Latest research in football - week 12 - 2017

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 Pneumomediastinum in a College-Aged Soccer Player: A Case Report
Reference: Curr Sports Med Rep. 2017 Mar/Apr;16(2):71-73. doi: 10.1249/JSR.0000000000000338.
Authors: Zarandy E, Counts S, Clemow C.
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#2 Proximal Neuromuscular Control Protects Against Hamstring Injuries in Male Soccer Players
Reference: Am J Sports Med. 2017 Mar 1:363546516687750. doi: 10.1177/0363546516687750. [Epub ahead of print]
Authors: Schuermans J, Danneels L, Van Tiggelen D, Palmans T, Witvrouw E
Summary: With their unremittingly high incidence rate and detrimental functional repercussions, hamstring injuries remain a substantial problem in male soccer. Proximal neuromuscular control ("core stability") is considered to be of key importance in primary and secondary hamstring injury prevention, although scientific evidence and insights on the exact nature of the core-hamstring association are nonexistent at present. The authors hypothesize that the muscle activation pattern throughout the running cycle would not differ between participants based on injury occurrence during follow-up. Sixty amateur soccer players participated in a multimuscle surface electromyography (sEMG) assessment during maximal acceleration to full-speed sprinting. Subsequently, hamstring injury occurrence was registered during a 1.5-season follow-up period. Hamstring, gluteal, and trunk muscle activity time series during the airborne and stance phases of acceleration were evaluated and statistically explored for a possible causal association with injury occurrence and absence from sport during follow-up. Players who did not experience a hamstring injury during follow-up had significantly higher amounts of gluteal muscle activity during the front swing phase ( P = .027) and higher amounts of trunk muscle activity during the backswing phase of sprinting ( P = .042). In particular, the risk of sustaining a hamstring injury during follow-up lowered by 20% and 6%, with a 10% increment in normalized muscle activity of the gluteus maximus during the front swing and the trunk muscles during the backswing, respectively ( P < .024). Muscle activity of the core unit during explosive running appeared to be associated with hamstring injury occurrence in male soccer players. Higher amounts of gluteal and trunk muscle activity during the airborne phases of sprinting were associated with a lower risk of hamstring injuries during follow-up. Hence, the present results provide a basis for improved, evidence-based rehabilitation and prevention, particularly focusing on increasing neuromuscular control of the gluteal and trunk muscles during sport-specific activities (eg, sprint drills, agility drills).

#3 Who runs the fastest? Anthropometric and physiological correlates of 20 m sprint performance in male soccer players
Reference: Res Sports Med. 2016 Oct-Dec;24(4):341-351. Epub 2016 Aug 22.
Authors: Nikolaidis PT, Ruano MA, de Oliveira NC, Portes LA, Freiwald J, Lepretre PM, Knechtle B
Summary: The aim of the present study was to examine the relationship of 20 m sprint performance with anthropometrical and physiological parameters in male soccer players. A hundred and 81 soccer players from the region of Athens (age 23.4 ± 5.0 yrs, body mass 73.4 ± 7.7 kg, height 180.0 ± 5.9 cm, body fat (BF) 14.4 ± 3.6%), classified into quartiles according to 20 m sprint time (group A, 2.84-3.03 s; group B, 3.04-3.09 s; group C, 3.10-3.18 s; group D, 3.19-3.61 s), participated. Soccer players in group A were younger and had better performance in vertical jumps and in the Wingate anaerobic test (WAnT, p < 0.05). Sprint time correlated to age (r = 0.27), body mass (r = 0.23), body height (r = 0.20), BF (r = 0.23), vertical jumps (-0.58 ≤ r ≤ -0.50) and the WAnT (-0.45 ≤ r ≤ -0.30, p < 0.05). In summary, the magnitude of correlations of sprint time with measures of lower limbs muscle strength and power (WAnT and jumps) was larger than with anthropometric measures (body mass and BF).

#4 The specificity of the Loughborough Intermittent Shuttle Test for recreational soccer players is independent of their intermittent running ability
Reference: Res Sports Med. 2016 Oct-Dec;24(4):363-374. Epub 2016 Aug 22.
Authors: Coratella G, Beato M, Schena F
Summary: The aim of the present study was to evaluate whether or not recreational soccer players (SP) and non-soccer players (non-SP) with similar intermittent-running ability had similar physiological responses to a soccer match-simulation protocol. Twenty-two recreational SP and 19 fitness-matched non-SP participated. Yo-Yo level 1 assessed intermittent-running ability, while the Loughborough Intermittent Shuttle Test served as soccer match-simulation protocol. Heart rate (HR), blood lactate concentration [La-] and rating of perceived exertion (RPE) were recorded after each bout (1-5, plus an exhaustive task). SP had lower HR after the third, fourth and fifth bout, compared to non-SP. Similarly, SP had lower [La-] after the third, fourth and the fifth bout. SP also had lower RPE after the third, fourth and fifth bout. The appropriateness of intermittent-running ability as the main determinant of physical performance in SP was questioned.

#5 Effects of horizontal plyometric training volume on soccer players' performance
Reference: Res Sports Med. 2016 Oct-Dec;24(4):308-319. Epub 2016 Aug 22.
Authors: Yanci J, Los Arcos A, Camara J, Castillo D, García A, Castagna C
Summary: The aim of this study was to examine the dose response effect of strength and conditioning programmes, involving horizontally oriented plyometric exercises, on relevant soccer performance variables. Sixteen soccer players were randomly allocated to two 6-week plyometric training groups (G1 and G2) differing by imposed (twice a week) training volume. Post-training G1 (4.13%; d = 0.43) and G2 (2.45%; d = 0.53) moderately improved their horizontal countermovement jump performance. Significant between-group differences (p < 0.01) in the vertical countermovement jump for force production time (T2) were detected post-training. No significant and practical (p > 0.05, d = trivial or small) post-training improvements in sprint, change of direction ability (CODA) and horizontal arm swing countermovement jump were reported in either group. Horizontal plyometric training was effective in promoting improvement in injury prevention variables. Doubling the volume of a horizontal plyometric training protocol was shown to have no additional effect over functional aspects of soccer players' performance.

#6 The effect of slope on repeated sprint ability in young soccer players
Reference: Res Sports Med. 2016 Oct-Dec;24(4):320-330. Epub 2016 Aug 18.
Authors: Padulo J, Ardigo LP, Attene G, Cava C, Wong DP, Chamari K, Migliaccio GM
Summary: This study aimed to describe a gradient repeated sprint ability (RSA) test in comparison with a standard level one by investigating performance, metabolic demand and muscular jumping performance as a proxy for running mechanics. Eighteen athletes performed two level RSA tests (40 m × 6) - for reliability evaluation - and one ±5% gradient RSA test, second leg downhill (RSAgrad). Rating of perceived exertion (RPE), blood lactate concentration (BLa) concentration, vertical jump heights were assessed as well. Level test measures resulted highly reliable (Intra-class correlation coefficient (ICC) ≥0.96). RSAgrad worsened only first sprints' performance (-2%) but not overall test performance (~45 s). RSAgrad resulted to be less deteriorating in terms of fatigue index (FI) (-36%), BLa (-23%), RPE (-11%), jumping performance (RSAgrad post-/pre-squat jump, countermovement jump heights (CMJh): -3%, -6%, respectively). RSAgrad could be used to diversify common training protocol without stressing excessively athletes' current metabolic-anaerobic capacity. Such physical conditioning procedures could improve acceleration/braking capability.

#7 Physical and technical performances are not associated with tactical prominence in U14 soccer matches
Reference: Res Sports Med. 2016 Oct-Dec;24(4):352-362. Epub 2016 Aug 17.
Authors: Clemente FM, Figueiredo AJ, Martins FM, Mendes RS, Wong DP
Summary: The aim of this study was to analyse the association between physical/technical variables and the tactical prominence variables in U14 soccer matches. Twenty-two young amateur soccer players (13.5 [Formula: see text] 0.5 years old, 5.4 [Formula: see text] 0.5 years of practice, 163.3 [Formula: see text] 9.8 cm in body height) from two teams of the Portuguese regional league volunteered for the study. Our results showed positive and moderate correlation between dribbling test and betweenness centrality (r = 0.324; p = 0.142), and negative moderate correlation between %fatigue index and betweenness centrality (r = -0.390; p = 0.073). Physical and technical variables had no statistical differences among tactical positions. Nevertheless, when tactical prominence of players from four tactical positions were compared, significant differences were found in terms of degree prestige (p = 0.001) and degree centrality (p = 0.002). This pilot study did not find strong correlations between physical/technical levels and tactical prominence in soccer matches.

#8 Predicting football injuries using size and ratio of the multifidus and quadratus lumborum muscles
Reference: Scand J Med Sci Sports. 2017 Apr;27(4):440-447. doi: 10.1111/sms.12643.
Authors: Hides JA, Stanton WR
Summary: Deficits in muscles of the lumbo-pelvic region, such as a relatively small multifidus muscle, have been used to predict lower limb injuries in professional football players. Results have been less consistent for the size of the quadratus lumborum (QL) muscle. Changes in size of the multifidus and QL muscles could be functionally related to each other, and modeling this relationship could improve prediction of lower limb injuries. Ultrasound imaging examinations were performed on male elite football players at the start of the Australian Football League (AFL) pre-season and playing season. Injury data were obtained from records collected by each club. Results indicated that the cross-sectional area of the multifidus muscle was related to the occurrence of an injury in the pre-season (odds ratio [OR] = 2.08/cm2 decrease below the mean; OR for dichotomized measure = 12.2) and in the season (OR = 2.43/cm2 ). The size of the QL muscle was significantly related to an injury in the pre-season (OR = 2.12/cm2 increase above the mean; OR for dichotomized measure = 7.26) but not in the season. A significant link was found between the ratio of the multifidus and QL muscles, and the incidence of pre-season (OR = 14.71) and season injuries (OR = 5.29). The sensitivity and specificity of the model in the pre-season were 75% and 85.7%, respectively; values for the playing season were 88.4% and 62.5%. A model was developed for prediction of lower limb injuries in football players. Combining size measurements of the multifidus and QL muscles improved predictive power. This information may have clinical implications for injury screening and prevention.

#9 Circannual rhythm of plasmatic vitamin D levels and the association with markers of psychophysical stress in a cohort of Italian professional soccer players
Reference: Chronobiol Int. 2017 Mar 17:1-9. doi: 10.1080/07420528.2017.1297820. [Epub ahead of print]
Authors: Lombardi G, Vitale JA, Logoluso S, Logoluso G, Cocco N, Cocco G, Cocco A, Banfi G
Summary: Adequate plasmatic Vitamin D levels are crucial to maintain calcium homeostasis and bone metabolism both in the general population and in athletes. Correct dietary supply and a regular sun exposure are fundamental for allowing the desired and effective fitness level. Past studies highlighted a scenario of Vitamin D insufficiency among professional soccer players in several countries, especially in North Europe, whilst a real deficiency in athletes is rare. The typical seasonal fluctuations of Vitamin D are wrongly described transversally in athletes belonging to teams that play at different latitudes and a chronobiologic approach studying the Vitamin D circannual rhythm in soccer players has not been described yet. Therefore, we studied plasma vitamin D, cortisol, testosterone, and creatin kinase (CK) concentrations in three different Italian professional teams training at the same latitude during a period of two consecutive competitive seasons (2013 and 2014). In this retrospective observational study, 167 professional soccer players were recruited (mean age at sampling 25.1 ± 4.7 years) and a total of 667 blood drawings were carried out to determine plasma 25(OH)D, serum cortisol, serum testosterone and CK levels. Testosterone to cortisol ratio (TC) was calculated based as a surrogate marker of overtraining and psychophysical stress and each athlete was drawn until a maximum of 5 times per season. Data extracted by a subgroup of players that underwent at least 4 sample drawings along a year (N = 45) were processed with the single and population mean cosinor tests to evaluate the presence of circannual rhythms: the amplitude (A), acrophase (Φ) and the MESOR (M) are described. In total, 55 players (32.9%) had an insufficient level of 25(OH)D during the seasons and other 15 athletes (9.0%) showed, at least once, a deficiency status of Vitamin D. The rhythmometric analyses applied to the data of Vitamin D revealed the presence of a significant circannual rhythm (p < 0.001) with the acrophase that occurred in August; the rhythms of Vitamin D levels were not different neither among the three soccer teams nor between competitive seasons. Cortisol, testosterone and TC showed significant circannual rhythms (p < 0.001): cortisol registered an acrophase during winter (February) while testosterone and TC registered their peaks in the summer months (July). On the contrary, CK did not display any seasonal fluctuations. In addition, we observed weak but significant correlations between 25(OH)D versus testosterone (r = 0.29 and p < 0.001), cortisol (r = -0.27 and p < 0.001) and TC (r = 0.37 and p < 0.001). No correlation was detected between Vitamin D and CK. In conclusion, the correct chronobiologic approach in the study of annual variations of Vitamin D, cortisol and testosterone could be decisive in the development of more specific supplementation and injury prevention strategies by athletic trainers and physicians.

#10 Predictors Of Linear And Multidirectional Acceleration In Elite Soccer Players
Reference: J Strength Cond Res. 2017 Mar 13. doi: 10.1519/JSC.0000000000001897. [Epub ahead of print]
Authors: Jonathan N, Russell M, Shearer D, Cook C, Kilduff L
Summary: Linear and multidirectional acceleration underpins success in professional soccer match-play. However, the physical qualities that determine these performance indicators are poorly understood in elite players. English Premier League players (n=26) performed isometric mid-thigh pulls (IMTP), bilateral and unilateral drop jumps (DJ; from 40 and 20 cm, respectively), bilateral and unilateral countermovement jumps (CMJ) and assessments of linear (5-, 10-, 20-m) and multidirectional (left/right pre-planned and reactive) acceleration. Regression analyses highlighted that 21% of variance in 5-m sprint time (1.02±0.07 s) was explained by relative peak power output (PPO) in bilateral CMJ (54.5±5.3 W·kg). A 5.4 W·kg increase in CMJ predicted a 0.03 s decrease in 5-m sprint time (P=0.02). For 10-m sprint time (1.72±0.09 s), 44% of variance was explained by isometric relative peak force (PF; 30.4±4.9 N·kg) and bilateral relative CMJ PPO (54.5±5.3 W·kg). A 5.4 W·kg increase in CMJ predicted reduced 10-m sprint times by 0.04 s (P=0.01). For 20-m sprint time (2.94±0.11 s), 55% of the total variance was explained by isometric relative PF (30.4±4.9 N·kg) and relative CMJ PPO (54.5±5.3 W·kg). Increases of 5.4 W·kg in bilateral CMJ predicted an improvement of 20-m sprint time by 0.06 s (P=0.002). Contributions were insignificant (P>0.05) for pre-planned and reactive multidirectional acceleration. Relativized indices, especially those related to force production during CMJ and IMTP tests, likely underpin linear but not multidirectional acceleration performance in professional soccer players. When linear acceleration is a training focus, practitioners should seek to monitor CMJ and IMTP test performance.

#11 Groin Problems in Male Soccer Players Are More Common Than Previously Reported
Reference: Am J Sports Med. 2017 Feb 1:363546516687539. doi: 10.1177/0363546516687539. [Epub ahead of print]
Authors: Haroy J, Clarsen B, Thorborg K, Holmich P, Bahr R, Andersen TE
Summary: The majority of surveillance studies in soccer have used a time-;loss injury definition, and many groin problems result from overuse, leading to gradually increasing pain and/or reduced performance without necessarily causing an absence from soccer training or match play. Thus, the magnitude of groin problems in soccer has probably been underestimated in previous studies based on traditional injury surveillance methods. The purpose of the study was to investigate the prevalence of groin problems among soccer players of both sexes and among male soccer players at different levels of play through a new surveillance method developed to capture acute and overuse problems. We registered groin problems during a 6-;week period of match congestion using the Oslo Sports Trauma Research Center Overuse Injury Questionnaire. A total of 240 players from 15 teams across different levels of play and from both sexes were included, and they responded to the weekly questionnaire. We calculated the average weekly prevalence of all groin problems and substantial groin problems. Of the 240 players, 112 male players (59%) and 20 female players (45%) reported at least 1 episode of groin problems. The average weekly prevalence of any groin problem and substantial groin problem for all male players was 29% (range, 23%-32% across different levels) and 10% (7%-13%), respectively. Elite male players had an increased risk of experiencing groin problems (odds ratio: 3.1, 95% CI: 1.5-6.4, P = .03) compared with elite female players. There was no difference in the risk of experiencing groin problems among elite, subelite, and amateur male players. For substantial problems, there was no difference between elite male and elite female players or among levels of play for senior male soccer players. We found a high prevalence of groin problems among male soccer players during a period with match congestion. Time-loss definition as used in previous injury surveillance studies captured only one-;third of the male groin problems registered with the new method. Elite male players had 3 times' higher risk of reporting groin problems as compared with elite female players, while playing level did not influence the risk of reporting a groin problem among males.

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