Latest research in football - week 3 - 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 Effects of Resisted Sprint With Changes of Direction Training Through Several Relative Loads on Physical Performance in Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Jan 24:1-20. doi: 10.1123/ijspp.2018-0702. [Epub ahead of print]
Authors: Rodríguez-Osorio D, Gonzalo-Skok O, Pareja-Blanco F
Summary: The purpose was to compare the effects of resisted change of direction (COD) movements, using several relative loads, on soccer players' physical performance. Fifty-four male soccer players were randomly assigned to one of the following 3 groups, which differed only in the magnitude of the external load used during the COD training: COD training without external load (COD-0; n = 16); COD training with a 12.5% body mass (BM) external load (COD-12.5; n = 19); and COD training with a 50% BM external load (COD-50; n = 19). Participants performed the specific COD training twice per week for 6 weeks. Before and after the training period a battery of tests was completed: countermovement jump (CMJ); 30 m running sprint (time in 10-m [T10], 20-m [T20] and 30-m [T30]); L-RUN test; and V-CUT test. Within-group comparisons showed substantial improvements in CMJ and T10 (likely) in COD-0, whereas CMJ, T10 and T20 were substantially enhanced (possibly to likely) in COD-50. COD-12.5 induced substantial improvements in all analyzed variables (likely to most likely). Between-groups comparisons showed better effects on all analyzed variables for COD-12.5 compared to COD-0 group (possibly to very likely), whereas COD-50 only showed possibly better effects than COD-0 on T10. In addition, COD-12.5 induced a better effect on L-RUN and V-CUT tests than COD-50 (possibly to likely). These results indicate that COD training, especially moderate load (12.5% BM) resisted COD training, may have a positive effect on COD skills, running sprint performance and jumping ability in young soccer players.

#2 The Arrowhead Agility Test: Reliability, Minimum Detectable Change, and Practical Applications in Soccer Players
Reference: J Strength Cond Res. 2019 Jan 22. doi: 10.1519/JSC.0000000000002987. [Epub ahead of print]
Authors: Rago V, Brito J, Figueiredo P, Ermidis G, Barreira D, Rebelo A
Summary: Four independent studies were conducted to examine the utility of the arrowhead agility test (AAT) to measure change of direction (COD) capacity in soccer players, specifically, (a) intersession reliability and minimum detectable change (n = 24); (b) power-dependent abilities associated with AAT performance (n = 56); and (c) fatigue sensitivity (n = 20); differences between competitive levels and age groups (n = 264). Irrespective of the AAT outcome measure (skillful side, less-skillful side, sum of both), intersession reliability and the ability to detect changes in performance were good (ICC = 0.80-0.83; CV = 1.25-2.21%; smallest worthwhile change, 0.06-0.12 >SEM, 0.01-0.03) except for the asymmetry index. A 15-m sprint explained a significant amount of variance in COD (p < 0.01; R = 0.42). Arrowhead agility test performance did not change from the prematch toward half time (p = 0.21). However, reduced COD performance was observed after an intense period in the second half and after the game, compared with prematch and half-time performance (p < 0.05; effect size [ES] = -0.85 to 0.42). Irrespective of age group, national players were more agile than regional players (p < 0.05; ES = -1.97 to -0.36). Moreover, independently of their competitive level, senior and U18 players had a better performance than U16 (p < 0.05; ES = -2.33 to -0.84), whereas no significant differences were observed between senior and U18. Percentiles were also reported in the results. The AAT is reliable to measure COD in soccer players. The test may simultaneously encompass 15-m sprint testing but should be implemented independently to countermovement jump. Furthermore, the test is sensitive to match-induced fatigue during the second half and discriminates players from different competitive levels.

#3 External Cueing Influences Drop Jump Performance in Trained Young Soccer Players
Reference: J Strength Cond Res. 2019 Jan 22. doi: 10.1519/JSC.0000000000002935. [Epub ahead of print]
Authors: Oliver JL, Barillas SR, Lloyd RS, Moore I, Pedley J
Summary: Drop jump (DJ) characteristics provide insight on power production and injury risk. The purpose of this study was to investigate the effect of external cueing on DJ characteristics in young male soccer players. Fourteen academy soccer players performed DJs with 4 different conditions, control (CONT), contact cue (CC), height cue (HC), and quiet cue (QC). Performance measures were reactive strength index (RSI), jump height, ground contact time (GCT), and take-off impulse, with injury risk reflected by impact peak, impact timing, and landing impulse. Contact cue showed a very large significant reduction in GCT (effect size [ES] > 2.0, p < 0.05), and moderate to large increase in RSI, landing impulse, and push-off impulse (ES 0.70-1.55, p < 0.05) compared with all other conditions. Contact cue also moderately increased impact peak when compared with HC and QC (ES ≥ 0.78, p < 0.05). Height cue led to a significant increase in jump height that was moderately greater than other external cues (ES ≥ 0.87, p < 0.05), but with only a small nonsignificant increase compared (ES 0.54, p > 0.05) with CONT. The data showed that all cues provided a specific response; CC reduced GCT and increased RSI, HC increased jump height, and QC reduced outcomes associated with injury risk. Height cue may be advantageous for young soccer players with a low training age because it shows a small to moderate increase in jump height without increasing injury risk. Young players may need to be safely progressed to be able to use a CC to facilitate high reactive strength without being exposed to undue injury risk.

#4 Measuring the Hip Adductor to Abductor Strength Ratio in Ice Hockey and Soccer Players: A Critically Appraised Topic
Reference: J Sport Rehabil. 2019 Jan 24:1-18. doi: 10.1123/jsr.2018-0250. [Epub ahead of print]
Author: Rodriguez R
Summary: Ice hockey and soccer are both dynamic sports that involve continuous, unpredictable play. These athletes consistently demonstrate higher rates of groin strains compared to other contact sports. Measuring the hip adductor/abductor ratio has the potential to expose at-risk players, reduce injury rates, and preserve groin health in players with chronic strains. What is the clinical utility of measuring the hip adductor/abductor ratio for pre-season and in-season ice hockey and soccer players? Three studies, all of which were prospective cohort designs, were included. One study involved assessing preseason strength and flexibility as a risk factor for adductor strains in professional ice hockey players. Another study performed in the same professional hockey team used preseason hip adductor/abductor strength ratios to screen for those players who would benefit from a strengthening intervention aimed at reducing the incidence of adductor strains. The final study, which was performed in elite U17 soccer players, assessed the effectiveness of monthly in-season strength monitoring as a guide to trigger in-season interventions to decrease injury incidence. Measuring the hip adductor/abductor strength ratio in hockey and soccer players can be a beneficial pre-season and in-season tool to predict future groin strain risk and screen for athletes who might benefit from a strengthening intervention. Evidence exists to support monitoring the hip adductor/abductor strength ratio to assess and reduce the risk of adductor strains in ice hockey and soccer players.

#5 Realistic Soccer-Specific Virtual Environment Exposes High-Risk Lower Extremity Biomechanics
Reference: J Sport Rehabil. 2019 Jan 24:1-23. doi: 10.1123/jsr.2018-0237. [Epub ahead of print]
Authors: DiCesare CA, Kiefer AW, Bonnette SH, Myer GD
Summary: Laboratory-based biomechanical analyses of sport-relevant movements such as landing and cutting have classically been used to quantify kinematic and kinetic factors in the context of injury risk, which are then used to inform targeted interventions designed to improve risky movement patterns during sport. However, the non-contextual nature of standard assessments presents challenges for assessing sport-relevant skill transfer. It may be more effective to examine injury-risk biomechanics on individuals performing sport-specific tasks within the actual sport environment, or more feasibly, within a simulated sport environment using virtual reality (VR). The purpose of this study was to examine biomechanical differences exhibited by athletes during a jump-landing task performed as part of both a standard biomechanical assessment and a sport-specific VR-based assessment.  22 female adolescent soccer athletes (age = 16.0 ± 1.4 years; height = 165.6 ± 4.9 cm; weight = 60.2 ± 11.4 kg) participated in this study. The landing performance of was analyzed for a drop vertical jump task and a VR-based, soccer-specific corner-kick scenario in which the athletes were required to jump to head a virtual soccer ball and land. Hip, knee and ankle joint kinematic differences in the frontal and sagittal planes were used as main outcome measures. Athletes exhibited reduced hip and ankle flexion, hip abduction, and frontal plane ankle excursion during landing in realistic sport scenario compared to the standard drop vertical jump task. VR-based assessments can provide a sport-specific context in which to assess biomechanical deficits that predispose athletes for lower extremity injury and offer a promising approach to better evaluate skill transfer to sport which can guide future injury prevention efforts.

#6 Associations Between Selected Training Stress Measures and Fitness Changes in Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Jan 24:1-23. doi: 10.1123/ijspp.2018-0462. [Epub ahead of print]
Authors: Rabbani A, Kargarfard M, Castagna C, Clemente FM, Twist C
Summary: The purpose of this study was to investigate the relationship of accumulated Global Positioning System (GPS)-accelerometer-based and heart rate (HR)-based training metrics to changes in high-intensity intermittent running capacity during an in-season phase in professional soccer players. Eleven male professional players (mean ± SD, age: 27.2 ± 4.5 years) performed the 30-15 Intermittent Fitness Test (30-15IFT) before and after a five-week in-season training phase, and the final velocity (VIFT) was considered as players' high-intensity intermittent running capacity. During all sessions, Edwards' training impulse (Edwards' TRIMP), Banister's TRIMP, Z5 TRIMP, training duration, total distance covered, New Body Load (NBL), high-intensity running performance (distance covered above 14.4 km·h-1), and very high-intensity running performance (distance covered above 19.8 km·h-1) were recorded. The players' VIFT showed a most likely moderate improvement (+4.3%, 90% confidence limits [3.1; 5.5%], effect size ES, 0.70 [0.51; 0.89]). Accumulated NBL, Banister's TRIMP and Edwards' TRIMP showed large associations (r = 0.51 to 0.54) with changes in VIFT. Very large relationship was also observed between accumulated Z5 TRIMP (r= 0.72) with changes in VIFT. Large-to-nearly perfect within-individual relationships were observed between NBL and some of the other training metrics (i.e., Edwards' TRIMP, Banister's TRIMP, training duration, and total distance) in 10 out of 11 players. HR-based training metrics can be used to monitor high-intensity intermittent running capacity changes in professional soccer players. The dose-response relationship is also largely detected using accelerometer-based metrics (i.e., NBL) to track changes in high-intensity intermittent running capacity of professional soccer players.

#7 Learning to Rate Player Positioning in Soccer
Reference: Big Data. 2019 Jan 23. doi: 10.1089/big.2018.0054. [Epub ahead of print]
Authors: Dick U, Brefeld U
Summary: We investigate how to learn functions that rate game situations on a soccer pitch according to their potential to lead to successful attacks. We follow a purely data-driven approach using techniques from deep reinforcement learning to valuate multiplayer positionings based on positional data. Empirically, the predicted scores highly correlate with dangerousness of actual situations and show that rating of player positioning without expert knowledge is possible.

#8 Match Running Performance in Young Soccer Players: A Systematic Review
Reference: Sports Med. 2019 Jan 22. doi: 10.1007/s40279-018-01048-8. [Epub ahead of print]
Authors: Palucci Vieira LH, Carling C, Barbieri FA, Aquino R, Santiago PRP
Summary: To date, athletic performance has been extensively assessed in youth soccer players through laboratory and field testing. Only recently has running performance via time-motion analysis been assessed during match play. Match running data are often useful in a practical context to aid game understanding and decision making regarding training content and prescriptions. A plethora of previous reviews have collated and appraised the literature on time-motion analysis in professional senior players, but none have solely examined youth players. The aim of the present systematic review was to provide a critical appraisal and summary of the original research articles that have evaluated match running performance in young male soccer players. Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, literature searches were performed in four databases: PubMed, ISI Web of Science, SPORTDiscus and SciELO. We used the following descriptors: soccer, football, young, youth, junior, physical performance, running performance, match running performance, movement patterns, time-motion analysis, distances covered, activity profile, work rate, match analysis, and match performance. Articles were included only if they were original articles written in the English language, studied populations of male children and/or adolescents (aged ≤ 20 years), were published/ahead of print on or before 31 December 2017 and showed at least one outcome measure regarding match running performance, such as total distance covered, peak game speed or indicators of activities performed at established speed thresholds. A total of 5801 records were found. After duplicates were removed and exclusion and inclusion criteria applied, 50 articles were included (n = 2615 participants). Their outcome measures were extracted and findings were synthesized. The majority of the reviewed papers covered the European continent (62%) and used global positioning systems (GPS) (64%). Measurement error of the tools used to obtain position data and running metrics was systematically overlooked among the studies. The main aims of studies were to examine differences across playing positions (20%), age groups (26%) and match halves (36%). Consistent findings pointed to the existence of positional role and age effects on match running output (using fixed running speed thresholds), but there was no clear consensus about reductions in activity over the course of match play. Congested schedules negatively affected players' running performance. While over 32% of all studies assessed the relationships between match running performance and physical capacity, biochemical markers and body composition, ~ 70% of these did not account for playing position. This review collated scientific evidence that can aid soccer conditioning professionals in understanding external match loads across youth categories. Coaches working with youth development programs should consider that data derived from a given population may not be relevant for other populations, since game rules, match format and configuration are essentially unstandardized among studies for age-matched players. Despite limited evidence, periodization training emphasizing technical-tactical content can improve match running performance. Occurrence of acute and residual impairments in the running performance of young soccer players is common. Prescription of postmatch recovery strategies, such as cold water immersion and spa treatment, can potentially help reduce these declines, although additional research is warranted. This review also highlighted areas requiring further investigation, such as the possible influence of environmental and contextual constraints and a more integrative approach combining tactical and technical data.

#9 Drop Jump Asymmetry is Associated with Reduced Sprint and Change-of-Direction Speed Performance in Adult Female Soccer Players
Reference: Sports (Basel). 2019 Jan 21;7(1). pii: E29. doi: 10.3390/sports7010029.
Authors: Bishop C, Turner A, Maloney S, Lake J, Loturco I, Bromley T, Read P
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Summary: Studies that examine the effects of inter-limb asymmetry on measures of physical performance are scarce, especially in adult female populations. The aim of the present study was to establish the relationship between inter-limb asymmetry and speed and change-of-direction speed (CODS) in adult female soccer players. Sixteen adult players performed a preseason test battery consisting of unilateral countermovement jump (CMJ), unilateral drop jump (DJ), 10 m, 30 m, and 505 CODS tests. Inter-limb asymmetry was calculated using a standard percentage difference equation for jump and CODS tests, and Pearson's r correlations were used to establish a relationship between asymmetry and physical performance as well as asymmetry scores themselves across tests. Jump-height asymmetry from the CMJ (8.65%) and DJ (9.16%) tests were significantly greater (p < 0.05) than asymmetry during the 505 test (2.39%). CMJ-height asymmetry showed no association with speed or CODS. However, DJ asymmetries were significantly associated with slower 10 m (r = 0.52; p < 0.05), 30 m (r = 0.58; p < 0.05), and 505 (r = 0.52⁻0.66; p < 0.05) performance. No significant relationships were present between asymmetry scores across tests. These findings suggest that the DJ is a useful test for detecting existent between-limb asymmetry that might in turn be detrimental to speed and CODS performance. Furthermore, the lack of relationships present between different asymmetry scores indicates the individual nature of asymmetry and precludes the use of a single test for the assessment of inter-limb differences.

#10 Hip Arthroscopic Management Can Improve Osteitis Pubis and Bone Marrow Edema in Competitive Soccer Players With Femoroacetabular Impingement
Reference: Am J Sports Med. 2019 Jan 21:363546518819099. doi: 10.1177/0363546518819099. [Epub ahead of print]
Authors: Saito M, Utsunomiya H, Hatakeyama A, Nakashima H, Nishimura H, Matsuda DK, Sakai A, Uchida S
Summary: There is a dearth of knowledge regarding the correlation between femoroacetabular impingement (FAI) and osteitis pubis (OP) among symptomatic soccer players. The purpose was to elucidate whether arthroscopic FAI correction is effective for young competitive soccer players with FAI combined with OP or perisymphyseal pubic bone marrow edema (BME). A total of 577 consecutive patients who underwent arthroscopic FAI correction were retrospectively reviewed with a minimum 2-year follow-up. Competitive soccer players who were professional, college, and high school athletes were included. The authors assessed the modified Harris Hip Score and Nonarthritic Hip Score preoperatively and at 6 months, 1 year, and 2 years after surgery. In addition, players were divided into groups according to radiographic evidence of OP and BME (2 groups each). Clinical outcomes, return to play, and radiographic assessments were compared between groups. Twenty-eight hips met the inclusion criteria. The median modified Harris Hip Score significantly improved after hip arthroscopy (81.4, preoperatively; 95.7 at 6 months, P = .0065; 100 at 1 year, P = .0098; 100 at 2 years, P = .013). The median Nonarthritic Hip Score also significantly improved (75.0, preoperatively; 96.3 at 6 months, P = .015; 98.8 at 1 year, P = .0029; 100 at 2 years, P = .015). Furthermore, 92.0% of players returned to play soccer at the same or higher level of competition at a median 5.5 months (range, 4-15 months); 67.8% had radiological confirmation of OP; and 35.7% had pubic BME. The alpha angle was significantly higher in pubic BME group than the no-pubic BME group (64.8° vs 59.2°, P = .027), although there was no significant difference between the OP and no-OP groups. The prevalence of tenderness of the pubic symphysis significantly decreased preoperatively (32.1%) to postoperatively (3.6%). Magnetic resonance imaging findings confirmed that pubic BME disappeared in all players at a median 11 months (range, 6-36) after initial surgery. Arthroscopic management for FAI provides favorable clinical outcomes, a high rate of return to sports, and, when present, resolution of pubic BME among competitive soccer players.

#11 Effects of Combined Surfaces vs. Single-Surface Plyometric Training on Soccer Players' Physical Fitness
Reference: J Strength Cond Res. 2019 Jan 17. doi: 10.1519/JSC.0000000000002929. [Epub ahead of print]
Authors: Ramirez-Campillo R, Álvarez C, García-Pinillos F, García-Ramos A, Loturco I, Chaabene H, Granacher U
Summary: The aim of this study was to compare the effects of a 8-week plyometric jump training (PJT) performed on different surfaces (grass, land-dirt, sand, wood, gym mat, and tartan-track) vs. a single-surface PJT (grass) on components of physical fitness (muscle power, speed, and change-of-direction speed [CODS] tasks) and sport-specific performance (i.e., maximal kicking velocity [MKV]) in male soccer players aged 11-14 years. Athletes were randomly assigned to a combined surfaces PJT (PJTc, n = 8), a single-surface PJT (PJTs, n = 8), or an active control (CON, n = 7). Although the PJT group trained on grass, the PJTc trained on 6 different surfaces and equally distributed the total jump volume according to the surface. Pre-post tests were conducted on grass. Significant main effects of time were observed for the countermovement jump, the standing-long-jump, the 20-cm drop jump, 30-m sprint time, CODS, and MKV (all p < 0.001; d = 0.53-0.87). Group × time interactions were identified for all jump tests, MKV, 30-m sprint time, and CODS (all p < 0.001; d = 0.58-0.71) in favor of PJTc. No significant pre-post changes were observed in the CON (all p > 0.05; d = 0.07-0.1). In conclusion, PJT is effective in improving physical fitness in young soccer players when conducted in combination with regular soccer training. Although general fitness testing and PJTs were performed on grass, larger physical fitness improvements were found after PJTc. Thus, PJTc is recommended, as it provides a better overload stimulus compared with more conventional training overload (e.g., increase in training volume or intensity). Future studies still have to address the underlying physiological adaptations after PJTc.

#12 Effect of deep oscillation as a recovery method after fatiguing soccer training: A randomized cross-over study
Reference: J Exerc Sci Fit. 2018 Dec;16(3):112-117. doi: 10.1016/j.jesf.2018.10.004. Epub 2018 Oct 16.
Authors: von Stengel S, Teschler M, Weissenfels A, Willert S, Kemmler W
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Summary: In soccer the recovery time between matches is often not long enough for complete restoration. Insufficient recovery can result in reduced performance and a higher risk of injuries. The purpose of this study was to evaluate the potential of Deep Oscillation (DO) as a recovery method. In a randomized crossover study including 8 male soccer players (22 ± 3.3 years) the following parameters were evaluated directly before and 48 h after a fatiguing soccer-specific exercise: Maximum isokinetic strength of the leg and hip extensors and flexors (Con-Trex® Leg Press, Physiomed, Germany), rating of perceived exertion (RPE) during isokinetic testing (Borg scale 6-20), creatine kinase (CK) serum levels and Delayed Onset Muscle Soreness (DOMS; visual analogue scale 1-10). By random allocation, half of the group performed a DO self-treatment twice daily (4 applications of 15min each), whilst the other half received no intervention. 4 weeks later a cross-over was conducted. Two-way repeated measures analysis of variance was used to compare treatment versus control. A significant treatment effect was observed for maximum leg flexion strength (p = 0.03; DO: 125 ± 206 N vs. CG: -115 ± 194; p = 0.03) and for RPE (DO: -0.13 ± 0.64; vs. CG: +1.13 ± 1.36; p = 0.03). There was a trend to better recovery for maximum leg extension strength (DO: -31 ± 165 N vs. CG: -138 ± 212; p = 0.028), CK values (DO: 72 ± 331 U/ml vs. CG: 535 ± 797 U/ml; p = 0.15) and DOMS (DO: 3.4 ± 1.5 vs. CG: 4.1 ± 2.6; p = 0.49). In the present study we found significant effects of DO on maximum leg flexion strength and perceived rate of exertion. Other variables showed a consistent trend in favour of DO compared with the control without significance. DO seems to be a promising method to accelerate the time-course of peripheral recovery of muscle which should be addressed in larger studies in future.

#13 In season adaptations to intense intermittent training and sprint interval training in sub-elite football players
Reference: Scand J Med Sci Sports. 2019 Jan 24. doi: 10.1111/sms.13395. [Epub ahead of print]
Authors: Hostrup M, Gunnarsson TP, Fiorenza M, Mørch K, Onslev J, Pedersen KM, Bangsbo J
Summary: This study investigated the in-season effect of intensified training comparing the efficacy of duration-matched intense intermittent exercise training with sprint interval training in increasing intermittent running performance, sprint ability, and muscle content of proteins related to ion handling and metabolism in football players. After the first two weeks in the season, 20 sub-elite football players completed either 10 weeks of intense intermittent training using the 10-20-30 training concept (10-20-30, n=12) or sprint interval training (SIT, n=10; work/rest-ratio: 6-s/54-s) three times weekly, with a ~20% reduction in weekly training time. Before and after the intervention, players performed a Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) and a 30-m sprint test. Furthermore, players had a muscle biopsy taken from the vastus lateralis. Yo-Yo IR1 performance increased by 330 m (95%CI: 178-482, P≤0.01) in 10-20-30, whereas no change was observed in SIT. Sprint time did not change in 10-20-30, but decreased by 0.04 s (95%CI: 0.00-0.09, P≤0.05) in SIT. Muscle content of HADHA (24%, P≤0.01), PDH-E1α (40%, P≤0.01), complex I-V of the electron transport chain (ETC) (51%, P≤0.01) and Na+ ,K+ -ATPase subunits α2 (33%, P≤0.05) and β1 (27%, P≤0.05) increased in 10-20-30, whereas content of DHPR (27%, P≤0.01) and complex I-V of the ETC (31%, P≤0.05) increased in SIT. Intense intermittent training, combining short sprints and a high aerobic load, is superior to regular sprint interval training in increasing intense intermittent running performance during a Yo-Yo IR1 test and muscle content of PDH-E1α and HADHA in sub-elite football players.

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