Latest research in football - week 6 - 2020

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 Hip and Groin Injuries in National Collegiate Athletic Association Women's Soccer Players
Reference: Orthop J Sports Med. 2020 Jan 22;8(1):2325967119892320. doi: 10.1177/2325967119892320. eCollection 2020 Jan.
Authors: Ralston B, Arthur J, Makovicka JL, Hassebrock J, Tummala S, Deckey DG, Patel K, Chhabra A, Hartigan D
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Summary: Hip and groin injuries are common in competitive soccer players and have been shown to be significant sources of time loss. There are few studies describing the epidemiology of hip and groin injuries in female National Collegiate Athletic Association (NCAA) soccer players. The purpose was to describe the epidemiology of hip and groin injuries in women's collegiate soccer players. The NCAA Injury Surveillance System/Program (ISS/ISP) was analyzed from 2004 through 2014 for data related to hip and groin injuries in female collegiate soccer players. Injuries and athlete-exposures (AEs) were reported by athletic trainers. Data were stratified by time of season, event type, injury type, treatment outcome, time loss, and player field position. Between 2004 and 2014, there were 439 recorded hip or groin injuries in female soccer players and an overall rate of injury of 0.57 per 1000 AEs. Injuries were 12.0 times more likely to occur during the preseason (4.41/1000 AEs) as opposed to during the regular season (0.37/1000 AEs) (injury rate ratio [IRR], 12.01; 95% confidence interval [CI], 9.92-14.55) or postseason (0.38/1000 AEs) (IRR, 11.55; 95% CI, 7.06-18.91). Rates of injury were similar during the regular season and postseason (IRR, 0.96; 95% CI, 0.59-1.58). Rates of injury were higher during competition (0.69/1000 AEs) than during practice (0.52/1000 AEs) (IRR, 1.33; 95% CI, 1.08-1.63). Most injuries were new (87.5%; n = 384) and unlikely to recur (12.5%; n = 55). Hip and groin injuries in female NCAA soccer players are uncommon, and fortunately, most players return to play quickly without recurrence. Future prospective studies should evaluate the effectiveness of strength and conditioning programs in preventing these injuries.

#2 The Influence of Playing Surface on the Loading Response to Soccer-Specific Activity
Reference: J Sport Rehabil. 2020 Feb 5:1-5. doi: 10.1123/jsr.2019-0327. [Epub ahead of print]
Authors: Jones A, Page R, Brogden C, Langley B, Greig M.
Summary: The influence of playing surface on injury risk in soccer is contentious, and contemporary technologies permit an in vivo assessment of mechanical loading on the player. The objective was to quantify the influence of playing surface on the PlayerLoad elicited during soccer-specific activity. Fifteen amateur soccer players (22.1 [2.4] y), injury free with ≥6 years competitive experience participated in this study. Each player completed randomized order trials of a soccer-specific field test on natural turf, astroturf, and third-generation artificial turf. GPS units were located at C7 and the mid-tibia of each leg to measure triaxial acceleration (100 Hz). Total accumulated PlayerLoad in each movement plane was calculated for each trial. Ratings of perceived exertion and visual analog scales assessing lower-limb muscle soreness were measured as markers of fatigue. Analysis of variance revealed no significant main effect for playing surface on total PlayerLoad (P = .55), distance covered (P = .75), or postexercise measures of ratings of perceived exertion (P = .98) and visual analog scales (P = .61). There was a significant main effect for GPS location (P < .001), with lower total loading elicited at C7 than mid-tibia (P < .001), but with no difference between limbs (P = .70). There was no unit placement × surface interaction (P = .98). There was also a significant main effect for GPS location on the relative planar contributions to loading (P < .001). Relative planar contributions to loading in the anterioposterior:mediolateral:vertical planes was 25:27:48 at C7 and 34:32:34 at mid-tibia. PlayerLoad metrics suggest that playing surface does not influence mechanical loading during soccer-specific activity (not including tackling). Clinical reasoning should consider that PlayerLoad magnitude and axial contributions were sensitive to unit placement, highlighting opportunities in the objective monitoring of load during rehabilitation.

#3 Anticipation and Situation-Assessment Skills in Soccer Under Varying Degrees of Informational Constraint
Reference: J Sport Exerc Psychol. 2020 Feb 6:1-11. doi: 10.1123/jsep.2019-0118. [Epub ahead of print]
Authors: Basevitch I, Tenenbaum G, Filho E, Razon S, Boiangin N, Ward P
Summary: The authors tested the notion that expertise effects would be more noticeable when access to situational information was reduced by occluding (i.e., noncued) or freezing (i.e., cued) the environment under temporal constraints. Using an adaptation of tasks developed by Ward, Ericsson, and Williams, the participants viewed video clips of attacking soccer plays frozen or occluded at 3 temporal points and then generated and prioritized situational options and anticipated the outcome. The high-skill players anticipated the outcomes more accurately, generated fewer task-irrelevant options, and were better at prioritizing task-relevant options than their low-skill counterparts. The anticipation scores were significantly and positively correlated with the option prioritization and task-relevant options generated but not with the total options generated. Counter to the authors' prediction, larger skill-based option-prioritization differences were observed when the play was frozen than when it was occluded. These results indicate that processing environmental information depends on temporal and contextual conditions.

#4 Determinant Factors of the Match-Based Internal Load in Elite Soccer Players
Reference: Res Q Exerc Sport. 2020 Feb 6:1-8. doi: 10.1080/02701367.2019.1710445. [Epub ahead of print]
Authors: Enes A, Oneda G, Alves DL, Palumbo DP, Cruz R, Moiano Junior JVM, Novack LF, Osiecki R
Summary: The purpose was to analyze the contribution of physical measures and external load in the match-based internal load of elite soccer players. Twenty-three elite soccer players (n = 23, age 26.69 ± 3.93 years, body mass 78.04 ± 5.03 kg, height 178.04 ± 5.19 cm, body fat 10.98 ± 1.25%) from a first division soccer team of the Brazilian Championship were evaluated first with anthropometric and physical measures (flexibility and muscle power of lower limbs), and after 24 hrs they were asked to perform an incremental treadmill test (VO2max and ventilatory thresholds). Subsequently, athletes were monitored for 6 weeks during nine official matches of a regional championship. On match days, the external load data (e.g., player load) were collected by triaxial accelerometers with GPS systems and post 30 min after the end of the match the internal load was assessed with the Session Rating of Perceived Exertion method (Session-RPE). Our main findings showed significant contributions of the Player Load (r = .62, p < .001; 42.3%) and Anaerobic Threshold (r = - .199, p = .05, 17%) for the predictive model of Session-RPE. Physical measures and external load have a significant influence on the internal load in elite soccer players. Our findings suggest that sport scientists can use the Session-RPE as a low-cost method for prescribing and monitoring training loads, by the influence of physical measures and external load on the match-based internal load, in order to optimize athletes' performance.

#5 Practitioner perceptions regarding the practices of soccer substitutes
Reference: PLoS One. 2020 Feb 7;15(2):e0228790. doi: 10.1371/journal.pone.0228790. eCollection 2020.
Authors: Hills SP, Radcliffe JN, Barwood MJ, Arent SM, Cooke CB, Russell M
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Summary: Despite empirical observations suggesting that practitioners value the use of substitutions during soccer match-play, limited research has sought to substantiate such claims. This study used online surveys to assess the perceptions of practitioners within professional soccer about the use and practices of substitutes. Thirty-three practitioners completed one of two surveys (each requiring both open and closed questions to be answered), depending upon whether their primary role related mostly to tactical ('tactical practitioners'; n = 7) or physical ('physical practitioners'; n = 26) aspects of player/team management. Thematic content analysis of responses identified four higher-order themes: 'impact of substitutions', 'planning and communication', 'player preparation and recovery' and 'regulations'. Eighty-five percent of practitioners believed that substitutes are important in determining success during soccer match-play, with the primary justification being the perceived ability of such players to provide a physical and/or tactical impact. However, contextual factors such as the match situation, timing of introduction, and players undergoing adequate pre-pitch-entry preparation, may be important for realising such aims. Although many practitioners believed that there was a need for substitutes to engage in bespoke non-match-day preparations and recovery strategies that differ from starting players, logistical considerations, such as scarcity of resources, often limit their scope. Notwithstanding, 96% of respondents indicated that substitutes frequently perform extra conditioning sessions to account for deficits in high-speed running loads compared with players exposed to a longer period of match-play. Substitutes' pre-match warm-ups are typically led by team staff, however practitioners reported providing varying levels of input with regards to the practices adopted between kick-off and pitch-entry. Uncertainty exists as to the efficacy of current pre-pitch-entry practices, and 100% of practitioners highlighted 'preparatory strategies' as at least a 'moderately important' direction for future research. This study presents novel insights and highlights areas that are considered future research priorities amongst those working in the field.

#6 The Effect of Transition Period on Performance Parameters in Elite Female Soccer Players
Reference: Int J Sports Med. 2020 Feb 14. doi: 10.1055/a-1103-2038. [Epub ahead of print]
Authors: Parpa KP, Michaelides MA.
Summary: The purpose of this study was to examine the effect of a 4-week off-season period (transition period) on the anthropometric and performance parameters in elite female soccer players who participated in the UEFA women's Champions league. Eighteen female players (age 23.6±4.3 years) underwent testing at the end of the competitive period and right after the transition period. An incremental cardiopulmonary testing, body composition assessment and isokinetic testing at 60 °/sec were performed on both occasions. The cardiopulmonary exercise testing revealed that VO2max (p=0.001) and time on the treadmill (p=0.000) were significantly reduced after the transition period that included a 2 times/week exercise regimen. Furthermore, the quadriceps torque production at 60 °/s was significantly reduced for both the right (p=0.013) and left quadriceps (p=0.004) following the transition period. Finally, body weight (p=0.001) and body fat (p=0.000) significantly increased after 4 weeks of significantly reduced training volume. It is concluded that the transition period negatively affected the anthropometric and performance parameters of the female players. These data maybe informative for coaches and trainers as they demonstrate that despite the efforts to keep the players physically active the performance parameters decreased significantly.

#7 Relative age effects in Elite Chinese soccer players: Implications of the 'one-child' policy
Reference: PLoS One. 2020 Feb 14;15(2):e0228611. doi: 10.1371/journal.pone.0228611. eCollection 2020.
Authors: Li Z, Mao L, Steingröver C, Wattie N, Baker J, Schorer J, Helsen WF
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Summary: The relative age effect (RAE) refers to the asymmetrical distribution of birthdates in a cohort found in many achievement domains, particularly in sports with many participants like soccer. Given the uniqueness of the one-child policy in China, this study examined the existence of the RAE in elite Chinese male and female soccer players generally and relative to their playing position on the field. Results showed a clear and obvious RAE for all age groups (U20 male, U18 male, adult female and U18 female) with the observed birthdate distributions for each age group significantly different from expected distributions (p<0.05). Additionally, we noticed a differential RAE according to the players' position on the field as reflected in different effect sizes. In male players, the RAE was significantly greater in Defenders (DF) and Goalkeepers (GK) compared to Midfielders (MF) and Forwards (FW) (VDF = 0.266>VGK = 0.215>VMF = 0.178>VFW = 0.175). In female players, GKs had a larger RAE (VGK = 0.184>0.17, VDF = 0.143, VMF = 0.127, VFW = 0.116). To reduce the negative consequences associated with RAEs throughout player development systems, potential solutions are discussed.

#8 Anthropometric and Body Composition Profile of Young Professional Soccer Players
Reference: J Strength Cond Res. 2020 Feb 13. doi: 10.1519/JSC.0000000000003416. [Epub ahead of print]
Authors: Bernal-Orozco MF, Posada-Falomir M, Quiñónez-Gastélum CM, Plascencia-Aguilera LP, Arana-Nuño JR, Badillo-Camacho N, Márquez-Sandoval F, Holway FE, Vizmanos-Lamotte B
Summary: The purpose was to describe the anthropometric and body composition profile of young professional soccer players and to compare the players profiles between different competitive divisions and playing positions. A retrospective cross-sectional study was carried out with anthropometric data obtained from the records of soccer players of Club Deportivo Guadalajara, S.A. de C.V. (Mexico) in the under-17, under-20, second, third, and fourth division categories. Body mass, height, sitting-height, skinfolds, girths, and bone breadths were measured by certified anthropometrists from September 2011 to March 2015, following the procedures recommended by the International Society for the Advancement of Kinanthropometry. Body composition was determined using the 5-way fractionation method. Comparisons between playing positions in each division and between divisions were performed using analysis of variance, and Bonferroni's post-hoc analyses (SPSS version 22 for Windows, p < 0.05 considered as significant). Data from 755 subjects were analyzed. The mean age was 18.1 ± 1.7 years old (minimum 14.8, maximum 23.2). The under-20 division registered higher anthropometric and body composition values than all other competitive divisions. In addition, goalkeepers were taller, heavier, and obtained the highest values for adipose mass, whereas forwards presented higher percentages of muscle mass. These tables can be used during nutritional assessment and nutritional monitoring of players to establish body composition goals. In addition, the strength and conditioning practitioner may also use these data to design effective and specific training programs most suitable to the anthropometric and body composition profile of each player, taking into consideration his competitive division and playing position.

#9 Anthropometric, Body Composition, and Morphological Lower Limb Asymmetries in Elite Soccer Players: A Prospective Cohort Study
Reference: Int J Environ Res Public Health. 2020 Feb 11;17(4). pii: E1140. doi: 10.3390/ijerph17041140.
Authors: Mala L, Maly T, Cabell L, Hank M, Bujnovsky D, Zahalka F
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Summary: The aim of this study was to identify and compare parameters related to anthropometry, body composition (BC), and morphological asymmetry in elite soccer players in nine age categories at the same soccer club (n = 355). We used a bio-impedance analyzer to measure the following indicators of BC: body height (BH); body mass (BM); relative fat-free mass (FFMr); percentage of fat mass (FM); and bilateral muscle mass differences in the lower extremities (BLD∆). Age showed a significant influence on all parameters observed (F64,1962 = 9.99, p = 0.00, λ = 14.75, η2p = 0.25). Adolescent players (from U16 through adults) had lower FM values (<10%) compared to players in the U12-U15 categories (>10%). The highest FFMr was observed in the U18 category. Players in the U12 and U13 categories showed more homogenous values compared to older players. With increasing age, significantly higher FFMr was observed in the lower extremities. An inter-limb comparison of the lower extremities showed significant differences in the U17 category (t27 = 2.77, p = 0.01) and in adult players (t68 = 5.02, p = 0.00). Our results suggest that the end of height growth occurs around the age of 16 years, while weight continues to increase until 20 years. This increase is not linked to decreasing FM, nor to the FFMr, which remains stable. We found morphological asymmetries between limbs in players of the U17 category and in adult players.

#10 The effect of low back pain and lower limb injury on lumbar multifidus muscle morphology and function in university soccer players
Reference: BMC Musculoskelet Disord. 2020 Feb 12;21(1):96. doi: 10.1186/s12891-020-3119-6.
Authors: Nandlall N, Rivaz H, Rizk A, Frenette S, Boily M, Fortin M
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Summary: The lumbar multifidus muscle (LMM) plays a critical role to stabilize the spine. While low back pain (LBP) is a common complaint in soccer players, few studies have examined LMM characteristics in this athletic population and their possible associations with LBP and lower limb injury. Therefore, the purpose of this study was to 1) investigate LMM characteristics in university soccer players and their potential association with LBP and lower limb injury; 2) examine the relationship between LMM characteristics and body composition measurements; and 3) examine seasonal changes in LMM characteristics. LMM ultrasound assessments were acquired in 27 soccer players (12 females, 15 males) from Concordia University during the preseason and assessments were repeated in 18 players at the end of the season. LMM cross-sectional area (CSA), echo-intensity and thickness at rest and during contraction (e.g. function) were assessed bilaterally in prone and standing positions, at the L5-S1 spinal level. A self-reported questionnaire was used to assess the history of LBP and lower limb injury. Dual-energy x-ray absorptiometry (DEXA) was used to acquire body composition measurements. Side-to-side asymmetry of the LMM was significantly greater in males (p = 0.02). LMM thickness when contracted in the prone position (p = 0.04) and LMM CSA in standing (p = 0.02) were also significantly greater on the left side in male players. The LMM % thickness change during contraction in the prone position was significantly greater in players who reported having LBP in the previous 3-months (p < 0.001). LMM CSA (r = - 0.41, p = 0.01) and echo-intensity (r = 0.69, p < 0.001) were positively correlated to total % body fat. There was a small decrease in LMM thickness at rest in the prone position over the course of the season (p = 0.03). The greater LMM contraction in players with LBP may be a maladaptive strategy to splint and project the spine. LMM morphology measurements were correlated to body composition. The results provide new insights with regards to LMM morphology and activation in soccer players and their associations with injury and body composition measurements.

#11 Seven Weeks of Jump Training with Superimposed Whole-Body Electromyostimulation Does Not Affect the Physiological and Cellular Parameters of Endurance Performance in Amateur Soccer Players
Reference: Int J Environ Res Public Health. 2020 Feb 10;17(3). pii: E1123. doi: 10.3390/ijerph17031123.
Authors: Wirtz N, Filipovic A, Gehlert S, Marées M, Schiffer T, Bloch W, Donath L
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Summary: Intramuscular density of monocarboxylate-transporter (MCT) could affect the ability to perform high amounts of fast and explosive actions during a soccer game. MCTs have been proven to be essential for lactate shuttling and pH regulation during exercise and can undergo notable adaptational changes depending on training. The aim of this study was to evaluate the occurrence and direction of potential effects of a 7-weeks training period of jumps with superimposed whole-body electromyostimulation on soccer relevant performance surrogates and MCT density in soccer players. For this purpose, 30 amateur soccer players were randomly assigned to three groups. One group performed dynamic whole-body strength training including 3 x 10 squat jumps with WB-EMS (EG, n = 10) twice a week in addition to their daily soccer training routine. A jump training group (TG, n = 10) performed the same training routine without EMS, whereas a control group (CG, n = 8) merely performed their daily soccer routine. 2 (Time: pre vs. post) x 3 (group: EG, TG, CG) repeated measures analyses of variance (rANOVA) revealed neither a significant time, group nor interaction effect for VO2peak, Total Time to Exhaustion and Lamax as well as MCT-1 density. Due to a lack of task-specificity of the underlying training stimuli, we conclude that seven weeks of WB-EMS superimposed to jump exercise twice a week does not relevantly influence aerobic performance or MCT density.


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