Latest research in football - week 37 - 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 Injury Profiles in Korean Youth Soccer
Reference: Int J Environ Res Public Health. 2020 Jul 16;17(14):E5125. doi: 10.3390/ijerph17145125.
Authors: Inje Lee, Hee Seong Jeong, Sae Yong Lee
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Summary: We aimed to analyze injury profiles and injury severity in Korean youth soccer players. Data on all injuries that occurred in U-15 youth soccer players during the 2019 season were collected from 681 players of 22 teams through a medical questionnaire. The questionnaire was based on injury surveillance procedures of the Federation International de Football Association Medical and Research Centre and International Olympic Committee, and it comprised questions on demographic characteristics, training conditions, and injury information. Among all players, defenders accounted for 33.0%, followed by attackers (30.7%), midfielders (26.8%), and goalkeepers (7.9%). Most players played soccer on artificial grounds (97.4%). Injuries occurred more frequently during training (56.3%) than during matches (43.7%). Recurrent injury rate was 4.4% and average days to return to full activities were 22.58. The ankle (26.6%) and knee joints (14.1%) were the most common injury locations, and ligament sprains (21.0%), contusions (15.6%), and fractures (13.9%) were the most frequent injury types. In conclusion, Korean youth soccer players have a high injury risk. Therefore, researchers and coaching staff need to consider these results as a key to prevent injuries in youth soccer players and injury prevention programs may help decrease injury rate by providing injury management.

#2 Salivary aldosterone and cortisone respond differently to high- and low-psychologically stressful soccer competitions
Reference:  J Sports Sci. 2020 Jul 24;1-10. doi: 10.1080/02640414.2020.1796164. Online ahead of print.
Authors: Timothy S McHale, Wai-Chi Chee, Carolyn R Hodges-Simeon, David T Zava, Graham Albert, Ka-Chun Chan, Peter B Gray
Summary: Aldosterone and cortisone are released in response to physical and psychological stress. However, aldosterone and cortisone responses in children engaged in physical competition have not been described. We examined salivary aldosterone and salivary cortisone responses among Hong Kongese boys, aged 8-11 years, during (1) a soccer match against unknown competitors (N = 84, high psychological stress condition) and (2) an intrasquad soccer scrimmage against teammates (N = 81, low psychological stress condition). Aldosterone levels increased during the soccer match and intrasquad soccer scrimmage conditions, consistent with the view that aldosterone responds to physical stress. During the soccer match, winning competitors experienced larger increases in aldosterone compared to losing competitors, indicating that the degree of aldosterone increase was attenuated by match outcome. Cortisone increased during the soccer match and decreased during the intrasquad soccer scrimmage. Competitors on teams that resulted in a tie had larger cortisone increases compared to winners or losers. These findings highlight that the degree of cortisone change is related to boy's cognitive appraisal of the competitor type (i.e., teammates vs. unknown competitors) and the competitive nature of the game (e.g., tie). These results shed new light on adrenal hormone mediators of stress and competition during middle childhood.

#3 Z-score values of left ventricular dimensions in adolescent elite male soccer players
Reference: Eur J Pediatr. 2020 Jul 24. doi: 10.1007/s00431-020-03741-1. Online ahead of print.
Authors: Stephan Gerling, Tobias Pollinger , Holger Michel, Markus-Johann Dechant , Michael Melter , Werner Krutsch
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Summary: Recent studies showed contrasting findings in morphological changes due to competitive soccer in adolescent players (SP). We present a prospective study in 315 consecutive adolescent (10-14 years) male elite SP and 53 healthy matched active controls (CON). All participants underwent a complete transthoracic two-dimensional echocardiography (TTE). The mean age in SP was 12.8 ± 0.65 years compared to 12.6 ± 0.8 years in CON. For all left ventricular (LV) dimensions, mean Z-score values were higher in SP. There was a significant Z-score increase in interventricular septum diastolic diameter (2.47z vs. 1.62z, p < 0.05), left ventricular posterior wall diastolic and systolic diameter (1.15z vs. 0.47z, p < 0.05 and 1.05z vs. - 0.4z, p < 0.05). Athletes had significant greater LV mass indexed for BSA (94 ± 12 g/m2 vs. 81 ± 13 g/m2, p < 0.05). There was no significant difference in LV function or diameters. Conclusion: Our findings suggest that elite soccer training in adolescent male is a type of sport predominantly related to cardiac resistance remodeling. Adolescent SP may develop supernormal left ventricular wall dimensions (+ 2.0 to + 2.5z). If in SP Z-scores, any LV dimension above + 2.5 is measured, primary or secondary cardiomyopathies should be excluded. What is Known: • Morphological cardiac adaptation in response to exercise depends on the type, duration, and intensity of training. • Morphological and functional changes due to competitive sports (athlete's heart) occur even in pre-adolescent athletes. What is New: • Our findings point out that German elite soccer training in adolescent male (10-14 years of age) is a type of sport predominantly related to cardiac resistance remodeling. • If in an adolescent competitive soccer player any LV dimension Z-score value above + 2.5 is measured, a primary or secondary cardiomyopathy should be excluded.

#4 Player Experience During the Junior to Senior Transition in Professional Football: A Longitudinal Case Study
Reference: Front Psychol. 2020 Jul 9;11:1672. doi: 10.3389/fpsyg.2020.01672. eCollection 2020.
Authors: Scott C Swainston, Mark R Wilson, Martin I Jones
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Summary: The purpose of this study was to explore the evolving perspectives of young players experiences going through the junior to senior transition in professional football. A primary objective was to adopt novel methods - weekly video diaries - to allow participants to control and report their own narratives as the transition unfolded over 40 weeks. Semi structured interviews, held at four time points, allowed the lead researcher to probe further on themes that were developing. Six participants from the academy volunteered to take part, but only the three who earned professional contracts completed the study. The primary themes in the academy were the pressure experienced waiting for the contract decision, and then preparation for senior football and the first team environment once contracts were awarded. Adaptation to senior football included not only increased physical and mental demands but also those related to the different style of play, the pressure to win, and how these both impacted decision-making. The football club set up two pathways to support this adaptation, loan moves and time with the U23's. In the following season, the move to the senior squad was characterized by a lack of opportunity to play for the first team, resulting in additional loan moves. These moves, and the associated perceived lack of support structures, led to the participants experiencing issues with their club identity, their motivation and their confidence. Internal (mindset) and external (social support) coping strategies were developed over the study's duration. Concluding comments from participants were related to greater acceptance of the need to be patient, perhaps reflecting on the club's reputation of giving young players a sound football education. These phases of the transition came with ups and downs for each participant illuminating key elements of the adaptation to senior competition, barriers to transition without early success, and social aspects of the transition. Enhanced detail to these key areas poses important questions for future research and applied practice.

#5 MRI and ultrasound criteria for the diagnosis of a sports hernia in football players
Reference: Wiad Lek. 2020;73(4):755-760.
Authors: Oleksandr Yu Ioffe , Natalia M Negria, Anastasiia V Omelchenko, Oleksandr P Stetsenko, Yuri A Dibrova, Mykola S Kryvopustov, Yuri P Tsiura, Tatiana V Tarasiuk
Summary: The aim of the study is to specify diagnostic MRI and ultrasound criteria for a sports hernia in order to verify its diagnosis in football players. The study included 50 professional and amateur football players aged 15 to 34 from 2016 to 2019. The criteria for inclusion in the study were: the presence of groin pain in football players, which prevented them from continuing to actively participate in sports activities. The findings of the study revealed that during MRI the two factors, which had the strongest influence, were "increased MR signal intensity on PDfs observed from the structures of the inguinal canal" and "increased MR signal intensity on PDfs observed from bone marrow of superior ramus of the pubic bone". During ultrasound of the inguinal area, the main criterion for a sports hernia diagnosis was "increased size of the inguinal canal". The verification of the diagnosis was carried out on the basis of the presence of a protrusion in the posterior wall of the inguinal canal. For a sports hernia diagnosis the MRI sensitivity is 91.67% (95% CI 77.5 - 98.2), specificity -78.57% (95% CI 49.2 - 95.3) and the sensitivity of ultrasound is 88.89% (95% CI 73.9 - 96.9), the specificity - 50% (95% CI 23.0 - 77). The combination of MRI and ultrasound makes it possible to accurately detect the presence of a sports hernia in the football player. Based on the findings of our study, we formulated MRI and ultrasound criteria for a sports hernia diagnosis.

#6 Influence of artificial turf temperature on physical performance and muscle contractile properties in football players after a repeated-sprint ability test
Reference: Sci Rep. 2020 Jul 29;10(1):12747. doi: 10.1038/s41598-020-69720-6.
Authors: Gabriel Calderón-Pellegrino, Leonor Gallardo, Víctor Paredes-Hernández, Jorge García-Unanue, Jesus Vicente Giménez, Enrique Colino, Jose Luis Felipe, Javier Sánchez-Sánchez
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Summary: This study aimed to analyse the effect of playing surface temperature on muscular and thermal response to a repeated-sprint ability (RSA) test in football players. Thirty-two male football players (23 ± 5 years; 1.77 ± 0.06 m; 71.2 ± 6.7 kg) from two squads of a third-division football club participated in the study. An RSA test was carried out at a high surface temperature (45.34 ± 2.53 °C) and low surface temperature (27.21 ± 2.17 °C). Before and after this test, the muscular response of the players was assessed through tensiomyography and thermograms. The results revealed that performance in the RSA test particularly increased at a higher surface temperature, especially in the first 5 m of the 30 m sprint test. While a reduction in maximal radial displacement (Dm) in the biceps femoris post-RSA was observed at lower surface temperatures, a higher temperature on the thigh, hamstring and calf was found in the higher surface temperature group. In conclusion, higher surface temperatures had an influence on players' thermal and tensiomyographic profile and improved performance in their repeated-sprint ability. These results suggest a need for coaches and players to be aware of these parameters to ensure adequate functionality and safety of the playing surface.

#7 Delayed ankle muscle reaction time in female amateur footballers after the first 15 min of a simulated prolonged football protocol
Reference: J Exp Orthop. 2020 Jul 25;7(1):54. doi: 10.1186/s40634-020-00275-1.
Authors: Daniel T P Fong, Wing-Ching Leung, Kam-Ming Mok, Patrick S H Yung
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Summary: Ankle sprain injury rate is reported to be higher towards the end of a football match. Muscle fatigue may contribute to the delayed muscle reaction and subsequent injury. This study investigated the ankle muscle reaction time during a simulated, prolonged football protocol. Seven amateur female football players participated in a 105-min simulated, prolonged football protocol. An ankle muscle reaction test was conducted with a pair of ankle sprain simulators at a scheduled interval every 15-min. The reaction times of peroneus longus, tibialis anterior, and lateral gastrocnemius were collected using an electromyography system sampling at 1000 Hz. Repeated measures one-way multivariate analysis of variance with post-hoc paired t-tests were conducted to evaluate if the reaction time at each time point significantly differed from baseline. Statistical significance was set at p < 0.05 level. Reaction times started from 40.5-47.7 ms at baseline and increased to 48.6-55.7 ms at the end. Reaction times significantly increased in all muscles after the first 15 min except for the dominant lateral gastrocnemius. Increased reaction times were seen in the non-dominant limb after 60 min for tibialis anterior, after 75 min for peroneus longus, and after 90 min for the lateral gastrocnemius. Delayed reaction time of the ankle muscles were found after the first 15 min and in the final 45 min of a simulated prolonged football protocol. Strategies for injury prevention should also focus on tackling the delayed ankle muscle reaction time in the acute phase (the first 15 min), in addition to the latter minutes in the second half.

#8 Elite Football Coaches Experiences and Sensemaking about Being Fired: An Interpretative Phenomenological Analysis
Reference: Int J Environ Res Public Health. 2020 Jul 18;17(14):E5196. doi: 10.3390/ijerph17145196.
Authors: Marte Bentzen, Göran Kenttä, Pierre-Nicolas Lemyre
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Summary: Chronic job insecurity seems to be a prominent feature within elite sport, where coaches work under pressure of dismissals if failing to meet performance expectations of stakeholders. The aim of the current study was to get a deeper understanding of elite football coaches' experiences of getting fired and how they made sense of that process. A qualitative design using semi-structured interviews was conducted with six elite football coaches who were fired within the same season. Interpretative phenomenological analysis was chosen as framework to analyze the data. The results reflected five emerging themes: Acceptance of having an insecure job, working for an unprofessional organization and management, micro-politics in the organization, unrealistic and changing performance expectation, and emotional responses. All coaches expressed awareness and acceptance regarding the risk of being fired. However, they experienced a lack of transparency and clear feedback regarding the causes of dismissal. This led to negative emotional reactions as the coaches experienced being evaluated by poorly defined expectations and by anonymous stakeholders. Sports organizations as employers should strive to be transparent during dismissal. In addition, job insecurity is a permanent stressor for coaches and should be acknowledged and targeted within coach education.

#9 Effectiveness of a Generic vs. Specific Program Training to Prevent the Short-Term Detraining on Repeated-Sprint Ability of Youth Soccer Players
Reference: J Strength Cond Res. 2020 Aug;34(8):2128-2135. doi: 10.1519/JSC.0000000000003670.
Authors: Alejandro Rodríguez-Fernández, José G Villa, Javier Sánchez-Sánchez, Jose A Rodríguez-Marroyo
Summary: The aim of this study was to analyze the effects of 2 short-term training programs to prevent the negative effect of detraining on repeated-sprint ability (RSA) performance. The study was performed during a 2-week midseason break without official matches. Forty-five youth soccer players (17.7 ± 0.8 years, 175.4 ± 5.5 cm, and 67.2 ± 5.1 kg) were split into 3 groups during the intervention period: inactivity group (IN; N = 16), generic high-intensity training group (GG; N = 15), and specific training group (SG; N = 14). IN was instructed to avoid performing physical activity during the 2-week training intervention. However, GG and SG performed 8 training sessions. GG performed a generic aerobic interval training consisting of 4 repetitions of 4 minutes of exercise at 90-95% of maximal heart rate. SG performed a specific conditioning through small-sided games (4 vs. 4, 4 × 4-minute) and repeated sprints (6 × 30-m). Testing sessions included an RSA test and a Yo-Yo intermittent recovery test level 1 (YYIR1). Repeated-sprint ability performance only improved after the training intervention in SG (∼2%, p < 0.01, (Equation is included in full-text article.)= 0.23-0.25). Both GG and IN declined their performance in post-test (∼2%, p < 0.01, (Equation is included in full-text article.)= 0.19-0.22). No significant effect, group × time, was analyzed for YYIR1 performance. This study suggests that only specific training, based on small-sided games and repeated sprints, leads to short-term improvements on RSA performance in youth soccer players.

#10 Basketball players possess a higher bone mineral density than matched non-athletes, swimming, soccer, and volleyball athletes: a systematic review and meta-analysis
Reference: Arch Osteoporos. 2020 Aug 5;15(1):123. doi: 10.1007/s11657-020-00803-7.
Authors: Emilija Stojanović, Dragan Radovanović, Vincent J Dalbo, Vladimir Jakovljević, Nenad Ponorac, Ricardo R Agostinete, Zdenek Svoboda, Aaron T Scanlan 
Summary: Basketball athletes possess a higher bone mineral density (BMD) than matched non-athletes and swimming, soccer, and volleyball athletes. Differences appear to be exacerbated with continued training and competition beyond adolescence. The greater BMD in basketball athletes compared to non-athletes, swimming, and soccer athletes is more pronounced in males than females. The aim of this study was to examine differences in total and regional bone mineral density (BMD) between basketball athletes, non-athletes, and athletes competing in swimming, soccer, and volleyball, considering age and sex. PubMed, MEDLINE, ERIC, Google Scholar, and Science Direct were searched. Included studies consisted of basketball players and at least one group of non-athletes, swimming, soccer, or volleyball athletes. BMD data were meta-analyzed. Cohen's d effect sizes [95% confidence intervals (CI)] were interpreted as: trivial ≤ 0.20, small = 0.20-0.59, moderate = 0.60-1.19, large = 1.20-1.99, and very large ≥ 2.00. Basketball athletes exhibited significantly (p < 0.05) higher BMD compared to non-athletes (small-moderate effect in total-body: d = 1.06, CI 0.55, 1.56; spine: d = 0.67, CI 0.40, 0.93; lumbar spine: d = 0.96, CI 0.57, 1.35; upper limbs: d = 0.70, CI 0.29, 1.10; lower limbs: d = 1.14, CI 0.60, 1.68; pelvis: d = 1.16, CI 0.05, 2.26; trunk: d = 1.00, CI 0.65, 1.35; and femoral neck: d = 0.57, CI 0.16, 0.99), swimming athletes (moderate-very large effect in total-body: d = 1.33, CI 0.59, 2.08; spine: d = 1.04, CI 0.60, 1.48; upper limbs: d = 1.19, CI 0.16, 2.22; lower limbs: d = 2.76, CI 1.45, 4.06; pelvis d = 1.72, CI 0.63, 2.81; and trunk: d = 1.61, CI 1.19, 2.04), soccer athletes (small effect in total-body: d = 0.58, CI 0.18, 0.97), and volleyball athletes (small effect in total-body: d = 0.32, CI 0.00, 0.65; and pelvis: d = 0.48, CI 0.07, 0.88). Differences in total and regional BMD between groups increased with age and appeared greater in males than in females. Basketball athletes exhibit a greater BMD compared to non-athletes, as well as athletes involved in swimming, soccer, and volleyball.

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