Latest research in football - week 15 - 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 The Influence of Soccer Playing Surface on the Loading Response to Ankle (P)Rehabilitation Exercises
Reference: J Sport Rehabil. 2020 Mar 31:1-7. doi: 10.1123/jsr.2019-0199. [Epub ahead of print]
Authors: Jones A, Brogden C, Page R, Langley B, Greig M.
Summary: Contemporary synthetic playing surfaces have been associated with an increased risk of ankle injury in the various types of football. Triaxial accelerometers facilitate in vivo assessment of planar mechanical loading on the player. The aim was to quantify the influence of playing surface on the PlayerLoad elicited during footwork and plyometric drills focused on the mechanism of ankle injury. A total of 15 amateur soccer players (22.1 [2.4] y), injury free with ≥6 years competitive experience. Each player completed a test battery comprising 3 footwork drills (anterior, lateral, and diagonal) and 4 plyometric drills (anterior hop, inversion hop, eversion hop, and diagonal hop) on natural turf (NT), third-generation artificial turf (3G), and AstroTurf. Global positioning system sensors were located at C7 and the mid-tibia of each leg to measure triaxial acceleration (100 Hz). PlayerLoad in each axial plane was calculated for each drill on each surface and at each global positioning system location were used as main outcome measures.  Analysis of variance revealed a significant main effect for sensor location in all drills, with PlayerLoad higher at mid-tibia than at C7 in all movement planes. AstroTurf elicited significantly higher PlayerLoad in the mediolateral and anteroposterior planes, with typically no difference between NT and 3G. In isolated inversion and eversion hopping trials, the 3G surface also elicited lower PlayerLoad than NT. PlayerLoad magnitude was sensitive to unit placement, advocating measurement with greater anatomical relevance when using microelectromechanical systems technology to monitor training or rehabilitation load. AstroTurf elicited higher PlayerLoad across all planes and drills and should be avoided for rehabilitative purposes, whereas 3G elicited a similar mechanical response to NT.

#2 Impact Of Contextual Variables On The Representative External Load Profile Of Spanish Professional Soccer Match-Play: A Full Season Study
Reference:  Eur J Sport Sci. 2020 Apr 1:1-22. doi: 10.1080/17461391.2020.1751305. [Epub ahead of print]
Authors: Oliva-Lozano JM, Rojas-Valverde D, Gómez-Carmona CD, Fortes V, Pino-Ortega J
Summary: The aims of this study were to: 1) identify the representative external load profile of match-play in Spanish professional soccer players by principal components analysis (PCA), and 2) analyze the effect of match location (home vs away), match outcome (win vs draw vs loss) and length of the microcycle (5 vs 6 vs 7 vs 8 vs 9 days) on the external load profile. Data was collected during one season consisting of 42 matches in LaLiga 123 and eleven external load variables were selected after the PCA. TD, total distance covered; DIS0-6: distance from 0 to 6 km/h; DIS21-24: distance from 21 to 24 km/h; HSRD: high-speed running distance above 21 km/h; HSRA: total of high-speed running actions above 21 km/h; VMAX: maximum speed in km/h; Sprints: total of actions above 24 km/h; ACC: total of accelerations; ACCG-avg: average accelerometer G-force; ACCMAX: maximum acceleration (m/s2); DECMAX: maximum deceleration (m/s2). Match location had an impact on HSRD (p<0.01; ES=0.05), DIS0-6 (p<0.01; ES = 0.05), and ACCMAX (p<0.01; ES = 0.05). Match outcome had a relation to TD (p<0.01; ES = 0.05), DIS0-6 (p<0.01; ES = 0.05) and HSRD (p<0.01; ES=0.05). Length of the microcycle had an impact on TD (p<0.01; ES=0.05), DIS0-6 (p<0.01; ES=0.11), ACC (p<0.01; ES = 0.04) and VMAX (p<0.01; ES=0.04). This study provides coaches a selection of variables for match-play analysis, which could represented two-thirds of external load profile. Then, professionals should consider that these contextual variables could have an impact on the external load profile.

#3 Low energy availability in group of Polish female soccer players
Reference: Rocz Panstw Zakl Hig. 2020;71(1):89-96. doi: 10.32394/rpzh.2020.0106.
Authors: Dobrowolski H, Włodarek D
Summary: The most important element of a well-balanced diet is a proper energetic value. Energy deficiencies are often observed in athletes, especially women. Energy deficiencies can lead to low energy availability which can cause serious health problems and affect exercise capacities. There is, therefore, a risk of health complications and reduced physical performance among female soccer players. The aim of this study was to check the frequency of low energy availability appearance in a group of women training soccer, which could results in negative health effects due to Relative Energy Deficiency in Sport (RED-S). Thirty-one professional female soccer players practicing on different league levels (Extra-league, I league, II league) participated in the study. The participants had their height and body mass measured. To assess the Energy Intake the method of 3-day dietary food recording was used. Total Energy Expenditure (TEE) and Exercise Energy Expenditure (EEE) was measured by means of an Armband SenseWear Pro3 device. The content of fat free mass was assessed with Akern BIA 101 Anniversary Sport Edition device. The body mass median of participants was 58 kg. The average height was 166±5 cm, and the average BMI was 21.4±2 kg/m2. TEE was 2703±392 kcal/day, while EEE was 515 kcal (203-597 kcal). Energy intake was 1548±452 kcal/day. Energy availability was 25±11 kcal/kg fat free mass/day. Twenty of the study participants had low energy availability. The percentage of EEE in TEE was 17.93±3.14%. Low energy availability was demonstrated in the vast majority of studied group, which may lead to negative health consequences or reduction of exercise capacity.

#4 Masculinity and soccer: gender issues in a psychosocial rehabilitation experience with men in Brazil's Federal District
Reference: Salud Colect. 2020 Feb 17;16:e2247. doi: 10.18294/sc.2020.2247.
Authors: Albuquerque FP, Schraiber LB
Summary: This article presents a study of men's participation in soccer workshops at a mental health services facility (CAPS). The sport is considered a relevant practice in terms of men's sociability processes. Qualitative research was conducted at two CAPS facilities in Brasilia, Federal District from August 2017 to September 2018. Data were collected through observations of daily activities and with 10 semi-structured interviews with male participants who were selected during observations. The findings of this study demonstrate the potential of therapeutic soccer workshops for the psychosocial rehabilitation of men with mental disorders - the users of these mental health services - based on social and cultural re-insertion through an activity that materially and symbolically constructs masculinity and what it means to be a man in Brazil. As patients with mental disorders who are customarily marginalized from hegemonic masculinity, the users of CAPS services were able to access possible masculinities and reconstruct their new identities as men.

#5 The role of different directions of attention on the extent of implicit perception in soccer penalty kicking
Reference: Hum Mov Sci. 2020 Apr;70:102586. doi: 10.1016/j.humov.2020.102586. Epub 2020 Jan 29.
Authors: Memmert D, Noël B, Machlitt D, van der Kamp J, Weigelt M
Summary: The role of different directions of attention on the extent of the off-center effect (penalty takers kick to the bigger side of the goal more often, although they explicitly perceive the goalkeeper in the center of the goal) was investigated for soccer penalty kicking. Regarding the directions of attention of the striker, two conflicting assumptions (attention is paid to the goalkeeper vs. attention is only spent on target) were directly contrasted. Participants viewed a goalkeeper standing either in the middle of the goal or being displaced by different distances to the left or right. In the goal-side-related instruction condition, participants had to indicate the greater goal side and already did so at above chance-level for small displacements of 0.1%, although they were not confident in their perceptual judgments, hinting at the occurrence of the off-center effect. They became mindful of displacements of 0.8% and larger when they indicated the goal side for kicking with greater confidence. In the goalkeeper-related instruction condition, participants were asked to choose a goal side for kicking, but only when they perceived the goalkeeper in the middle of the goal. Participants chose the greater goal side at above chance-level for small displacements of 0.2%. They became mindful of the displacement for a difference of 0.8%. However, when comparing the results of both instruction conditions statistically it turned out that the effect of different directions of attention on the off-center's extent differs from those previously reported. Participants were implicitly influenced by comparably small goalkeeper displacements, but became earlier aware of goalkeeper displacements in the goal-side-related instruction condition.

#6 Concussion-Prevention Strategies Used in National Collegiate Athletic Association Divisions I and II Women's Soccer
Reference: J Athl Train. 2020 Mar 27. doi: 10.4085/1062-6050-142-19. [Epub ahead of print]
Authors: Jeffries KK, Girouard TJ, Tandy RD, Radzak KN
Summary: Whereas much attention has been paid to identifying mechanisms for decreasing concussion rates in women's soccer players, which strategies currently being used is unknown. In addition, athletic trainers' (ATs') knowledge and beliefs about the efficacy of concussion-prevention practices have not been studied. The aim was to evaluate the concussion-prevention strategies being used in National Collegiate Athletic Association Division I and Division II women's soccer and identify the beliefs of certified ATs regarding mechanisms for preventing concussion. A total of 223 women's soccer team ATs employed at Division I or II universities participated in this study. A survey instrument of structured questions and open-ended, follow-up questions was developed to identify the use of cervical-strengthening programs, headgear, and other techniques for preventing concussion. Questions also addressed ATs' beliefs regarding the effectiveness of cervical strengthening, headgear, and mouthguards in concussion prevention. Data were collected via questionnaire in Qualtrics survey software. Descriptive statistics of frequencies and percentages were calculated for close-ended questions. Open-ended questions were evaluated for common themes, which were then reported by response frequency. Cervical strengthening or stability for concussion prevention was reported by 38 (17.12%) respondents; 153 (69.86%) ATs believed that cervical strengthening would aid in concussion prevention. Seventy-eight (35.49%) reported that their players wore headgear. Nineteen (8.76%) believed that soccer headgear prevented concussions; 45 (20.74%) believed that mouthguards prevented concussions. Education in proper soccer technique was reported by 151 (69.59%) respondents. Fourteen (0.06%) respondents cited nutritional strategies for concussion prevention. Although ATs believed that cervical strengthening could help prevent concussions, few had implemented this strategy. However, the ATs whose teams used headgear outnumbered those who believed that headgear was an effective prevention strategy. Based on our findings, we saw a disconnect among the current use of concussion-prevention strategies, ATs' beliefs, and the available evidence.

#7 Effect of Two Strength Training Models on Muscle Power and Strength in Elite Women's Football Players
Reference: Sports (Basel). 2020 Mar 30;8(4). pii: E42. doi: 10.3390/sports8040042.
Authors: Pacholek M, Zemková E
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Summary: This study evaluates changes in power and strength after implementing two different models of 9-week strength training in elite women's football players. A group of 13 players (age 20.2 ± 3.3 years, body mass 57.2 ± 3.7 kg, height 163.6 ± 5.3 cm, VO2max 45.2 ± ml/min) underwent either a complex (the intermittent load type) or combined (the maximal strength and dynamic method) model of training. The training load was tailored to each athlete. Results showed that the complex model of training improved power (10 W/kg, p = 0.006) and height of vertical jump (5.3 cm, p = 0.001), weight of 1 Repeat Maximum (1RM) which was (5.8 kg, p = 0.015), power and speed in the acceleration phase of barbell half squats (BHS) at weights from 20 to 60 kg, and the number of repetitions in BHS (10.3%, p = 0.012). The combined model of training improved the time of shuttle run (0.44 s, p = 0.000), weight of 1RM in BHS (9.6kg, p = 0.000) and BP (4 kg, p = 0.000), power in the acceleration phase of BHS at weights from 50 to 60 kg, the number of repetitions in BP (14.3%, p = 0.000), BHS (9.4%, p = 0.002), barbell bench pulls (11.9%, p = 0.002) and sit-ups (7.7%, p = 0.001). These findings indicate that the complex model of training improves explosive abilities, whereas the combined model is effective for developing strength at weights close to players' 1RM and for repeatedly overcoming resistance. Therefore, coaches should choose the training model based on the needs of individual players.

#8 Urine metabolomic analysis for monitoring internal load in professional football players
Reference: Metabolomics. 2020 Mar 28;16(4):45. doi: 10.1007/s11306-020-01668-0.
Authors: Quintas G, Reche X, Sanjuan-Herráez JD, Martínez H, Herrero M, Valle X, Masa M, Rodas G
Summary: The design of training programs for football players is not straightforward due to intra- and inter-individual variability that leads to different physiological responses under similar training loads. The aim was to study the association between the external load, defined by variables obtained using electronic performance tracking systems (EPTS), and the urinary metabolome as a surrogate of the metabolic adaptation to training. Urine metabolic and EPTS data from 80 professional football players collected in an observational longitudinal study were analyzed by ultra-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry and assessed by partial least squares (PLS) regression. PLS models identified steroid hormone metabolites, hypoxanthine metabolites, acetylated amino acids, intermediates in phenylalanine metabolism, tyrosine, tryptophan metabolites, and riboflavin among the most relevant variables associated with external load. Metabolic network analysis identified enriched pathways including steroid hormone biosynthesis and metabolism of tyrosine and tryptophan. The ratio of players showing a deviation from the PLS model of adaptation to exercise was higher among those who suffered a muscular lesion compared to those who did not. There was a significant association between the external load and the urinary metabolic profile, with alteration of biochemical pathways associated with long-term adaptation to training. Future studies should focus on the validation of these findings and the development of metabolic models to identify professional football players at risk of developing muscular injuries.

#9 Sleep Dysfunction and Mood in Collegiate Soccer Athletes
Reference: Sports Health. 2020 Apr 9:1941738120916735. doi: 10.1177/1941738120916735. [Epub ahead of print]
Authors: Benjamin CL, Curtis RM, Huggins RA, Sekiguchi Y, Jain RK, McFadden BA, Casa DJ
Summary: Sleep and mood are critical factors that contribute to health and wellness and are of particular interest to collegiate athletes who are juggling high physical, academic, and social demands. The aim of this study was to examine how psychological measures, player status, and sex-related factors were associated with perceived sleep quality. Higher levels of global sleep dysfunction will be related to poor mood and increased anxiety, and there will be differences in sleep dysfunction in male compared with female athletes as well as regarding playing status. During the 2016 through 2018 National Collegiate Athletic Association (NCAA) seasons, the Pittsburgh Sleep Quality Index (PSQI), Profile of Mood States, and Sports Anxiety Scale-2 questionnaires were administered to 230 soccer athletes at 6 separate time points throughout each season. PSQI results yielded scores ≥5 in 54% of observations. Increased sleep dysfunction was significantly related to decreased vigor and increased tension, depression, anger, fatigue, somatic anxiety, worry, and concentration disruption, although effect sizes (ES) were trivial (ES, -0.03 to 0.15). The odds ratio (OR) of reporting global sleep dysfunction increased by 8%, 9%, and 25% for every 1-unit increase in tension (OR, 1.08; 95% CI, 1.02-1.16; P = 0.015), fatigue (OR, 1.09; 95% CI, 1.03-1.16; P = 0.002), and concentration disruption (OR, 1.25; 95% CI, 1.09-1.45; P = 0.002), respectively. The odds of reporting global sleep dysfunction were 55% lower for males than females (OR, 0.45; 95% CI, 0.25-0.79; P = 0.006). Global sleep dysfunction was prevalent in NCAA soccer players and was related to negative mental health outcomes. Female participants experienced increased odds of reporting global sleep dysfunction. Regular monitoring allows for a greater understanding of the interrelatedness between sleep and mental health in athletes.

#10 Eccentric hamstring strength is associated with age and duration of previous season hamstring injury in male soccer players
Reference: Int J Sports Phys Ther. 2020 Apr;15(2):246-253.
Authors: Vicens-Bordas J, Esteve E, Fort-Vanmeerhaeghe A, Clausen MB, Bandholm T, Opar D, Shield A, Thorborg K
Summary: Eccentric hamstring strength seems important in reducing the odds of future hamstring injuries. While age and previous injury are well-known risk factors for future hamstring injuries, the association of age and previous hamstring injury with eccentric hamstring strength in the following season is unknown. The purpose was to investigate the association of age and previous hamstring injury with preseason eccentric hamstring strength in soccer players, and to investigate the association between previous hamstring injury duration and preseason eccentric hamstring strength. A convenience sample of 284 male amateur soccer players (age 18-38 years) was included in the analyses. Self-reported information about previous season hamstring injury and its duration (three weeks or less; more than three weeks) was collected. Preseason eccentric hamstring strength was obtained during the Nordic hamstring exercise using a field-based device. Age had a negative association with preseason eccentric hamstring strength with 0.9% reduction per year. Players with a previous hamstring injury duration of more than three weeks (n=27) had 13% lower preseason eccentric hamstring strength compared to players without previous hamstring injury. Older players have lower preseason eccentric hamstring strength than younger players. Players with a previous hamstring injury duration of more than three weeks have lower preseason eccentric hamstring strength than the rest of the players. These results highlight the need to monitor and address the identified weaknesses in eccentric hamstring strength in amateur soccer players, with specific emphasis on older players with a previous hamstring injury of longer duration.

#11 Application of Individualized Speed Zones to Quantify External Training Load in Professional Soccer
Reference: J Hum Kinet. 2020 Mar 31;72:279-289. doi: 10.2478/hukin-2019-0113. eCollection 2020 Mar.
Authors: Rago V, Brito J, Figueiredo P, Krustrup P, Rebelo A
Summary: This study aimed to examine the interchangeability of two external training load (ETL) monitoring methods: arbitrary vs. individualized speed zones. Thirteen male outfield players from a professional soccer team were monitored during training sessions using 10-Hz GPS units over an 8-week competitive period (n = 302 observations). Low-speed activities (LSA), moderate-speed running (MSR), high-speed running (HSR) and sprinting were defined using arbitrary speed zones as <14.4, 14.4-19.8, 19.8-25.1 and ≥25.2 km·h-1, and using individualized speed zones based on a combination of maximal aerobic speed (MAS, derived from the Yo-yo Intermittent recovery test level 1), maximal sprinting speed (MSS, derived from the maximal speed reached during training) and anaerobic speed reserve (ASR) as <80% MAS, 80-100% MAS, 100% MAS or 29% ASR and ≥30% ASR. Distance covered in both arbitrary and individualized methods was almost certainly correlated in all speed zones (p < 0.01; r = 0.67-0.78). However, significant differences between methods were observed in all speed zones (p < 0.01). LSA was almost certainly higher when using the arbitrary method than when using the individualized method (p < 0.01; ES = 5.47 [5.18; 5.76], respectively). Conversely, MSR, HSR and sprinting speed were higher in the individualized method than in the arbitrary method (p < 0.01; ES = 5.10 [4.82; 5.37], 0.86 [0.72; 1.00] and 1.22 [1.08; 1.37], respectively). Arbitrary and individualized methods for ETL quantification based on speed zones showed similar sensitivity in depicting player locomotor demands. However, since these methods significantly differ at absolute level (based on measurement bias), arbitrary and individualized speed zones should not be used interchangeably.

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