Latest research in football - week 51 - 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 The Effects of Lower-Extremity Plyometric Training on Soccer-Specific Outcomes in Adult Male Soccer Players: A Systematic Review and Meta-Analysis
Reference: Int J Sports Physiol Perform. 2019 Dec 4:1-15. doi: 10.1123/ijspp.2019-0565. [Epub ahead of print]
Authors: van de Hoef PA, Brauers JJ, van Smeden M, Backx FJG, Brink MS.
Summary: Plyometric training is a specific form of strength training that is used to improve the physical performance of athletes. An overview of the effects of plyometric training on soccer-specific outcomes in adult male soccer players is not available yet. The purpose was to systematically review and meta-analyze the effects of plyometric training on soccer-specific outcome measures in adult male soccer players and to identify which programs are most effective. PubMed, Embase/Medline, Cochrane, PEDro, and Scopus were searched. Extensive quality and risk of bias assessments were performed using the Cochrane ROBINS 2.0 for randomized trials. A random effects meta-analysis was performed using Cochrane Review Manager 5.3. Seventeen randomized trials were included in the meta-analysis. The impact of plyometric training on strength, jump height, sprint speed, agility, and endurance was assessed. Only jump height, 20-m sprint speed, and endurance were significantly improved by plyometric training in soccer players. Results of the risk of bias assessment of the included studies resulted in overall scores of some concerns for risk of bias and high risk of bias. This review and meta-analysis showed that plyometric training improved jump height, 20-m sprint speed, and endurance, but not strength, sprint speed over other distances, or agility in male adult soccer players. However, the low quality of the included studies and substantial heterogeneity means that results need to be interpreted with caution. Future high-quality research should indicate whether or not plyometric training can be used to improve soccer-specific outcomes and thereby enhance performance.

#2 The influence of playing position in soccer on the recovery kinetics of cognitive and physical performance
Reference: J Sports Med Phys Fitness. 2019 Nov;59(11):1812-1819. doi: 10.23736/S0022-4707.19.09433-7.
Authors: Nedelec M, Dupont G
Summary: The physical activity and playing actions performed during a soccer match vary according to player position. The aim of the present study was to analyze the recovery kinetics of cognitive performance, physical performance and subjective ratings after a competitive soccer match. Eight goalkeepers and eight outfield players played in the match with data collected before, 45 min, 24 h and 48 h after the match. Subjective ratings, Vienna Reaction Test (reaction time, motor time), Vienna Determination Test (number of stimuli, number of correct responses), squat jump, countermovement jump and 6-s sprint were analyzed. No significant interaction between position and time was found for Vienna Reaction Test and Vienna Determination Test performance. No significant interaction between position and time was found for squat jump and countermovement jump but squat jump and countermovement jump significantly decreased (P<0.01) at 24 h. Countermovement jump performance was still significantly affected at 48h (P<0.05). A significant interaction between position and time (P<0.05) was found for 6-s sprint. Sprint performance was significantly reduced for outfield players only immediately after the match (P<0.01). There was no interaction effect of position and time on subjective ratings. A significant correlation was found between number of jumps and ball kicks performed during the match by goalkeepers and the change score in squat jump (r =-0.90; P<0.01) and countermovement jump (r =-0.90; P<0.01) observed at 48 h. Outfield players require a longer time than goalkeepers to recover sprint performance whilst cognitive function tested in the present study is not affected by the match whatever the position.

#3 Accuracy of the functional movement screen (FMS) active straight leg raise test to evaluate hamstring flexibility in soccer players
Reference: Int J Sports Phys Ther. 2019 Dec;14(6):877-884.
Authors: Medeiros DM, Miranda LLP, Marques VB, de Araujo Ribeiro-Alvares JB, Baroni BM
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Summary: Poor flexibility is considered a risk factor for the hamstring strain injury, and the active straight leg raise (ASLR) test proposed as a part of the Functional Movement Screen™ (FMS™) has been used to assess athletes hamstring flexibility. However, the accuracy of this screening test remains undescribed. The purpose was to examine the accuracy of the FMS™ ASLR test for assessment of hamstring flexibility in soccer players. One-hundred and one male soccer players (age, 21 ± 3 years; height, 179 ± 7 cm; weight, 75 ± 9 kg) were bilaterally evaluated. All players performed a gold standard test for hamstring flexibility evaluation: the passive straight leg raise (PSLR) test measured using a gravitational inclinometer. All players also performed the ASLR test and were scored using the criteria proposed by the FMS™. Of the 202 lower limbs evaluated, 17.82% scored a 1 on the ASLR [mean passive flexibility: 80.44 ± 14.69 ° (55 °-110 °)], 50.99% scored a 2 on the ASLR [mean passive flexibility = 84.60 ± 10.59 ° (56 °-115 °)], and 31.18% scored a 3 on the ASLR [mean passive flexibility = 92.32 ± 11.53 ° (70 °-120 °)]. Limbs with FMS™ score of 3 presented significantly higher values for passive flexibility than limbs with scores of 1 and 2 (p < 0.05), but there was no significant difference between limbs with scores of 1 and 2 (p > 0.05). The score obtained in the FMS™ ASLR test does not satisfactorily stratify the level of hamstring flexibility in soccer players.

#4 Workload and Injury in Professional Soccer Players: Role of Injury Tissue Type and Injury Severity
Reference: Int J Sports Med. 2019 Dec 4. doi: 10.1055/a-0997-6741. [Epub ahead of print]
Authors: Enright K, Green M, Hay G, Malone JJ
Summary: The purpose of the present study was to examine the influence of workload prior to injury on injury (tissue type and severity) in professional soccer players. Twenty-eight days of retrospective training data prior to non-contact injuries (n=264) were collated from 192 professional soccer players. Each injury tissue type (muscle, tendon and ligament) and severity (days missed) were categorised by medical staff. Training data were recorded using global positioning system (GPS) devices for total distance (TD), high speed distance (HSD,>5.5 m/s-1), and sprint distance (SPR,>7.0 m/s-1). Accumulated 1, 2, 3, 4-weekly loads and acute:chronic workload ratios (ACWR) (coupled, uncoupled and exponentially weighted moving average (EWMA) approaches) were calculated. Workload variables and injury tissue type were compared using a one-way ANOVA. The association between workload variables and injury severity were examined using a bivariate correlation. There were no differences in accumulated weekly loads and ACWR calculations between muscle, ligament, and tendon injuries (P>0.05). Correlations between each workload variable and injury severity highlighted no significant associations (P>0.05). The present findings suggest that the ability of accumulated weekly workload or ACWR methods to differentiate between injury type and injury severity are limited using the present variables.

#5 Variations of training load, monotony, and strain and dose-response relationships with maximal aerobic speed, maximal oxygen uptake, and isokinetic strength in professional soccer players
Reference: PLoS One. 2019 Dec 4;14(12):e0225522. doi: 10.1371/journal.pone.0225522. eCollection 2019.
Authors: Clemente FM, Clark C, Castillo D, Sarmento H, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: This study aimed to identify variations in weekly training load, training monotony, and training strain across a 10-week period (during both, pre- and in-season phases); and to analyze the dose-response relationships between training markers and maximal aerobic speed (MAS), maximal oxygen uptake, and isokinetic strength. Twenty-seven professional soccer players (24.9±3.5 years old) were monitored across the 10-week period using global positioning system units. Players were also tested for maximal aerobic speed, maximal oxygen uptake, and isokinetic strength before and after 10 weeks of training. Large positive correlations were found between sum of training load and extension peak torque in the right lower limb (r = 0.57, 90%CI[0.15;0.82]) and the ratio agonist/antagonist in the right lower limb (r = 0.51, [0.06;0.78]). It was observed that loading measures fluctuated across the period of the study and that the load was meaningfully associated with changes in the fitness status of players. However, those magnitudes of correlations were small-to-large, suggesting that variations in fitness level cannot be exclusively explained by the accumulated load and loading profile.

#6 A Comparison of Training Modality and Total Genotype Scores to Enhance Sport-Specific Biomotor Abilities in Under 19 Male Soccer Players
Reference: J Strength Cond Res. 2019 Nov 27. doi: 10.1519/JSC.0000000000003299. [Epub ahead of print]
Authors: Suraci BR, Quigley C, Thelwell RC, Milligan GS
Summary: Soccer-specific training (SST) and small-sided games (SSGs) have been shown to develop physical proficiency in soccer. Research on genetics and epigenetics in the prescription of training is limited. The aims of this study were to compare the impact of 3 different SST/SSG methods and investigate if a total genotype score (TGS) influences training response. Subjects (n = 30 male soccer players, mean ± SD; age 17.2 ± 0.9 years, stature = 172.6 ± 6.2 cm; body mass = 71.7 ± 10.1 kg) were stratified into a "power" (PG) or "endurance" (EG) gene profile group, where a 15 single nucleotide polymorphism panel was used to produce an algorithmically weighted TGS. Training 1 (T1-SSGs only), training 2 (T2-SSGs/SST), and training 3 (T3-SST only) were completed (in that respective order), lasting 8 weeks each, interspersed by 4-week washouts. Acceleration (10-m sprint) was improved by T2 only (1.84 ± 0.09 seconds vs. 1.73 ± 0.05 seconds; Effect Size [ES] = 1.59, p < 0.001). Speed (30-m sprint) was improved by T2 (4.46 ± 0.22 seconds vs. 4.30 ± 0.19 seconds; ES = 0.81, p < 0.001) and T3 (4.48 ± 0.22 seconds vs. 4.35 ± 0.21 seconds; ES = 0.58, p < 0.001). Agility (T-test) was improved by T1 (10.14 ± 0.40 seconds vs. 9.84 ± 0.42 seconds; ES = 0.73, p < 0.05) and T3 (9.93 ± 0.38 seconds vs. 9.66 ± 0.45 seconds; ES = 0.66, p < 0.001). Endurance (Yo-Yo level 1) was improved by T1 (1,682.22 ± 497.23 m vs. 2,028.89 ± 604.74 m; ES = 0.63, p < 0.05), T2 (1,904.35 ± 526.77 m vs. 2,299.13 ± 606.97 m; ES = 0.69, p < 0.001), and T3 (1,851.76 ± 490.46 m vs. 2,024.35 ± 588.13 m; ES = 0.35, p < 0.05). Power (countermovement jump) was improved by T3 only (36.01 ± 5.73 cm vs. 37.14 ± 5.62 cm; ES = 0.20, p < 0.05). There were no differences in T1, T2, and T3 combined when comparing PG and EG. The PG reported significantly (χ(20) = 4.42, p = 0.035, ES = 0.48) better training responses to T3 for power than the EG. These results demonstrate the efficacy of SSGs and SSTs in developing biomotor abilities. Although these results refute talent identification through the use of a TGS, there may be use in aligning the training method to TGS to develop power-based qualities in soccer.

#7 To Measure Peak Velocity in Soccer, Let the Players Sprint
Reference: J Strength Cond Res. 2019 Nov 27. doi: 10.1519/JSC.0000000000003406. [Epub ahead of print]
Authors: Kyprianou E, Di Salvo V, Lolli L, Al Haddad H, Villanueva AM, Gregson W, Weston M
Summary: Expressing externals loads relative to a player's individual capacities has potential to enhance understanding of dose-response. Peak velocity is an important metric for the individualization process and is usually measured during a sprint test. Recently, however, peak velocity was reported to be faster during soccer matches when compared with a 40-m sprint test. With the aim of developing the practice of individualized training prescription and match evaluation, we examined whether the aforementioned finding replicates in a group of elite youth soccer players across a broader range of soccer activities. To do this, we compared the peak velocities of 12 full-time male youth soccer players (age 16.3 ± 0.8 years) recorded during a 40-m sprint test with peak velocity recorded during their routine activities (matches, sprints, and skill-based conditioning drills: small-sided games [SSG], medium-sided games [MSG], large-sided games [LSG]). All activities were monitored with 10-Hz global positioning systems (Catapult Optimeye S5, version 7.32) with the highest speed attained during each activity retained as the instantaneous peak velocity. Interpretation of clear between-activity differences in peak velocity was based on nonoverlap of the 95% confidence intervals for the mean difference between activities with sprint testing. Peak velocity was clearly faster for the sprint test (8.76 ± 0.39 m·s) when compared with matches (7.94 ± 0.49 m·s), LSG (6.94 ± 0.65 m·s), MSG (6.40 ± 0.75 m·s), and SSG (5.25 ± 0.92 m·s), but not sprints (8.50 ± 0.36 m·s). Our data show the necessity for 40-m sprint testing to determine peak velocity.

#8 Contribution of Eccentric Strength to Cutting Performance in Female Soccer Players
Reference: J Strength Cond Res. 2019 Nov 28. doi: 10.1519/JSC.0000000000003433. [Epub ahead of print]
Authors: Jones PA, Dos'Santos T, McMahon JJ, Graham-Smith P
Summary: The aim of this study was to examine the contribution of eccentric strength to performance of a 70-90° cutting task (CUT) (time to complete: 5 m approach, 70-90° cut, 3 m exit). Nineteen female soccer players (mean ± SD age, height, and mass; 21.7 ± 4.3 years, 1.67 ± 0.07 m, and 60.5 ± 6.1 kg) from the top 2 tiers of English women's soccer participated in the study. Each player performed 6 trials of the CUT task whereby three-dimensional motion data from 10 Qualisys proreflex cameras (240 Hz) and ground reaction forces from 2 Advanced Mechanical Technology, Inc. force platforms (1,200 Hz) were collected. Relative eccentric knee extensor (ECC-KE) and flexor peak moments (ECC-KF) were collected from both limbs at 60°·s using a Kin-Com isokinetic dynamometer. Hierarchical multiple regression revealed that minimum center of mass (CM) and approach velocities (CM velocity at touchdown of penultimate foot contact) could explain 82% (79% adjusted) of the variation in CUT completion time (F(1,16) = 36.086, p < 0.0001). ECC-KE was significantly (p < 0.05) moderately associated (R ≥ 0.610) with velocities at key instances during the CUT. High (upper 50th percentile) ECC-KE individuals (n = 9) had significantly (p ≤ 0.01; d ≥ 1.34) greater velocities at key instances during the CUT. The findings suggest that individuals with higher ECC-KE produce faster CUT performance, by approaching with greater velocity and maintaining a higher velocity during penultimate and final contact, as they are better able to tolerate the larger loads associated with a faster approach.

#9 Epidemiology of Anterior Cruciate Ligament Injury in Italian First Division Soccer Players
Reference: Sports Health. 2019 Dec 4:1941738119885642. doi: 10.1177/1941738119885642. [Epub ahead of print]
Authors: Grassi A, Macchiarola L, Filippini M, Lucidi GA, Della Villa F, Zaffagnini S
Summary: The burden of anterior cruciate ligament (ACL) injury in professional soccer players is particularly relevant as it represents a potentially career-threatening injury. Our hypotheses were that (1) injury incidence rate would be similar to that reported in the literature, (2) we would identify a uniform distribution of the injuries along the season, and (3) injury incidence rate would be similar in high-ranked and lower ranked teams, based on final placement in the league. Professional male soccer players participating in the Serie A championship league in 7 consecutive seasons (2011-2012 to 2017-2018) were screened to identify ACL injuries through the online football archive . Exposure in matches and training were calculated. There were 84 ACL injuries found (mean player age, 25.3 ± 4.2 years). Overall, 25% of ACL injuries were reruptures (15%) or contralateral injuries (10%). ACL incidence rate was 0.4215 per 1000 hours of play during Serie A matches, 0.0305 per 1000 hours of training (rate ratio [RR], 13.8; 95% CI, 8.4-22.7; P < 0.0001), and 0.0618 per 1000 hours of total play. Injury distribution had a bimodal peak, with the highest number of events in October and March. Alternatively, training injuries peaked in June and July. A significantly higher incidence rate was found for the teams ranked from 1st to the 4th place compared with those ranked 5th to 20th (0.1256 vs 0.0559 per 1000 hours of play; RR, 2.2; 95% CI, 1.4-3.6; P = 0.0003). A similar finding was found for injury incidence proportion (3.76% vs 1.64%; P = 0.0003). The overall incidence rate of ACL injuries in Italian Serie A was 0.062 per 1000 hours, with a 14-fold risk in matches compared with training. Relevantly, 25% were second injuries. Most injuries occurred in October and March, and an almost 2-fold incidence rate and incidence proportion were noted in those teams ranked in the first 4 positions of the championship league. Knowing the precise epidemiology of ACL injury in one of the most competitive professional football championship leagues could help delineate fields of research aimed to investigate its risk factors.

#10 Factors Associated With Knee Pain and Heel Pain in Youth Soccer Players Aged 8 to 12 Years
Reference: Orthop J Sports Med. 2019 Nov 20;7(11):2325967119883370. doi: 10.1177/2325967119883370. eCollection 2019 Nov.
Authors: Iwame T, Matsuura T, Suzue N, Iwase J, Uemura H, Sairyo K
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Summary: Soccer is played by many children younger than 12 years. Despite its health benefits, soccer has also been linked to a high number of sport-related injuries. The purpose was to investigate the relationship between clinical factors and knee or heel pain in youth soccer players. Study participants included 602 soccer players aged 8 to 12 years who were asked whether they had experienced episodes of knee or heel pain. Data were collected on age, body mass index, years of playing soccer, playing position, and training hours per week. Associations of clinical factors with the prevalence of knee or heel pain were examined by univariate and multivariate logistic regression analyses. Episodes of knee and heel pain were reported by 29.4% and 31.1% of players, respectively. Multivariate analyses revealed that older age and more years of playing soccer were significantly and positively associated with the prevalence of knee pain (P = .037 and P = .015 for trend, respectively) but did not identify any significant associations for heel pain. In this study of youth soccer players, knee pain was associated with older age and more years of play, but heel pain was not significantly associated with any factor.

#11 Intra- and Post-match Time-Course of Indicators Related to Perceived and Performance Fatigability and Recovery in Elite Youth Soccer Players
Reference: Front Physiol. 2019 Nov 15;10:1383. doi: 10.3389/fphys.2019.01383. eCollection 2019.
Authors: Kunz P, Zinner C, Holmberg HC, Sperlich B
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Summary: Our aims were to examine (i) the internal load during simulated soccer match-play by elite youth players; and (ii) the time-course of subsequent recovery from perceived and performance fatigability. Eleven male youth players (16 ± 1 years, 178 ± 7 cm, 67 ± 7 kg) participated in a 2 × 40-min simulated soccer match, completing 30 rounds (160 s each) with every round including multidirectional and linear sprinting (LS20m), jumping (CMJ) and running at different intensities. During each round, LS20m, CMJ, agility, heart rate (HR), oxygen uptake (VO2), energy expenditure (EE), substrate utilization and perceived exertion RPE were assessed. In addition, the blood level of lactate (Lac) was obtained after each of the five rounds. Creatine kinase (CK) concentration, maximal voluntary isometric knee extension and flexion, CMJ, number of skippings in 30 s, and subjective ratings on the Acute Recovery and Stress Scale (ARSS) were examined before and immediately, 24 and 48 h after the simulation. During the game %HRpeak (p < 0.05, d = 1.08), %VO2 peak (p < 0.05; d = 0.68), Lac (p < 0.05, d = 2.59), RPEtotal (p < 0.05, d = 4.59), and RPElegs (p < 0.05, d = 4.45) all increased with time during both halves (all p < 0.05). Agility improved (p < 0.05, d = 0.70) over the time-course of the game, with no changes in LS20m (p ≥ 0.05, d = 0.34) or CMJ (p ≥ 0.05, d = 0.27). EE was similar during both halves (528 ± 58 vs. 514 ± 61 kcal; p = 0.60; d = 0.23), with 62% (second half: 65%) carbohydrate, 9% (9%) protein and 26% (27%) fat utilization. With respect to recovery, maximal voluntary knee extension (p ≥ 0.05, d = 0.50) and flexion force (p ≥ 0.05, d = 0.19), CMJ (p ≥ 0.05, d = 0.13), number of ground contacts (p ≥ 0.05, d = 0.57) and average contact time (p ≥ 0.05, d = 0.39) during 30-s of skipping remained unaltered 24 and 48 h after the game. Most ARSS dimensions of load (p < 0.05, d = 3.79) and recovery (p < 0.05, d = 3.22) returned to baseline levels after 24 h of recovery. Relative to baseline values, CK was elevated immediately and 24 h after (p < 0.05, d = 2.03) and normalized 48 h later. In youth soccer players the simulated match evoked considerable circulatory, metabolic and perceptual load, with an EE of 1042 ± 118 kcal. Among the indicators of perceived and performance fatigability examined, the level of CK and certain subjective ratings differed considerably immediately following or 24-48 h after a 2 × 40-min simulated soccer match in comparison to baseline. Accordingly, monitoring these variables may assist coaches in assessing a U17 player's perceived and performance fatigability in connection with scheduling training following a soccer match.

#12 Injury Incidence and Workloads during congested Schedules in Football
Reference: Int J Sports Med. 2019 Dec 2. doi: 10.1055/a-1028-7600. [Epub ahead of print]
Authors: Howle K, Waterson A, Duffield R
Summary: This study compared injury incidence and training loads between single and multi-match weeks, and seasons with and without congested scheduling. Measures of internal (session-Rating of Perceived Exertion × duration for training/match and % maximal heart rate) and external load (total, low-, high-, and very high-intensity running distances) along with injury incidence rates were determined from 42 players over 3 seasons; including 1 without and 2 (season 2 and 3) with regular multi-match weeks. Within-player analyses compared 1 (n=214) vs. 2-match (n=86) weeks (>75min in matches), whilst team data was compared between seasons. Total injury rates were increased during multi-match weeks (p=0.001), resulting from increased match and training injuries (50.3, 16.9/1000h). Between-season total injury rates were highest when congested scheduling was greatest in season 3 (27.3/1000h) and season 2 (22.7/1000h) vs. season 1 (14.1/1000h; p=0.021). All external load measures were reduced in multi-match weeks (p<0.05). Furthermore, all internal and external training loads were lowest in seasons with congestion (p<0.05). In conclusion, increased injury rates in training and matches exist. Total loads remain comparable between single and multi-match weeks, though reduce in congested seasons. Whether injuries result from reduced recovery, increased match exposure or the discreet match external loads remain to be elucidated.

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