Latest research in football - week 24 - 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 Maximal Strength, Sprint, and Jump Performance in High-Level Female Football Players Are Maintained With a Customized Training Program During the COVID-19 Lockdown

Reference: Front Physiol. 2021 Feb 26;12:623885.  doi: 10.3389/fphys.2021.623885. eCollection 2021.

Authors: Sigurd Pedersen, Dag Johansen, Andrea Casolo, Morten B Randers, Edvard H Sagelv, Boye Welde, Andreas Kjæreng Winther, Svein Arne Pettersen

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Summary: The COVID-19 outbreak with partial lockdown has inevitably led to an alteration in training routines for football players worldwide. Thus, coaches had to face with the novel challenge of minimizing the potential decline in fitness during this period of training disruption. In this observational pre- to posttest study involving Norwegian female football players (18.8 ± 1.9 years, height 1.68 ± 0.4 m, mass 61.3 ± 3.7 kg), we investigated the effects of a prescribed home-based and group-based intervention, implemented during the COVID-19 lockdown, on maximal muscular force production and high velocity variables. Specifically, maximal partial squat strength one repetition maximum (1RM), counter movement jump (CMJ) and 15 m sprint time were assessed 1 week prior to the lockdown and 12 weeks after the onset of lockdown. We also collected training content and volume from the prescribed training program and self-reported perceived training quality and motivation toward training. We observed no change in 1RM [pretest: 104 ± 12 kg, posttest: 101 ± 11 kg (P = 0.28)], CMJ height [pretest: 28.1 ± 2.3 cm, posttest: 26.8 ± 1.9 (P = 0.09)], and 15 m sprint time [pretest: 2.60 ± 0.08 s, posttest: 2.61 ± 0.07 s (P = 0.52)]. Our findings suggest that a prescribed home-based and group-based intervention with increased training time devoted to strength, jump, and sprint ability, and regulated to obtain a sufficient infection control level is feasible and effective to preserve strength, jumping, and sprinting abilities of high-level female football players during a ∼ 3-month period of a pandemic-induced lockdown.



#2 Mapping default mode connectivity alterations following a single season of subconcussive impact exposure in youth football

Reference: Hum Brain Mapp. 2021 Mar 18. doi: 10.1002/hbm.25384.

Authors: Jesse C DeSimone, Elizabeth M Davenport, Jillian Urban, Yin Xi, James M Holcomb, Mireille E Kelley, Christopher T Whitlow, Alexander K Powers, Joel D Stitzel, Joseph A Maldjian

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Summary: Repetitive head impact (RHI) exposure in collision sports may contribute to adverse neurological outcomes in former players. In contrast to a concussion, or mild traumatic brain injury, "subconcussive" RHIs represent a more frequent and asymptomatic form of exposure. The neural network-level signatures characterizing subconcussive RHIs in youth collision-sport cohorts such as American Football are not known. Here, we used resting-state functional MRI to examine default mode network (DMN) functional connectivity (FC) following a single football season in youth players (n = 50, ages 8-14) without concussion. Football players demonstrated reduced FC across widespread DMN regions compared with non-collision sport controls at postseason but not preseason. In a subsample from the original cohort (n = 17), players revealed a negative change in FC between preseason and postseason and a positive and compensatory change in FC during the offseason across the majority of DMN regions. Lastly, significant FC changes, including between preseason and postseason and between in- and off-season, were specific to players at the upper end of the head impact frequency distribution. These findings represent initial evidence of network-level FC abnormalities following repetitive, non-concussive RHIs in youth football. Furthermore, the number of subconcussive RHIs proved to be a key factor influencing DMN FC.



#3 A ninety-minute football match increases hamstring flexibility in professional players

Reference: J Biol Regul Homeost Agents. Sep-Oct 2020;34(5 Suppl. 1):87-92. IORS Special Issue on Orthopedics.

Authors: G Kakavas, N Malliaropoulos, A Kaliakmanis, B Georgios, N Maffulli

Summary: Flexibility is an integral component in any conditioning program. Flexibility has been defined as the ability of a muscle to lengthen and allow one or more joints in a kinetic chain to move through a range of motion. The lack of flexibility of the hamstring muscle group has been associated with a higher risk of non-contact muscle injury, and for several other conditions, such as changes in lumbopelvic rhythm, greater thoracic kyphosis and lumbar flexion, and lower back pain. The present study explored the effects of a 90-minute soccer match on hamstring group flexibility. Our study shows that a 90-minute football match favorably impacts the flexibility of the hamstring muscle group. Flexibility is a modifiable risk factor for muscle strain injury. It remains to be ascertained how long this effect lasts, and whether it may be associated with the risk of developing or avoiding noncontact injury to the hamstring muscle group.



#4 Epidemiological analysis of injury occurrence and current prevention strategies on international amateur football level during the UEFA Regions Cup 2019

Reference: Arch Orthop Trauma Surg. 2021 Mar 19. doi: 10.1007/s00402-021-03861-9.

Authors: Dominik Szymski, Volker Krutsch, Leonard Achenbach, Stephan Gerling, Christian Pfeifer, Volker Alt, Werner Krutsch, Oliver Loose

Summary: Football is the most popular sport worldwide and results in a high frequency of injuries. So far, mainly injuries in professional football have been investigated, and the literature lacks data regarding detailed injury epidemiology and current prevention data in amateur football tournaments. A prospective cohort study investigated an international amateur football tournament, the UEFA Regions' Cup, which took place in 2019 in Germany. Injury epidemiology, current prevention strategies of the teams and the implementation of the UEFA concussion protocol were investigated in detail by means of standardized injury definitions and data samples for football (Fuller et al., Scand J Med Sci Sports 16:83-92, , 2006). 138 player of 8 teams participated in this study, while 39 players were excluded. Overall injury incidence was 12.5 per 1000 h total football exposure, 43.5 per 1000 h for match exposure. No injuries were registered during training. Injury prevalence was 14.1% per player and 1.1 injuries per match were registered. The lower extremity was predominantly affected by injuries (71.4%) and the majority of injuries (78.6%) were non-severe injury types like contusions (50%) and sprains (18.2%). Two head injuries, one contusion and one skin lesion, were handled by the guidelines of the UEFA concussion protocol. 44.4% of the players indicated at least one previous injury before tournament, 45.3% of them during the last two football seasons before start of the tournament. Injury prevention performance was included in all participating teams during the tournament by warm up or training strategies (100%). During the warm-up program just 5 exercises of the FIFA 11 + program was detected by this investigation in participating teams to be done by more half of the teams. Running exercises were the most frequently performed exercises, while trunk muscle exercises were less represented (14.3%). This study presents for the first time epidemiological injury and prevention data of the UEFA Regions Cup. Injury incidence was higher compared to injury reports of regular seasons, but lower compared to other amateur football tournaments. Currently used prevention programs revealed trunk muscle exercises as often neglected.



#5 Long-Term Patterns of Bone Mineral Density in an Elite Soccer Player

Reference: Front Physiol. 2021 Feb 25;12:631543.  doi:10.3389/fphys.2021.631543. eCollection 2021.

Authors: Chiara Milanese, Valentina Cavedon, Giuliano Corradini, Aiace Rusciano, Carlo Zancanaro

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Summary: Changes in bone mineral density (BMD) have been associated with association football (soccer) participation. Seasonal changes in BMD of soccer players have been proposed as well. However, previous investigations were based on short-term observations. Actually, longitudinal investigation of BMD in soccer players is lacking, possibly because of frequent inter-club transfer, changes in club policy or continued availability of the relevant facilities. Dual-energy X-ray Absorptiometry (DXA)-measured areal BMD (aBMD) was obtained during the competitive season in an elite soccer player along 10 consecutive years. Findings showed that (1) aBMD tends to increase with age, independently of body mass; (2) The right (preferred, kicking) leg has higher aBMD than the left (non-preferred, support) one; (3) Meaningful (i.e., >least significant change, LSC) changes in aBMD take place along the season; and (4) The off-season (transition) period has no effect on aBMD. Findings prompt for future research aimed at clarifying the long-term and seasonal patterns of bone characteristics in soccer in relation with age and type/dose of training. Season-around, long-term scrutiny of bone status in soccer players would help controlling for possible changes/asymmetries in bone mineralization/strength.



#6 Head Impact Situations in Professional Football (Soccer)

Reference: Sports Med Int Open. 2021 Mar 10;5(2):E37-E44. doi: 10.1055/a-1338-1402. eCollection 2021 Mar.

Authors: Florian Beaudouin, Daniel Demmerle, Christoph Fuhr, Tobias Tröß, Tim Meyer

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Summary: The aim was to assess head impact incidents (HIIs) and to distinguish diagnosed head injuries from other incidents, a video observation analysis of match HIIs was conducted in the German Bundesliga (2017/18 season). Video recordings of each match were screened to identify the respective events. Head injury data were identified by a prospective injury registry. HII and head injury incidence rates (IR) were calculated with 95% CIs. The total number of HIIs was 1,362 corresponding to an IR of 134.9/1000 match hours (95% CI 127.9–142.2). In 123 HII (IR 12.2, 95% CI 10.2–14.5) the contact was classified as severe. Head contact with the opponent was the most frequent cause (85%). The most frequent mechanism was in 44% (combined) the arm and elbow-to-head, followed by head-to-head and hand-to-head contacts (each 13%). In 58%, the HIIs occurred during header duels. Twenty-nine head injuries were recorded (IR 2.9, 95% CI 2.0–4.1). Concussions/traumatic brain injuries accounted for 48%, head/facial fractures 24%, head/facial contusions 21%, and lacerations/abrasions 7%. The number of HIIs not classified as concussions/more severe trauma was high. Identification of HIIs and head injury severity should be improved during on-field assessment as many head injuries might go unrecognised based on the large number of HIIs.



#7 Musculoskeletal Injuries and Their Association With Previous Concussion History: A Prospective Study of High School Volleyball and Soccer Players

Reference: Am J Sports Med. 2021 Mar 15;363546521997116.  doi: 10.1177/0363546521997116. 

Authors: Kevin M Biese, Stephanie A Kliethermes, Andrew M Watson, Timothy A McGuine, Pamela J Lang, David R Bell, M Alison Brooks

Summary: Sports-related concussions may have a neurobiological recovery period that exceeds the period of clinical recovery, and one consequence of an extended neurobiological recovery may be the risk of subsequent musculoskeletal injuries. Most literature citing an increased risk of musculoskeletal injury after a sports-related concussion has been reported in populations other than adolescent athletes. The purpose was to prospectively determine if incidence rates of musculoskeletal injury differ between adolescent athletes with and without a previous sports-related concussion, while controlling for sex, sport, and age. A secondary aim was to determine if this relationship differs between male and female athletes of the same sport. Our hypotheses were that acute-noncontact injury rates would be higher in athletes with a previous sports-related concussion when compared with athletes without a previous sports-related concussion, and that this relationship would exist only in female athletes and not male athletes. High school soccer and volleyball players were recruited in 2 prospective cohort studies that observed 4837 athletes during their sporting season (females, 80%; soccer, 57%; mean [SD] age, 15.6 [1.1] years). At preseason, all participants self-reported demographics and previous sports-related concussion within the past 12 months. During the sport season, team athletic trainers electronically recorded athlete exposures and injury data, including injury characteristics. Injury rates per 1000 athlete exposures and injury rate ratios (IRRs) with 95% confidence intervals were calculated. All injury rates and IRRs were adjusted for sex, age, and sport.

Results: The rate of acute-noncontact lower extremity injury was 87% greater (IRR, 1.87; 95% CI, 1.29-2.74) in participants with a previous sports-related concussion versus those without one. The acute-noncontact lower extremity injury rates (IRRs) for females and males with a previous sports-related concussion were 1.76 (95% CI, 1.19-2.59) and 2.83 (95% CI, 0.85-9.50), respectively. No difference was detected in acute-contact (IRR, 0.98; 95% CI, 0.56-1.73) or overuse (IRR, 1.09; 95% CI, 0.51-2.37) lower extremity injury rates by previous sports-related concussion. Female adolescent athletes who reported a sports-related concussion within the past 12 months were more likely to sustain an acute-noncontact lower extremity injury during their high school sports season when compared with female athletes without a previous sport-related concussion.



#8 External and internal load during Small-Sided Games in soccer: use or not floaters

Reference: J Sports Med Phys Fitness. 2021 Mar 15.  doi: 10.23736/S0022-4707.21.12103-6. Online ahead of print.

Authors: Jose A Asian-Clemente, Alberto Rabano-MuÑoz, Francisco J NuÑez, Luis Suarez-Arrones

Summary: The purpose of the present study was to analyse the internal and external loads on regular and floater players during standardized small-sided games (SSGs) with different numbers of players (teams of 3, 5, or 7 players). Fifteen male semi-professional football players played different SSGs maintaining the same relative area per player. Total distance (TD), distance covered at different speeds (DC), the number of accelerations and decelerations, maximal (HRmax) and mean (HRmean) heart rate and rate of perceived exertion (RPE) were registered. Regular players showed greater internal and external loads in SSGs with 3 and 5 players without floaters than with floaters (ES 0.60-to-1.27). Likewise, with floaters, regular players in the SSGs with 3 performed more accelerations (ES 1.40 and 1.17) and with 7 achieved higher TD, DC > 14 km·h-1, HRmax and HRmean (ES 0.66-to-2.79) than any other. During SSGs with 7 players the floaters showed a higher TD and decelerations than in other SSGs (ES 0.47-to-1.70), and a higher DC (0-6.9 km·h-1,14-17.9 km·h-1) and RPE than in SSGs with 3 players (ES 0.59-to-0.89). During SSGs with 5, the floaters showed a higher TD, HRmax, HRmean and RPE than in SSGs with 3 (ES 0.86-to-1.45). In all SSGs, regular players showed higher TD, DC (14-17.9 km·h-1), accelerations, decelerations and HRmean than floaters (ES 1.24-to-6.23). Coaches must carefully design SSGs because the number of players and the presence or absence of floaters can affect the external-internal load expressed.



#9 Effect of whey vs. soy protein supplementation on recovery kinetics following speed endurance training in competitive male soccer players: a randomized controlled trial

Reference: J Int Soc Sports Nutr. 2021 Mar 16;18(1):23.  doi: 10.1186/s12970-021-00420-w.

Authors: Savvas Kritikos, Konstantinos Papanikolaou, Dimitrios Draganidis, Athanasios Poulios, Kalliopi Georgakouli, Panagiotis Tsimeas, Theofanis Tzatzakis, Dimitrios Batsilas, Alexios Batrakoulis, Chariklia K Deli, Athanasios Chatzinikolaou, Magni Mohr, Athanasios Z Jamurtas, Ioannis G Fatouros

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Summary: Soccer-specific speed-endurance training induces short-term neuromuscular fatigue and performance deterioration over a 72-h recovery period, associated with elevated markers of exercise-induced muscle damage. We compared the effects of whey vs. soy protein supplementation on field activity, performance, muscle damage and redox responses following speed-endurance training in soccer players. Ten well-trained, male soccer players completed three speed-endurance training trials, receiving whey protein (WP), soy protein (SP) or an isoenergetic placebo (PL; maltodextrin) according to a randomized, double-blind, crossover, repeated-measures design. A pre-loading period was applied in each trial during which protein supplementation was individually adjusted to reach a total protein intake of 1.5 g/kg/day, whereas in PL protein intake was adjusted at 0.8-1 g/kg/day. Following pre-loading, two speed-endurance training sessions (1 and 2) were performed 1 day apart, over a 3-day experimental period. During each session, field activity and heart rate were continuously monitored using global positioning system and heart rate monitors, respectively. Performance (isokinetic strength of knee extensors and flexors, maximal voluntary isometric contraction, speed, repeated sprint ability, countermovement jump), muscle damage (delayed-onset of muscle soreness, creatine kinase activity) and redox status (glutathione, total antioxidant capacity, protein carbonyls) were evaluated at baseline (pre), following pre-loading (post-load), and during recovery from speed-endurance training. High-intensity and high-speed running decreased (P ≤ 0.05) during speed-endurance training in all trials, but WP and SP mitigated this response. Isokinetic strength, maximal voluntary isometric contraction, 30-m speed, repeated sprint ability and countermovement jump performance were similarly deteriorated during recovery following speed-endurance training in all trials (P ≤ 0.05). 10 m speed was impaired at 24 h only in PL. Delayed-onset of muscle soreness, creatine kinase, total antioxidant capacity and protein carbonyls increased and glutathione decreased equally among trials following speed-endurance training (P ≤ 0.05), with SP inducing a faster recovery of protein carbonyls only at 48 h (P ≤ 0.05) compared to WP and PL. In conclusion, increasing daily protein intake to 1.5 g/kg through ingestion of either whey or soy protein supplements mitigates field performance deterioration during successive speed-endurance training sessions without affecting exercise-induced muscle damage and redox status markers.



#10 Coding Body Language in Sports: The Nonverbal Behavior Coding System for Soccer Penalties

Reference: J Sport Exerc Psychol. 2021 Mar 17;1-15.  doi: 10.1123/jsep.2020-0066. Online ahead of print.

Authors: Philip Furley, Alexander Roth

Summary: Nonverbal behavior (NVB) plays an important role in sports. However, it has been difficult to measure, as no coding schemes exist to objectively measure NVB in sports. Therefore, the authors adapted the Body Action and Posture Coding System to the context of soccer penalties, validated it, and initially used this system (Nonverbal Behavior Coding System for Soccer Penalties [NBCSP]) to explore NVB in penalties. Study 1 demonstrated that the NBCSP had good to excellent intercoder reliability regarding the occurrence and temporal precision of NVBs. It also showed that the coding system could differentiate certain postures and behaviors as a function of emotional valence (i.e., positive vs. negative emotional states). Study 2 identified differences in NVB for successful and missed shots in a sample of penalties (time spent looking toward the goal, toward the ground, right arm movement, and how upright the body posture was). The authors discuss the utility of the coding system for different sport contexts.



#11 Effects of Small-Sided Games vs. Running-Based High-Intensity Interval Training on Physical Performance in Soccer Players: A Meta-Analytical Comparison

Reference: Front Physiol. 2021 Mar 1;12:642703.  doi: 10.3389/fphys.2021.642703. eCollection 2021.

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, José Afonso, Hugo Sarmento

Summary: This systematic review with meta-analysis (SRMA) was conducted to compare the effects of SSG-based interventions vs. running-based HIIT interventions on soccer players' sprinting time (ST), vertical height jump (VJH), and change of direction time (CODt).  The data sources utilized were Web of Science, Scopus, SPORTDiscus, and PubMed. Results: An electronic search yielded 650 articles, six of which were included in the present study. Between-group analysis found a significant favoring effect of HIIT-based over SSG-based training interventions for the improvement of linear sprinting time (ES = 0.42; p = 0.012). A within-group analysis revealed a significant favoring effect of HIIT-based training interventions for improving linear sprinting time (ES = 0.42; p = 0.008) and CODt (ES = 1.04; p = 0.005) despite a non-significant effect on VJH (ES = 0.47; p = 0.22).  The meta-analytical comparison revealed favoring the effect of running-based HIIT over SSG-based interventions in sprinting performance, although no significant differences were observed for jumping and CODt performance. The findings suggest that SSG-based programs should be supplemented by other training methods that benefit determinant capacities in soccer players.



#12 The Risk of Knee Osteoarthritis in Professional Soccer Players

Reference: Dtsch Arztebl Int. 2021 Jan 29;118(4):49-55.  doi: 10.3238/arztebl.m2021.0007.

Authors: Alice Freiberg, Ulrich Bolm-Audorff, Andreas Seidler

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Summary: We address the question whether professional soccer players with and without macroinjury of the knee joint are at an elevated risk for knee osteoarthritis. A systematic review with meta-analyses was conducted. The study protocol was prospectively registered (registration number CRD42019137139). The MEDLINE, EMBASE, and Web of Science databases were searched for relevant publications; in addition, forward searching was performed, and the listed references were considered. All steps of the process were undertaken independently by two reviewers, and any discordances were resolved by consensus. For all publications whose full text was included, the methods used were critically evaluated. The quality of the evidence was judged using the GRADE criteria. The pooled odds ratio for objectively ascertained osteoarthrosis of the knee was 2.25 (95% confidence interval [1.41-3.61], I2 = 71%). When only radiologically ascertained knee osteoarthrosis was considered, the odds ratio was 3.98 [1.34; 11.83], I2 = 58%). The pooled risk estimator in studies in which knee joint macroinjury was excluded was 2.81 ([1.25; 6.32], I2 = 71%). A marked association was found between soccer playing and knee osteoarthritis in male professional soccer players. For female professional soccer players, the risk of knee osteoarthritis could not be assessed because of the lack of data. Knee injuries seem to play an important role in the development of knee osteoarthritis in professional soccer players.



#13 Effects of 12 weeks of recreational football (soccer) with caloric control on the glycemia and cardiovascular health of adolescent boys with type 1 diabetes

Reference: Pediatr Diabetes. 2021 Mar 21.  doi: 10.1111/pedi.13203. Online ahead of print.

Authors: Mohammed Hamdan Hashem Mohammed, Mohammad Hussain Hassan Al-Qahtani, Tim Takken

Summary: Though 12 weeks of physical activity alone improves the health of people with type 1 diabetes, there is little evidence that physical activity alone can improve glycemia in 12 weeks. The aim was to determine the effects of recreational football combined with caloric control on glycemia and cardiovascular health of adolescent boys with type 1 diabetes. The participants were divided into four groups as follows: football with diet, football-only, diet-only, and the control groups. Each group consisted of 10 participants. The football with diet and the football-only groups had 1.5 h of football twice a week for 12 weeks. The following outcomes were measured before and after 12 weeks: Glycated hemoglobin, fasting blood glucose, total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, and resting blood pressures. Changes were considered significant when p ≤ 0.050 and common language effect size ≤ 42 % or common language effect size ≥ 58 %. Glycated hemoglobin decreased in the football with diet group (mean change (standard deviation) = -0.9 (1.0) %, p = 0.019, and common language effect size = 31.5 %) and was different from the control group (p = 2.4×10-4 and common language effect size = 95.5 %.). However, none of the intervention groups showed a clear change in blood lipids nor blood pressure. Twelve weeks of combined football with diet intervention provides the greatest improvement in glycemia in adolescent boys with type 1 diabetes. 



#14 Kick Start to an Epidemiological Report of Soccer-Related Craniofacial Trauma Analysis

Reference: J Craniofac Surg. 2021 Mar 17.  doi: 10.1097/SCS.0000000000007639. Online ahead of print.

Authors: John V Nahas, Melinda J Choi, Erin M Wolfe, Randall G Pierrot, Benjamin R Slavin, Ethan L Plotsker, Prakash J Mathew, Seth R Thaller

Summary: Soccer is a global sport played by millions annually with an increasing popularity in the United States. Game is played by a wide range of participants from all ages and levels of competition. This scenario leads to a potential disparity in the injury profile based on quantifiable demographics. As the game continues to grow, injury detection and side-line assessment must change as well. Utilizing a national injury database, a retrospective cohort study was conducted using 10 years of data collected from randomly selected emergency departments across the United States. Patient demographics, injury sites, and diagnosis were recorded. Diagnoses examined included concussion, contusion or abrasion, dental injury, fracture, hematoma, hemorrhage, internal injury, and laceration. Highest percentage of craniofacial injuries was observed in soccer players between the ages of 12 and 18. In ages 6 to 11 the most common injuries were contusions and dental injuries, with a significantly low number of fractures. Within the age group of 12 to 18 the highest percentage of injuries was concussions. Finally, the highest percentage of injury in the ages of 19 to 34 were fractures and lacerations. There is a shift in injury profile as the age of soccer players increases and the level of play becomes faster-paced. In youth players, there is a higher percentage of soft tissue injury. Older players are more likely to suffer a higher degree of injury including fractures, concussions, and lacerations. This suggests a great utility for a layperson-friendly educational intervention initiative applicable to all demographics for the sport of soccer.


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