Latest research in football - week 32 - 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 Short and Long-Term Effects of a Simple-Strength-Training Program on Injuries Among Elite U-19 Soccer Players
Reference: Res Q Exerc Sport. 2020 Jul 7;1-9. doi: 10.1080/02701367.2020.1741498. Online ahead of print.
Authors: Javier Raya-González, Luis Suarez-Arrones, Javier Sanchez-Sanchez, Rodrigo Ramirez-Campillo, Fabio Y Nakamura, Eduardo Sáez De Villarreal
Summary: The aim of this study was to examine the short and long-term effects of a simple strength training program on muscle injury prevention in soccer players. Twenty-seven U-19 elite male soccer players participated in the study. The investigation was conducted over two consecutive and similar seasons (e.g., the same staff, players, weekly training schedule), the first being the control and the second the experimental season. The strength program was carried out 2 times per week, for 10 weeks, during part of the preseason and in-season. Injury incidence and absence days were compared between both seasons, according to the injury rate ratio (IRR), with 95% CI and the Z test. A lower number of total and hamstring injuries were recorded during the experimental (9 and 2, respectively) compared to the control (15 and 7, respectively) period. During the 10 weeks intervention period, the injury rate ratio (IRR) was lower in the experimental season than in the control season (IRR = 8.12; 95% CI: 1.00-66.03; effect size (ES) = 3.30, large). In addition, there was a decline in absence days per injury and in the number of absence days/1000 h (IRR = 2.44; 95% CI: 1.90-3.14; ES = 1.12) during the experimental season. The results of this study suggest that this simple strength-training program could reduce the muscle injury incidence during its application period in young soccer players.

#2 Role of Sports Psychology and Sports Nutrition in Return to Play From Musculoskeletal Injuries in Professional Soccer: An Interdisciplinary Approach
Reference: Eur J Sport Sci. 2020 Jul 7;1-19. doi: 10.1080/17461391.2020.1792558. Online ahead of print.
Authors: Ian Rollo, James M Carter, Graeme L Close, Javier Yanguas Leyes, Antonio Gomez, Daniel Medina Leal, Joan L Duda, Donough Holohan, Sam J Erith, Leslie Podlog
Summary: Musculoskeletal injuries are prevalent in professional soccer and can result in lost training time or match play. It is intuitive that the "return to play" (RTP) pathway will depend, in large part, on the expertise of sports medicine practitioners (e.g., surgeons, physicians, physiotherapists) responsible for player's recovery. Consensus statements on returning athletes to sport following injury acknowledge the contributions of sport psychology and sports nutrition. However, specific consideration on how to integrate these two recognized - but often overlooked components of injury rehabilitation - into existing sport medicine approaches has yet to be examined. Using a framework of milestones directed by the medical physician and physical trainer, evidence is summarised and suggestions provided on the integration of sports psychology and sports nutrition into an interdisciplinary RTP approach. We examine recovery from a phase approach (acute injury and functional recovery) to highlight interdisciplinary opportunities in the management of musculoskeletal soccer injuries. An interdisciplinary approach is understood to achieve outcomes that could not be achieved within the framework of a single discipline. The incorporation of sports psychology and nutrition theoretically compliment milestones used in current medically-based RTP models. Our hope is that this article serves as a catalyst for interdisciplinary practice and research - not only in sports nutrition and sports psychology - but across all sport and exercise disciplines.

#3 Assessment of Energy Availability and Associated Risk Factors in Professional Female Soccer Players
Reference: Eur J Sport Sci. 2020 Jul 7;1-27. doi: 10.1080/17461391.2020.1788647. Online ahead of print.
Authors: Samantha L Moss, Rebecca K Randell, Darren Burgess, Stephanie Ridley, Caibre ÓCairealláin, Richard Allison, Ian Rollo
Summary: This study aimed to assess energy availability (EA), alongside possible risk factors of reduced or low EA of professional female soccer players during a competitive season. Thirteen players (age: 23.7 ± 3.4 y, stature: 1.69 ± 0.08 m, body mass: 63.7 ± 7.0 kg) engaged in a 5-day (two rest days, one light training, heavy training and match day) monitoring period. Energy intake (EI) and expenditure during exercise (EEE) were measured. EA was calculated and categorised as optimal, reduced or low (≥45, 31-44, ≤30 kcal·kg FFM-1·day-1, respectively). Relationships between EA and bone mineral density, resting metabolic rate (RMR), plasma micronutrient status, biochemical markers and survey data were assessed. EA was optimal for 15%, reduced for 62% and low for 23% of players. Higher EA was observed on rest days compared to others (P<0.05). EA was higher for the light compared to the heavy training day (P<0.001). EEE differed significantly between days (P<0.05). EI (2124 ± 444 kcal), carbohydrate (3.31 ± 0.64 g·kg·day-1) and protein (1.83 ± 0.41 g·kg·day-1) intake remained similar (P>0.05). Survey data revealed 23% scored ≥ 8 on the Low Energy Availability in Females Questionnaire and met criteria for low RMR (ratio <0.90). Relationships between EA and risk factors were inconclusive. Most players displayed reduced EA and did not alter EI or carbohydrate intake to training or match demands. Although cases of low EA were identified, further work is needed to investigate possible long-term effects and risk factors of low and reduced EA separately to inform player recommendations.

#4 The Influence of a Soccer Season on Non-Contact Injury and Isokinetic Peak Torque of the Quadriceps and Hamstrings in Professional Youth Soccer Players
Reference: Res Sports Med. 2020 Jul 6;1-14. doi: 10.1080/15438627.2020.1771336. Online ahead of print.
Authors: Colin Charles Brow, Andisheh Bakhshi, Russ Wrigely, Viswanath B Unnithan
Summary: Isokinetic strength screening is utilized in professional soccer. However, there has been little research on the interaction between seasonal changes in players' peak torque (PT) and injury incidence. Twenty-five (age 16.5[Formula: see text]0.68 years) professional youth soccer players participated in the study. Bilateral isokinetic concentric (CON) and eccentric (ECC) testing of Quadriceps (Q) and Hamstrings (H) were conducted at three time-points across the season. Absolute CON and ECC PT were measured at 60 degree/sec and in a supine 170-degree position. Testing data was normalized to body mass. A mixed design (2 by 3) repeated measures ANOVA with injury as a co-variate was conducted to evaluate the effect of season and/or limb dominance on PT and injury incidence. With regard to the seasonal variation and injury incidence, an interaction was identified with respect to non-dominant limb (NDL) QCON (p = 0.01) and to a lesser extent the dominant limb (DL) QCON (p = 0.05). The seasonal variation of the PT of the NDL QCON was different between the injured and non-injured individuals. Non-injured individuals, QCON strength increased over the course of the season. While for the Injured players, QCON declined from pre-season to mid-season then increased but never recovered to starting pre-season values.

#5 Muscular Strength Imbalances Are Not Associated With Skin Temperature Asymmetries in Soccer Players
Reference: Life (Basel). 2020 Jul 2;10(7):E102. doi: 10.3390/life10070102.
Authors: Rodrigo Mendonça Teixeira, Rodolfo A Dellagrana, Jose I Priego-Quesada, João Claudio B P Machado, Juliano Fernandes da Silva, Tallyne Mayara Pacheco Dos Reis, Mateus Rossato
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Summary: Although strength imbalances using isokinetic dynamometer have been examined for injury risk screening in soccer players, it is very expensive and time-consuming, making the evaluation of new methods appealing. The aim of the study was to analyze the agreement between muscular strength imbalances and skin temperature bilateral asymmetries as well as skin temperature differences in the hamstrings and quadriceps. The skin temperature of the anterior and posterior thigh of 59 healthy male soccer athletes was assessed at baseline using infrared thermography for the identification of hamstrings-quadriceps skin temperature differences and thermal asymmetries (>0.5 °C). Subsequently, concentric and eccentric peak torque of the quadriceps and hamstrings were considered in the determination of the ratios, as well as muscular asymmetries (>15%). When considering the torque parameters, 37.3% (n = 22) of the players would be classified as high risk for injuries. The percentage of those presenting skin temperature imbalances superior to 0.5 °C was 52.5% (n = 31). The skin temperature assessment showed sensitivity (22%) and specificity (32.2%) to identify torque asymmetries, demonstrating the inability to identify false negatives (15.3%) and false positives (30.5%) from all soccer athletes. In conclusion, skin temperature differences between hamstrings and quadriceps could be more related to thermoregulatory factors than strength imbalances.

#6 Effects of a 20-min Nap After Sleep Deprivation on Brain Activity and Soccer Performance
Reference: Int J Sports Med. 2020 Jul 6. doi: 10.1055/a-1192-6187. Online ahead of print.
Authors: Amornpan Ajjimaporn, Papatsorn Ramyarangsi, Vorasith Siripornpanich
Summary: We examined effects of a 20-min nap following 3 h of sleep deprivation on brain wave activity, auditory reaction time, the running-based anaerobic sprint test, leg muscle strength and the rating of perceived exertion in male college soccer players. Eleven players underwent three sleep conditions; normal sleep, sleep deprivation and 20-min nap after sleep deprivation. The sleep deprivation demonstrated an increase in the mean power of delta waves over the frontal area and a decrease in the mean power of alpha waves over the parietal area compared to the normal sleep. The nap and the sleep deprivation showed an increase in auditory reaction time compared with those in the normal sleep. The sleep deprivation demonstrated a decrease in the running-based anaerobic sprint test compared to the normal sleep, whereas the nap has partially reversed only minimal power and average power of the running-based anaerobic sprint test. The nap showed a recovery effect on leg muscle strength, but not on the rating of perceived exertion compared with the sleep deprivation. Thus, a 20-min nap after sleep deprivation did not completely return brain activity back to active state and did not entirely reverse the negative impact of sleep deprivation on soccer performance in soccer players.

#7 Physical Match Performance in Sub-elite Soccer Players - Introduction of a New Index
Reference: Int J Sports Med. 2020 Jul 6. doi: 10.1055/a-1165-1950. Online ahead of print.
Authors: Lars Reinhardt, Stephan Schulze, Rene Schwesig, Eduard Kurz
Summary: This investigation examined the position-specific physical performance in different locomotor categories and physiological demands concurrently in official games of sub-elite players and to present a new performance index (PI). Time-motion (distance, velocity, acceleration) and heart rate data of 55 soccer players were simultaneously captured via a GPS tracking system. The relationship between external and internal match-load (PI) was determined on the basis of heart rate, average velocity and acceleration. In contrast to the mean heart rate (85.2±3.2%, P=0.806, ηp²=0.03), the average total distance covered (9946±715 m) was largely affected by players' position (P<0.001, ηp²=0.63). Furthermore, a mixed design ANOVA showed a large interaction effect between position and locomotor category (P<0.001, ηp²=0.44). On average, PI was 1.57±0.37 m/min²/%, with notably lower values in the 2nd half. The position-specific profiles already reported for higher leagues were also present in sub-elite soccer players. Despite lower values for total distance and smaller distances in the high-intensity zones (>14.4 km/h), internal loads were comparable to those observed in European top leagues. In comparison to a performance measure that ignores accelerations, PI was shown to be less dependent on the playing position and had higher variability. Consequently, PI is better suited to distinguish between players' performance

#8 The Developmental and Professional Activities of Female International Soccer Players From Five High-Performing Nations
Reference: J Sports Sci. 2020 Jul 4;1-9. doi: 10.1080/02640414.2020.1789384. Online ahead of print.
Authors: Paul R Ford, Nicola J Hodges, David Broadbent, Donna O'Connor , Dawn Scott, Naomi Datson, Helena A Andersson, A Mark Williams
Summary: We study the developmental and professional activities engaged in by 86 female adult soccer players from the senior national teams of Australia, Canada, England, Sweden, and the United States of America. Players completed the Participation History Questionnaire (PHQ) to elicit the amount and type of activities engaged in across their developmental and professional years, including milestones, soccer-specific activity and engagement in other sport activity. Greater specialisation than diversification characterised their childhood developmental activities, including all players starting in soccer in childhood and accumulating more hours in soccer activity than other sports during this period. However, interindividual variation further characterised these childhood activities, with a proportion of players diversifying into other sports and/or soccer play to a greater or lesser degree during childhood when compared to the other players. The amount of coach-led soccer practice increased for all players across their development culminating in an average of 15-16 h/wk across a 40-week season in early adulthood. In contrast, the amount of engagement in other sports and soccer peer-led play varied between players but generally decreased across adolescence to negligible amounts in late adolescence. Findings are commensurate with the deliberate practice framework and early engagement.

#9 Effects of Acute Inspiratory Loading During Treadmill Running on Cerebral, Locomotor and Respiratory Muscle Oxygenation in Women Soccer Players
Reference: Respir Physiol Neurobiol. 2020 Jul 2;103488. doi: 10.1016/j.resp.2020.103488. Online ahead of print.
Authors: Flavia Rossi Caruso, Bruno Archiza, Daniela Kuguimoto Andaku, Renata Trimer, José Carlos Bonjorno-Junior, Claudio Ricardo de Oliveira, Cleiton A Libardi, Shane A Phillips, Ross Arena, Renata Gonçalves Mendes, Audrey Borghi-Silva
Summary: Respiratory limitation can be a primary mechanism for exercise cessation in female athletes. This study aimed to assess the effects of IL on intercostal (IM), vastus lateralis (VL) and cerebral (Cox) oxygenation in women soccer players during high-intensity dynamic exercise. Ten female soccer players were randomized to perform in order two constant-load tests on a treadmill until the exhaustion time (Tlim) (100% of maximal oxygen uptake- V̇O2). They breathed freely or against a fixed inspiratory loading (IL) of 41 cm H2O (∼30% of maximal inspiratory pressure). Oxygenated (Δ[OxyHb]), deoxygenated (Δ[DeoxyHb]), total hemoglobin (Δ[tHb]) and tissue saturation index (ΔTSI) were obtained by NIRs. Also, blood lactate [La-] was obtained. IL significantly reduced Tlim (224 ± 54 vs 78 ± 20 sec; P < 0.05) and increased [La-], V̇O2, respiratory cycles and dyspnea when corrected to Tlim (P < 0.05). IL also resulted in decrease of Δ[OxyHb] of Cox and IM during exercise compared with rest condition. In addition, decrease of Δ[OxyHb] was observed on IM during exercise when contrasted with Sham (P < 0.05). Furthermore, significant higher Δ[DeoxyHb] of IM and significant lower Δ[DeoxyHb] of Cox were observed when IL was applied during exercise in contrast with Sham (P < 0.05). These results were accompanied with significant reduction of Δ[tHb] and ΔTSI of IM and VL when IL was applied (P < 0.05). High-intensity exercise with IL decreased respiratory and peripheral muscle oxygenation with negative impact on exercise performance. However, the increase in ventilatory work did not impact cerebral oxygenation in soccer players.

#10 Body Composition of National Collegiate Athletic Association (NCAA) Division I Female Soccer Athletes Through Competitive Seasons
Reference: Int J Sports Med. 2020 Jul 10. doi: 10.1055/a-1177-0716. Online ahead of print.
Authors: Erica Roelofs, April Bockin, Tyler Bosch, Jonathan Oliver, Christopher W Bach, Aaron Carbuhn, Philip R Stanforth, Donald R Dengel
Summary: The purpose of this study was to examine body composition of National Collegiate Athletic Association Division I female soccer players by position and season. One hundred seventy-five female athletes were categorized by positions of forward (n=47), midfielder (n=51), defender (n=57), and goalkeeper (n=20). A dual X-ray absorptiometry scan assessed percent body fat, total lean mass, total fat mass, arm and leg lean mass and fat mass, and visceral adipose tissue. Goalkeepers had significantly higher total, arm, and leg lean mass and fat mass compared to all other positions (p<0.05). For seasonal changes, body fat percentage was significantly higher in winter off-season (26.7%) compared to summer off-season (25.7%) and pre-season (25.8%; p<0.01) for all positions. Total and leg lean mass was significantly lower in winter off-season compared to all other seasons, and total lean mass was significantly higher in summer off-season than pre-season (p<0.01). Overall, goalkeepers were significantly different than all other positions. Body fat percentage increased and lean mass decreased in winter off-season indicating potential undesired changes in training and/or nutrition over the break whereas lean mass was the highest in summer off-season potentially reflecting the emphasis on resistance training and increased volume of training.

#11 Developing a Two-Dimensional Landscape Model of Opportunities for Penetrative Passing in Association Football - Stage I
Reference: J Sports Sci. 2020 Jul 10;1-8. doi: 10.1080/02640414.2020.1786991. Online ahead of print.
Authors: Pedro Passos, Rodrigo Amaro E Silva, Luís Gomez-Jordana, Keith Davids
Summary: This study investigated a method for modelling a landscape of opportunities for penetrative passing completed on the ground by ball carriers in association football. Analysis of video footage of competitive, professional football performance was undertaken, identifying a sample (n = 20) of attacking sub-phases of gameplay which ended in a penetrative pass being made between defenders to a receiver. Players' relative co-positioning during performance was modelled using bi-dimensional x and y coordinates of each player recorded at 25 fps. Data on player movements during competitive interactions were captured using an automatic video tracking system, recording player co-locations emerging over time, as well as current and estimated running velocities. Results revealed that the half spaces between the midfield and both sidelines were the key locations on field providing most affordances for penetrating passes in the competitive performance sample analysed. Due to the dynamics of players' co-adaptive performance behaviours, it was expected that opportunities for penetrative passing by ball carriers would not display a homogeneous space-time spread across the entire field. Results agreed with these expectations, showing how a landscape of opportunities for penetrative passing might be specified by information emerging from continuous player interactions in competitive performance.

#12 Influence of Training Schedules on Objective Measures of Sleep in Adolescent Academy Football Players
Reference: J Strength Cond Res. 2020 Jul 7. doi: 10.1519/JSC.0000000000003724. Online ahead of print.
Authors: Georgia A Brown, Stella Veith, John A Sampson, Matthew Whalan, Hugh H K Fullagar
Summary: Football academy settings may pose risks to adolescent athletes achieving sufficient sleep because of the contextual challenges these players face (e.g., psychosocial pressure, changes in training, competition, and academic stress). Given the importance of sleep to overall health as well as physical athletic development and injury risk, this study aimed to investigate whether differences in training schedules (morning vs. evening training sessions) affected objective measures of sleep in adolescent academy football (soccer) players. Twelve academy players (mean age 14.18 ± 1.36 years) wore an ActiGraph accelerometer on nights before, and nights of, training days in 2 separate weeks where morning (09:00-11:00 hours) and evening (18:00-20:00 hours) training occurred. Objective sleep parameters and training load data were collected. Night-time sleep periods were categorized as sleep preceding morning training, preceding evening training, or after evening training. One-way univariate and multivariate analyses of variance for repeated measures were performed to determine the impact of the training schedule on sleep. Significance levels were set at p < 0.05. The total sleep time was below the recommended guidelines (<8 hours) across conditions. A large significant effect of the training schedule on time attempted to fall asleep (p = 0.004, effect size [ES] = 0.40) and time of sleep (p = 0.003, ES = 0.41) was present, with post-evening sessions resulting in the latest times. Overall, the players' sleep behavior was resilient to changes in training schedules. However, the low sleep durations (and potential risks to physical performance/injury) suggest that sleep education coupled with practical interventions are required in this cohort.

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