Latest research in football - week 32 - 2018

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 Age-Matched Z-Scores for Longitudinal Monitoring of Center of Pressure Speed in Single-Leg Stance Performance in Elite Male Youth Soccer Players
Reference: J Strength Cond Res. 2018 Jul 26. doi: 10.1519/JSC.0000000000002765. [Epub ahead of print]
Authors: Huurnink A, Fransz DP, de Boode VA, Kingma I, van Dieën JH
Summary: Coordination of corrective motor actions is considered important for soccer performance and injury prevention. A single-leg stance (SLS) test assesses the integrity and proficiency of the sensorimotor control system, quantified by center of pressure averaged speed (COPspeed). We aimed to provide age-matched z-scores for COPspeed in elite male youth soccer players. Second, we assessed a threshold for abnormal long-term change in performance, i.e., critical difference (CD). In a youth academy program, 133 soccer players of 9-18 years were tested twice for both legs (2 repetitions), and one repetition follow-up was conducted at 5.8 months (SD 2.7). Linear regression between age and COPspeed was performed to provide age-matched z-scores. Variance of differences in z-scores at baseline and between sessions was used to estimate the CD up to 5 repetitions. Intraclass correlation coefficients (ICCs) were assessed within and between sessions. The age significantly affected COPspeed (p < 0.0001), with lower values in older players (95% confidence interval; 3.45-9.17 to 2.88-5.13 cm·s, for 9 and 18 years, respectively). The z-score CD ranged from 1.72 (one repetition) to 1.34 (5 repetitions). The ICC of z-scores was 0.88 within session and 0.81 between sessions. In conclusion, the SLS performance in elite male youth soccer players improves with age. We determined age-matched z-scores of COPspeed, which reliably determined performance according to age. The CD allows for detection of abnormal variations in COPspeed to identify players with a (temporary) deterioration of sensorimotor function. This could be applied to concussion management, or to detect underlying physical impairments.

#2 Profiling the Responses of Soccer Substitutes: A Review of Current Literature
Reference: Sports Med. 2018 Jul 26. doi: 10.1007/s40279-018-0962-9. [Epub ahead of print]
Authors: Hills SP, Barwood MJ, Radcliffe JN, Cooke CB, Kilduff LP, Cook CJ, Russell M
Summary: Depending upon competition regulations, the laws of soccer allow between three and an unlimited number of substitutions that can be made on either a permanent or rolling basis. Substitutes are typically introduced to minimise/offset the effects of fatigue, alter tactics, replace players deemed as underperforming or injured, and/or give playing time to youth players or to squad members returning from injury. While the match-day practices of substitutes include participation in the pre-match warm-up, and sporadic periods of rewarm-up activity, it is currently unclear as to whether these pre-entry preparations facilitate optimal match performance thereafter. Acknowledging the contextual factors that possibly influence substitutes' performance, this review summarises the presently available literature on soccer substitutes, and makes recommendations for future research. Literature searching and screening yielded 13 studies, which have typically focused on characterising: (1) the patterns, including timing, of substitutes' introduction; (2) indices of match-performance; and (3) the emotional experiences of soccer substitutes. The majority of substitutions occur after the first-half has ended (i.e. at half-time or during the second-half), with introduced players exceeding the second-half physical performances of those who started the match. Observations of progressive improvements in running performance as playing time increases, and findings that substitutes mostly experience negative emotions, highlight the potential inadequacies of pre-match preparations, and present future research opportunities. Additional work is therefore needed to confirm these findings and to determine the efficacy of current preparation strategies, thereby providing opportunities to assess then address substitutes' pre-pitch entry preparations, on-field performance and emotional responses.

#3 Leg Fracture Associated with Synostosis of Interosseous Membrane During Running in A Soccer Player
Reference: Transl Med UniSa. 2018 Mar 31;17:1-5. eCollection 2017 Jul.
Authors: Oliva F, Buharaja R, Iundusi R, Tarantino U
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Summary: Leg fractures may occur frequently in sport injuries but it is very rare to find this kind of injury associated with interosseous membrane synostosis. This case report describes a unique case of 42 B1.2 fracture of the leg associated with an interosseous membrane synostosis and literature review on Pubmed, Google scholar and Medscape. A 26 year old male amateur soccer player came to our attention at the emergency room after a fall while he was running without any direct trauma following a referred ankle sprain. X-ray and CT scan of the left leg showed a comminuted displaced fracture of the lower middle third of tibial and peroneus diaphysis, and moreover, a fracture of peroneal malleolus associated with a bone bridge between the tibia and fibula. The patient was treated with a surgical osteosynthesis the day after trauma. We think that the interosseous membrane plays an important role in biomechanics of the leg even during running. To our knowledge, this is the first case reported which show the fractures of the tibia and fibula associated with an ipsilateral synostosis of the interosseous membrane.

#4 Dynamics of Recovery of Physiological Parameters After a Small-Sided Game in Women Soccer Players
Reference: Front Physiol. 2018 Jul 11;9:887. doi: 10.3389/fphys.2018.00887. eCollection 2018.
Authors: Mascarin RB, De Andrade VL, Barbieri RA, Loures JP, Kalva-Filho CA, Papoti M
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Summary: Training methods based on small-sided game (SSG) seem to promote physiological and tactical benefits for soccer players as they present characteristics more specific to the game. Thus, the main objective of the present study was to analyze the hormonal, biochemical, and autonomic parameters in an acute manner and the recovery dynamics (up to 72 h after) in a SSG. Thirteen professional female soccer players participated in the study (18.8 ± 0.8 years, body mass 59.4 ± 6.2 kg, and height 1.68 ± 0.05 m). During and after the SSG session (4 min × 4 min separated by 3 min of passive interval and 120 m2 coverage per player), autonomic modulation was analyzed in the time and frequency domains using heart rate variability, and blood samples (5 ml) were collected before (0 h) and after (10 min and 24, 48, 72 h) the SSG for biochemical and hormonal analysis. The SSG induced an increase effect for LF (low frequency) (92,52%; Very likely increase) and a decrease effect for HF (high frequency) values (-65,72%; Very likely decrease), after 10 min of recovery. The LF/HF increase after 10 min of recovery (386,21%; Very likely increase). The RMSSD (square root of the mean squared differences of the successive N-N intervals) and pNN50 (measure of the number of adjacent NN intervals which differ by more than 50 ms) values presented a decrease effect 10 min after SSG (61,38%; Very likely decrease and-90%; Very likely decrease). The CK (creatine kinase) values presented no changes 10 min after SSG. The LDH (lactate dehydrogenase) values presented an increase effect 10 min after the SSG (19,22%; Likely increase). Both testosterone and cortisol concentrations presented the same behavior after SSG, where no alterations were observed with after 10 min (<0,37%; Most likely trivial). The SSG promoted significant cardiovascular stress that was restored within the first 24 h of recovery. Parasympathetic parameters continued to increase while sympathetic parameters declined significantly during the 72 h of recovery. In addition, the reduced game did not alter biochemical or hormonal responses during the 72 h.

#5 Effective injury forecasting in soccer with GPS training data and machine learning
Reference: PLoS One. 2018 Jul 25;13(7):e0201264. doi: 10.1371/journal.pone.0201264. eCollection 2018.
Authors: Rossi A, Pappalardo L, Cintia P, Iaia FM, Fernàndez J, Medina D
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Summary: Injuries have a great impact on professional soccer, due to their large influence on team performance and the considerable costs of rehabilitation for players. Existing studies in the literature provide just a preliminary understanding of which factors mostly affect injury risk, while an evaluation of the potential of statistical models in forecasting injuries is still missing. In this paper, we propose a multi-dimensional approach to injury forecasting in professional soccer that is based on GPS measurements and machine learning. By using GPS tracking technology, we collect data describing the training workload of players in a professional soccer club during a season. We then construct an injury forecaster and show that it is both accurate and interpretable by providing a set of case studies of interest to soccer practitioners. Our approach opens a novel perspective on injury prevention, providing a set of simple and practical rules for evaluating and interpreting the complex relations between injury risk and training performance in professional soccer.

#6 Mixed-methods pre-match cooling improves simulated soccer performance in the heat
Reference: Eur J Sport Sci. 2018 Jul 24:1-10. doi: 10.1080/17461391.2018.1498542. [Epub ahead of print]
Authors: Aldous JWF, Chrismas BCR, Akubat I, Stringer CA, Abt G, Taylor L
Summary: This investigation examined the effects of three pre-match and half-time cooling manoeuvres on physical performance and associated physiological and perceptual responses in eight University soccer players during a non-motorised treadmill based individualised soccer-specific simulation [intermittent soccer performance test (iSPT)] at 30°C. Four randomised experimental trials were completed; following 30-min (pre-match) and 15-min (half-time) cooling manoeuvres via (1) ice slurry ingestion (SLURRY); (2) ice-packs placed on the quadriceps and hamstrings (PACKS); (3) mixed-methods (MM; PACKS and SLURRY concurrently); or no-cooling (CON). In iSPT first half, a moderate increase in total (Mean ± Standard Deviation: 108 ± 57 m, qualitative inference: most likely, Cohen's d: 0.87, 90%CL: ±0.31), high-speed (56 ± 46 m, very likely, 0.68 ± 0.38) and variable run (15 ± 5 m, very likely, 0.81 ± 0.47) distance covered was reported in MM compared with CON. Additionally, pre-match reductions in thermal sensation (-1.0 ± 0.5, most likely, -0.91 ± 0.36), rectal (-0.6 ± 0.1°C, very likely, -0.86 ± 0.35) and skin temperature (-1.1 ± 0.3°C, very likely, -0.88 ± 0.42) continued throughout iSPT first half. Physical performance during iSPT first half was unaltered in SLURRY and PACKS compared to CON. Rectal temperature was moderately increased in SLURRY at 45-min (0.2 ± 0.1°C, very likely, 0.67 ± 0.36). Condition did not influence any measure in iSPT second half compared to CON. Only MM pre-match cooling augmented physical performance during iSPT first half, likely due to peripheral and central thermoregulatory factors favourably influencing first half iSPT performance. Further practical half-time cooling manoeuvres which enhance second half performance are still required.

#7 Association Between the Force-Velocity Profile and Performance Variables Obtained in Jumping and Sprinting in Elite Female Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Jul 24:1-21. doi: 10.1123/ijspp.2018-0233. [Epub ahead of print]
Authors: Marcote-Pequeño R, García-Ramos A, Cuadrado-Peñafiel V, González-Hernández JM, Gómez MÁ, Jiménez-Reyes P
Summary: The aims of this study were (I) to quantify the magnitude of the association between the same variables of the force-velocity (FV) profile and the performance variables (unloaded squat jump [SJ] height and 20 m sprint time) obtained during the jumping and sprinting testing procedures, and (II) to determine which mechanical capacity (i.e., maximum force [F0], maximum velocity [V0] or maximum power [Pmax]) presents the highest association with the performance variables. The FV profile of 19 elite female soccer players (age: 23.4±3.8 years, height: 166.4±5.6 cm, body mass: 59.7±4.7 kg) was determined during the jumping and sprinting tasks. The F0, V0, FV slope, Pmax, and FV imbalance (difference respect to the optimal FV profile in jumping and the decrease in the ratio of horizontal force production in sprinting) were determined for each task. Very large correlations between both tasks were observed for Pmax (r= 0.75) and the performance variables (r= -0.73), moderate correlations for V0 (r= 0.49), while the F0 (r= -0.14), the FV slope (r= -0.09), and the FV imbalance (r= 0.07) were not significantly correlated between both tasks. The Pmax obtained during each specific task was the mechanical capacity most correlated with its performance variable (r= 0.84 in jumping and r= 0.99 in sprinting). The absence of significant correlations between some of the FV relationship parameters suggests that for an individualized training prescription based on the FV profile both jumping and sprinting testing procedures should be performed with elite female soccer players.

#8 Acute Avulsion of the Iliac Crest Apophysis in an Adolescent Indoor Soccer
Reference: J Belg Soc Radiol. 2015 Dec 30;99(2):20-24. doi: 10.5334/jbr-btr.876.
Author: Coulier B
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Summary: We report a typical case of acute avulsion of the anterior iliac crest apophysis diagnosed in an indoor football player. The injury occurred as a result of a sudden twist of the trunk while kicking. Plain radiographs made the diagnosis. Complementary CT with 3D reconstructions was preferred to ultrasound because of the very strong habitus - 110 kilograms for 1,73 meter - of the 15-year old adolescent. CT confirmed that occult chronic mechanical stress on the iliac apophysis had preceded the acute avulsion and also emphasized the crucial role of the tensor fascia lata in the mechanism of the injury. The patient was successfully treated conservatively. The case is presented with a short review of the literature.

#9 Can Squat Jump Performance Differentiate Starters vs. Nonstarters in Division I Female Soccer Players?
Reference: J Strength Cond Res. 2018 Aug;32(8):2348-2355. doi: 10.1519/JSC.0000000000002053.
Authors: Magrini MA, Colquhoun RJ, Sellers JH, Conchola EC, Hester GM, Thiele RM, Pope ZK, Smith DB
Summary: Although soccer is predominately an endurance sport, high velocity movements may be an important indicator of athletic success. The purpose of this investigation was to establish whether squat jumps (SJs) can differentiate starters from nonstarters with a female collegiate division I soccer team. Eighteen female division I soccer athletes were separated into 2 groups: 9 starters (age: 19.5 ± 1.0; mass = 64.8 ± 11.5 kg; height = 167.5 ± 7.7 cm; games started = 18.2 ± 4.7; and minutes played = 1633.8 ± 478.2 minutes) and 9 nonstarters (age: 19.4 ± 1.4 years; mass = 63.3 ± 4.2 kg; height = 164.7 ± 6.8 cm; games started 0.7 ± 1.3; and minutes played 158.2 ± 269.3 minutes). Each athlete performed 3 maximal SJs at a starting knee angle of 110° without arm swing. Each participant's SJ height, mean power (MP), peak power (PP), mean velocity (MV), and peak velocity (PV) were measured during each attempt by a linear position transducer. No statistically significant differences (p ≥ 0.05) in MP and PP between the starters and nonstarters were observed. However, starters performed significantly better than nonstarters in SJ height (p = 0.002), MV (p = 0.025), and PV (p = 0.015). In addition, SJ height was strongly correlated with MV (r = 0.628) and PV (r = 0.647). These findings suggest that SJ height, MV, and PV may be important variables for discriminating differences between starters and nonstarters in division I female soccer athletes and a strong indicator of explosive performance.

#10 Quantified Soccer Using Positional Data: A Case Study
Reference: Front Physiol. 2018 Jul 6;9:866. doi: 10.3389/fphys.2018.00866. eCollection 2018.
Authors: Pettersen SA, Johansen HD, Baptista IAM, Halvorsen P, Johansen D
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Summary: Performance development in international soccer is undergoing a silent revolution fueled by the rapidly increasing availability of athlete quantification data and advanced analytics. Objective performance data from teams and individual players are increasingly being collected automatically during practices and more recently also in matches after FIFA's 2015 approval of wearables in electronic performance and tracking systems. Some clubs have even started collecting data from players outside of the sport arenas. Further algorithmic analysis of these data might provide vital insights for individual training personalization and injury prevention, and also provide a foundation for evidence-based decisions for team performance improvements. This paper presents our experiences from using a detailed radio-based wearable positioning data system in an elite soccer club. We demonstrate how such a system can detect and find anomalies, trends, and insights vital for individual athletic and soccer team performance development. As an example, during a normal microcycle (6 days) full backs only covered 26% of the sprint distance they covered in the next match. This indicates that practitioners must carefully consider to proximity size and physical work pattern in microcycles to better resemble match performance. We also compare and discuss the accuracy between radio waves and GPS in sampling tracking data. Finally, we present how we are extending the radio-based positional system with a novel soccer analytics annotation system, and a real-time video processing system using a video camera array. This provides a novel toolkit for modern forward-looking soccer coaches that we hope to integrate in future studies.

#11 Acute high-intensity exercise test in soccer athletes affects salivary biochemical markers
Reference: Free Radic Res. 2018 Jul 20:1-6. doi: 10.1080/10715762.2018.1481288. [Epub ahead of print]
Authors: Rodrigues de Araujo V, Lisboa P, Boaventura G, Caramez F, Pires L, Oliveira E, Moura E, Casimiro-Lopes G
Summary: Saliva has been reported as a potential biological fluid for biochemical monitoring. This study investigated salivary markers of exercise intensity, oral mucosal immunity, and redox homeostasis in soccer athletes subjected to an acute high-intensity interval exercise (HIIE) protocol characterised by a repeated sprint ability test. Thirty-two professional soccer athletes were recruited and saliva aliquots were collected at rest and immediately after HIIE protocol. When compared with pre-test values we observed that HIIE protocol induced moderate changes for total protein (p = .015; effect size (ES) = 0.51; smallest worthwhile change (SWC)factor = 5.7) and for cortisol levels (p < .0001; ES = 0.49; SWCfactor = 3.9). Lactate levels showed very large changes (p < .000; ES = 1.35; SWCfactor  = 10.8), while Ig-A alterations were considered unclear. Besides, transferrin changes were trivial and maintained its levels at rest and after HIIE below the proposed threshold of 0.5 mg/dL. Regarding redox homeostasis we observed unclear effects for TBARs, MDA, GSH, GSSG, CAT, and SOD while uric acid showed large decreases (p = .005; ES = 0.80; SWCfactor  = -5.4). HIIE protocol as a physical test conducted in soccer athletes increased salivary concentration of exercise intensity markers, such as lactate, total protein, and cortisol, but did not affect Ig-A levels. Redox homeostasis in saliva seems to be more related with uric acid levels as a possible key factor TBARs homeostasis.

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