Latest research in football - week 19 - 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 Performing more than 20 purposeful gameplay headers in a soccer season may alter autonomic function in female youth soccer players 

Reference: Res Sports Med. 2021 Feb 17;1-9. doi: 10.1080/15438627.2021.1888098. Online ahead of print. 

Authors: Marquise M Bonn, Alexandra B Harriss, James W G Thompson, James P Dickey 

Summary: This study evaluated the effects of cumulative purposeful soccer heading on autonomic nervous system function in 22 female youth soccer players (13.3 ± 0.9 years). A 10 minute electrocardiogram recording was collected at baseline and following the 20 game season (post-season) to calculate measures of heart rate variability (HRV), including standard deviation of the normal-normal intervals, total power, high frequency (HF), low frequency (LF), LF:HF, normalized HF and normalized LF. Participants were categorized into low- (<20 headers per season; n = 13) and high- (>20 headers per season; n = 9) exposure groups. Mann-Whitney U tests demonstrated no significant differences between groups for any HRV metric. However, the increased normalized LF power (low exposure 8.67 and high exposure -31.17, respectively; r = 0.35) and LF:HF power (-6.39 and 15.80, respectively; r = 0.35), between groups had moderate practical significance. Therefore, female youth players who perform more than 20 purposeful headers during a soccer season may exhibit altered autonomic function. 



#2 Short-Term Psychological and Hormonal Effects of Virtual Reality Training on Chronic Low Back Pain in Soccer Players

Reference: J Sport Rehabil. 2021 Feb 16;1-10. doi: 10.1123/jsr.2020-0075. Online ahead of print. 

Authors: Gopal Nambi, Walid Kamal Abdelbasset, Saud F Alsubaie, Ayman K Saleh, Anju Verma, Mohamed A Abdelaziz, Abdulaziz A Alkathiry 

Summary: The aim was to find the short-term psychological and hormonal effects of virtual reality training on chronic low back pain in American soccer players. The 3-block random sampling method was used on 54 university American soccer players with chronic low back pain, and they were allocated into 3 groups: virtual reality training (VRT; n = 18), combined physical rehabilitation (n = 18), and control (n = 18) groups at University Hospital. They underwent different balance training exercises for 4 weeks. The participants and the therapist who is assessing the outcomes were blinded. Psychological (pain intensity and kinesiophobia) and hormonal (glucose, insulin, Homeostatic Model Assessment of Insulin Resistance, growth hormone, prolactin, adrenocorticotropic hormone, and cortisol) values were measured at baseline, after 4 weeks, and after 6 months. The baseline demographic, psychological, and hormonal data between the VRT, combined physical rehabilitation, and control groups show no statistical difference (P ≥ .05). Four weeks following training, the VRT group shows more significant changes in pain intensity and kinesiophobia than the combined physical rehabilitation and control groups (P < .001), and the improvement was noted in the 6-month follow-up. All the hormonal variables (glucose, insulin, growth hormone, prolactin, adrenocorticotropic hormone, and cortisol) show significant changes at 4-week training (P < .001), except for the Homeostatic Model Assessment of Insulin Resistance (P = .075) between the 3 groups. At 6-month follow-up glucose, prolactin, adrenocorticotropic hormone, and cortisol show more significant difference in the VRT group than the other 2 groups (P < .001). At the same time, insulin (P = .694), Homeostatic Model Assessment of Insulin Resistance (P = .272), and growth hormone (P = .145) failed to show significant changes between the groups. Training through virtual reality is an effective treatment program when compared with conventional exercise training programs from a psychological and hormonal analysis perspective in American soccer players with chronic low back pain. 



#3 Effects of Plyometric Training with Agility Ladder on Physical Fitness in Youth Soccer Players

Reference: Int J Sports Med. 2021 Feb 16. doi: 10.1055/a-1308-3316. Online ahead of print. 

Authors: Alexis Padrón-Cabo, Miguel Lorenzo-Martínez , Alexandra Pérez-Ferreirós, Pablo B Costa, Ezequiel Rey

Summary: The aim of this study was to assess the effects of plyometric training with an agility ladder on components of physical fitness in youth soccer players. A total of twenty male under-13 soccer players were randomly assigned to a plyometric training group with an agility ladder (n=10) or a control group (n=10). Before and after training intervention linear sprint test (5 m, 10 m, 20 m), vertical jump ability (squat jump, countermovement jump and countermovement jump with arms), agility test, and slalom dribble test were assessed. The plyometric training with agility ladder was applied two times per week over six weeks. Data were analyzed using linear mixed model. The plyometric training group showed significant improvements (p<0.001) from pre-test to post-test in countermovement jump, countermovement jump with arms, and slalom dribble test. In the control group, no significant enhancements were obtained in all performance tests (p>0.05). The between-group analysis showed significant differences in countermovement jump with arms (p=0.03), but no significant differences (p>0.05) were found in squat jump, countermovement jump, sprint, agility test, and slalom dribble test. In conclusion, the short-term plyometric training with agility ladder seems to be ineffective and not time-efficient to improve physical fitness in youth soccer players. However, the interpretation of these results must be understood within the sample size limitations. 



#4 Hamstring Injury Prevention for Elite Soccer Players: A Real-World Prevention Program Showing the Effect of Players' Compliance on the Outcome 

Reference: J Strength Cond Res. 2020 Feb 14. doi: 10.1519/JSC.0000000000003505. Online ahead of print. 

Authors: Souhail Chebbi, Karim Chamari, Nicol Van Dyk, Tim Gabbett, Montassar Tabben 

Summary: The aim of this study was to determine the effect of implementing the Nordic hamstring exercise (NHE) to prevent hamstring injuries in soccer. A professional team was followed by the same medical team during 5 successive seasons (2012/2013 through 2016/2017). During the first and last seasons (2012/2013 and 2016/2017), no hamstring preventive action was implemented. For the seasons 2013/2014, 2014/2015, and 2015/2016, a noncompulsory (few players refusing to participate) NHE prevention program was implemented with accurate recording of the players' training and match exposure and attendance to the prevention sessions. The first 10 weeks of the season were used to progressively increase the volume and intensity of the NHE exercises, and at the end of the season, players were split in low-, moderate-, and high-attendance groups to the prevention sessions. Overall, 35 time-loss hamstring strain injuries were accounted for. The injury incidence was 0.30 per player per season, and the injury rate was 0.95 injury/1000 hour of exposure. A nonstatistically significant higher risk of hamstring injury was observed in the control, low, and moderate attendance groups compared with the high-attendance group. The greatest risk of hamstring injury was observed in the low-attendance group (odds ratio 1.77, confidence interval 0.57-5.47, p = 0.32). Implementing a NHE prevention program has a positive effect on the injury rate in a soccer team; however, the compliance of players with such interventions may be critical for its success. 



#5 Resuming professional football (soccer) during the COVID-19 pandemic in a country with high infection rates: a prospective cohort study 

Reference: Br J Sports Med. 2021 Feb 15;bjsports-2020-103724. doi: 10.1136/bjsports-2020-103724.

Authors: Yorck Olaf Schumacher, Montassar Tabben, Khalid Hassoun, Asmaa Al Marwani, Ibrahim Al Hussein, Peter Coyle, Ahmed Khellil Abbassi, Hani Taleb Ballan, Abdulaziz Al-Kuwari, Karim Chamari, Roald Bahr

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Summary: The risk of viral transmission associated with contact sports such as football (soccer) during the COVID-19 pandemic is unknown. The aim of this study was to describe the infective and immune status of professional football players, team staff and league officials over a truncated football season resumed at the height of the COVID-19 pandemic in a country with high infection rates and to investigate the clinical symptoms related to COVID-19 infection in professional football players. Prospective cohort study of 1337 football players, staff and officials during a truncated football season (9 weeks) with a tailored infection control programme based on preventive measures and regular SARS-CoV-2 PCR swab testing (every 3-5 days) combined with serology testing for immunity (every 4 weeks). Clinical symptoms in positive participants were recorded using a 26-item, Likert-Scale-based scoring system. During the study period, 85 subjects returned positive (cycle threshold (cT) ≤30) or reactive (30<cT<40) PCR tests, of which 36 were players. The infection rate was consistent with that of the general population during the same time period. More than half of infected subjects were asymptomatic, and the remaining had only mild symptoms with no one requiring hospitalisation. Symptom severity was associated with lower cT values. Social contacts and family were the most common sources of infection, and no infection could be traced to training or matches. Of the 36 infected players, 15 presented positive serology during the study period. Football played outdoors involving close contact between athletes represents a limited risk for SARS-CoV-2 infection and severe illness when preventive measures are in place. 



#6 Effect of 10 Weeks of Complex Training on Speed and Power in Academy Soccer Players 

Reference: Int J Sports Physiol Perform. 2021 Feb 14;1-6. doi: 10.1123/ijspp.2020-0139. Online ahead of print. 

Authors: Thomas I Gee, Paul Harsley, Daniel C Bishop 

Summary: This study investigated the effects of complex-paired and reverse-contrast 10-week training programs on sprint, power, and change-of-direction speed performance of elite academy soccer players. Seventeen elite academy soccer players each performed assessments of the 10- and 40-m sprint, Abalakov vertical jump, seated medicine-ball throw, and Arrowhead change-of-direction speed test, both prior to and after a twice-weekly 10-week resistance-training program. The participants were randomly split into 2 groups; the complex-paired training group (CPT, n = 9) performed 4 different complex pairs (heavy-resistance exercises paired with plyometric and Olympic lifting-style exercises), with each pair being interspersed with an 8-minute recovery period in line with recommended guidelines. The comparative group-the reverse-contrast training group (RCT, n = 8)-performed the same exercises; however, all of the plyometric and Olympic lifting exercises preceded the heavy-resistance exercises. Both groups achieved postintervention increases in the seated medicine-ball throw test (CPT +1.8% and RCT +1.6%, P < .05), whereas VJ performance improved only in the CPT group (+3.4%, P = .003). No significant improvements were observed in either the 10- and the 40-m sprint or Arrowhead change-of-direction speed test for either group. The CPT experienced a small but significant within-group improvement in jump performance. However, no significant between-groups differences were observed in any of the testing variables postintervention. Subsequently, for academy soccer athletes, the CPT approach did not produce meaningful benefits to performance compared with a more time-efficient reverse-contrast approach. 



#7 Injuries in elite level male beach soccer players: A prospective three year study

Reference: Phys Sportsmed. 2021 Feb 15. doi: 10.1080/00913847.2021.1889933. Online ahead of print. 

Authors: Yavuz Lima, Bulent Bayraktar

Summary: The aim of this study was to investigate the incidence and characteristics of match and training injuries in elite-level national male beach soccer players. The incidence, mechanism, location, type, severity, and burden of injuries of the Turkish national beach soccer team were recorded between 2017-2019. A total of 136 injuries occurred during the study period. Total injury incidence was 238.9 injuries/1,000 match hours (MHs) and 37.7 injuries/1,000 training hours (THs) (p<0.001). Twenty-seven injuries led to time-loss, and the incidences for match and training injuries were 36.7 and 7.9 per 1,000 hours, respectively. Of medical attention injuries (MAI) caused by trauma, 54.6% (n=53) were due to another player and, 60.9% (n=14) of time-loss injuries (TLI) caused by trauma were due to non-contact trauma (p<0.001). While 82% (n=91) of training injuries occurred in lower extremities, 29% (n=9) of match injuries occurred in the head/neck region (p<0.001). Head injury incidence was 45.9 per 1,000 match hours. Of MAI, 50% (n=57) were contusion, and 32.1% (n=9) of TLI were strain (p<0.001). Also, the most common injury subtype was foot/toe contusion during match and training (19.4%; n=6, 27.9%; n=31, respectively). The majority of injuries 91.9% (n=125) had slight severity. Head trauma, tendon injury and foot/toe contusion are important for clinical practice in beach soccer. Protective measures (rule regulation, use of protective equipment, etc.) should be considered to prevent these injuries. 



#8 Bone Mineral Density Differences Across Female Olympic Lifters, Power Lifters, and Soccer Players 

Reference: J Strength Cond Res. 2021 Mar 1;35(3):638-643. doi: 10.1519/JSC.0000000000003944. 

Authors: Woohyoung Jeon, John Michael Harrison, Philip R Stanforth, Lisa Griffin 

Summary: Athletic training improves bone mineral density (BMD) through repeated mechanical loading. The location, intensity, and direction of applied mechanical pressure play an important role in determining BMD, making some sports more advantageous at improving BMD at specific regions. Thirty-seven (10 power lifters [PL], 8 Olympic lifters [OL], 8 soccer players [SP], and 11 recreationally active [RA]) women participated in a cross-sectional study. We measured lumbar spine (L1-L4), femoral neck, total-body BMD, and overall body composition (total fat mass, lean mass, percent body fat) with dual-energy x-ray absorptiometry. All athletic groups had greater total BMD than RA (p = 0.01 [PL]; p < 0.001 [OL]; p = 0.01 [SP]). Olympic lifters had the highest total BMD than all other athletic groups. Olympic lifters had the significantly greater total BMD than PL (p = 0.018), but there was no difference in total BMD between PL and SP. As compared with RA, OL showed greater BMD at both the total lumbar spine (p = 0.002) and the femoral neck (p = 0.007), whereas PL showed greater BMD only for the total lumbar spine (p = 0.019) and SP showed greater BMD only for the femoral neck (p = 0.002). Olympic-style lifting includes both high-impact and odd-impact loading modalities that are associated with the highest BMD at both the lumbar spine and femoral neck. 



#9 Specific physical performances among male elite youth soccer players: effect of maturity status

Reference: J Sports Med Phys Fitness. 2021 Feb 15. doi: 10.23736/S0022-4707.21.11766-9. Online ahead of print. 

Authors: Mohamed Tounsi, Chirine Aouichaoui, Zouhair Tabka, Yassine Trabelsi

Summary: There is a lack of studies that investigated the relationship between anthropometric profile, biological maturity and specific soccer performances. Therefore, the aims of the present study were to establish normative data of anthropometric and specific physical performances and to determine the impact age and somatic maturation on young soccer players (U13-U19, n=487). Measurements include anthropometric variables to determine the age of peak height velocity (PHV), leg muscle volume (LMV) and soccer specific test (SST); Squat jump (SJ), Counter Movement jump (CMJ), sprint 10 meter (T10m), sprint 20 meter (T20m), sprint 30 meter (T30m) and intermittent-endurance tests (YYIRT-L1). Reference values showed a significant difference between anthropometric variables, LMV and SST according to PHV categories. (M)ANOVA analysis showed a significant age using maturity interaction effect of all anthropometric variables. A significant result was reported in the majority of SST performances for the age, the T10m and for T20m performances. The full model of multiple regressions and the multiple equations was used to determine the best predictors of physical performances according to anthropometric variables. This study provides normative data for anthropometric characteristics and physical performances according to chronological age (U13-U19) and maturity groups of young soccer players. 



#10 Injury analysis of a professional female soccer team in first division Italian season 

Reference: J Sports Med Phys Fitness. 2021 Feb 15. doi: 10.23736/S0022-4707.21.11688-3. Online ahead of print. 

Authors: Andrea Pellegrini, Martina Lombardi, Nicola Riva, Franco Combi, Claudio Pecci, Giuseppe Porcellini

Summary: Soccer, the most popular sport worldwide, has seen an exponential increase in women's participation at the elite level in the last few years. The main purpose of the current epidemiological study was to analyze the injury incidence, characteristics, and burden among elite female soccer players during a regular season. We recorded all injuries that occurred throughout the 2018-2019 competitive soccer season (August-April). The studied group consisted of 22 elite players, who were militant in the first national leagues from the first team of the same soccer club in the north of Italy. The 2006 FIFA consensus statement was used to design the injury registration form. Throughout the 2018-2019 season, medical staff treated 35 injuries in 22 females. Of the total number of injuries reported in 9 months (5.8 injuries per 1000 hours of exposure), 7 (20%) occurred during matches and 28 (80%) during training sessions. The most common injury was represented by muscular disorders (18; 51.43%) which affected the thigh in 16 cases, and the lower leg and trunk in one case each. According to an anatomic site, most injuries occurred in the lower limbs (94,28%), with the majority affecting thighs (16; 45%), ankles (8; 23%), and knees (5; 14%). Non-contact injuries are shown to be more frequent than contact injuries, which may be connected to the increasing athletic burden among athletes. Further prospective investigations are needed with a focus on prevention protocols. 



#11 Does aerobic performance define match running performance among professional soccer players? A position-specific analysis 

Reference: Res Sports Med. 2021 Feb 14;1-13. doi: 10.1080/15438627.2021.1888107. Online ahead of print. 

Authors: Toni Modric, Sime Versic, Damir Sekulic

Summary: Aerobic performance is considered an important determinant of match running performance in soccer, but studies have rarely investigated this issue in top-level players. This study examined the possible associations between direct measures of aerobic performance and match running performance in elite soccer players. Aerobic performance was tested at the beginning of the season in laboratory settings. The match-running performance was measured by a global positioning system over a competitive half-season for a total of 82 match performances in professional players from Croatia (age: 23.76 ± 2.64; body height: 181.62 ± 7.09 cm; body mass: 77.01 ± 6.34 kg) and clustered as central player (n = 57) and side player (n = 25) performance. No significant differences in aerobic performance were noted between central and side players. The anaerobic threshold was correlated with high-speed running (19.8-25.1 km/h), sprint running (>25.1 km/h), and high-intensity running (>19.8 km/h) among side players (r = 0.52, 0.53, and 0.59, respectively; p < 0.01). For central players, the aerobic threshold was correlated with the total distance covered, low-intensity running (<14.3 km/h), and distance covered in the zone of running (14.4-19.7 km/h) (r = 0.47, 0.49, and 0.39; p < 0.01, 0.01, and 0.03, respectively). Conditioning for central players should include activities with intensities corresponding to aerobic thresholds, while conditioning of side players should be focused on the development of anaerobic thresholds. 



#12 "He's Just a Wee Laddie": The Relative Age Effect in Male Scottish Soccer 

Reference: Front Psychol. 2021 Jan 28;12:633469. doi: 10.3389/fpsyg.2021.633469. eCollection 2021. 

Authors: James H Dugdale, Allistair P McRobert, Viswanath B Unnithan

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Summary: Significant structural, developmental, and financial constraints exist in Scottish soccer that may predicate a different approach to talent identification and development. To our knowledge, no published reports exist evaluating the prevalence of the relative age effect (RAE) in Scottish soccer players. Consequently, the aim of this study was to investigate the prevalence of the RAE among varied playing levels and ages of male Scottish youth soccer players. Birthdates of male youth players (n = 1,230) from U10 to U17 age groups and from playing levels: "Amateur" (n = 482), "Development" (n = 214), and "Performance" (n = 534), alongside a group of male Scottish senior professional players (n = 261) were recorded and categorized into quartiles (Q1 = January-March; Q2 = April-June; Q3 = July-September; and Q4 = October-December) and semesters (S1 = January-June and S2 = July-December) from the start of the selection year. Birthdates were analyzed for: (a) each playing level and (b) each age group irrespective of playing level. For the varied playing levels examined, an RAE was evident in "Development" and "Performance" playing levels only at youth level. When examining each age group, an RAE was observed in U12-U17 players only. While there was a slight asymmetry favoring Q1 born senior professional players, the RAE was not present within this group of our sample. Results from our study suggest that a bias in selecting individuals born earlier in the selection year may exist within male soccer academy structures, but not at amateur level. The asymmetry favoring chronologically older players at youth but not professional level questions the efficacy of this (un)conscious bias within male Scottish soccer players. 



#13 Effects of Percutaneous Electrical Nerve Stimulation on Countermovement Jump and Squat Performance Speed in Male Soccer Players: A Pilot Randomized Clinical Trial 

Reference: J Clin Med. 2021 Feb 10;10(4):690. doi: 10.3390/jcm10040690. 

Authors: Gracia María Gallego-Sendarrubias, José Luis Arias-Buría, Edurne Úbeda-D'Ocasar, Juan Pablo Hervás-Pérez, Manuel Antonio Rubio-Palomino, César Fernández-de-Las-Peñas, Juan Antonio Valera-Calero

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Summary: It has been suggested that Percutaneous Electrical Nerve Stimulation (PENS) can increase muscle strength. No previous study has investigated changes in performance in semiprofessional soccer players. This study compares the effects of adding two sessions of PENS to a training program versus the single training program over sport performance attributes (e.g., jump height and squat speed) in healthy soccer players. A cluster-randomized controlled trial was conducted on twenty-three semiprofessional soccer players who were randomized into an experimental (PENS + training program) or control (single training program) group. The training program consisted of endurance and strength exercises separated by 15-min recovery period, three times/week. The experimental group received two single sessions of PENS one-week apart. Flight time and vertical jump height during the countermovement jump and squat performance speed were assessed before and after each session, and 30 days after the last session. Male soccer players receiving the PENS intervention before the training session experienced greater increases in the flight time, and therefore, in vertical jump height, after both sessions, but not one month after than those who did not receive the PENS intervention (F = 4.289, p = 0.003, η 2 p: 0.170). Similarly, soccer players receiving the PENS intervention experienced a greater increase in the squat performance speed after the second session, but not after the first session or one month after (F = 7.947, p < 0.001, η 2 p: 0.275). Adding two sessions of ultrasound-guided PENS before a training strength program improves countermovement jump and squat performance speed in soccer players. 



#14 The effects of home confinement on physical activity level and mental status in professional football players during COVID-19 outbreak 

Reference: Phys Sportsmed. 2021 Feb 21;1-7. doi: 10.1080/00913847.2021.1888630. Online ahead of print. 

Authors: Gürhan Dönmez, Ömer Özkan, Yiğitcan Menderes, Şerife Şeyma Torgutalp, Levend Karaçoban, Nevzad Denerel, Savaş Kudaş

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Summary: The coronavirus outbreak caused significant changes in football around the world, such as the suspension of leagues and home isolation of players, etc. The main purpose of the present study was to assess the psychological impacts of lockdown and similar restrictions on professional football players during the coronavirus pandemic. The players from 36 professional football teams (n = 977) among Turkish Super League and First League teams were invited to complete a questionnaire including the Center for Epidemiologic Studies Depression Scale (CES-D), Impact of Event Scale-Revised Scores (IES-R) and short form of International Physical Activity Questionnaire (IPAQ). The online survey was completed by 237 players (24.3%). The mean number of self-quarantine day of participants was 26.9 ± 6.2 days. The median CES-D Scale and IES-R scores were 6.0 (min:0, max:42) and 23.0 (min:0, max:59), respectively. IPAQ scores of the players showed that four-fifths of the players still maintain high physical activity levels. There were negative, very weak and significant correlations between CES-D score and being married (r = -0.146, p = 0.024), as well as between CES-D score and IPAQ-Walking (r = -0.189, p = 0.004). A significant positive very weak correlation was observed between CES-D score and self-quarantine days (r = 0.148, p = 0.024). IPAQ-Walking was an independent predictor of CES-D. These findings support that maintaining regular physical activity and routinely exercising in a safe home environment is one of the most important strategies to ensure healthy mental state. 


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