Latest research in football - week 17 - 2014

#1 Effects of short- and long-term physical activity on DNA stability and oxidative stress status in young soccer players
Reference: J Sports Med Phys Fitness. 2014 Jun;54(3):354-61.
Authors: Sopić M, Bogavac-Stanojević N, Baralić I, Kotur-Stevuljević J, Dorđević B, Stefanović A, Jelić-Ivanović Z.
Summary: The aim of the study was to determine whether single soccer training is able to cause oxidative stress and DNA instability. We have also sought to investigate if adaptive response will be developed during 45 days training period and to what extent. This study was conducted on 16 soccer players aged 18.13±0.35 years. We used single cells gel electrophoresis (comet assay) to investigate leukocyte DNA stability. The results were presented as DNA score and percent of cells with medium and high damage. Oxidative status of our subjects was estimated through blood levels of superoxide anion, the thiobarbituric acid-reacting substances (TBARs), total antioxidant status (TAS), total oxidant status (TOS), prooxidant-antioxidant balance (PAB) and sulfhydryl-groups (SH-groups). During single soccer training, DNA score and percent of the cells with medium and high damage were increased after training but without significance. Sulphydryl-groups (P=0.033), TOS (P=0.002) and PAB (P=0.045) were significantly lower after training. After 45 days training period DNA score was decreased but with no significance. However, percent of cells with medium and high damage was significantly lower (P=0.01). TOS (P=0.001) and MDA (P=0.038) levels were also significantly lower, while sulphydryl-groups levels were significantly higher (P=0.006). This study demonstrated that single soccer training had not compromised DNA stability. Possible development of oxidative stress was effectively neutralized by very well preserved antioxidative mechanisms. It was also shown that during 45 days adaptive response was induced. All measured parameters should be considered as useful information on oxidative status of trainees.


#2 Maturity-associated variation in change of direction and dribbling speed in early pubertal years and 5-year developmental changes in young soccer players
Reference: J Sports Med Phys Fitness. 2014 Jun;54(3):307-16.
Authors: Valente-Dos-Santos J, Coelho-E-Silva MJ, Vaz V, Figueiredo AJ, Capranica L, Sherar LB, Elferink-Gemser MT, Malina RM.
Summary: The purpose of the current study was to assess the developmental changes in change of direction and dribbling speed in youth soccer players taking into account skeletal age (SA), maturity status, body size, estimated fat mass, aerobic endurance, lower limb explosive strength and annual volume of training. Eighty-three male soccer players aged 10-15 years (SA) at baseline were annually followed over 5 years, resulting in an average 4.4 observations per player. After testing for multicollinearity, multi-level regression modeling was used to examine the longitudinal developmental changes on change of direction and dribbling speed. Maturity-associated variability was significant in change of direction and also dribbling speed among young soccer players aged 12-14 years with better scores being performed by late maturers. Moreover, the predicted longitudinal scores for change of direction and dribbling speed improved with SA (P<0.01), SA2 (P<0.01) and skeletal maturity status entered as an additional developmental predictor (P<0.05). Estimated fat-free mass (P<0.01), aerobic endurance (P<0.01) and lower limb strength (P<0.01) were additional predictors in both models. The soccer-specific skill, dibbling speed, was also explained by annual volume of training (P<0.05). Skeletal maturity status explains inter-individual variability on maximal short-term run performances with and without the ball possession at early ages of participation in competitive soccer. The effects tend to persist across ages combined with longitudinal changes in body composition and functional fitness. In the particular case of the ball test, annual volume of training was also a longitudinal performance predictor.


#3 The Efficacy of Acute Nutritional Interventions on Soccer Skill Performance
Reference: Sports Med. 2014 Apr 12. [Epub ahead of print]
Authors: Russell M, Kingsley M.
Summary: The use of nutritional ergogenic aids in team sports such as soccer is now commonplace. Aligned with the primary aim of soccer, which is to score more goals than the opposition within the allotted time, the quality of performance of technical actions (i.e., skills) executed during soccer-specific exercise is likely to determine success. However, when seeking to maintain soccer skill performance, information about the efficacy of nutritional interventions is lacking and factors which might modulate the efficacy of such strategies are unclear. This review aimed (i) to systematically evaluate the current research that examines the efficacy of nutritional interventions on soccer skills, and (ii) to provide a qualitative commentary on factors that have the potential to modulate the efficacy of such strategies. Relevant databases (PubMed and SPORTDiscus) were searched up to and including 1 July, 2013 for studies that investigated the efficacy of acute nutritional interventions on soccer skill performances. Overall, 279 records were retrieved. Articles were sequentially excluded from the review based on specific criteria, being: (A) articles that did not report outcomes directly relating to skilled performances in soccer, (B) articles that examined the influence of interventions that were not nutritional in origin and/or were nutritional in origin but provided >3 hours before skill testing commenced, (C) articles that were review papers, and (D) post-acceptance withdrawal of articles methods from database. Articles were independently assessed for the quality of the methods employed based upon the Physiotherapy Evidence Database (PEDro) scale. Records achieving a minimum PEDro score of 5 out of 10 were included in this review. Qualitative appraisal of 13 articles was performed after the application of exclusion criteria and quality assurance processes. The majority (n = 8) of articles examined the influence of carbohydrates on technical performance whereas fewer studies investigated the influence of caffeine ingestion (n = 2) and fluid provision (n = 3). Findings were reported for a total of 171 participants and all but one of the included articles used cross-over study designs. Most participants (94 %) were male, highly trained (reported maximal aerobic capacity range 50-59 ml·kg-1·min-1) and exercised in temperate environments (reported temperature range 13-25 °C). Six of the eight studies reported that carbohydrates, consumed in the form of a 6-8 % solution of glucose, sucrose or maltodextrin at rates of 30-60 g·h-1, enhanced at least one aspect of skilled performance over the duration of exercise (75-90 min). Although some evidence exists to support the consumption of caffeine (6 mg·kg-1 body mass [BM]) and prescribed fluid to preserve skills performed during soccer-specific exercise, findings from the small number of included studies were inconsistent. The outcome measures and methods used to quantify skilled performance were not consistent across studies; consequently, it was not possible to perform meta-analyses to produce pooled effect sizes in this review. The findings from this systematic review suggest that nutritional interventions, which provide carbohydrate, caffeine and fluid, have potential to preserve skills performed under conditions that induce soccer-specific fatigue. The weight of current evidence supports the consumption of carbohydrate, but is less conclusive with respect to caffeine and fluid provision. It is likely that the efficacy of a nutritional intervention will be modulated by factors including the dose consumed, the mode of administration, individual responsiveness to the intervention and interactions with other physiological changes occurring during soccer-specific exercise. Consequently, these factors should be considered when using carbohydrates, caffeine and fluid provision to maintain skilled performances in soccer. Future research should seek to optimise the nutritional strategies employed to maintain technical performance throughout match-play.


#4 A survey of "mental hardiness" and "mental toughness" in professional male football players
Reference: Chiropr Man Therap. 2014 Apr 15;22(1):17. [Epub ahead of print]
Authors: Wieser R, Thiel H.
Summary: It is not uncommon for chiropractors to be associated with sports teams for injury prevention, treatment, or performance enhancement. There is increasing acceptance of the importance of sports psychology in the overall management of athletes. Recent findings indicate mental hardiness can be determined reliably using specific self-assessment questionnaires. This study set out to investigate the hardiness scores of professional footballers and examine the correlation between two questionnaires. It also included a mental hardiness rating of players by two coaches, and examined differences in hardiness and mental toughness between national and international players. Two self-assessment questionnaires (modified Sports Mental Toughness Questionnaire [SMTQ-M] and Psychological Performance Inventory [PPI-A] ) were completed by 20 male professional footballers. Two coaches, independently rated each player. A percentage score from each questionnaire was awarded each player and an average score was calculated ({SMTQ-M % + PPI-A %} / 2). The PPI-A and SMTQ-M scores obtained for each player were analysed for correlation with Pearson's correlation coefficient. Cohen's kappa inter-reliability coefficient was used to determine agreement between coaches, and between the players' hardiness scores and coaches' ratings. The independent t-test was used to examine differences between national and international players. The players' scores obtained from PPI-A and SMTQ-M correlated well (r = 0.709, p < 0.001). The coaches ratings showed significant, weak to moderate agreement (Cohen's kappa = 0.33). No significant agreement was found between player self-assessments and coaches' ratings.The average ({SMTQ-M % + PPI-A %} / 2) mean score was 77 % (SD = 7.98) with international players scoring 7.4 % (p = 0.04) higher than non-international players. The questionnaires (SMTQ-M and PPI-A) correlated well in their outcome scores. These findings suggest that coaches moderately agree when assessing the level of mental hardiness of football players. There was no agreement between player self-assessment and ratings by coaches. Footballers who play or had played for national teams achieved slightly higher mental hardiness scores. Either questionnaire can offer the clinician a cost-effective, valuable measure of an individual's psychological attributes, which could be relevant within the wider context of bio-psycho-social model of care.


#5 Incidence of trauma in young football players aged 15-19
Reference: Ann Acad Med Stetin. 2013;59(1):120-2 [Article in Polish].
Authors: Zołnowski B, Wrona-Zolnowska L, Gebska M, Wojciechowska A, Zyzniewska-Banaszak E.
Summary: It is obvious that sports have beneficial effects on health, but they often pose a certain risk to health. Recent studies point to the growing number of injuries and accidents among players practicing football. Players are injured during a match (65.68%) more often than during training (34.31%). The most common injuries include damage to the lower extremities (97%) including: bruising (56.70%), muscle and ligament injuries (17%), tearing muscles and ligaments (13.40%) and fractures (13%). A forced break in training activity contributes to the weakening of the player's performance, which is why one of the main goals of rehabilitation is to restore it as soon as possible. This paper is devoted to the characteristics of injuries among players practicing football. The survey comprised 102 athletes of both sexes, practicing in Polish football clubs, at various levels of competition, e.g. junior team of players aged under 17 years representing Poland.


#6 Physiotherapists Can Identify Female Football Players With High Knee Valgus Angles During Vertical Drop Jumps Using Real-Time Observational Screening
Reference: J Orthop Sports Phys Ther. 2014 Apr 14. [Epub ahead of print]
Authors: Nilstad A, Andersen TE, Kristianslund E, Bahr R, Myklebust G, Steffen K, Krosshaug T.
Summary: Study Design Clinical measurement; controlled laboratory study. Objectives To assess the relationships among real-time observational screening of frontal plane knee control and knee valgus angles and abduction moments calculated from three-dimensional (3D) motion analysis during a vertical drop jump. A secondary purpose was to investigate inter-rater agreement for 3 independent physiotherapists. Background Current approaches to screen for anterior cruciate ligament injury risk are based on complex biomechanical analyses or two-dimensional video reviews. There is a need for simple and efficient low-cost screening methods. Methods Sixty Norwegian elite female football (soccer) players performed a vertical drop jump task. Using real-time observational screening, 3 physiotherapists independently scored each participant`s frontal plane knee control as "good", "reduced" or "poor", based on specific criteria. Screening test scores were correlated to frontal plane knee kinematics and kinetics using 3D motion analysis. Inter-rater agreement was determined using kappa correlation coefficients. Results Players rated as having poor knee control had higher mean knee valgus angles compared to players rated as having good control (10.3 ± 3.4° versus 1.9 ± 4.3°, P≤0.001). The correlation between the observation test scores and valgus angles was moderate for all raters (0.54-0.60, P≤0.001), whereas the observation scores correlated poorly with abduction moments (0.09-0.11, P>0.05). The highest discriminative accuracy was found for knee valgus angles across all raters (area under the ROC curve (AUC) 0.85-0.89). The inter-rater agreement between the physiotherapists was substantial to almost perfect, with percentage agreement and kappa coefficients ranging from 70% to 95% and 0.52 to 0.92, respectively. Conclusion Physiotherapists can reliably identify female athletes with high knee valgus angles in a vertical drop jump landing using real-time observational screening. J Orthop Sports Phys Ther, Epub 14 April 2014. doi:10.2519/jospt.2014.4969.


#7 Association of leg bias with bipedal speed and power in developing soccer players
Reference: Percept Mot Skills. 2014 Feb;118(1):293-303.
Authors: Witkowski Z, Lipecki K, Lyakh V.
Summary: The aim of this research was to determine whether there is any association between leg bias and bipedal locomotion in young male soccer players. 227 participants, members of a Polish football club, were tested. Leg dominancy and maximal specific power of each leg were recorded.


#8 Rate of perceived exertion as a useful tool during a football competition in young soccer players
Reference: Cuadernos de Psicología del Deporte 2014, Vol. 14 Issue 1, p75 7p.
Authors: Calahorro Cañada F, Torres-Luque G, Lara-Sánchez A,
Summary: The purpose of this study is to analyze an official football competition between young soccer players and test the effectiveness of the Rate of Perceived Exertion (RPE) to measure the intensity during the match. 22 players were selected (17,43 ± 0,84 years, 71,71 ± 5,71 kg, 178,65 ± 4,10 cm) from of a youth football team from the first Spanish division. An official football competition was assessed, carrying out 6 measurements (first and second halves, halftime and fulltime) from three variables: RPE (6 - 20 items); Heart Rate (FC) and Blood Lactate Concentration) ([Lac]). The results show an average values of RPE of 14,13; a FC of 158,65 lat·min-1; and a [Lac] de 3,75 mmol·l-1. It has been found in general, a similar behavior between the RPE - FC and RPE - [Lac]. RPE might be a good indicator to register the intensity for young soccer players, being an easy and effective tool for coaches to use it while controlling the internal load that involves the official competition.


#9 Gender differences in match performance characteristics of soccer players competing in the UEFA Champions League
Reference: Hum Mov Sci. 2014 Feb;33:159-71. doi: 10.1016/j.humov.2013.07.024. Epub 2013 Oct 16
Authors: Bradley PS, Dellal A, Mohr M, Castellano J, Wilkie A
Summary: The aim of this study was to examine gender differences in match performance characteristics of elite soccer players. Fifty-four male and fifty-nine female soccer players were tracked during UEFA Champions League matches using a multi-camera system (Amisco, Nice, France). Male players covered more (P<.01) distance than female players in total during a match (Effect Size [ES]: 0.5) and at higher speed thresholds (>15, >18, 18-21, 21-23, 23-25 and >27kmh(-1); ES: 0.7-1.4). Decrements in the second versus first half (P<.01) were only evident in female players for the distance covered in total and at selected speed thresholds (12-15, >12 and >15kmh(-1); ES: 0.6). Male central midfielders covered more (P<.01) total distance during a match than female central midfielders and at selected speed thresholds (15-23kmh(-1); ES: 1.3-2.2). Male full-backs and wide midfielders covered a greater distance (P<.01) than female players in the same positions at higher speed thresholds (>15, 21-23, 23-25, 25-27 and >27kmh(-1); ES: 1.5-3.1). The distance covered during the most intense 5min period of the match (>15kmh(-1)) was higher (P<.01) in male compared to female players (ES: 1.0) but no distance deficit in the next versus the average 5min period was observed for either gender (ES: 0.1-0.2). No gender differences were found for technical events such as the number of ball touches, time in possession of the ball or total duels won during both halves and the entire match (ES: 0.1-0.3). However, female players lost the ball more often (P<.05) and displayed lower pass completion rates than male players during both halves and the entire match (ES: 0.5-0.9). The data demonstrate that large gender differences exist for match performance characteristics of players competing at the highest competitive standard of European soccer. Such detailed analyses could be useful for gender-specific training information for optimal preparation. However, more research is warranted to establish gender-specific speed thresholds for elite soccer players

#10 Morphological, maturational, functional and technical profile of young Brazilian soccer players
Reference: Brazilian Journal of Kineanthropometry & Human Performance 2014, Vol. 16 Issue 3, p277 10p
Authors: de Oliveira M, Barata Figueiredo AJ, Garcia ES, Teixeira Seabra AF.
Summary: The objectives of this study were to describe and compare the anthropometric profile, physical fitness and soccer-specific skills between under-15 and under-17 Brazilian soccer players, as well as to evaluate possible differences in these variables according to biological maturation in the age categories. The sample consisted of 245 male soccer players (under-15: n=161; under-17: n=84). Anthropometric measures included weight, height and skinfolds. Biological maturation was assessed based on pubic hair development. The following tests were used for functional assessment: static and countermovement jump, Yo-Yo intermittent endurance test (level 2), RAST, 5- and 30-meter running speed, and agility T-test. Soccer-specific skills were assessed using three tests: ball control, dribbling, and kick accuracy. Descriptive statistics, t-test and analysis of variance (ANOVA) were used for statistical analysis. The results showed a larger body size (stature and body mass), longer sports experience (years of formal training) and better performance in most of the functional tests for under-17 soccer players compared to under-15 players. There were no significant differences in adiposity or soccer-specific skills between levels of competition. Significant differences as a function of maturation stage were observed in anthropometric and functional variables only in the under-15 category. In conclusion, the under-17 category differs from the under-15 category in terms of anthropometric and physical fitness characteristics. However, no difference was observed in two of the three soccer-specific skills. Physical fitness components and soccer-specific skills were associated with maturity only in the under-15 category.


#11 Analysis of pain threshold and tolerance of super league soccer players
Reference: Sports Medicine Journal / Medicina Sportivâ 2014, Vol. 10 Issue 1, p2271 5p.
Authors: Lokmaoğlu R, Yağcı N, Cavlak U.
Summary: The aim of this study is to measure pain threshold and pain tolerance in male soccer players playing in super league and to compare with sedentary healthy male subjects. Materials and Methods. Thirty-seven male soccer players playing in Denizlispor Club aged 19-32 years an twenty-four sedentary healthy male subjects were included in this study. Pain threshold and pain tolerance were measured from both right and left side upper and lower extremities. In this study, it was used experimental pain by electrical stimulation to measure pain threshold and tolerance. Body Mass Index (BMI) score was calculated for each subject. Results. Pain threshold values of the soccer players were found to be lower than sedentary subjects, pain tolerance of the soccer players was found to be higher than sedentary subjects (p=0.0001). Conclusion. The results obtained from this study indicate that soccer players had lower pain threshold compared with sedentary subjects; however, pain tolerance of the soccer players was higher.