Latest research in football - week 7 - 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 Ankle Structures of Professional Soccer (Football) Players With Proximal Diaphyseal Stress Fractures of the Fifth Metatarsal
Reference: J Foot Ankle Surg. 2019 Feb 11. pii: S1067-2516(18)30428-9. doi: 10.1053/j.jfas.2018.09.024. [Epub ahead of print]
Authors: Kizaki K, Yamashita F, Mori D, Funakoshi N
Summary: Despite a high incidence of proximal diaphyseal stress fractures of the fifth metatarsal (zone 3) in soccer (football) players, studies that examine risk factors of the fractures in professional soccer players are scarce; in particular, ankle structures have not yet been investigated. This study was designed to investigate ankle structures of professional soccer players with proximal diaphyseal stress fractures of the fifth metatarsal. We reviewed the ankle radiographs of 100 professional soccer players (stress fractures n = 15; controls n = 85) and measured the medial malleolar slip angle (MMSA), the ratio of the medial malleolar length to the width of the talar dome (MML:TD ratio), the ratio of the lateral malleolar length to the width of the TD (LML:TD ratio), and the ratio of the MML to the LML (MML:LML ratio). The MMSA (p < .01: 28.7° ± 5.8° versus 23.0° ± 4.9°) in the stress fractures was significantly wider and the MML:TD ratio (p = .08: 0.49 ± 0.08 versus 0.52 ± 0.07) had a trend to be smaller compared with the values of the controls. Logistic regression analysis revealed that a wider malleolar slip angle became a factor associated with stress fractures in professional soccer players (p < .01: odds ratio 1.27, 95% confidence interval 1.110 to 1.463). Receiver operating characteristic curve with MMSA for the stress fractures was depicted with an area under the curve of 0.778, and the suitable cut-off point was set at MMSA >27° with a positive likelihood ratio of 3.67 (95% confidence interval 2.173 to 6.188). Our study results show that a wide MMSA was associated with proximal diaphyseal stress fractures of the fifth metatarsal in professional soccer players.

#2 The acute effects of a short technique-intense training period on side-foot kick performance among elite female soccer players
Reference: J Sports Med Phys Fitness. 2019 Feb 13. doi: 10.23736/S0022-4707.19.09449-0. [Epub ahead of print]
Authors: Carlsson M, Isberg J, Nilsson J, Carlsson T
Summary: Previously, it was shown that elite soccer teams were 24% more likely to win matches if their passing effectiveness were increased by 1%. However, research interventions aiming to improve passing performance are scarce. The current study aimed to investigate the effect of a short technique-intense training period on side-foot kick performance among elite female soccer players. Four side-foot kick tests were completed before and after a training period: kicking a stationary ball using match-relevant (SBRS) and maximal ball speed (SBMS), passing the ball on the move using match-relevant ball speed (RBRS), and repeated side-foot kicks onto a rebound-box with continuously increasing passing distance (RRB). The players were assigned to either the intervention group or the control group. The training intervention consisted of six 55-min training sessions with five side-foot kick exercises. Within-group and between-group differences were investigated using paired-samples t-test and Mann-Whitney U test, respectively. The intervention group improved the performance in the RBRS and RRB tests (both P < 0.05), but no differences were found for the SBRS and SBMS tests (both P > 0.05). No improvements were found for the control group independent of test condition (all P > 0.05). Significant between-group differences were found for the RBRS and RRB tests (both P < 0.05), whereas no differences were found for the SBRS and SBMS tests (both P > 0.05). The fundamental soccer skill of passing a moving ball was improved in elite female soccer players by a short technique-intense training period.

#3 Head Injury in Soccer: From Science to the Field; summary of the head injury summit held in April 2017 in New York City, New York
Reference: Br J Sports Med. 2019 Feb 13. pii: bjsports-2018-100232. doi: 10.1136/bjsports-2018-100232. [Epub ahead of print]
Authors: Putukian M, Echemendia RJ, Chiampas G, Dvorak J, Mandelbaum B, Lemak LJ, Kirkendall D
Summary: There has been an increased focus and awareness of head injury and sport-related concussion (SRC) across all sports from the medical and scientific communities, sports organisations, legislators, the media and the general population. Soccer, in particular, has been a focus of attention due to the popularity of the game, the frequency of SRC and the hypothesised effects of repetitive heading of the ball. Major League Soccer, US Soccer and the National Women's Soccer League jointly hosted a conference entitled, 'Head Injury in Soccer: From Science to the Field', on 21-22 April 2017 in New York City, New York. The mission of this conference was to identify, discuss and disseminate evidence-based science related to the findings and conclusions of the fifth International Conference on Concussion in Sport held by the Concussion in Sport Group and apply them to the sport of soccer. In addition, we reviewed information regarding the epidemiology and mechanism of head injuries in soccer at all levels of play, data regarding the biomechanics and effects of repetitive head impacts and other soccer-specific considerations. We discussed how to release the information raised during the summit to key stakeholders including athletes, parents, coaches and healthcare providers. We identified future areas for research and collaboration to enhance the health and safety of soccer (football) players.

#4 The use of adaptive neuro-stimulation for rebalancing posture and muscular tone in a soccer team
Reference: J Sports Med Phys Fitness. 2019 Feb 12. doi: 10.23736/S0022-4707.19.09311-3. [Epub ahead of print]
Authors: Barassi G, Bellomo RG, Porreca A, Giannuzzo G, Giannandrea N, Pezzi L, Crudeli M, Visciano C, Saggini R
Summary: Posture and somatic structure could positively influence athletic gestures for their biomechanical implications. Working on neuromuscular activity, offers the possibility of intervention on postural control. The aim is demonstrating the possibility of interacting with the human body system through the spinal reflex pathway, starting from the stimulation of cutaneous receptors. In this study, developed inside the Chair in Physical and Rehabilitative Medicine, at G. d'Annunzio University, twenty soccer players were recruited. Males between 25.5 ± 10.6 years old participated in this study. Patients were divided using a single-blind criterion into two groups, each containing ten subjects. The experimental group was treated with 2 pre-set programs 4 times a week with an Adaptive Neuro-Stimulation (ANS) able to interact with cutaneous receptors through an ENF Physio® device with a range of electrical frequency of about 15-350 Hz; the placebo-controlled group received the treatment with the device switched off. Patients performed a myometric evaluation with the MyotonPRO® system and a postural one with the Rarog system at T0 before the treatment and at T1 after the four-week treatment. After our intervention, we identified an improvement in muscular tone, in particular in the hamstring muscles (17.69%, R p<0.01 / L p<0.05 ) and a rebalancing of the principal bone points in the postural system (shoulder 71%, p<0.05, hips 65.6%, p=0.056, sagittal "AP" and frontal "LL" centre of gravity, respectively 40%, p<0.05 and 52.7%, p=0.01 ). In conclusion, we could hypothesise the usefulness of an Adaptive Neuro-Stimulation to act on these parameters. Clinical rehabilitation impact - Adaptive Neuro-Stimulation could be used not only for treatment of injuries but also in the field of prevention.

#5 Plantar pressures in male adolescent soccer players and its associations with bone geometry and strength
Reference: J Sports Med Phys Fitness. 2019 Feb 12. doi: 10.23736/S0022-4707.19.09267-3. [Epub ahead of print]
Authors: Lozano-Berges G, Matute-Llorente Á, Gómez-Bruton A, Alfaro-Santafé V, González-Agüero A, Vicente-Rodríguez G, Casajús JA
Summary: Mechanical loads exerted by soccer-specific actions increase bone remodeling activity. Nevertheless, little is known about the relationship between plantar pressure and bone structure. Therefore, the aim of this study was to compare bone geometry and strength between soccer players who exhibited different maximum values of the average pressures (MP) when performing a combination of soccer-specific tasks. Forty male adolescent soccer players (mean age 13.20.5 y) and 13 controls (mean age 13.10.9 y) participated in this study. Biofoot system was used to measure MP at the non-dominant foot during a circuit of soccer-specific tasks. Cluster analysis was performed to classify players into groups of similar MP profiles resulting two different groups as follows: 15 players with high MP (SOC-HP; mean MP: 392.768.2 kPa) and 25 with low MP (SOC-LP; mean MP: 261.049.6 kPa). Total and cortical volumetric bone mineral content (Tt.BMC/Ct.BMC), cross-sectional area (Tt.Ar/Ct.Ar), cortical thickness (Ct.Th), fracture load in X-axis, and polar strength index (SSIp) were measured at 38% of the non-dominant tibia by peripheral quantitative computed tomography. Bone geometry and strength comparisons between SOC-HP and SOC-LP were performed using analyses of covariance controlling by weight and tibia length. Greater Tt.BMC, Ct.BMC and Tt.Ar. were found in SOC-HP compared to CG (Tt.BMC: 3.22vs2.95 g, Ct.BMC: 2.95vs2.68 g, Ct.Ar: 280vs253 mm2; p<.05). Nevertheless, no significant bone geometry and strength differences were found between soccer groups and between SOC-LP and CG (p>.05). Developing high MP when training and playing soccer might be favourable to bone development.

#6 Sex-Related Hip Strength Measures Among Professional Soccer Players
Reference: J Strength Cond Res. 2019 Feb 7. doi: 10.1519/JSC.0000000000003003. [Epub ahead of print]
Authors: Hedt CA, Pearson JM, Lambert BS, McCulloch PC, Harris JD
Summary: Lower-extremity musculoskeletal injuries in soccer are common among sexes. However, it remains unknown whether differences between sexes exist with regard to absolute or relative hip strength and how these differences may relate to injury. In the current study, we performed a retrospective cross-sectional analysis of pre-season data from male (♂n = 21) and female (♀n = 19) professional United States soccer organizations. Two years of pre-season data were collected for peak strength of lower extremity and hip musculature (no duplicates used). A 2 × 2 multivariate analysis of variance was used to detect differences in hip strength between sexes and dominant compared with nondominant legs. For all significant multivariate effects indicated by Wilks lambda and follow-up univariate analysis, a Tukey's post hoc test was used for pairwise univariate comparisons. A 2-tailed independent-samples T-test was used for comparison of height, body mass, body mass index (BMI), mean leg length, and strength ratios between dominant and nondominant limbs between sexes. Type I error was set at α = 0.05 for all analyses. Height (♂183.1 ± 6.8 cm, ♀170.0 ± 5.5 cm), body mass (♂79.0 ± 8.7 kg, ♀65.1 ± 5.6 kg), BMI (♂23.5 ± 1.3 kg·m, ♀22.5 ± 1.4 kg·m), and mean leg length (♂95.5 ± 4.34 cm, ♀ 88.3 ± 3.24 cm) differed between groups (p < 0.05). Sex differences (p < 0.05) were also found for hip abduction (dominant ♂19.5 ± 3.6 kg, ♀17.3 ± 2.2 kg; nondominant ♂18.5 ± 3.7 kg, ♀16.0 ± 2.3 kg), adduction (dominant ♂19.8 ± 3.0 kg, ♀16.7 ± 2.3 kg; nondominant ♂20.1 ± 2.9 kg, ♀17.6 ± 2.9 kg), external rotation (dominant ♂21.7 ± 3.4 kg, ♀17.7 ± 2.4 kg; nondominant ♂21.6 ± 3.9 kg, ♀16.8 ± 2.1 kg), and dominant hamstring strength (♂27.9 ± 6.5 kg, ♀23.0 ± 4.9 kg). The ratio of hip internal to external rotation strength differed in the nondominant leg (♂1.1 ± 0.2, ♀0.9 ± 0.2, p < 0.05). No significant differences were found between males and females when measures were normalized to body mass. These findings provide baseline pre-season normative data for professional soccer athletes and indicate that strength differences can be expected among different sexes, but are attenuated with attention to body mass. Further research should indicate how pre-season strength measures relate to injury.

#7 Prevalence of Hamstring Strain Injury Risk Factors in Professional and Under-20 Male Football (Soccer) Players
Reference: J Sport Rehabil. 2019 Feb 12:1-23. doi: 10.1123/jsr.2018-0084. [Epub ahead of print]
Authors: Ribeiro-Alvares JB, Dornelles MP, Fritsch CG, de Lima-E-Silva FX, Medeiros TM, Severo-Silveira L, Marques VB, Baroni BM
Summary: Hamstring strain injury (HSI) is the most prevalent injury in football (soccer), and a few intrinsic factors have been associated with higher injury rates. The purpose was to describe the prevalence of the main intrinsic risk factors for HSI in professional and under-20 football players. One-hundred and one football players (52 professionals; 49 under-20) participated in this study. Anamnesis, hamstrings ultrasonography, passive straight-leg raise test, functional movement screen, and isokinetic dynamometry were performed. Eleven HSI risk factors for each leg were assessed, besides the player's age as a systemic risk factor. Reports were delivered to the coaching staff. Professionals had greater prevalence of HSI history compared to under-20 players (40% vs. 18%). No between-group differences were found for the other screening tests. Altogether, thirty percent of players had already sustained at least one HSI; 58% had history of injuries in adjacent regions; 49% had short biceps femoris fascicles; 66% and 21% had poor passive and active flexibility, respectively; 42% and 29% had deficits in functional movements and core stability, respectively; 7% and 26% presented bilateral imbalance for hamstring concentric and eccentric strength, respectively; 87% and 94% obtained low values for hamstring-to-quadriceps conventional and functional ratios, respectively. Two-thirds of players had 3 to 5 risk factors per leg. None of the players was fully free of HSI risk factors. Most football players present multiple risk factors for sustaining an HSI. Hamstring weakness is the most prevalent risk factor, but the teams should also be aware of deficits in flexibility, core stability, functional movements, and hamstring fascicle length.

#8 Hydrothermally Modified Corn Starch Ingestion Attenuates Soccer Skill Performance Decrements in the Second Half of a Simulated Soccer Match
Reference: Int J Sport Nutr Exerc Metab. 2019 Feb 12:1-26. doi: 10.1123/ijsnem.2018-0217. [Epub ahead of print]
Authors: Quinones MD, Lemon PWR
Summary: Hydrothermally modified non-GMO corn starch (HMS) ingestion may enhance endurance exercise performance via sparing carbohydrate oxidation. To determine whether similar effects occur with intermittent, high intensity exercise we investigated the effects of HMS ingestion prior to and at half time on soccer skill performance and repeated sprint ability during the later stages of a simulated soccer match. Eleven, male, university varsity, soccer players (177.7±6.8 cm, 77.3±7.9 kg, 22±3 y, 12.8±4.9 %BF, V̇O2max = 57.1±3.9 ml∙kg BM-1∙min-1) completed the match with HMS (8% CHO containing a total of 0.7 g∙kg BM-1∙h-1; 2.8 kcal∙kg BM-1∙h-1) or isoenergetic dextrose (DEX). Blood glucose was lower (p<0.001) with HMS at 15 (5.3 vs 7.7 mmol∙L-1) and 30 min (5.6 vs 8.3 mmol∙L-1) following ingestion, there were no treatment differences in blood lactate, and the respiratory exchange ratio was lower with HMS at 15 (0.84 vs 0.86, p = 0.003), 30 (0.83 vs 0.85, p = 0.004) and 45 min (0.83 vs 0.85, p = 0.007) of the first half. Repeated sprint performance was similar for both treatments (p>0.05) but soccer dribbling time was slower with DEX vs baseline (15.63 s vs 14.43 s, p < 0.05) but not so with HMS (15.04 vs 14.43 s, p > 0.05). Further, during the passing test, penalty time was reduced (4.27 s vs 7.73 s, p = 0.004) with HMS. During situations where glycogen availability is expected to become limiting, HMS ingestion pre-match and at half time could attenuate the decline in skill performance often seen late in contests.

#9 Are Soccer Players Older Now Than Before? Aging Trends and Market Value in the Last Three Decades of the UEFA Champions League
Reference: Front Psychol. 2019 Jan 28;10:76. doi: 10.3389/fpsyg.2019.00076. eCollection 2019.
Authors: Kalén A, Rey E, de Rellán-Guerra AS, Lago-Peñas C
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Summary: The aims of the current study were to analyze the evolution of players' age in the UEFA Champions League since the start of its modern-day format in 1992-1993 up until 2017-2018 and to determine how the players' age relates to their market value. The sample consisted of all players participating in the UEFA Champions League from the 1992-1993 to 2017-2018 seasons (n = 16062). The following variables were used in this study: players' age, number of seasons in the club, number of Champions Leagues won, team performance, and market value of the player in the season. Data were examined using a one-way ANOVA and a linear regression. The main finding of the current study is that an aging trend has occurred in the last three decades in the Champions League. A significant increase in average players' age (>1.6 years) was observed, rising from an age of 24.9 to 26.5 years. Goalkeepers and Center Backs tend to peak later than attackers, and their peak performance can last until an age of about 31 years. Finally, an inverted-U curve defines the association between market value and age, with peak value appearing in the 26-30 age range. These results provide useful information regarding at which age soccer players are likely to perform at the highest level, as well as the age they are likely to have the highest market value.

#10 Young Soccer Players With Higher Tactical Knowledge Display Lower Cognitive Effort
Reference: Percept Mot Skills. 2019 Feb 11:31512519826437. doi: 10.1177/0031512519826437. [Epub ahead of print]
Authors: Cardoso FDSL, González-Víllora S, Guilherme J, Teoldo I
Summary: The present study aimed to investigate whether the form and amount of declarative tactical knowledge (DTK) and procedural tactical knowledge (PTK) influence cognitive effort during soccer performance among young players. We assessed 36 male players from a Brazilian first-division soccer club; participants averaged 14.89 ( SD = 1.42) years of age. We evaluated DTK from video simulation tests and PTK through the System of Tactical Assessment in Soccer. We assessed cognitive effort by measures of pupil diameter using Mobile Eye Tracking-XG while players viewed soccer video scenes and made game-related play decisions. After the assessment of tactical knowledge, we categorized the sample according to players' tactical knowledge into participants with higher and lower PTK and higher and lower DTK. Subsequently, we examined the both PTK and DTK groups on cognitive effort. Our results suggest that tactical knowledge influences cognitive effort in that players with higher PTK and DTK displayed less cognitive effort during soccer performance tasks. In conclusion, we observed that PTK and DTK influenced the cognitive effort younger soccer players expended while viewing soccer scenes and making soccer performance decisions.

#11 Differences in Acceleration and High-Intensity Activities Between Small-Sided Games and Peak Periods of Official Matches in Elite Soccer Players
Reference: J Strength Cond Res. 2019 Feb 6. doi: 10.1519/JSC.0000000000003081. [Epub ahead of print]
Authors: Dalen T, Sandmæl S, Stevens TGA, Hjelde GH, Kjøsnes TN, Wisløff U
Summary: The purpose of this study was to compare whether the physical performance of players during 4 vs. 4 + goalkeeper (4 vs. 4) and 6 vs. 6 + goalkeeper (6 vs. 6) small-sided games (SSGs) is equivalent to those experienced during the most intense 5-minute period of soccer match play. Twenty-six male soccer players from an elite Norwegian league team took part. Players were monitored during 18 matches, 56 SSGs: twenty-eight 4 vs. 4 and twenty-eight 6 vs. 6 games. The ZXY Sport Tracking System was used to measure for each player the total distance covered, high-intensity running distance, sprint distance, number of accelerations, and player load (all expressed per minute). To compare the physical performance variables on players during the SSGs formats and match play, a 1-way analysis of variance with repeated measures was used. Players performed the same number of accelerations and player load in 4 vs. 4 (1.7 and 248, respectively) as in peak match (1.6 and 227, respectively), whereas in 6 vs. 6, there were 63% fewer accelerations and 15% lower player load (1.2 and 198, respectively), than in peak match. High-intensity running and sprint distance were significantly lower than mean match values in both 4 vs. 4 (4.1 and 0.2 m vs. 8.2 and 1.7 m) and 6 vs. 6 games (2.7 and 0.21 m vs. 8.2 and 1.7 m) (p < 0.05). In conclusion, only 4 vs. 4 SSGs are highly valuable, and in that, they elicit player load and accelerations to a level that is (at least) equivalent with peak periods of official match play.

#12 Effects of Plyometric Training on Physical Performance of Young Male Soccer Players: Potential Effects of Different Drop Jump Heights
Reference: Pediatr Exerc Sci. 2019 Feb 8:1-8. doi: 10.1123/pes.2018-0207. [Epub ahead of print]
Authors: Ramirez-Campillo R, Alvarez C, García-Pinillos F, Gentil P, Moran J, Pereira LA, Loturco I
Summary: The purpose was to compare the effects of plyometric drop jump (DJ) training against those induced by regular soccer training and assess the transference effect coefficient (TEC) of DJs ("trained exercises") performed from 20- (DJ20) and 40-cm (DJ40) height boxes with respect to different physical qualities (jumping, linear and change of direction speed, kicking, endurance, and maximal strength) in youth male soccer players. Participants were randomly divided into a control group (n = 20; age: 13.5 [1.9] y) and a DJ training group (n = 19; age: 13.2 [1.8] y), and trained for 7 weeks. A 2-way analysis of variance for repeated measures with the within-subject factor time (preintervention and postintervention) and between-subject factor group (intervention vs control) was performed. To calculate the TECs between the trained exercises (DJ20 and DJ40) and the physical tests, the ratio between the "result gains" (effect size [ES]) in the analyzed physical qualities and the result gains in the trained exercises were calculated. The TECs were only calculated for variables presenting an ES ≥ 0.2. Significant improvements (ES = 0.21-0.46; P < .05) were observed in the DJ training group, except in linear sprint performance. The control group improved only the maximal strength (ES = 0.28; P < .05). Significant differences were observed in all variables (ES = 0.20-0.55; P < .05) in favor of the DJ training group, except for maximal strength (group × time interaction). A plyometric training scheme based on DJs was able to significantly improve the physical performance of youth male soccer players. Overall, greater TECs were observed for DJ40 (0.58-1.28) than DJ20 (0.55-1.21).

#13 Vitamin D Supplementation and Physical Activity of Young Soccer Players during High-Intensity Training
Reference: Nutrients. 2019 Feb 6;11(2). pii: E349. doi: 10.3390/nu11020349.
Authors: Skalska M, Nikolaidis PT, Knechtle B, Rosemann TJ, Radzimiński Ł, Jastrzębska J, Kaczmarczyk M, Myśliwiec A, Dragos P, López-Sánchez GF, Jastrzębski Z
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Summary: The aim of this study was to confirm that vitamin D supplementation of young soccer players during eight-week high-intensity training would have a significant effect on their motion activity. The subjects were divided into two groups: the experimental one, which was supplemented with vitamin D (SG, n = 20), and the placebo group (PG, n = 16), which was not supplemented with vitamin D. All the players were subjected to the same soccer training, described as High-Intensity Interval Training (HIIT). The data of the vitamin D status, time motion parameters and heart rate were collected just before and after the intervention. A significant increase in 25(OH)D concentration (119%) was observed in the supplemented group, while the non-supplemented group showed a decrease of 8.4%. Based on the obtained results, it was found that physical activity indicators in the players were significantly improved during small-sided games at the last stage of the experiment. However, taking into account the effect of supplementation with vitamin D, there were no statistically significant differences between the placebo and the supplemented groups; thus, the effect size of the conducted experiment was trivial.

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