Latest research in football - week 20 - 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 Vertical Force-velocity Profiling and Relationship to Sprinting in Elite Female Soccer Players

Reference: Int J Sports Med. 2021 Feb 18. doi: 10.1055/a-1345-8917. Online ahead of print. 

Authors: Sarah A Manson, Cody Low, Hayley Legg, Stephen D Patterson, César Meylan 

Summary: Explosive actions are integral to soccer performance and highly influenced by the ability to generate maximal power. The purpose of this study was to investigate the relationship between force-velocity profile, jump performance, acceleration and maximal sprint speed in elite female soccer players. Thirty-nine international female soccer players (24.3±4.7 years) performed 40-m sprints, maximal countermovement jumps and five loaded squat jumps at increasing loads to determine individual force-velocity profiles. Theoretical maximal velocity, theoretical maximal force, maximal power output, one repetition maximal back squat and one repetition maximal back squat relative to body mass were determined using the force-velocity profile. Counter movement jump, squat jump and maximal power output demonstrated moderate to large correlation with acceleration and maximal sprint speed (r=- 0.32 to -0.44 and -0.32 to -0.67 respectively, p<0.05). Theoretical maximal velocity and force, one repetition maximal and relative back squat demonstrated a trivial to small relationship to acceleration and maximal sprint speed (p>0.05). Vertical force-velocity profiling and maximal strength can provide valuable insight into the neuromuscular qualities of an athlete to individualize training, but the ability to produce force, maximal power, and further transference into sprint performance, must be central to program design. 



#2 Psychological Correlates of Insomnia in Professional Soccer Players: An Exploratory Study

Reference: Eur J Sport Sci. 2021 Feb 18;1-20. doi: 10.1080/17461391.2021.1892197. Online ahead of print. 

Authors: Andrea Ballesio, Mariacarolina Vacca, Valeria Bacaro, Adriano Benazzi, Paola De Bartolo, Fabio Alivernini, Fabio Lucidi, Caterina Lombardo, Chiara Baglioni 

Summary: Sleep promotes health, wellbeing, recovery and athletic performance. As a consequence, sleep problems in athletes may have detrimental effects. Previous investigations showed that professional athletes often reported to suffer of poor sleep quality and insomnia (e.g., difficulties falling asleep and/or maintaining sleep). However, psychological variables exacerbating and maintaining insomnia in professional athletes as well as its mechanistic pathways are still largely unknown. Available literature mostly focused on effects of sport-related variables, such as evening training and stimulant consumption on athletes' sleep. Instead, the contribution of cognitive and emotional variables globally associated with insomnia in athletes in clinical models has been largely neglected. To address these limitations, this study explored the associations between emotional experience, pre-sleep arousal, pre-sleep worry and rumination and insomnia severity in a sample of 210 (25.93±6.68 years) male professional soccer players. Bivariate correlations, multiple regression, and structural equation modelling with manifest variables (path analysis) were computed. Results showed that insomnia severity was associated with stimulants consumption, pre-sleep arousal, negative emotions, positive emotions, and pre-sleep worry/rumination (all p < .05). Path analysis showed that relationship between stimulant consumption, emotional experience, worry/rumination and insomnia was mediated by pre-sleep arousal (p < .05). Our results suggest that preventive and interventional studies in professional soccer players would benefit from considering global cognitive-emotional variables as targets of interventions. 



#3 An objective description of routine sleep habits in elite youth football players from the Middle-East

Reference: Sleep Med. 2021 Jan 23;80:96-99. doi: 10.1016/j.sleep.2021.01.029. Online ahead of print. 

Authors: Lorenzo Lolli, Marco Cardinale, Emmanuel Lopez, Mohd Firdaus Maasar, Johannes Marthinussen, Daniele Bonanno, Warren Gregson, Valter Di Salvo

Summary: Adequate sleep is essential to support preparation and recovery processes for training and competition in athletes. A limited number of studies have examined whether adolescents from the Middle-East meet the minimum age-specific recommendations ranging from 8 to 9 h of night sleep based on objective measurements. This study aimed to provide an objective description of routine sleep habits in elite youth football players from the Middle-East. Using wrist-worn actigraphy, we examined objective measures of sleep over a 14-day surveillance period from fifty-nine, male, Middle-Eastern elite youth football players (age range: 12.1 to 16 years). The observed median sleep duration was approximately 5.5 to 6 h during weekdays and 6.5 to 7.5 h over weekend days. Sleep intermissions resulting in two or more periods of sleep accounted for 8% and 17% of the data during weekdays and weekends, respectively. For the first time, we reported an objective quantification of sleep measures indicating that elite youth athletes from the Middle-East do not meet the age-specific sleep recommendations. Integration of sleep tracking into the routine training monitoring process can be valuable to inform decisions relevant to the adoption of potential multidisciplinary interventions to address sleep insufficiency and disorders in youth athletes. 



#4 Comparative external workload analysis based on the new functional classification in cerebral palsy football 7-a-side. A full-season study 

Reference: Res Sports Med. 2021 Feb 12;1-13. doi: 10.1080/15438627.2021.1888105. Online ahead of print. 

Authors: J M Gamonales, J Muñoz-Jiménez, Carlos D Gómez-Carmona, S J Ibáñez 

Summary: The evolution of functional classification (FT) is important for promoting competitive balance. Technological advances allow the objective monitoring of competitive demands that is required to manage and individualize workloads. Therefore, this study aimed to characterize external workload in all matches from the 2018/2019 season of the CPF7 Spanish National League and to compare demands based on the new FT (FT1, FT2 yFT3) in time-motion (locomotion and speed changes) and accelerometer-based workload (impacts). Statistical analysis was composed of one-way ANOVA with Bonferroni post-hoc and omega partial squared effect size. Differences were found among all FT in total distance, running, high-intensity, sprinting, very high accelerations and decelerations (FT3> FT2> FT1; p < .01; ωp 2= 0.29-to-0.43); and with respect to the highest functional limitation (FT3 = FT2> FT1) in maximum sprinting, moderate-high accelerations and decelerations, total impacts and at very-low intensity (ωp 2= 0.13-to-0.29). In conclusion, FT3 players presented a physical advantage with respect to FT2-FT1 players in competition, especially in high-intensity actions that are crucial in team-sports performance. The present results facilitate designing specific training workloads according to FT, players' disability and competition demands, being the first approach to characterize match demands with inertial devices based on the new FT. 



#5 Psychological Parameters in Sub-Elite, Male, Youth Soccer Players with Jumper's Knee Following Physical Therapy Compared to Healthy Controls: A Longitudinal Examination

Reference: Int J Sports Phys Ther. 2021 Feb 1;16(1):114-125. Differences in Physical and 

Authors: Marc Niering, Thomas Muehlbauer 

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Summary: Many adolescent athletes suffer from jumper's knee (JK) over a long period of time and return to sports before symptoms are fully resolved. Current treatment methods may not reduce pain in the short term, especially not during a competitive season. The purpose of this study was to investigate differences in physical, psychological, and injury-/pain-related parameters in sub-elite male youth soccer players, who previously underwent physical therapy for JK compared to healthy controls (HC) over the course of a season. All subjects were tested four times (start of the season [T1], 6 [T2], 16 [T3], and 20 [T4] weeks after the start of the season). Outcome measures included muscle power (drop jump, jump-and-reach), change of direction speed [CODS] (acyclic sprint), speed (tapping, 30-m linear sprint), endurance (Yo-Yo intermittent recovery test level 1), the Achievement Motives Scale (AMS) Sport, and injury-/pain-related data. Univariate analysis of variance was used to compare differences in variables between the two groups over the course of a soccer season. Over the season, the jumper's knee group (JK; 15.1 ± 0.8 yr) demonstrated significantly worse physical performance in CODS (to the left side: 1.37≤ Cohen's d ≤ 1.51 [T1-T4]; p < 0.001 / to the right side: 1.24 ≤ d ≤ 1.53 [T1-T4]; p < 0.001) and speed (0.48 ≤ d ≤ 1.26 [T1-T4]; p < 0.007) compared to healthy controls (HC; 15.0 ± 1.0 yr). Further, psychological parameters showed worse values in JK than in HC for the AMS Sport items "hope for success" and "fear of failure" that especially showed a significant difference at T1 (d = 0.65; p = 0.032 / d = 0.68; p = 0.027) and T2 (d = 0.50; p = 0.076 / d = 0.80; p = 0.012). Moreover, the JK group showed significantly higher incident rates for non-contact lower limb injuries (d = 0.69; p = 0.049) per 1,000 hours (i.e., practices/competitions), injury-related rest periods (d = 2.06; p = 0.043), and pain-related training interruptions (d = 1.35; p < 0.001). The observed findings imply that there are significant differences in physical and psychological performance of youth soccer players after physical therapy for JK compared to HC. When designing rehabilitation and/or training programs, as well as determining the point of return to sport the impact of the injury needs to be taken into account. 



#6 The ACE and ACTN3 polymorphisms in female soccer athletes 

Reference: Genes Environ. 2021 Feb 18;43(1):5. doi: 10.1186/s41021-021-00177-3. 

Authors: Qi Wei

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Summary: We investigated the association of ACE I/D and ACTN3 R577X polymorphisms with the performance of Chinese elite female soccer athletes for the first time. The genotype distributions of ACE I/D and ACTN3 R577X in the athlete group and the control group of Chinese females were evaluated via PCR and compared. VO2max value was tested as per standard protocol. Regarding the distribution of ACE polymorphisms, the genotype frequency was indifferent between the athletes (II 40 %, ID 46.7 %, DD 13.3 %) and the controls (II 42 %, ID 48 %, DD 10 %). No difference in the I/D allele frequency was observed between the athlete group and the control group. Regarding the distribution of ACTN3 polymorphisms, the genotype frequency was significantly different between the athletes (XX 0 %, XR 53.3 %, RR 46.7 %) and the controls (XX 16 %, XR 44 %, RR 40 %). The allele frequency was observed no different between the athlete and the control group. The ACE ID and ACTN3 RR genotype combination was associated with higher VO2max values among defenders than among other players. According to VO2max values,The ACE and ACTN3 genotype combinations (II/ID/DD + RR/XR) significantly differed between the athletes and the controls (p < 0.05). These results suggested that the Chinese elite female soccer athletes were more likely to harbor the I allele and the R allele and that the combination of ACE II/ID and ACTN3 RR/XR was a synergetic determinant of the athletic performance of females in soccer. 



#7 Relationship Between Subjective and External Training Load Variables in Youth Soccer Players 

Reference: Int J Sports Physiol Perform. 2021 Feb 19;1-7. doi: 10.1123/ijspp.2019-0956. Online ahead of print. 

Authors: Patrick C Maughan, Niall G MacFarlane, Paul A Swinton 

Summary: The purpose was to quantify and describe relationships between subjective and external measures of training load in professional youth soccer players. Data from differential ratings of perceived exertion (dRPE) and 7 measures of external training load were collected from 20 professional youth soccer players over a 46-week season. Relationships were described by repeated-measures correlation, principal component analysis, and factor analysis with oblimin rotation. Significant positive (.44 ≤ r ≤ .99; P < .001) within-individual correlations were obtained across dRPE and all external training load measures. Correlation magnitudes were found to decrease when training load variables were expressed per minute. Principal component analysis provided 2 components, which described 83.3% of variance. The first component, which described 72.9% of variance, was heavily loaded by all measures of training load, while the second component, which described 10.4% of the variance, appeared to have a split between objective and subjective measures of volume and intensity. Exploratory factor analysis identified 4 theoretical factors, with correlations between factors ranging from .5 to .8. These factors could be theoretically described as objective volume, subjective volume, objective running, and objective high-intensity measures. Removing dRPE measures from the analysis altered the structure of the model, providing a 3-factor solution. The dRPE measures are significantly correlated with a range of external training load measures and with each other. More in-depth analysis showed that dRPE measures were highly related to each other, suggesting that, in this population, they would provide practitioners with similar information. Further analysis provided characteristic groupings of variables. 



#8 Effects of Different Recovery Times on Internal and External Load During Small-Sided Games in Soccer 

Reference: Sports Health. 2021 Feb 23;1941738121995469. doi: 10.1177/1941738121995469.

Authors: Luis Branquinho, Ricardo Ferraz, Bruno Travassos, Daniel A Marinho, Mário C Marques

Summary: The ability to maintain a high intensity of exercise over several repetitions depends on recovery from previous exercises. This study aimed to identify the effects of different recovery times on internal and external load during small-sided soccer games. An increase in recovery time will increase the external training load and decrease the internal exercise load, which will result in a greater physical impact of the exercise. Twenty male semiprofessional soccer players participated in the present study. They performed the same exercise (5-a-side game format) continuously (1 × 18 minutes) and repeatedly/fractionated (3 × 6 minutes) with different recovery times (30 seconds, 1 minute, 1.5 minutes, and 2 minutes). Their internal load (ie, average heart rate (HR) and maximum HR) and external load (ie, total distance, maximum speed, and ratio meters) were measured using an HR band and an inertial device equipped with a global positioning system, respectively. The manipulation of recovery times induced differences in the internal and external load. For the same total duration, the external and internal load indicators exhibited higher values during the fractionated method, particularly with short recovery periods. The application of small-sided soccer games with different recovery times induced varying responses in training load. To maintain high physical performance and high training load, the fractional method with short recovery periods (ie, 30 seconds) should be used. In contrast, to carefully manage players' efforts and decrease response to training load, continuous or fractional methods with longer recovery periods (ie, 1-2 minutes) should be used. The proper prescription of recovery time between exercises facilitates enhanced training efficiency and optimized performance. 



#9 Impact of COVID-19 Lockdown on Serie A Soccer Players' Physical Qualities 

Reference: Int J Sports Med. 2021 Feb 23. doi: 10.1055/a-1345-9262. Online ahead of print. 

Authors: Ermanno Rampinini, Federico Donghi, Marco Martin, Andrea Bosio, Marco Riggio, Nicola A Maffiuletti

Summary: In March 2020, the COVID-19 pandemic forced most activities in Italy, including soccer, to cease. During lockdown, players could only train at home, with limited evidence regarding the effect of this period. Therefore, this study aimed to investigate the effect of COVID-19 lockdown on professional soccer players' physical performance. Aerobic fitness and vertical jump were assessed before and after four periods in two different seasons: COVID-19 lockdown, competitive period before lockdown, competitive period and summer break of the 2016-2017 season. Linear mixed models were used to examine within-period changes and between-period differences in changes observed during COVID-19 lockdown and the three other periods. Within-period changes in aerobic fitness showed a significant improvement following COVID-19 lockdown (p<0.001) and a significant decline during summer break (p<0.001). Between-period differences were significant in the comparison of COVID-19 lockdown with both the competitive 2019-2020 season (p<0.01) and summer break (p<0.001). For the vertical jump, only the between-period comparison revealed significant differences as the changes associated with COVID-19 lockdown were worse than those of the two competitive periods, for both absolute (p<0.05; p<0.001) and relative peak power (p<0.01; p<0.001). Home-based training during lockdown was effective to improve aerobic fitness, although it did not allow players to maintain their competitive period's power levels. 



#10 Change in dynamic postural control after a training program in collegiate soccer players with unilateral chronic ankle instability 

Reference: J Sports Med Phys Fitness. 2021 Feb 23. doi: 10.23736/S0022-4707.21.11920-6. Online ahead of print. 

Authors: Daichi Sadakuni, Kosuke Takeuchi, Fumiko Tsukuda, Takeshi Komatsu

Summary: Improving dynamic postural stability after lateral ankle sprain due to chronic ankle instability helps prevent recurrence, and changes in dynamic postural stability can be assessed with the Star Excursion Balance Test. To date, no studies have examined the change in Star Excursion Balance Test score after the end of a balance training program or whether chronic ankle instability affects the rate of change. To examine the effect of chronic ankle instability on changes in Star Excursion Balance Test. score over time after a balance training program. Fifteen collegiate soccer players with chronic ankle instability selected with the Cumberland Ankle Instability Tool and ultrasonography. Participants completed a 6-week balance training program. We assessed the Star Excursion Balance Test 5 times (before and immediately after the program and 2, 4, and 6 weeks later) and examined differences in the duration of training effects by a 2-way analysis of variance, with Bonferroni correction for post hoc comparisons to explain any significant interactions. The significance level for all analyses was set at P < .05. We performed statistical analyses with SPSS version 25. Analysis of the posterolateral and posteromedial scores in Star Excursion Balance Test showed a significant effect of time. Post hoc analysis of the posterolateral score showed that for each leg, participants reached significantly farther after the program than before (P = .012). The posterolateral scores at 2, 4, and 6 weeks after the training program did not differ from before the program, but the posteromedial score was significantly improved immediately after the program (P = .008) and also 2 (P = .004) and 4 weeks later (P = .006). A 6-week balance training program to improve dynamic postural control can improve posterolateral and posteromedial scores in people with chronic ankle instability, and the improvements in posteromedial are still present 4 weeks after program completion. 



#11 Concordance between the weight of Spanish adolescent soccer players, their self-perceived weight, and their weight as perceived by their parents 

Reference: J Pediatr Nurs. 2021 Feb 20;S0882-5963(21)00052-X. doi: 10.1016/j.pedn.2021.02.011. 

Authors: María Del Mar Fernández-Álvarez, Rubén Martín-Payo, Edurne Zabaleta-Del-Olmo, Rebeca García-García, Xana González-Méndez, Sergio Carrasco-Santos

Summary: In the context of soccer clubs, to analyze the concordance between players' actual weight, their self-perceived weight, and their weight as perceived by their parents; to determine which variables might explain the presence of concordance between parents' perception of adolescents' weight and their actual weight. Design and study: A cross-sectional study involving 330 soccer players aged between 13 and 16. Data on personal characteristics of adolescents and parents were analyzed, as well as parents' perceptions of adolescents' weight status and their self-perception. A descriptive analysis of the personal characteristics of the sample (adolescents and parents) and an analysis of the variables explaining the presence of concordance between the parents' perception of adolescents' weight and their actual weight were performed. 19% of the adolescents were overweight and 3.4% were obese. The concordance between parents' perceptions of players' weight and players' actual weight was weak. The concordance between adolescents' self-perceived weight and their actual weight was moderate. The difference in BMI scores according to presence or absence of concordance was statistically significant: these scores were higher in the absence of concordance. Discordance between adolescents' weight and their parents' perception of their weight was associated with parents having lower levels of education. A high percentage of parents and players misperceived their actual weight. This discrepancy was associated with higher BMI scores for adolescents. Nurses should include promotion of accurate weight perception in educational interventions on excess weight. 



#12 The influence of training status on right ventricular morphology and segmental strain in elite pre-adolescent soccer players 

Reference: Eur J Appl Physiol. 2021 Feb 22. doi: 10.1007/s00421-021-04634-3. Online ahead of print. 

Authors: Viswanath B Unnithan, Alexander Beaumont, Thomas W Rowland, Nicholas Sculthorpe, Keith George, Rachel Lord, David Oxborough

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Summary: Cardiac modifications to training are a product of the genetic pre-disposition for adaptation and the repetitive haemodynamic loads that are placed on the myocardium. Elite pre-adolescent athletes are exposed to high-intensity training at a young age with little understanding of the physiological and clinical consequences. It is unclear how right ventricular (RV) structure and function may respond to this type of stimulus. The aim of this study was to compare RV structure and strain across the cardiac cycle and within individual segments in elite soccer players (SP) and controls (CON). Twenty-two highly trained, male pre-adolescent SP and 22 age-and sex-matched recreationally active individuals CON were investigated using 2D echocardiography, including myocardial speckle tracking to assess basal, mid-wall, apical and global longitudinal strain and strain rate during systole (SRS) and diastole (SRE and SRA). greater RV cavity size was identified in the SP compared to CON (RVD1 SP: 32.3 ± 3.1 vs. CON: 29.6 ± 2.8 (mm/m2)0.5; p = 0.005). No inter-group differences were noted for peak global RV strain (SP: - 28.6 ± 4.9 vs CON: - 30.3 ± 4.0%, p = 0.11). Lower mid-wall strain was demonstrated in the SP compared to CON (SP: - 27.9 ± 5.8 vs. CON: - 32.2 ± 4.4%, p = 0.007). Soccer training has the potential to increase RV size in pre-adolescent players. The unique segmental analyses used in this study have identified inter-group differences that were masked by global strain evaluations. The clinical and physiological implications of these findings warrant further investigation. 



#13 Asymptomatic Foot and Ankle Abnormalities in Elite Professional Soccer Players 

Reference: Orthop J Sports Med. 2021 Jan 29;9(1):2325967120979994. doi: 10.1177/2325967120979994. eCollection 2021 Jan. 

Authors: Eduard Bezuglov, Vladimir Khaitin, Artemii Lazarev, Alesia Brodskaia, Anastasiya Lyubushkina, Kamila Kubacheva, Zbigniew Waśkiewicz, Arseniy Petrov , Nicola Maffulli 

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Summary: Professional soccer players are often evaluated with asymptomatic lesions of the ankle and foot, and such abnormalities may eventually become clinically relevant. The purpose was to ascertain the prevalence of foot and ankle abnormalities in elite professional adult soccer players. Professional adult male elite soccer players (n = 37) underwent magnetic resonance imaging (MRI) scans of both their feet and ankles. All competed for their respective national junior or adult soccer teams. MRI scans were performed with 1.5-T scanners and analyzed independently by 2 experienced radiologists. The MRI scans of 86.5% of the players showed degenerative joint disease (DJD) in at least 1 of the joints of the foot and ankle. Articular cartilage lesions in the joints of the foot and ankle were evident in 42% of the scans. Of all lesions, 17% were grade 3 or 4 (Noyes and Stabler classification) cartilage lesions and accompanied by subchondral bone marrow edema. The greater the age, weight, and height of the players, the greater was the odds ratio of DJD of the ankle joint. Synovitis in at least 1 of the joints of the foot was detected in 64% of the MRI scans. Leg dominance significantly correlated with bone marrow edema of the talus. Elite professional soccer players are often evaluated with a high prevalence of asymptomatic osteochondral lesions with subchondral bone marrow edema in the foot and ankle. These osteochondral lesions may remain asymptomatic or, with the continuing high-intensity stresses that modern professional soccer demands of its athletes, may evolve and cause foot and ankle pain. It is unclear whether and which interventions can be implemented to prevent the occurrence of these abnormalities in the first place. 


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