Latest research in football - week 12 - 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 Physical performance development in a female national team soccer program 

Reference: J Sci Med Sport . 2020 Dec 31;S1440-2440(20)30864-1. doi: 10.1016/j.jsams.2020.12.009.

Authors: Robert A Poehling, Ming-Chang Tsai, Sarah A Manson, Michael S Koehle, Cesar M P Meylan

Summary: Significant resources are invested in maximizing player performance without extensive knowledge of the athletic progression of elite female soccer players during their career. The aim of the current study was therefore to investigate the change in physical performance characteristics in 12- to 34-year-old female soccer players in a national team program. Physical performance was assessed across five years and 657 testing occasions (n = 143) using anthropometrics, 40 m sprint (10 m split), broad jump, countermovement jump, squat jump, and 30-15 intermittent fitness test (IFT). Using a Gaussian mixture model, Youth and Senior groups were bifurcated at approximately 23 years old. Subsequent linear mixed models for each group and variable identified significant improvements in the Youth group in maximal speed (30-40 m split), broad jump, countermovement jump, and final velocity30-15IFT (p ≤ 0.002), and a decrease in squat jump height with increasing age (p = 0.04). The Senior group recorded slower 10 m sprint time and a decrease in squat jump height with increasing age (p < 0.001). Body mass increased from 12 to 34 years old (Youth and Senior: p ≤ 0.001). The Youth group significantly differed in the rate of change compared to the Senior group in body mass, 10 m sprint time, countermovement jump, squat jump, and final velocity30-15IFT (p ≤ 0.001). This information can be used to identify average rates of physical performance improvement and decay to help guide optimal physical training and maximize the longevity of a female soccer players' career. 



#2 The Effect of Coach Feedback and Awareness of Head Impact Exposure on Practice Structure in Youth Football

Reference: J Neurotrauma. 2021 Jan 4. doi: 10.1089/neu.2020.7224. Online ahead of print. 

Authors: Daniella M DiGuglielmo, Gabriella M Milef, Justin B Moore, Mireille E Kelley, Alexander K Powers, Joel D Stitzel, Jillian E Urban

Summary: With the concern of concussion risk and repetitive head impacts in youth football, organizations have adopted rules that limit contact during practice. However, rule changes are not ubiquitous among organizations and are challenging to monitor and enforce. Ultimately, football practice activities are determined by coaches, but it is unknown whether providing objective data to coaches relating activities to their athletes' head impact exposure (HIE) would alter practice structure or help reduce HIE. This study evaluated the effect of coach awareness of HIE on practice structure over time. Head impact data from three intervention (56 players) and control (38 players) teams were collected over two youth football seasons. Athletes were instrumented with the Head Impact Telemetry (HIT) System and time-synchronized video was recorded for practices and games. Impact frequencies and head accelerations were compiled into weekly HIE practice and game reports shared with the head coach of each intervention team. Time per drill, impact rate, and impact magnitude were compared among three time frames (pre-season, mid-season, and late-season) using generalized linear models. Control teams had higher impact rates than intervention teams in all drills across time frames. Among all teams, 95th percentile linear and rotational accelerations were highest during mid-season. Among intervention teams, more time was spent on scrimmage and skill development from pre-season to late-season, with less time spent on tackling. This study suggests receiving objective data informing HIE in practice may contribute to changes in practice structure and help inform intervention efforts to improve head impact safety in football. 



#3 Injury and illness epidemiology in professional Asian football: lower general incidence and burden but higher ACL and hamstring injury burden compared with Europe

Reference: Br J Sports Med. 2021 Jan 5;bjsports-2020-102945. doi: 10.1136/bjsports-2020-102945. 

Authors: Montassar Tabben, Cristiano Eirale, Gurcharan Singh, Abdulaziz Al-Kuwari, Jan Ekstrand, Hakim Chalabi, Roald Bahr, Karim Chamari

Summary: While football injury and illness epidemiology surveillance at professional club level in Europe is available, epidemiological data from other continents are lacking. The aim was to investigate injury and illness epidemiology in professional Asian football. Professional teams from the Asian Football Confederation (AFC) league were followed prospectively for three consecutive AFC seasons (2017 through 2019, 13 teams per season, 322 team months). Time-loss injuries and illnesses in addition to individual match and training exposure were recorded using standardised digital tools in accordance with international consensus procedures. In total, 232 665 hours of exposure (88.6% training and 11.4% matches) and 1159 injuries were recorded; 496 (42.8%) occurred during matches, 610 (52.6%) during training; 32 (2.8%) were reported as 'not applicable' and for 21 injuries (1.8%) information was missing. Injury incidence was significantly greater during match play (19.2±8.6 injuries per 1000 hours) than training (2.8±1.4, p<0.0001), resulting in a low overall incidence of 5.1±2.2.The injury burden for match injuries was greater than from training injuries (456±336 days per 1000 hours vs 54±34 days, p<0.0001). The two specific injuries causing the greatest burden were complete ACL ruptures (0.14 injuries (95% CI 0.9 to 0.19) and 29.8 days lost (29.1 to 30.5) per 1000 hours) and hamstring strains (0.86 injuries (0.74 to 0.99) and 17.5 days (17.0 to 18.1) lost per 1000 hours).Reinjuries constituted 9.9% of all injuries. Index injuries caused 22.6±40.8 days of absence compared with 25.1±39 for reinjuries (p=0.62). The 175 illnesses recorded resulted in 1.4±2.9 days of time loss per team per month. Professional Asian football is characterised by an overall injury incidence similar to that reported from Europe, but with a high rate of ACL ruptures and hamstring injury, warranting further investigations. 



#4 Convergent Validity of CR100-Based Session Ratings of Perceived Exertion in Elite Youth Football Players of Different Ages 

Reference: Int J Sports Physiol Perform. 2021 Jan 6;1-5. doi: 10.1123/ijspp.2020-0047. Online ahead of print. 

Authors: Fabio R Serpiello, Will G Hopkins 

Summary: The purpose was to assess the convergent validity of internal load measured with the CR100 scale in youth football players of 3 age groups. A total of 59 players, age 12-17 years, from the youth academy of a professional football club were involved in this study. Convergent validity was examined by calculating the correlation between session ratings of perceived exertion (sRPE) and Edwards load, a commonly used load index derived from the heart rate, with the data originating from 1 competitive season. The magnitude of the relationship between sRPE and Edwards load was obtained with weighted mean correlations and by assessing the effect of the change of the Edwards load on sRPE. Differences between the individuals' intercepts and slopes were assessed by interpreting the SD representing the random effects (player identity and the interaction of player identity and scaled Edwards load). Probabilistic decisions about true (infinite sample) magnitudes accounting for sampling uncertainty were based on 1-sided hypothesis tests of substantial magnitudes, followed by reference Bayesian analysis. Very high relationships exist between the sRPE and Edwards load across all age groups, with no meaningful differences in the magnitudes of the relationships between groups. Moderate to large differences between training sessions and games were found in the slopes of the relationships between the sRPE and Edwards load in all age groups. Finally, mostly small to moderate differences were observed between individuals for the intercepts and slopes of the relationships between the sRPE and Edwards load. Practitioners working in youth team sports can safely use the CR100 scale to track internal load. 



#5 Experiences and Strategies Influencing Older Adults to Continue Playing Walking Football 

Reference: J Aging Phys Act. 2021 Jan 7;1-13. doi: 10.1123/japa.2020-0058. Online ahead of print. 

Authors: Rachel Cholerton, Helen Quirk, Jeff Breckon, Joanne Butt 

Summary: Adults aged 55+ years are most likely to be inactive, despite research suggesting that older adults experience multiple benefits when participating in physical activity and sport. Limited research focuses on long-term continuation of sport participation in this population, especially in "adapted sports" like walking football. This study explored the experiences of walking football maintenance in 55- to 75-year-old players. Semistructured interviews were conducted, with 17 older adults maintaining walking football play over 6 months. The inductive analysis revealed five higher-order themes representing maintenance influences and two higher-order themes relating to maintenance mechanisms (i.e., the conscious process by which players maintain). Influences when maintaining walking football included individual- and culture-level influences (e.g., perceived benefits of maintenance and ability acceptance). Maintenance mechanisms included cognitions and behaviors (e.g., scheduling sessions and redefining physical activity expectations). Findings highlight novel implications for policy and practice, which are important to consider when delivering walking football to older adults. 



#6 Upper-Body Resistance Training Following Soccer Match Play: Compatible, Complementary, or Contraindicated?

Reference: Int J Sports Physiol Perform. 2021 Jan 13;1-11. doi: 10.1123/ijspp.2020-0762. Online ahead of print. 

Authors: Angelo Sabag, Ric Lovell, Neil P Walsh, Nick Grantham, Mathieu Lacome, Martin Buchheit 

Summary: During heavily congested schedules, professional soccer players can experience exacerbated fatigue responses, which are thought to contribute to an increased risk of injury. Given that match-induced residual fatigue can last up to 72 hours, many coaches naturally prioritize recovery in the days immediately following match day. While it is intuitive for coaches and training staff to decrease the amount of auxiliary training practices to focus on recovery, prescribing upper-body resistance training on the day after match play has recently emerged as a specific training modality in this context. While these sessions may be implemented to increase training stimulus, there are limited data available regarding the efficacy of such a practice to improve recovery kinetics. In this narrative review, the authors look at the theoretical implications of performing upper-body resistance training on the day after match play on the status of various physiological and psychological systems, including neuromuscular, metabolic, hormonal, perceptual, and immunological recovery. The available evidence suggests that in most cases this practice, as currently implemented (ie, low volume, low intensity), is unlikely to be complementary (ie, does not accelerate recovery) but is potentially compatible (ie, does not impair recovery). Overall, because the perception of such sessions may be player dependent, their programming requires an individualized approach and should take into account match dynamics (eg, fixture scheduling, playing time, travel). 



#7 The Risk of Knee Osteoarthritis in Professional Soccer Players 

Reference: Dtsch Arztebl Int. 2021 Jan 1;118(1):arztebl.m2021.0007. doi: 10.3238/arztebl.m2021.0007. 

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

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. 



#8 Analyzing the Magnitude of Interlimb Asymmetries in Young Female Soccer Players: A Preliminary Study 

Reference: Int J Environ Res Public Health. 2021 Jan 8;18(2):E475. doi: 10.3390/ijerph18020475. 

Authors: Javier Raya-González, Filipe Manuel Clemente, Daniel Castillo

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Summary: Although asymmetries in lower limbs have been linked with players' performance in male soccer players, literature that has been published addressing female soccer is scarce. Thus, the aim of this study was twofold: (i) describe the asymmetries of women soccer players during jumping, change-of-direction and range-of-motion tests; and (ii) test possible relationships between asymmetries and injury risk in female soccer players. Sixteen female players (15.5 ± 1.5 years) performed a battery of fitness tests (i.e., jump ability, change-of-direction ability and passive range-of-motion) and muscle mass analysis via dual-energy X-ray absorptiometry, through which the specific asymmetry index and the related injury risk were calculated. Significant (p < 0.05) lower asymmetries in the change-of-direction test were observed in comparison to those observed in jumping and range-of-motion tests; significant (p < 0.05) lower asymmetries in muscle mass were also reported compared to those found in the change-of-direction and countermovement jump tests. Additionally, increased injury risk for countermovement jump and hip flexion with extended knee range-of-motion (relating to asymmetry values) and for ankle flexion with flexed knee range-of-motion in both legs (relating to reference range-of-motion values), as well as increased individual injury risk values, were observed across all tests. These findings suggest the necessity to implement individual approaches for asymmetry and injury risk analyses. 



#9 Physical performance and perception of foot discomfort during a soccer-specific match simulation. A comparison of football boots

Reference: J Sports Sci. 2021 Jan 12;1-9. doi: 10.1080/02640414.2020.1856461. Online ahead of print. 

Authors: Katrine Okholm Kryger, Kumbirai Mutamba, Séan Mitchell, Stuart Charles Miller, Steph Forrester

Summary: Football boots are marketed with emphasis on a single key performance characteristic (e.g. speed). Little is known on how design parameters impact players' performance. This study investigated the impact of boot design on performance maintenance and perceived foot comfort during a 90-minute match simulation drill. Eleven male university football players tested two commercially available "sprint boots" known to generate significantly different plantar pressures (high=Boot H and low=Boot L) . Players completed a modified Soccer-specific Aerobic Field Test on a 3G pitch. Heart rate, rated perceived exertion and perceived foot discomfort were assessed for each 15-min interval. Power generation was assessed pre- and post-match simulation. A significantly higher mean heart rate was seen for Boot L in the 60th-75th and 75th-90th minute intervals (P = 0.017, P = 0.012 respectively). Perceived exertion did not differ between boots (P ≥ 0.302). Power generation significantly decreased in Boot H between pre- and post-match (P = 0.042). Both boots increased discomfort with significantly more plantar discomfort felt in the last 30 min in Boot H (75th min: P = 0.037; 90th min: P = 0.048). The results imply that a comfortable boot design may improve maintenance of performance during match-play. 



#10 The Association Between Training Load and Injury Risk in Elite Youth Soccer Players: a Systematic Review and Best Evidence Synthesis 

Reference: Sports Med Open. 2021 Jan 11;7(1):6. doi: 10.1186/s40798-020-00296-1. 

Authors: Sven Verstappen, Rogier M van Rijn, Rick Cost, Janine H Stubbe

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Summary: Injury risk in elite youth soccer players is high. Implementing an optimal training load is of utmost importance to reduce the risk of injuries. The aim was to conduct a systematic review and best evidence synthesis to explore the effects of internal and external training load on injury risk in elite youth soccer players. MEDLINE, Embase, Web of Science, CENTRAL, and CINAHL were searched up until 17 January 2020. Each article had to meet all of the following criteria: (1) the study population consisted of male elite youth soccer players aged between 12 and 21 years; (2) a longitudinal, prospective study design was used; (3) soccer-related injuries were registered (i.e., self-reported or by medical staff); (4) external and/or internal load parameters were described; and (5) the article was published in an English peer-reviewed scientific journal. The quality of the included articles was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS). A best evidence synthesis was performed to rank the level of evidence. Five studies (2 high quality, 3 low quality) were included. Best evidence synthesis highlighted that there was moderate evidence for (1) no association between 2-, 3-, and 4-week cumulative loads for total distance covered; (2) no association between 1-week workloads (sRPE × duration); and (3) no association between A:C workload ratios (4 weeks) and injury risk. For all other comparisons, only insufficient or conflicting evidence was found. There is a paucity of evidence for an association between internal and external training load parameters and injury risk in elite youth soccer players. 



#11 Effects of high-intensity interval training in men soccer player's physical fitness: A systematic review with meta-analysis of randomized-controlled and non-controlled trials

Reference: J Sports Sci. 2021 Jan 11;1-22. doi: 10.1080/02640414.2020.1863644. Online ahead of print. 

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Fábio Yuzo Nakamura, Hugo Sarmento

Summary: This systematic review with meta-analysis (SRMA) was conducted to assess the effects of high-intensity interval training (HIIT) programmes on men soccer players' aerobic fitness (maximal oxygen uptake and aerobic performance), repeated sprint ability (RSA), vertical jump height (VJH), and linear sprinting time (ST). An electronic search yielded 1,714 articles, 33 of which were included in the present study. Meta-analyses revealed significant benefits of HIIT compared to controls in maximal oxygen uptake (p = 0.018), AP (p = 0.041), and RSA (p = 0.049). No significant effects were found in terms of ST (p = 0.080). The meta-analyses of non-controlled studies revealed significant improvements after HIIT in maximal oxygen uptake (p = 0.001), AP (p = 0.007), RSA (p = 0.001), and ST (p < 0.001). However, no significant improvements in VHJ were found (p = 0.063). Furthermore, no significant differences were found in sub-group analysis (comparisons between HIIT types). In conclusion, HIIT is effective for improving maximal oxygen uptake, AP, and RSA regardless of the HIIT type. For VHJ and ST outcomes, it seems reasonable to complement the HIIT since it might not be enough to achieve significant changes. 



#12 The Validity of an Updated Metabolic Power Algorithm Based upon di Prampero's Theoretical Model in Elite Soccer Players

Reference: Int J Environ Res Public Health. 2020 Dec 20;17(24):9554. doi: 10.3390/ijerph17249554. 

Authors: Cristian Savoia, Johnny Padulo, Roberto Colli, Emanuele Marra, Allistair McRobert, Neil Chester, Vito Azzone, Samuel A Pullinger, Dominic A Doran

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Summary: The aim of this study was to update the metabolic power (MP) algorithm (PV˙O2, W·kg-1) related to the kinematics data (PGPS, W·kg-1) in a soccer-specific performance model. For this aim, seventeen professional (Serie A) male soccer players (V˙O2max 55.7 ± 3.4 mL·min-1·kg-1) performed a 6 min run at 10.29 km·h-1 to determine linear-running energy cost (Cr). On a separate day, thirteen also performed an 8 min soccer-specific intermittent exercise protocol. For both procedures, a portable Cosmed K4b2 gas-analyzer and GPS (10 Hz) was used to assess the energy cost above resting (C). From this aim, the MP was estimated through a newly derived C equation (PGPSn) and compared with both the commonly used (PGPSo) equation and direct measurement (PV˙O2). Both PGPSn and PGPSo correlated with PV˙O2 (r = 0.66, p < 0.05). Estimates of fixed bias were negligible (PGPSn = -0.80 W·kg-1 and PGPSo = -1.59 W·kg-1), and the bounds of the 95% CIs show that they were not statistically significant from 0. Proportional bias estimates were negligible (absolute differences from one being 0.03 W·kg-1 for PGPSn and 0.01 W·kg-1 for PGPSo) and not statistically significant as both 95% CIs span 1. All variables were distributed around the line of unity and resulted in an under- or overestimation of PGPSn, while PGPSo routinely underestimated MP across ranges. Repeated-measures ANOVA showed differences over MP conditions (F1,38 = 16.929 and p < 0.001). Following Bonferroni post hoc test significant differences regarding the MP between PGPSo and PV˙O2/PGPSn (p < 0.001) were established, while no differences were found between PV˙O2 and PGPSn (p = 0.853). The new approach showed it can help the coaches and the soccer trainers to better monitor external training load during the training seasons. 



#13 Effects of Strength vs. Plyometric Training Programs on Vertical Jumping, Linear Sprint and Change of Direction Speed Performance in Female Soccer Players: A Systematic Review and Meta-Analysis

Reference: Int J Environ Res Public Health. 2021 Jan 6;18(2):E401. doi: 10.3390/ijerph18020401. 

Authors: Elena Pardos-Mainer, Demetrio Lozano, Marcelino Torrontegui-Duarte, Antonio Cartón-Llorente, Alberto Roso-Moliner

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Summary: The main purpose of this systematic review and meta-analysis was to compare the effects of strength training (ST) and plyometric training (PT) on vertical jump, linear sprint and change of direction (COD) performance in female soccer players. A systematic search of the PubMed, Web of Science, Google Scholar and SportDiscus databases revealed 12 studies satisfying the inclusion criteria. The inverse-variance random-effects model for meta-analyses was used. Effect sizes (ES) were represented by the standardized mean difference and presented alongside 95% confidence intervals (CI). The magnitude of the main effect was small to moderate (vertical jump (ES 0.53 (95% CI-0.11, 0.95), Z = 2.47 (p = 0.01); linear sprint (ES -0.66 (95% CI-2.03, -0.21), Z = 2.20 (p = 0.03); COD (ES -0.36 (95% CI-0.68, -0.03), Z = 2.17 (p = 0.03)). Subgroup analyses were performed (i.e., ST and PT duration, frequency, session duration and total number of sessions), revealing no significant subgroup differences (p = 0.12-0.88). In conclusion, PT provides better benefits than ST to improve vertical jump, linear sprint and COD performance in female soccer players. However, significant limitations in the current literature prevent assured PT and ST prescription recommendations being made. 


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