Latest research in football - week 40 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Cardio-respiratory values during recovery from exercise in soccer Spanish leagues
Reference: Physiol Meas. 2018 Oct 11;39(10):105003. doi: 10.1088/1361-6579/aae0e8.
Authors: Ramos-Álvarez JJ, Maffulli N, Bragazzi NL, Ardigò LP, Jiménez-Herranz E, Naranjo-Ortiz C, Padulo J, Calderón Montero FJ
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Summary: In this cross-sectional study, we compared Spanish division one (n  =  114) and division two (n  =  80) soccer players in terms of their cardio-respiratory response during recovery following a maximum laboratory effort test. Following the maximum laboratory effort protocol, we measured oxygen consumption ([Formula: see text]), heart rate (HR), and ventilation ([Formula: see text]) during recovery. Over the first 60 s of recovery, no significant differences were seen in either [Formula: see text] (28.7 versus 28.3 ml/kg/m, in division one and two players, respectively), HR, or [Formula: see text] (p  >  0.05). After 90 s, however, significant differences appeared between the players of the two divisions (p  <  0.01), although not among playing positions. Significant differences in [Formula: see text] (21.1 versus 26.0 ml/kg/m, in division one and two players, respectively) and HR were still apparent at 180 s into the recovery period. The change in professional soccer players' cardio-respiratory values over the recovery period following maximum effort are independent of the position played, but are associated with the division in which a player competes. Second division players show significantly higher [Formula: see text] and HR values than first division players at 180 s into the recovery period. These differences might influence performance in soccer and in other athletes whose sports require intermittent bouts of maximum effort and consequently times to repeat high-intensity efforts as short as possible.

#2 Lower limb injury prevention programs in youth soccer: a survey of coach knowledge, usage, and barriers
Reference: J Exp Orthop. 2018 Oct 11;5(1):43. doi: 10.1186/s40634-018-0160-6.
Authors: Mawson R, Creech MJ, Peterson DC, Farrokhyar F, Ayeni OR
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Summary: Participation in youth soccer carries a significant risk of injury, most commonly non-contact injuries of the lower extremity. A growing body of research supports the use of neuromuscular interventions by teams to prevent such injuries, yet the uptake of these recommendations by soccer teams remains largely unexplored. The purposes of the study were to determine (1) the level of awareness by youth coaches of injury prevention programs and their efficacy; (2) the number of youth coaches that use these interventions; and (3) barriers and potential facilitators to implementing a sustainable injury prevention program. Four hundred eighteen coaches of male and female youth soccer teams were emailed an online blinded survey. This survey consisted of 26 questions covering coaches' demographics, level of training, experience with injuries among players, and use of injury prevention programs. Question development was guided by the RE-AIM Sports Setting Matrix in combination with findings from the literature review and expert experience from orthopaedic surgeons specializing in sport medicine. Of the 418 coaches contacted, 101 responded. Only 29.8% of respondents used an injury prevention program in the prior soccer season. Coaches that had completed one or more coaching courses were more likely to use an intervention. Of those that did not already use an intervention, coaches agreed or strongly agreed that they would consider using one if it could be used in place of the warm up and take no more than 20 min (74.0%), if they could access information about the exercises (84.0%), and if the exercises could be properly demonstrated (84.0%). Additionally, 84% of coaches that did not already use an intervention agreed or strongly agreed that knowing that interventions may reduce a player's risk of injury by 45% would affect whether they would use one. This study suggests that the current use and awareness of injury prevention programs is limited by a lack of communication and education between sporting associations and coaches, as well as perceived time constraints. The results also suggest that improving coaching education of injury prevention could increase the frequency of intervention use.

#3 Low Doses of Caffeine: Enhancement of Physical Performance in Elite Adolescent Male Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Oct 9:1-21. doi: 10.1123/ijspp.2018-0536. [Epub ahead of print]
Authors: Ellis M, Noon M, Myers T, Clarke N
Summary: Large doses of ~6 mg·kg-1 body mass have improved performance during intermittent running, jumping, and agility protocols. However, there are sparse data on low doses of caffeine, especially in elite adolescent soccer players. Fifteen elite youth soccer players (177.3±4.8 cm, 66.9±7.9 kg and 16±1 y) participated in the study, consuming 1, 2, or 3 mg·kg-1 caffeine in a gelatin capsule or a 2-mg·kg-1 placebo in a single-blind, randomized, crossover study design. Testing consisted of a 20-m sprint, arrowhead agility (change of direction [CoD] right or left), countermovement jump (CMJ), and Yo-Yo Intermittent Recovery Test Level-1 (Yo-Yo IR1). Post-exercise CMJ performance was assessed as participants exited the Yo-Yo IR1. Data were analyzed using a Bayesian multilevel regression model to provide explained variance and probabilities of improvement (p=%). 3 mg·kg-1 caffeine presented the highest probabilities of change compared with placebo across a range of tests (mean ± SD, p= %). Times for 20-m sprint were 3.15±0.10s vs 3.18±0.09s (p=73%), CoD-R times were 8.43±0.24s vs 8.55±0.25s (p=99%), CoD-L times were 8.44±0.22s vs 8.52±0.18s (p=85%), Yo-Yo IR1 distance was 2440±531m vs 2308±540m (p=15%), and preexercise CMJ height was 41.6±7.2cm vs 38±8.5cm (p=96%). Postexercise CMJ was higher with 3 mg·kg-1 than with placebo (42.3±8cm vs 36.6±8cm [p=100%]). Doses of 1 or 2 mg·kg-1 caffeine also demonstrated the ability to enhance performance but were task dependent. Low doses of caffeine improve performance but are dose and task dependent. A dose of 3 mg·kg-1 caffeine improved performance across the majority of tests with potential to further improve postexercise CMJ height.

#4 The efficacy of lower limb screening tests in predicting PlayerLoad within a professional soccer academy
Reference: J Sport Rehabil. 2018 Oct 9:1-20. doi: 10.1123/jsr.2018-0175. [Epub ahead of print]
Authors: Bowen C, Weaver K, Relph N, Greig M
Summary: Training exposure has been associated with injury epidemiology in elite youth soccer, where lower limb musculoskeletal screening is commonly used to highlight injury risk. However, there has been little consideration of the relationship between lower limb screening and the loading response to soccer activities. The purpose was to quantify the efficacy of using screening tests to predict the loading elicited in soccer-specific activities, and to develop a hierarchical ordering of musculoskeletal screening tests to identify test redundancy and inform practice. 21 elite male soccer players aged 15.7 ± 0.9 years participated in this study. Players completed a battery of five screening tests (knee to wall, hip internal rotation, adductor squeeze, single leg hop, anterior reach), and a 25min standardised soccer session with a GPS unit placed at C7 to collect multi-planar PlayerLoad data. Baseline data on each screening test, along with uni-axial PlayerLoad in the medio-lateral, anterio-posterior and vertical planes were utilized as outcome measures. Stepwise hierarchical modelling of the screening tests revealed that dominant leg knee to wall distance was the most prevalent and powerful predictor of multi-planar PlayerLoad, accounting for up to 42% of variation in uni-axial loading. The adductor squeeze test was the least powerful predictor of PlayerLoad. Of note, one player who incurred a knee injury within three weeks of testing had shown a 20% reduction in knee to wall distance compared with peers, and elicited 23% greater PlayerLoad, supporting the hierarchical model. There was some evidence of redundancy in the screening battery, with implications for clinical choice. Hierarchical ordering and a concurrent case study highlight dominant leg knee to wall distance as the primary predictor of multi-axial loading in soccer. This has implications for the design and interpretation of screening data in elite youth soccer.

#5 Differences in Sprint Mechanical Force-Velocity Profile Between Trained Soccer and Futsal Players
Reference: Int J Sports Physiol Perform. 2018 Oct 9:1-21. doi: 10.1123/ijspp.2018-0402. [Epub ahead of print]
Authors: Jiménez-Reyes P, García-Ramos A, Cuadrado-Peñafiel V, Párraga-Montilla JA, Morcillo-Losa JA, Samozino P, Morin JB
Summary: This study aimed to compare the sprint mechanical force-velocity (F-V) profile between soccer and futsal players. A secondary aim was, within each sport, to study the differences in sprint mechanical F-V profile between sexes and players of different levels. 102 soccer players (63 men) and 77 futsal players (49 men) that were competing from the elite to amateur levels in the Spanish league participated in this investigation. The testing procedure consisted of 3 unloaded maximal 40-m sprints. The velocity-time data recorded by a radar device was used to calculate the variables of the sprint acceleration F-V profile (maximal theoretical force [F0], maximal theoretical velocity [V0], maximal power [Pmax], decrease in the ratio of horizontal-to-resultant force [DRF], and maximal ratio of horizontal-to-resultant force [RFpeak]). Futsal players showed a higher F0 than soccer players (effect size [ES] range: 0.11 to 0.74), while V0 (ES range: -0.48 to -1.15) and DRF (ES range: -0.75 to -1.45) was higher for soccer players. No significant differences were observed between soccer and futsal players for Pmax (ES range: -0.43 to 0.19) and RFpeak (ES range: -0.49 to 0.30). Men and high-level players presented an overall enhanced F-V profile compared to women and their lower-level counterparts, respectively. The higher F0 and lower V0 of futsal players could be caused by the specific game's demand (larger number of accelerations but of shorter distances compared to soccer). These results show that the sprint mechanical F-V profile is able to distinguish between soccer and futsal players.

#6 The temporal pattern of recovery in eccentric hamstring strength post-soccer specific fatigue
Reference: Res Sports Med. 2018 Oct 8:1-12. doi: 10.1080/15438627.2018.1523168. [Epub ahead of print]
Authors: Rhodes D, McNaughton L, Greig M
Summary: Eccentric hamstring strength is an aetiological risk factor for soccer injury. The temporal pattern of recovery post-exercise is critical in injury management. 18 male professional soccer players completed baseline assessments of eccentric hamstring strength at isokinetic speeds of 60, 150 and 300°· s-1. Post SAFT90 measures were repeated immediately, + 24 hrs, + 48 hrs and + 72 hrs. Main effects for recovery time and testing speed in average torque (AvT), peak torque (PT) and the corresponding angle (Ɵ) were supplemented by regression modelling to describe the temporal pattern of recovery. A main effect for isokinetic testing speed was observed in PT and AvT. A main effect for recovery time highlighted greater strength pre-exercise, with a quadratic pattern to temporal recovery highlighting minima achieved at between 40-48 hrs. Strength parameters are not fully recovered until 96 hrs post soccer specific fatigue, with implications for training design and injury management, particularly within fixture-congested periods.

#7 Manual therapy and early return to sport in football players with adductor-related groin pain: A prospective case series
Reference: Physiother Theory Pract. 2018 Oct 11:1-10. doi: 10.1080/09593985.2018.1531096. [Epub ahead of print]
Authors: Tak I PhD, MScPT, Langhout R MMT PT, Bertrand B MScPT, Barendrecht M MPTS, Stubbe J PhD, Kerkhoffs G PhD, MD, Weir A PhD, MBBS
Summary: The purpose was to study the clinical course including return to sport success rates of football players with adductor-related groin pain (ARGP) after manual therapy of the adductor muscles. Thirty-four football players with ARGP with median pre-injury Tegner scores of 9 (IQR 25-75: 9-9) were treated with manual therapy of the adductor muscles. Main outcome measures were numeric pain rating scale (NPRS), Hip and Groin Outcome Score (HAGOS) and global perceived effect (GPE) for treatment and patient satisfaction at 2, 6 and 12 weeks. Return to sport was documented. Pain during (NPRS 7 (6-8) and after (NPRS 8 (6-8) sports decreased to NPRS 1 (0.2-3) and 1 (0.8-3), respectively (p < 0.001). Within 2 weeks 82% of the players returned to pre-injury playing levels with improved (p < 0.001) HAGOS subscale scores. Eighty-five percent reported clinically relevant improvement, 82% reported to be satisfied. At 12 weeks, 88% had returned to pre-injury playing levels. HAGOS showed symptoms were still present. Early return to sport seems possible and safe after manual therapy of the adductor muscles in football players with ARGP in the short term. While the majority of injured football players return to sport within two weeks, caution is advised regarding effectiveness as hip and groin symptoms were still present and no control groups were available.

#8 Effects of pitch spatial references on players' positioning and physical performances during football small-sided games
Reference: J Sports Sci. 2018 Oct 11:1-7. doi: 10.1080/02640414.2018.1523671. [Epub ahead of print]
Authors: Coutinho D, Gonçalves B, Travassos B, Abade E, Wong DP, Sampaio J
Summary: The aim of this study was to identify the effects of adding spatial references during football small-sided games in youth players' tactical and physical performance. Twelve under-15 players performed a Gk+ 6v6+ Gk game under two playing conditions: (i) without spatial references (CONTROL condition); (ii) with spatial references, by dividing equally the pitch into three corridors and three sectors (experimental situation, LINES). Players' positional data was used to compute time-motion and tactical-related variables. The results revealed that performance under LINES situation increased the regularity in the zones occupied (~14%, Cohen's d: 0.5; ±0.3; p = 0.003) and in the distance between teammates' dyads (~19%, 0.9; ±0.2; p < 0.001). Oppositely, LINES condition decreased the longitudinal synchronization of players' displacements (0.4; ±0.2; p = 0.002), players' average speed (0.5; ±0.3; p = 0.002) and distance covered at lower (0.9; ±0.3; p < 0.001) and moderate speed (0.5; ±0.3; p < 0.001). Adding spatial references seems to promote a more structured pattern of play and increase positional regularity. However, coaches should be aware that this constraint may decrease the synchronization between players. Overall, these findings may be generalized to most invasion team sports.

#9 Top 50 most-cited articles in medicine and science in football
Reference: BMJ Open Sport Exerc Med. 2018 Oct 1;4(1):e000388. doi: 10.1136/bmjsem-2018-000388. eCollection 2018.
Authors: Brito J, Nassis GP, Seabra AT, Figueiredo P
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Summary: The purpose was to conduct a comprehensive mapping analysis to the scientific literature published in football aiming to identify the areas of bigger interest and potential for further exploration. The data were obtained by a search conducted on the Web of Science. Articles were listed based on citation frequency. We used an open-source bibliometrix R-package for the comprehensive bibliometric analyses. The number of citations per article ranged from 251 to 869 (median 323; IQR 125). The yearly number of citations ranged from 8 to 54 (median 26; IQR 11). Most of the articles (76%) were of level III of evidence, 10% were level II and 14% were level IV. Within the top 50 most-cited articles, 40 articles were original research (37 observational and 3 experimental studies), 9 were review articles and 1 was a thesis. From the 40 original research articles, 50% involved elite players, 73% were exclusive to male players and 80% involved adult players only. The topic area with the highest number of articles was sports medicine (44%), followed by training and testing (32%), performance analysis (14%) and physiology (10%). No study within the top 50 was devoted to biomechanics, nutrition, sport psychology, coaching or social sciences. The lack of experimental studies within the top 50 most-cited articles in football clearly underpins how far we still are from establishing the theoretical and methodological guidelines for the applied science and medicine in football.

#10 Effect of the Fatigue on the Physical Performance in Different Small-Sided Games in Elite Football Players
Reference: J Strength Cond Res. 2018 Oct 5. doi: 10.1519/JSC.0000000000002858. [Epub ahead of print]
Authors: Calderón Pellegrino G, Paredes-Hernández V, Sánchez-Sánchez J, García-Unanue J, Gallardo L
Summary: Football players need to be able to perform high-intensity efforts of short duration with brief recovery periods. The aim of this study was to analyze the influence of the pitch dimension on high-intensity actions and the effect of a repeated sprint ability (RSA) test on the physical performance in different 4-against-4 (4v4) small-sided games (SSG) dimensions. Sixteen U-18 elite football players performed an RSA test between two 4v4 SSGs (pre and post) to induce fatigue and compare physical data. Speed, sprint number, accelerations, sprint distance, total distance covered, and total distance covered of the players at different intensities were evaluated in 3 different SSGs (125, 150, 250, and 300 m). Results revealed a significant detriment of physical performance in the 125-m SSG after RSA, mostly in number of sprints (-6.56; confidence interval [CI] 95%: -10.13 to -3.00; effect size [ES]: 1.13 p < 0.001), accelerations (-2.69; CI 95%: -5.13 to -0.24; ES: 0.68; p = 0.032), and sprint distance (-65.44 m; CI 95%: -103.73 to -27.16; ES: 1.20; p = 0.001). In bigger SSGs (250 and 300 m), higher distance at high intensity was covered and Vmax, Vmean, and sprint distance were greater. In summary, accelerations, sprint number, and fatigue were higher in smaller pitches, and higher velocities were reached in bigger SSGs. Football players should be aware that changes in pitch size can modify the physical performance on high-intensity actions in SSGs.

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