Latest research in football - week 37 - 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 Dynamic balance asymmetries in pre-season injury-prevention screening in healthy young soccer players using the Modified Star Excursion Balance Test-a pilot study
Reference: J Phys Ther Sci. 2018 Sep;30(9):1141-1144. doi: 10.1589/jpts.30.1141. Epub 2018 Sep 4.
Authors: Gkrilias P, Zavvos A, Fousekis K, Billis E, Matzaroglou C, Tsepis E
Summary: The purpose of this preliminary study was to investigate whether young players with no history of injury, have developed early asymmetries in dynamic balance ability tested via the recommended for screening in sports, Modified Star Excursion Balance Test (MSEBT). Twenty-four young healthy male soccer players participated in the study having at least 4 years of systematic soccer training. The Waterloo Footedness Questionnaire was used to discriminate the stability dominant leg (STAB) from the non-stability dominant leg (NSTAB). Dynamic balance was assessed via the MSEBT. Participants, after familiarization, made 3 attempts in each direction for both legs: a) Anterior (AN), b) Posterolateral (PL) and c) Posteromedial (PM). The sole statistically significant performance asymmetry was in the PL direction, in favor of the STAB (94.5 ± 13.3 cm vs. 98.1 ± 10.4 cm). The results of this pilot study showed a potential for developing dynamic balance asymmetries, in soccer players at the age of 13-14 years. Since asymmetry was significant in only one direction, further long term monitoring would be helpful to evaluate whether this is a growing functional deficit, potentially involving any of the other two directions of testing or if it is alleviated with increasing training age. These asymmetries could comprise an injury risk factor.

#2 Energy Balance Coexists With Disproportionate Macronutrient Consumption Across Pretraining, During Training, and Posttraining Among Indian Junior Soccer Players
Reference: Pediatr Exerc Sci. 2018 Sep 12:1-10. doi: 10.1123/pes.2017-0276. [Epub ahead of print]
Authors: Cherian KS, Sainoji A, Nagalla B, Yagnambhatt VR
Summary: The purpose was to evaluate energy expenditure, energy intake, and nutrient adequacy of Indian junior soccer players. Forty junior national-level soccer players (Under-12 and Under-16 age groups) were assessed for 3-day weighed food records and 3-day energy expenditure. Energy and nutrient intake was analyzed from food records, and energy expenditure was measured using a portable metabolic analyzer and activity records. Nutrient adequacy was determined by comparing intake with prevailing recommendations. Players exhibited no significant difference between energy intake (boys = 3062 [340.9] and girls = 2243 [320.3] kcal·d-1) and expenditure (boys = 2875 [717.3] and girls = 2442 [350.3] kcal·d-1). Across age groups, the Under-12 boys showed positive energy balance as against energy deficits in Under-16. Girls showed energy deficits, although not significant. There were 58% of girls showing energy availability <30 kcal·kg-1 fat-free mass, of which 37% were Under-16 players. Carbohydrates contributed to >60% of energy expenditure among 95.2% boys and 73.7% girls. Among 52.4% boys and 47.4% girls, <25% of energy expenditure was contributed by fat. More than 95% players consumed <1 g·kg-1 carbohydrates pretraining and 100% of them consumed >1.2 g·kg-1 carbohydrates posttraining. Junior soccer players consumed more than recommended carbohydrates in the diet, although not aligning with the pretraining, during training, and posttraining meal requirements. Considering the energy deficits observed among Under-16 players, a suitable dietary modification is warranted.

#3 Effects of Plyometric and Directional Training on Physical Fitness Parameters in Youth Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Sep 11:1-22. doi: 10.1123/ijspp.2018-0545. [Epub ahead of print]
Authors: Michailidis Y, Tabouris A, Metaxas T
Summary: The aim of this study is to investigate whether the combination of a soccer training session, plyometric training (PT) and change of direction (COD) exercises would enhance soccer ability to a greater extent than training on its own in youth soccer players. Thirty-one youth players participated in this study (age 12±0.8 years). Players were randomly separated into 2 groups: control group (CG, n=14) and intervention group (INTG) which performed extra PT and COD exercises (INTG, n=17). The duration of the training program was 6 weeks. Sprint 10m, 30m, countermovement jump (CMJ), squat jump (SJ), long jump (LJ), multiple 5-bound (5MB), T-test, and YO-YO intermitted endurance test 1 (YYIET1) were measured pre and post of the training program. The performance in acceleration, T-test and LJ improved in both groups (P=0.03, P=0.002 and P=0.001, respectively). SJ performance increased in INTG (15.2 %, P=0.003) and slightly decreased in CG (P=0.003). The performances of the 2 groups differed significantly in SJ and LJ (P=0.003 and P=0.038, respectively). This study supports that a short-term combined program of PT and COD exercises can improve jumping ability, acceleration, and endurance parameters in youth soccer players. The small training effect could be explained when taking into account the level of the participants, the duration of the program and the low volume of COD exercises that were used.

#4 Presleep Casein Protein Ingestion: Acceleration of Functional Recovery in Professional Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Sep 11:1-24. doi: 10.1123/ijspp.2018-0385. [Epub ahead of print]
Authors: Abbott W, Brett A, Cockburn E, Clifford T
Summary: This study examined whether consuming casein protein (CP) before sleep would enhance recovery after a night-time soccer match in professional players. In a randomized, crossover design, ten professional soccer players from the reserve squad of a team in the highest tier of English soccer consumed 40 g of CP or 40 g of carbohydrates (CON) 30 min pre-sleep after a soccer match (kick off 19:00). To assess recovery, countermovement jump (CMJ) height, reactive strength index (RSI), muscle soreness (MS), and the adapted Brief Assessment of Mood Questionnaire (BAM+) were measured before, 12, 36 and 60 h after each match. Dietary intake across the testing period was also recorded. There were unclear differences in external load in the matches and dietary intake between CON and CP. CP had a most likely and likely beneficial effect on CMJ recovery at 12 and 36 h post-match (CP -1.6; ±1.2% vs. CON -6.6; ±1.7%; -4.1; ±2.3% vs. -0.4; ±1.1%, respectively). RSI recovery was most likely enhanced with CP at 12 and 36 h post-match and muscle soreness, as measured with a visual analogue scale (mm), was most likely greater in CON vs. CP at 12 h post (72; ±17 vs. 42; ±20 mm). BAM+ was possibly lower in CON at 36 h post but unaffected at other time points. Pre-sleep CP accelerates functional recovery in professional soccer players and therefore provides a practical means of attenuating performance deficits in the days after a match.

#5 Determining the Relationship Between Internal Load Markers and Non-Contact Injuries in Young Elite Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Sep 11:1-19. doi: 10.1123/ijspp.2018-0466. [Epub ahead of print]
Authors: Raya-González J, Nakamura FY, Castillo D, Yanci J, Fanchini M
Summary: The purpose was to examine the association and predictive ability of internal load markers with regards to non-contact injuries in young elite soccer players. Twenty-two soccer players (18.6 ± .6 years) who competed in the Spanish U19 League participated in the study. During a full season, non-contact injuries were recorded and, using session rating of perceived exertion (s-RPE), internal weekly load (sum of load of all training sessions and matches for each week) and acute:chronic workload ratio (typically, acute = current week and chronic = rolling 4 week average) were calculated. A Generalized Estimating Equation analysis was used to examine association of weekly and acute:chronic load ratio markers with a non-contact injury in the subsequent week. Load variables were also analyzed for predictive ability with Receiver Operating Characteristic (ROC) curve and area under the curve (AUC). No association was found for weekly load (CI 1.00, .99 to 1.00) and acute:chronic load ratio (CI .16, .01 to 1.84) with respect to injury occurrence. In addition, the analyzed load markers showed poor ability to predict injury occurrence (AUC<.50). The results of this study suggest that internal load markers are not associated with non-contact injuries in young soccer players and present poor predictive capacity with regards to the latter.

#6 Physical Characteristics of Elite Youth Female Soccer Players Characterized by Maturity Status
Reference: J Strength Cond Res. 2018 Sep 7. doi: 10.1519/JSC.0000000000002795. [Epub ahead of print]
Authors: Emmonds S, Scantlebury S, Murray E, Turner L, Robsinon C, Jones B
Summary: The purpose of this study was to investigate the influence of maturity status on the physical characteristics of youth female soccer players. One hundred fifty-seven players from 3 elite soccer academies in England completed assessments of anthropometry, strength (isometric midthigh pull), lower-body power (countermovement jump [CMJ]), aerobic capacity (Yo-Yo intermittent recovery test level 1), change of direction (CoD: 505-left/right), and speed (10 and 30 m). Each player was classified into 1 of 6 maturity groups based on their estimated years from peak height velocity (YPHV). Magnitude-based inferences were used to assess for the practical significance between consecutive groups. Speed, CoD time, CMJ, and aerobic capacity were all possibly most likely better in more mature players. However, there was a likely difference in relative peak force between maturity groups -0.5 YPHV (27.13 ± 4.24 N·Kg) and 0.5 YPHV (24.62 ± 3.70 N·Kg), which was associated with a likely difference in 10-m sprint time (-0.5 YPHV: 2.00 ± 0.12 vs. 0.5 YPHV 2.08 ± 0.16 seconds) and unclear changes in CMJ and CoD time. Findings provide novel comparative data for this cohort relative to maturity status and can be used by strength and conditioning coaches to inform the design of training programs for youth female soccer players. Strength and conditioning coaches should be aware that youth female soccer players may experience a decrease in relative strength around peak height velocity, which may impact upon the speed, CoD time, and CMJ of players.

#7 Post-football Gonathrosis: Injuries and Surgeries are A Risk
Reference: Cureus. 2018 Jul 10;10(7):e2953. doi: 10.7759/cureus.2953.
Authors: Ali Khan MM, Siddiqui AA, Yaqoob U, Yaqub MD, Khan OJ, -Ul-Haq F
Summary: Football is one of the most popular sports in the world. Many studies have shown there is a high incidence of gonarthrosis in football players. The reason for this increase is said to be injuries to the meniscus, the anterior cruciate ligament (ACL) and the resulting surgeries. The incidence is significantly increased in players with knee injuries. The knee is also the most commonly injured site in football and the most common cause of surgery in football players. Together these injuries, particularly of the ACL or meniscus and the resulting surgeries, increase the risk of developing gonarthrosis in post-football years.

#8 Validity of Session Rating of Perceived Exertion Assessed via the CR100® Scale to Track Internal Load in Elite Youth Football Players
Reference: Int J Sports Physiol Perform. 2018 Sep 11:1-14. doi: 10.1123/ijspp.2018-0432. [Epub ahead of print]
Authors: Naidu SA, Fanchini M, Cox A, Smeaton J, Hopkins WG, Serpiello FR
Summary: The purpose of the study was to assess the convergent validity of the Borg CR100® scale to track internal training load (TL) in youth football players. Nineteen youth football players (age 15 ± 1 y, height 175.9 ± 12.3 cm, body mass 69 ± 15.4 kg) were monitored for 27 sessions, including training and games. Internal training load was assessed via session rating of perceived exertion (sRPE) and two heart rate (HR)-based methods; Banister's training impulse (TRIMP) and Edwards' TL. The correlations between sRPE and HR-based TL, the differences in individual player intercepts and slopes, and the differences between types of sessions (training vs. games) were assessed using a general linear mixed model with magnitude-based inferences. Correlations between sRPE and Banister's TRIMP were very large at overall group level (r=0.77, 90% confidence limits (CL) 0.72 to 0.80), and individual level (range 0.70 - 0.95). Correlations between sRPE and Edwards' TL were very large at overall group level (r=0.84, 90% CL 0.82 to 0.86), and large to very large at individual level (range 0.64 - 0.93). A very likely small difference was found in the comparison between games and training sessions for the relationship between sRPE and Banister's TRIMP. The Borg CR100® scale is a valid method for monitoring training load in youth football players.

#9 There are more football injury prevention reviews than randomised controlled trials. Time for more RCT action!
Reference: Br J Sports Med. 2018 Sep 10. pii: bjsports-2018-099373. doi: 10.1136/bjsports-2018-099373. [Epub ahead of print]
Authors: Bricca A, Juhl CB, Bizzini M, Andersen TE, Thorborg K

#10 Quantification of a Professional Football Team's External Load Using a Microcycle Structure
Reference: J Strength Cond Res. 2018 Sep 7. doi: 10.1519/JSC.0000000000002816. [Epub ahead of print]
Authors: Martín-García A, Gómez Díaz A, Bradley PS, Morera F, Casamichana D
Summary: The aims of this study were to (a) determine the external load of a football team across playing position and relative to competition for a structured microcycle and (b) examine the loading and variation the day after competition for players with or without game time. Training and match data were obtained from 24 professional football players who belonging to the reserve squad of a Spanish La Liga club during the 2015/16 season using global positioning technology (n = 37 matches and n = 42 training weeks). Training load data were analyzed with respect to the number of days before or after a match (match day [MD] minus or plus). Training load metrics declined as competition approached (MD-4 > MD-3 > MD-2 > MD-1; p < 0.05; effect sizes [ES]: 0.4-3.1). On the day after competition, players without game time demonstrated greater load in a compensatory session (MD + 1C) that replicated competition compared with a recovery session (MD + 1R) completed by players with game time (MD + 1C > MD + 1R; p < 0.05; ES: 1.4-1.6). Acceleration and deceleration metrics during training exceeded 50% of that performed in competition for MD + 1C (80-86%), MD-4 (71-72%), MD-3 (62-69%), and MD-2 (56-61%). Full backs performed more high-speed running and sprint distance than other positions at MD-3 and MD-4 (p < 0.05; ES: 0.8-1.7). The coefficient of variation for weekly training sessions ranged from ∼40% for MD-3 and MD-4 to ∼80% for MD + 1R. The data demonstrate that the external load of a structured microcycle varied substantially based on the players training day and position. This information could be useful for applied sports scientists when trying to systematically manage load, particularly compensatory conditioning for players without game time.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

#11 Normative Data and Physical Determinants of Multiple Sprint Sets in Young Soccer Players Aged 11-18 Years: Effect of Maturity Status
Reference: J Strength Cond Res. 2018 Sep 19. doi: 10.1519/JSC.0000000000002810. [Epub ahead of print]
Authors: Selmi MA, Sassi RH, Yahmed MH, Giannini S, Perroni F, Elloumi M
Summary: The aims of the study were: (a) to establish normative data for repeated-sprint sets (RSS) test based on the maturity status (age at peak height velocity [PHV]) and (2) to investigate the relationship between anthropometrical variables (stature, sitting height, body mass, and body fat percentage), RSS (2 × 5 × 20 m with 15-second recovery between sprints and 1-minute recovery between sets), and fitness tests {squat jump, countermovement jump, standing long jump, standing triple jump, 5-jump test, and 20-m shuttle run (multistage shuttle run test [MSRT])}. Young male soccer players (n = 262; age: 14.5 ± 2.9 years) were evaluated and classified into 4 groups according to their maturity status: pre-PHV, circum-PHV1, circum-PHV2, post-PHV. An analysis of variance and Bonferroni post hoc were used to determine maturity group differences (p ≤ 0.05), whereas Pearson's correlation was used between variables. Repeated-sprint sets' indices (sum of sprint times [SST] and best sprint time [BST]) were significantly different between the maturity groups. Significant correlations between SST with body mass (from -0.73 to -0.33) and MSRT (from -0.49 to -0.30) among each maturity group were found. With the different maturity groups, correlations between SST (s), BST (s), and vertical jump (cm) (r = -0.63 to -0.25 and r = -0.68 to -0.23) and horizontal jump (m) (r = -0.70 to -0.38 and r = -0.63 to -0.43) were observed. Repeated-sprint sets' values improve during maturation of young soccer players and the correlations between RSS and fitness tests vary through the maturity groups. This information could be useful for the coach to identify talent and to prescribe specific physical training to improve performance.

#12 Effects of Two Different Tapering Protocols on Fitness and Physical Match Performance in Elite Junior Soccer Players
Reference: J Strength Cond Res. 2018 Sep 19. doi: 10.1519/JSC.0000000000002861. [Epub ahead of print]
Authors: Krespi M, Sporiš G, Trajković N
Summary: The purpose of this study was to determine the effects of 2 different tapering protocols on fitness and physical match performance in elite junior soccer players. One-hundred fifty-eight elite junior soccer players (mean age: 17.1 ± 0.79 years; mean height: 177.9 ± 6.64 cm; mean body mass: 71.3 ± 7.96 kg; and mean body mass index: 22.5 ± 1.66 kg·m) were randomly assigned to 2 groups: an exponential (n = 79) and a linear tapering (n = 79) group. Training sessions were conducted 3 times per week for 8 weeks. After 4 weeks of training and 4 weeks of tapering, participants were assessed in terms of body composition, physical fitness, and distance covered within a match. Both groups showed similar changes for body composition. The exponential group showed better improvement than the linear group in the 5- and 30-m sprints, countermovement jump, and V[Combining Dot Above]O2max (p < 0.05). The exponential tapering group had larger changes (p < 0.05) than the linear group in medium running (8-13 km·h) (6%; effect size = 0.26 compared with 5.5%; effect size = 0.22) and sprinting (>18 km·h) (26%; effect size = 0.72 compared to 21.7%; effect size = 0.60). The results show that exponential tapering produced better effects on speed, power, and endurance abilities than the linear protocol. Our results confirmed the reports of others that suggest that volume is the optimal variable to manipulate while maintaining both the intensity and the frequency of sessions.

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