Latest research in football - week 22 - 2021

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 Effect of training day, match, and length of the microcycle on the worst-case scenarios in professional soccer players 

Reference: Res Sports Med. 2021 Mar 4;1-14. doi: 10.1080/15438627.2021.1895786. Online ahead of print. 

Authors: José M Oliva-Lozano, Carlos D Gómez-Carmona, Daniel Rojas-Valverde, Víctor Fortes, José Pino-Ortega

Summary: This study aimed to describe in-season worst-case scenarios (WCS) of professional soccer players and compare the WCS between training and match days (MD), considering the length of microcycle. A cohort study was designed for four competitive mesocycles in LaLiga123. The WCS of distance covered (DIS), high-speed running distance (HSRD), and sprinting distance (SPD) for four different WCS durations (1', 3', 5', 10') were analysed. Statistical differences between the WCS from training and MD were found at all intensities and periods. The magnitude of differences was moderate in DIS-1' (F= 15.49; p< 0.01; ωp2= 0.09) and DIS-3' (F= 20.99; p< 0.01; ωp2= 0.12), and high in the rest of variables (F= 26.53-89.41; p< 0.01; ωp2= 0.15-0.38). Specifically, the WCS from MD reported the highest values at all intensities and periods. Regarding training days, the greatest WCS of DIS, HSRD, and SPD were found on MD-4, MD-3, and MD+1. Considering the length of microcycle, significant differences (p< 0.05) in training-days' WCS, but not in MD (p> 0.05). In conclusion, specific WCS training programmes (e.g., including 1 min to 10-min training drills in MD-4) may be useful to prepare the demands required on MD. 



#2 The distribution of match activities relative to the maximal intensities in elite soccer players: implications for practice 

Reference: Res Sports Med. 2021 Mar 3;1-12. doi: 10.1080/15438627.2021.1895788. Online ahead of print. 

Authors: Andrea Riboli, Fabio Esposito, Giuseppe Coratella

Summary: The purpose was to determine the distribution of match-activities relative to maximum-intensities during official match in elite soccer players. One hundred and forty-eight Italian Serie A soccer players were monitored during 46 official matches (680 individual-samples). Total distance (TD), high-speed running (HSR), very high-speed running (VHSR), sprint, acceleration and deceleration were calculated. Maximum-intensities (1-minpeak) were used as the reference value to determine the distribution of relative intensity across the whole-match demands (90-minavg). Time and distance higher than 90-minavg (>90-minavg) were also calculated. The relative (m·min-1) 90-minavg vs1-minpeak was 59.6(4.4)% for TD, 26.2(4.4)% for HSR, 16.0(3.5)% for VHSR, 9.3(2.3)% for sprint, 19.2(4.6)% for acceleration and 15.4(5.2)% for deceleration. Total distance covered >90-minavg was ~61.4(5.0)% for TD, ~68.6(1.9)% for HSR, ~80.2(1.3)% for VHSR, ~95.7(0.4)% for sprint, ~75.5(1.3)% for acceleration and ~64.0(2.6)% for deceleration. With the exception of small [ES: 0.50 (0.26 to 0.73)] difference for acceleration, the relative distance >90-minavg was largely to very largely (ES: 1.64 to 7.78) higher (P< 0.05) than the 90-minavg for each metric. While no between-position difference (P> 0.05) was found for total minutes >90-minavg, between-position differences (P< 0.05) for the total distance >90-minavg were retrieved across each metric. The distribution of the activities relative to maximal intensities could assist coaches for soccer training prescriptions. 



#3 COVID-19 in Youth Soccer During Summer 2020 

Reference: J Athl Train. 2021 Mar 3. doi: 10.4085/610-20. Online ahead of print. 

Authors: Andrew M Watson, Kristin Haraldsdottir, Kevin Biese, Leslie Goodavish, Bethany Stevens, Timothy McGuine

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Summary: As sports reinitiate around the country, the incidence of COVID-19 among youth soccer athletes remains unknown. The purpose was to determine the incidence of COVID-19 among youth soccer athletes and the risk mitigation practices utilized by youth soccer organizations. Youth soccer club directors throughout the United States participated in this study. Surveys were completed in late August 2020 regarding phase of return to soccer (individual only, group non-contact, group contact), date of reinitiation, number of players, cases of COVID-19, and risk reduction procedures being implemented. Case and incidence rates were compared to national pediatric data and county data from the prior 10 weeks. A negative binomial regression model was developed to predict club COVID-19 cases with local incidence rate and phase of return as covariates and the log of club player-days as an offset. 124 respondents had reinitiated soccer, representing 91,007 players with a median duration of 73 days (IQR: 53-83 days) since restarting. Of the 119 that had progressed to group activities, 218 cases of COVID-19 were reported among 85,861 players. Youth soccer players had a lower case rate and incidence rate than children in the US (254 v. 477 cases per 100,000; incidence rate ratio [IRR]=0.511, 95% CI = [0.40-0.57], p<0.001) and the general population from the counties where data was available (268 v. 864 cases per 100,000; IRR=0.202 [0.19-0.21], p<0.001). After adjusting for local COVID-19 incidence, there was no relationship between club COVID-19 incidence and phase of return (non-contact: b=0.35±0.67, p=0.61; contact: b=0.18±0.67, p=0.79). Soccer clubs reported utilizing a median of 8 (IQR: 6-10) risk reduction procedures. The incidence of COVID-19 among youth soccer athletes is relatively low when compared to the background incidence among children in the United States in summer of 2020. No relationship was identified between club COVID-19 incidence and phase of return to soccer. 



#4 Facial Fractures Related to Soccer: A Review 

Reference: J Craniofac Surg. 2021 Mar 1. doi: 10.1097/SCS.0000000000007575. Online ahead of print. 

Authors: Murilo Sagrbi Secanho, Balduino Ferreira Menezes Neto, Leticia Perez Mazzoni, Larissa Perez Mazzoni, Felipe Lucas Parra, Aristides Augusto Palhares Neto 

Summary: Soccer is one of the most popular sports in the world. Despite the concept that soccer is not a violent game, it can lead to several injuries in amateur and professional settings, including facial fractures. Previous studies of facial fractures in soccer were all retrospective and, to date, no prospective studies are available in the literature. The authors performed a comprehensive literature search using the terms "soccer" AND "facial fracture" OR "craniofacial fracture" and "football" AND "facial fracture" OR "craniofacial fracture" and retrieved 693 articles. After applying inclusion and exclusion criteria, 11 articles were included in the present study.A total of 647 patients had suffered facial trauma, with a male-to-female ratio of 63.7:1. The patients' mean age was 27.3 years.The articles reported 670 fractures as follows: 219 (32.7%) in the zygoma, 197 (29.4%) in the nasal bone, 153 (23.6%) in the mandibula, 54 (8.0%) in the orbital wall, 12 (1.8%) in the frontal sinus, 10 (1.5%) in the alveolar bone, 3 (0.4%) in the maxilla, 3 (0.4%) in a Le Fort pattern, and 1 (0.1%) in a naso-orbito-ethmoid (NOE) pattern.Sports are a frequent cause of maxillofacial trauma and are responsible for 9.2% to 33.2% of such injuries. Soccer is a contact sport more associated with lower-limb injuries, but with a significant rate of facial fractures. As soccer is a popular sport played without facial protection and involving high-intensity movements and contact, the prevention of facial fractures related to this sport is crucial to improve the players' safety. 



#5 Curve Sprint in Elite Female Soccer Players: Relationship with Linear Sprint and Jump Performance 

Reference: Int J Environ Res Public Health. 2021 Feb 26;18(5):2306. doi: 10.3390/ijerph18052306. 

Authors: Ronaldo Kobal, Tomás T Freitas, Alberto Fílter, Bernardo Requena, Renato Barroso, Marcelo Rossetti, Renato M Jorge, Leonardo Carvalho, Lucas A Pereira, Irineu Loturco

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Summary: The aim of this study was to examine the associations between linear sprint, curve sprint (CS), change of direction (COD) speed, and jump performance in a sample of 17 professional female soccer players. All athletes performed squat and countermovement jumps, single leg horizontal triple jumps, 17 m linear sprints, CS tests, and a 17 m Zigzag COD test. A Pearson product-moment test was performed to determine the relationships among the assessed variables. The significance level was set at p < 0.05. Nearly perfect associations (r > 0.9) were found between linear and CS velocities. Players faster in linear sprints and CS exhibited greater COD deficits. No significant associations were found between COD deficit and either body mass or sprint momentum. Jumping ability was significantly correlated with linear sprint and CS performance, but not to COD performance. These findings may be used by coaches and practitioners to guide testing and training prescriptions in this population. The associations observed here suggest that training methods designed to improve linear sprint and CS velocities may benefit from the implementation of vertically and horizontally oriented plyometric exercises. 



#6 Effects of an eccentric overload and small-side games training in match accelerations and decelerations performance in female under-23 soccer players

Reference: J Sports Med Phys Fitness. 2021 Mar;61(3):365-371. doi: 10.23736/S0022-4707.20.11232-5.

Authors: Fabio Nevado-Garrosa, Víctor Torreblanca-MartÍnez, Víctor Paredes-HernÁndez, Juan Del Campo-Vecino, Carlos Balsalobre-FernÁndez

Summary: The aims of this study were: 1) to investigate the impacts that an eccentric overload training (EOT) and a small-side game training (SSGT) have on the characteristics of the accelerations (ACC) and decelerations (DCC) of the players in a soccer match; and 2) to determine if EOT and SSGT could affect the ACC and DCC reduction over time in a soccer match. Twenty-three female soccer players from a Spanish professional club were split into three groups: a small-sided game training group (SGG), an eccentric overload training group (EOG) and a control group (CG). The SSG improved the high intensity distance performed (ES [CI]=0.72 [0.22; 1.22]), the number of high intensity actions (ES [CI]=0.65 [0.01; 1.29]), the percentage of repeated high intensity actions (ES [CI]=0.54 [-0.17; 1.25]), the initial velocity of the ACC (ES [CI]=0.55 [-0.08; 1.17]) and the percentage of repeated accelerations (ES [CI]=0.87 [-0.18; 1.91]) with respect to the control group. The EOG obtained better results in distance travelling accelerating (ES [CI]=0.84 [0.09; 1.60]) and decelerating (ES [CI]=0.87 [0.23; 1.51]) above 3 m/s2, maximum ACC (ES [CI]=1.92 [0.90; 2.94]) and DCC (ES [CI]=1.29 [0.44; 2.14]) and the average of maximum ACC (ES [CI]=0.89 [0.23; 1.54]) and DCC (ES [CI]=1.08 [0.62; 1.55]) with respect to the CG. A decrement in the ACC and DCC performance was observed between the first and last 15 minutes of the competition, except for the EOG. The SSG obtained mainly improvements in variables related with efforts repetitions and the capacity of maintaining the ACC and the DCC over time, while improvements in the EOG were related to intensity in the ACC and DCC. 



#7 Using Soccer Games as an Instrument to Forecast the Spread of COVID-19 in Europe 

Reference: Financ Res Lett. 2021 Feb 23;101992. doi: 10.1016/ Online ahead of print. 

Authors: Juan-Pedro Gómez, Maxim Mironov

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Summary: We provide strong empirical support for the contribution of soccer games held in Europe to the spread of the COVID-19 virus in March 2020. We analyze more than 1,000 games across 194 regions from 10 European countries. Daily cases of COVID-19 grow significantly faster in regions where at least one soccer game took place two weeks earlier, consistent with the existence of an incubation period. These results weaken as we include stadiums with smaller capacity. We discuss the relevance of these variables as instruments for the identification of the causal effect of COVID-19 on firms, the economy, and financial markets. 



#8 Marker location and knee joint constraint affect the reporting of overhead squat kinematics in elite youth football players 

Reference: Sports Biomech. 2021 Mar 5;1-18. doi: 10.1080/14763141.2021.1890197. Online ahead of print. 

Authors: Lara M Coyne, Micheál Newell, Marco J M Hoozemans, Andrew Morrison, Susan J Brown

Summary: Motion capture systems are used in the analysis and interpretation of athlete movement patterns for a variety of reasons, but data integrity remains critical regardless. The extent to which marker location or constraining degrees of freedom (DOF) in the biomechanical model impacts on this integrity lacks consensus. Ten elite academy footballers performed bilateral overhead squats using a marker-based motion capture system. Kinematic data were calculated using four different marker sets with 3DOF and 6DOF configurations for the three joint rotations of the right knee. Root mean squared error differences between marker sets ranged in the sagittal plane between 1.02 and 4.19 degrees to larger values in the frontal (1.30-6.39 degrees) and transverse planes (1.33 and 7.97 degrees). The cross-correlation function of the knee kinematic time series for all eight marker-sets ranged from excellent for sagittal plane motion (>0.99) but reduced for both coronal and transverse planes (<0.9). Two-way ANOVA repeated measures calculated at peak knee flexion revealed significant differences between marker sets for frontal and transverse planes (p < 0.05). Pairwise comparisons showed significant differences between some marker sets. Marker location and constraining DOF while measuring relatively large ranges of motion in this population are important considerations for data integrity. 



#9 Performance Analysis in Football-Specific Tests by Para-Footballers With Cerebral Palsy: Implications for Evidence-Based Classification 

Reference: Int J Sports Physiol Perform. 2021 Mar 3;1-7. doi: 10.1123/ijspp.2020-0370. Online ahead of print. 

Authors: Javier Yanci, Daniel Castillo, Aitor Iturricastillo, Astrid Aracama, Alba Roldan, Raúl Reina 

Summary: The objectives of this study were to analyze whether there were differences among para-footballers with different types and degrees of brain impairment (ie, bilateral spasticity, athetosis/ataxia, unilateral spasticity, minimum impairment criteria, or no impairment) in performing 3 football-specific tests requiring ball dribbling, to analyze whether there was an association among the results obtained in the 3 tests, and to determine whether the performance in the tests was associated with competitive level, level of training, or years' experience in para-footballers with cerebral palsy (CP). A total of 123 footballers took part in the study, 87 of whom were footballers with CP and 36 who were without impairment. Both groups were assessed in 3 football-specific tests (Stop and Go, Turning and Dribbling, and the Illinois Agility Test). The results showed that the footballers without impairment recorded a better performance in all tests (P < .01) in comparison with the CP players. No significant differences in test performance were observed among the CP players from different competitive levels. However, significant differences (P < .01) were observed between players with diplegia or athetosis/ataxia compared with players with hemiplegia or minimum impairment level. Performance in the tests did not correlate with years of football experience, weekly strength training sessions, or specific football training in the footballers with CP (P = .12-.95). These findings suggest the possible inclusion of these tests in the classification process for footballers with CP because they discriminate among functional classes and are resistant to training and competitive level. 



#10 Common international trends in football stadium attendance 

Reference: PLoS One. 2021 Mar 3;16(3):e0247761. doi: 10.1371/journal.pone.0247761. eCollection 2021. 

Authors: Jan C van Ours

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Summary: This paper examines long-term developments in stadium attendance in professional football in the Netherlands. As in many other European countries attendance had a U-shaped development with the lowest numbers in the mid-1980s. The developments in the Netherlands do not seem to have been affected by hooliganism but by socioeconomic factors. Furthermore, the association with stadium attendance in other European leagues in particular the English Premier League is very high. This suggests that stadium attendance is affected not only by national developments but also by common international trends in the interest in football matches. 



#11 Determinants of lower-extremity injury severity and recovery in U.S. High School Soccer Players 

Reference: Res Sports Med. 2021 Mar 7;1-11. doi: 10.1080/15438627.2021.1895782. Online ahead of print. 

Authors: Avinash Chandran, Angelo Elmi, Heather Young, Loretta DiPietro

Summary: Lower-extremity injuries are common among soccer players, yet few studies have attempted to identify determinants of lower-extremity injury severity and recovery within this group. We aim to identify determinants of lower-extremity injury severity and recovery among high school (HS) soccer players in the US. We used soccer-related injury observations recorded within the NATION-SP during 2011/12-2013/14. Odds of a season-ending game-related injury were higher than a season-ending practice-related injury (Adj. OR = 2.64, 95% CI = [1.39, 5.01]). Gender, setting, and playing surface emerged as significant determinants of any time loss following lower-extremity injuries in multivariable logistic regression models, and multivariable random effects Poisson regression models also revealed significant differences in recovery durations across levels of these variables for "similarly severe" injuries. Findings suggest that gender, injury setting, playing surface contribute to injury corollaries differently. Similar multi-method approaches are needed to identify determinants of injury severity and recovery in this group. 



#12 The Relationships Between Perceived Wellness, Sleep, and Acute: Chronic Training Load in National Collegiate Athletics Association Division I Male Soccer Players 

Reference: J Strength Cond Res. 2021 Mar 3. doi: 10.1519/JSC.0000000000004003. Online ahead of print. 

Authors: Yasuki Sekiguchi, Ryan M Curtis, Robert A Huggins, Courteney L Benjamin, Alan J Walker, Shawn M Arent, William M Adams, Travis Anderson, Douglas J Casa 

Summary: The purpose of this study was to investigate relationships between perceived wellness, sleep, and acute: chronic workload ratio (ACWR) throughout a collegiate men's soccer season. Sixty male collegiate soccer players (mean[M] ± SD; age, 21±2 year; body mass, 77.6 ± 6.5 kg; height, 180.1 ± 6.4 cm; body fat%, 9.9 ± 3.9% ; and V[Combining Dot Above]O2max, 53.1 ± 5.0 ml·kg-1·min-1) participated in this study. During each session, players used a heart rate and global positioning satellite-enabled chest strap to measure training impulse and ACWR. The ACWR values were trichotomized at the individual level giving an equal number of observations within each ACWR category of low, moderate, and high ACWR (M ± SD; low, 0.658 ± 0.23; moderate, 0.92 ± 0.15; and high, 1.17 ± 0.16). Stress, fatigue, and soreness levels were collected using 1-10 Likert scales and sleep duration, and sleep quality were measured by the Karolinska Sleep Diary. Stress, fatigue, soreness levels, and sleep quality were transformed to corresponding z-scores at the individual level. Fatigue levels were significantly higher when ACWR was high compared with low (mean difference [95% confidence intervals], effect size, p-value; 0.31 [0.21, 0.42], 0.29, p < 0.001) and moderate (0.14 [0.03, 0.24], 0.13, p = 0.01). Fatigue levels were also significantly higher when the ACWR was moderate compared with low (0.18 [0.07, 0.28], 0.16, p = 0.001). Soreness levels were significantly higher when the ACWR was high compared with low (0.25 [0.14, 0.36], 0.23, p < 0.001). Stress levels were significantly greater when the ACWR was high compared with low (0.19, [0.08, 0.29], 0.18, p < 0.001) and compared with moderate (0.15, [0.05, 0.25], 0.14, p = 0.004). There were no differences in sleep duration or sleep quality in different ACWR. The ACWR may be a useful tool to achieve an appropriate balance between training and recovery to manage daily fatigue and soreness levels in athletes. 



#13 Relationship Between External Load and Self-Reported Wellness Measures Across a Men's Collegiate Soccer Preseason 

Reference: J Strength Cond Res. 2021 Mar 3. doi: 10.1519/JSC.0000000000003997. Online ahead of print. 

Authors: Jennifer B Fields, Diane M Lameira, Jerome L Short, Justin M Merrigan, Sina Gallo, Jason B White, Margaret T Jones 

Summary: Monitoring athlete training load is important to training programming and can help balance training and recovery periods. Furthermore, psychological factors can affect athlete's performance. Therefore, the purpose was to examine the relationship between external load and self-reported wellness measures during soccer preseason. Collegiate men soccer athletes (n = 20; mean ± SD age: 20.3 ± 0.9 years; body mass: 77.9 ± 6.8 kg; body height: 178.87 ± 7.18cm; body fat: 10.0 ± 5.0%; V[Combining Dot Above]O2max: 65.39 ± 7.61ml·kg-1·min-1) participated. Likert scale self-assessments of fatigue, soreness, sleep, stress, and energy were collected daily in conjunction with the Brief Assessment of Mood (vigor, depression, anger, fatigue, and confusion). Total distance (TD), player load (PL), high-speed distance (HSD, >13 mph [5.8 m·s-1]), high inertial movement analysis (IMA, >3.5 m·s-2), and repeated high-intensity efforts (RHIEs) were collected in each training session using positional monitoring (global positioning system/global navigation satellite system [GPS/GNSS]) technology. Session rate of perceived exertion (sRPE) was determined from athlete's post-training rating (Borg CR-10 Scale) and time of training session. Multilevel models revealed the bidirectional prediction of load markers on fatigue, soreness, sleep, energy, and sRPE (p < 0.05). Morning ratings of soreness and fatigue were predicted by previous afternoon's practice measures of TD, PL, HSD, IMA, RHIE, and sRPE. Morning soreness and fatigue negatively predicted that day's afternoon practice TD, PL, HSD, IMA, RHIE, and sRPE. Morning ratings of negative mood were positively predicted by previous day's afternoon practice HSD. In addition, negative morning mood states inversely predicted HSD (p = 0.011), TD (p = 0.002), and PL (p < 0.001) for that day's afternoon practice. Using self-reported wellness measures with GPS/GNSS technology may enhance the understanding of training responses and inform program development. 



#14 Quality of Life: Changes in Self-Perception in People with down Syndrome as a Result of Being Part of a Football/Soccer Team. Self-Reports and External Reports 

Reference: Brain Sci. 2021 Feb 12;11(2):226. doi: 10.3390/brainsci11020226. 

Authors: Rocío Camacho, Cristina Castejón-Riber, Francisco Requena, Julio Camacho, Begoña M Escribano, Arturo Gallego, Roberto Espejo, Amaranta De Miguel-Rubio, Estrella I Agüera

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Summary: The hypothesis posed was whether being part of a football/soccer team influenced the quality of life (QL) of the people who participated in it since their perception of themselves is enhanced by factors, such as self-determination, social inclusion, emotional well-being, physical well-being, material well-being, rights, personal development, and internal relationships. The objective was to evaluate the QL of people with Down Syndrome (DS) using their self-perception (n = 39) and the perception of the informants (family members, teachers) (n = 39). The KidsLife-Down Scale, with a few modifications, was used. In general, differences of opinion between the subgroups of participants with DS and informants showed that results were higher in terms of perception for participants in the DS subgroup. Scores for all variables were higher for those participants with DS who said they did engage in practicing competitive football/soccer. Although the perception of informants provides a great deal of information regarding the QL of participants with DS, participants with DS should also be involved in the evaluation process and their self-perceptions taken into account. It is not participating in a football team that causes the conclusions of the study, but training (which includes the friendly matches that are played), the cause correlated with the improvements detected in the athlete's DS. 



#15 Comparison of Running Distance Variables and Body Load in Competitions Based on Their Results: A Full-Season Study of Professional Soccer Players 

Reference: Int J Environ Res Public Health. 2021 Feb 20;18(4):2077. doi: 10.3390/ijerph18042077. 

Authors: Hadi Nobari, Rafael Oliveira, João Paulo Brito, Jorge Pérez-Gómez, Filipe Manuel Clemente, Luca Paolo Ardigò

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Summary: The aims of this study were to compare the external workload in win, draw and defeat matches and to compare first and second halves in the Iranian Premier League. Observations on individual match performance measures were undertaken on thirteen outfield players (age, 28.6 ± 2.7 years; height, 182.1 ± 8.6 cm; body mass, 75.3 ± 8.2 kg; BMI, 22.6 ± 0.7 kg/m2) competing in the Iranian Premier League. High-speed activities selected for analysis included total duration of matches, total distance, average speed, high-speed running distance, sprint distance, maximal speed and GPS-derived body load data. In general, there were higher workloads in win matches when compared with draw or defeat for all variables; higher workloads in the first halves of win and draw matches; higher total distance, high-speed running distance and body load in the second half in defeat matches. Specifically, lower average speed was found in matches with a win than with draw or defeat (p < 0.05). Sprint distance was higher in the first half of win than defeat matches and high-speed running distance was lower in draw than defeat matches (all, p < 0.05). In addition, first half presented higher values for all variables, regardless of the match result. Specifically, high-speed running distance was higher in the first half of matches with a win (p = 0.08) and total distance was higher in the first half of matches with a draw (p = 0.012). In conclusion, match result influences the external workload demands and must be considered in subsequent training sessions and matches. 



#16 Sleep Indices and Cardiac Autonomic Activity Responses during an International Tournament in a Youth National Soccer Team 

Reference: Int J Environ Res Public Health. 2021 Feb 20;18(4):2076. doi: 10.3390/ijerph18042076. 

Authors: Pedro Figueiredo, Júlio Costa, Michele Lastella, João Morais, João Brito

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Summary: This study aimed to describe habitual sleep and nocturnal cardiac autonomic activity (CAA), and their relationship with training/match load in male youth soccer players during an international tournament. Eighteen elite male youth soccer players (aged 14.8 ± 0.3 years; mean ± SD) participated in the study. Sleep indices were measured using wrist actigraphy, and heart rate (HR) monitors were used to measure CAA during night-sleep throughout 5 consecutive days. Training and match loads were characterized using the session-rating of perceived exertion (s-RPE). During the five nights 8 to 17 players slept less than <8 h and only one to two players had a sleep efficiency <75%. Players' sleep duration coefficient of variation (CV) ranged between 4 and 17%. Nocturnal heart rate variability (HRV) indices for the time-domain analyses ranged from 3.8 (95% confidence interval, 3.6; 4.0) to 4.1 ln[ms] (3.9; 4.3) and for the frequency-domain analyses ranged from 5.9 (5.6; 6.5) to 6.6 (6.3; 7.4). Time-domain HRV CV ranged from 3 to 10% and frequency-domain HRV ranged from 2 to 12%. A moderate within-subjects correlation was found between s-RPE and sleep duration [r = -0.41 (-0.62; -0.14); p = 0.003]. The present findings suggest that youth soccer players slept less than the recommended during the international tournament, and sleep duration was negatively associated with training/match load. 



#17 Effects of Short-Term Plyometric Training on Agility, Jump and Repeated Sprint Performance in Female Soccer Players 

Reference: Int J Environ Res Public Health. 2021 Feb 25;18(5):2274. 

doi: 10.3390/ijerph18052274.

Authors: Marcin Maciejczyk, Renata Błyszczuk, Aleksander Drwal, Beata Nowak, Marek Strzała

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Summary: The aim of the study was to determine the effects of short-term (4 weeks, twice a week: 8 sessions) plyometric training on agility, jump, and repeated sprint performance in female soccer players. The study comprised 17 females performing this sports discipline. The players were randomly divided into two groups: with plyometric training (PLY) and the control (CON). All players followed the same training program, but the PLY group also performed plyometric exercises. Tests used to evaluate physical performance were carried out immediately before and after PLY. After implementing the short PLY training, significant improvement in jump performance (squat jump: p = 0.04, ES = 0.48, countermovement jump: p = 0.009, ES = 0.42) and agility (p = 0.003, ES = 0.7) was noted in the PLY group. In the CON group, no significant (p > 0.05) changes in physical performance were observed. In contrast, PLY did not improve repeated sprint performance (p > 0.05) among female soccer players. In our research, it was shown that PLY can also be effective when performed for only 4 weeks instead of the 6-12 weeks typically applied.

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