parameter was calculated through mean heart rate. Statistical approaches showed progressive increases in all parameters according to categories (U11< U13< U15< U17< U20; p < 0.05; ES = 0.42-23.68). Even controlling for chronological age, all parameters showed likely to almost certain correlations between 6v6-SSG and official matches (r = 0.25-0.92). Collectively, the proposed protocol indicates good reliability (CV% = 2.0-12.6; TE% = 2.3-2.7%; ICC = 0.78-0.90). This research suggests that the 6v6-SSG is an alternative tool to indicate match-related physical performance in youth soccer players.

#7 Improvements in soccer specific fitness and exercise tolerance following 8 weeks of inspiratory muscle training in adolescent males
Reference: J Sports Med Phys Fitness. 2019 Apr 30. doi: 10.23736/S0022-4707.19.09578-1. [Epub ahead of print]
Authors: Najafi A, Ebrahim K, Ahmadizad S, Jahani Ghaeh Ghashlagh GR, Javidi M, Hackett D
Summary: Inspiratory muscle training has been shown to improve exercise performance, however there is limited evidence for its effectiveness in soccer players. This study investigates the effect of inspiratory muscle training on soccer-specific fitness and exercise tolerance in adolescent male players. Thirty highly trained soccer players (16-19 y) were randomly assigned into one of three groups: experimental 1 (n=10), experimental 2 (n=10) and sham-control (sham, n=10). All groups performed inspiratory muscle training twice per day and five times per week for 8 weeks. Experimental 1 performed 25-35 breaths at 55% maximal inspiratory pressure, experimental 2 performed 45-55 breaths at 40% maximal inspiratory pressure, whereas sham performed 30 breaths at 15% maximal inspiratory pressure. Measures before and after the intervention involved the Yo-Yo intermittent recovery test level 1, running-based anaerobic test, repeated high-intensity endurance test, and maximal inspiratory pressure, and spirometry. Yo-Yo intermittent recovery test level 1 distance increased for experimental groups 1 and 2 compared to sham (P = 0.012 and P = 0.031, respectively), with no difference between experimental groups. Fatigue index calculated from running-based anaerobic test improved for experimental groups 1 and 2 compared to sham (P = 0.014 and P = 0.011, respectively), with no difference between experimental groups. Exercise tolerance (i.e. blood lactate concentration, perceived exertion and perceived breathlessness) following the repeated high-intensity endurance test decreased in experimental groups 1 and 2 compared to sham (P <0.05), with no difference between experimental groups. Maximal inspiratory pressure increased for experimental groups 1 and 2 compared to sham (P = 0.000), with no difference between experimental groups. There were no changes for the spirometry measures. Improvements in soccer-specific fitness and exercise tolerance can be achieved using inspiratory muscle training protocols of varying intensities and volumes.

#8 Effects of Strength Training on Body Composition in Young Male Professional Soccer Players
Reference: Sports (Basel). 2019 May 5;7(5). pii: E104. doi: 10.3390/sports7050104.
Authors: Suarez-Arrones L, Lara-Lopez P, Torreno N, Saez de Villarreal E, Di Salvo V, Mendez-Villanueva A
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Summary: The present prospective cohort study investigated changes in body composition (BC) in young male football players (n = 18, 16.1 ± 0.8 years; 181.0 ± 0.1 cm; 71.3 ± 4.9 kg) after combined football and strength training (ST) during a whole in-season period (26 weeks). BC was measured at whole-body absolute and regional levels by dual-energy X-ray absorptiometry in eighteen players at the beginning and at the end of the competitive period. The ST was organized into three different session types: ST in the gym, specific ST on the field, and individual ST (weak points). The results of the present study indicated that fat-free mass (FFM) was substantially higher following the competitive period (5.1% ± 1.2%), while percentage of fat showed no changes during the competitive period. At the regional level, arms' and legs' FFM increased at the end of the season, and bone mineral content (BMC) and density (BMD) increased in arms, legs, pelvis, thoracic spine, and lumbar spine. In conclusion, within the limitation of the potential positive impact of growth and/or maturation, present results seem to indicate that an ST program that supplements football-related training sessions could be an effective option to increase FFM, BMC, and BMD at both whole-body and regional level across the competitive season in young male professional football players.

#9 Dose-Response Relationship Between External Load Variables, Body Composition, and Fitness Variables in Professional Soccer Players
Reference: Front Physiol. 2019 Apr 17;10:443. doi: 10.3389/fphys.2019.00443. eCollection 2019.
Authors: Clemente FM, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The aim of this study was to test associations between accumulated external load and changes in body composition, isokinetic strength, and aerobic capacity of soccer players. Twenty-three professional soccer players (age: 24.7 ± 2.8 years; height: 179.2 ± 6.3; experience: 9.7 ± 2.1 years) participated in this study. This pre-post study design was performed during 10 weeks from July to August of 2017 (4 weeks of pre-season and 6 weeks during the early season). Players were monitored daily by GPS technology and were assessed before and after a 10-week period in terms of body mass (BM), fat mass, lean mass, isokinetic strength at 60°/s, VO2max, and HRmax. Large-to-very large positive correlations were found between the sum of sprinting distance and % differences of BM [0.70, (-0.09;0.95)], HRmax [0.51, (-0.37;0.91)], agonist (quadriceps)/antagonist (hamstrings) left ratio [0.84, (0.27;0.97)] and agonist/antagonist right ratio [0.92, (0.58;0.99)]. Large positive correlations were found between the acceleration sum and % differences of VO2max [0.58, (-0.29;0.92)], quadriceps left peak torque [0.66, (-0.16;0.94)], hamstrings left peak torque [0.68, (-0.13;0.94)] and hamstrings right peak torque [0.62, (-0.22;0.93)]. Sprinting load was largely and positively associated with changes in knee strength asymmetries. Acceleration sum was largely and positively correlated with variations at VO2max and peak torques at hamstrings. In addition, dose-response relationships using external load variables were identified in professional soccer players.

#10 Biological maturation and match running performance: A national football (soccer) federation perspective
Reference: J Sci Med Sport. 2019 Apr 22. pii: S1440-2440(18)30984-8. doi: 10.1016/j.jsams.2019.04.007. [Epub ahead of print]
Authors: Lovell R, Fransen J, Ryan R, Massard T, Cross R, Eggers T, Duffield R
Summary: The purpose was to examine the influence of maturation and its interaction with playing position upon physical match performances in U15 footballers from a national federation. 278 male outfield players competing in a national tournament were assessed for somatic maturity and match physical performances according to playing position. Stature, sitting height, and body mass were measured and entered into an algorithm to estimate the age at peak height velocity (APHV). Players match movements were recorded by Global Positioning System devices (10 Hz), to determine peak speed, and total- (TD), low-speed running (LSR; ≤13.0 km h-1), high-speed running (HSR; 13.1-16.0 km h-1), very high-speed running (VHSR; 16.1-20.0 km h-1) and sprint distances (SPR; >20.0 km h-1) expressed relative to match exposure (m min-1). Linear-mixed models using log transformed response variables revealed a significant contribution of estimated APHV upon TD (1.01; 95% CI: 0.99-1.02 m·min-1; p < 0.001), HSR (1.05; 95% CI: 0.98-1.13 m min-1; p < 0.001) and VHSR (1.07; 95% CI: 1.00-1.14 m min-1; p = 0.047). An increase by one year in APHV was associated with an increase of 0.6, 5.4 and 6.9% in TD, HSR and VHSR respectively. No effects of APHV were observed for LSR, SPR, and peak speed. Further, no APHV effects were observed relative to players' field position. Later maturing players covered substantially more higher-intensity (HSR and VHSR) running in matches, irrespective of playing position. The greater match intensity of later maturing players may inform talent identification and athletic development processes within a national federation.

#11 Short-Term Cardiac Autonomic Recovery after a Repeated Sprint Test in Young Soccer Players
Reference: Sports (Basel). 2019 Apr 30;7(5). pii: E102. doi: 10.3390/sports7050102.
Authors: Abad CCC, Pereira LA, Zanetti V, Kobal R, Loturco I, Nakamura FY
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Summary: The aim of this study was to describe the time course (within 2 h post-exercise) of heart rate variability (HRV) recovery following a traditional repeated sprint ability (RSA) test applied to youth soccer players. Twenty-four young soccer players (18.4 ± 0.5 years) undertook the following assessments: (1) 10 min rest in the seated position for HRV assessment; (2) a repeated sprint ability (RSA) test; (3) passive recovery in the seated position for 10 min, immediately after finishing the RSA test and 1 h and 2 h post-RSA test. During the HRV measurements (using the natural log of root mean square difference of successive normal RR intervals-lnRMSSD) the participants were instructed to assume a comfortable sitting position, remaining awake and breathing spontaneously for 10 min. Magnitude-based inference was used in the analyses. After the RSA test, the post-1 h measure was almost certainly lower than the resting measure, but almost certainly higher than the lnRMSSD measured post-RSA test. The lnRMSSD post-2 h was likely lower than the resting lnRMSSD and very likely higher than post-1 h. In conclusion, lnRMSSD is severely depressed after performing an RSA test, and reactivation is incomplete after 2 h of passive recovery. This result should be considered by practitioners when applying successive training sessions within intervals shorter than 2 h.

#12 A comparison of the isometric force fatigue-recovery profile in two posterior chain lower limb tests following simulated soccer competition
Reference: PLoS One. 2019 May 3;14(5):e0206561. doi: 10.1371/journal.pone.0206561. eCollection 2019.
Authors: Matinlauri A, Alcaraz PE, Freitas TT, Mendiguchia J, Abedin-Maghanaki A, Castillo A, Martínez-Ruiz E, Carlos-Vivas J, Cohen DD
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Summary: The aim was to evaluate the reliability of isometric peak force (IPF) in a novel "long-length" 90°Hip:20°Knee (90:20) strength test and to compare the simulated soccer match induced fatigue-recovery profile of IPF in this test with that of an isometric 90°Hip:90°Knee (90:90) position test. Twenty semi-professional soccer players volunteered for the study of which 14 participated in the first part of the study which assessed 90:20 reliability (age = 21.3 ± 2.5 years, height = 1.79 ± 0.07 m, body mass = 73.2 ± 8.8 kg), while 17 completed the second part of the study evaluating fatigue-recovery (age 21.2±2.4 yrs., height = 180 ± 0.09 m, body mass 73.8 ± 8.9 kg). We evaluated the inter-session reliability of IPF in two 90:20 test protocols (hands on the wall (HW); and hands on chest (HC)) both performed on two occasions, 7 days apart. We then assessed 90:20 (HC) and 90:90 IPF immediately before (PRE) and after (POST) after a simulated soccer match protocol (BEAST90mod) and 48 (+48 h) and 72 hours (+72 h) later. Part one: the 90:20 showed moderate to high overall reliability (CV's of 7.3% to 11.0%) across test positions and limbs. CV's were lower in the HW than HC in the dominant (7.3% vs 11.0%) but the opposite happened in the non-dominant limb where CV's were higher in the HW than HC (9.7% vs 7.3%). Based on these results, the HC position was used in part two of the study. Part two: 90:20 and 90:90 IPF was significantly lower POST compared to PRE BEAST90mod across all testing positions (p<0.001). IPF was significantly lower at +48 h compared to PRE in the 90:20 in both limbs (Dominant: p<0.01,Non-dominant: p≤0.05), but not in the 90:90. At +72 h, IPF was not significantly different from PRE in either test. Simple to implement posterior IPF tests can help to define recovery from competition and training load in football and, potentially, in other multiple sprint athletes. Testing posterior chain IPF in a more knee extended 90:20 position may provide greater sensitivity to fatigue at 48 h post simulated competition than testing in the 90:90 position, but also may require greater degree of familiarization due to more functional testing position.

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