Latest research in football - week 28 - 2014

#1 Long-term Soccer-specific Training Enhances the Rate of Physical Development of Academy Soccer Players Independent of Maturation Status
Reference: Int J Sports Med. 2014 Jul 10. [Epub ahead of print]
Authors: Wrigley RD, Drust B, Stratton G, Atkinson G, Gregson W.
Summary: The aim of the study was to compare 3-year changes in physical performance between junior soccer players selected for an elite academy and age-matched controls. The 3-year changes in indicators of the physical performance were quantified in 12-16-year-old Premier League Academy (n=27) and non-academy soccer players (n=18). Data were analysed with an age-group×competitive level general linear model, covariate-adjusted for initial performance level and change in maturation. Covariate adjusted mean±SD changes were greater (standardised effect size>0.7) for the academy players in terms of countermovement jump (7.3±2.6 vs. 5.4±2.5 cm), 10 m sprint (- 0.15±0.05 vs. - 0.10±0.04 s), 20 m sprint (- 0.30±0.16 s vs. - 0.15±0.13 s), agility (- 0.19±0.01 s vs. - 0.08±0.08 s), repeated sprint (- 0.60±0.26 s vs. - 0.41±2.1 s) and intermittent endurance capacity (1 128±406 vs. 315±370 m). These data indicate that a 3-year programme of training in an elite soccer academy is associated with greater changes in physical performance indicators independently from the initial performance level of the child and change in maturation over the same period of time.


#2 Acute responses of soccer match play on hip strength and flexibility measures: potential measure of injury risk
Reference: J Sports Sci. 2014 Jul;32(13):1318-23. doi: 10.1080/02640414.2014.927069.
Authors: Paul DJ, Nassis GP, Whiteley R, Marques JB, Kenneally D, Chalabi H.
Summary: Regular measurements of groin risk factors may offer a preventive measure against injury. Therefore, the aim of this study was to (1) determine minimal detectable change (MDC) and reliability of hip flexibility and strength measures and to (2) identify the effect soccer match play load has on these measures. Reliability was determined for bent knee fall out test, hip abduction and adduction (hand-held dynamometry (HHD)) in 20 trained youth male soccer players. Reliability was evaluated with the intra-class correlation coefficient (ICC[2,1]), 95% confidence intervals (CI). Hip strength and flexibility measures were taken before and after an international friendly match. Intra-rater reliability ICC ranges were bent knee fall out (0.75-0.90), abduction (0.83-0.90) and adduction (0.72-0.96). Inter-rater ICCs (95% CI) were bent knee fall out test [0.75 (0.39-0.90) right, 0.71 (0.27-0.89) left hip]; abduction [0.80 (0.50-0.92) right, 0.81 (0.53-0.92) left hip] and adduction [0.72 (0.31-0.89) right, 0.70 (0.26-0.88) left hip]. MDCs were as low as 20.7% of the mean for hip flexibility and 12.5% for strength. In conclusion, HHD and the bent knee fall out test are reliable tools to measure changes in hip strength and flexibility. Finally, a threshold may exist in which match play load negatively impacts hip flexibility.


#3 Acute effects of two different initial heart rates on testing the Repeated Sprint Ability in young soccer players
Reference: J Sports Med Phys Fitness. 2014 Jul 7. [Epub ahead of print]
Authors: Ruscello B, Briotti G, Tozzo N, Partipilo F, Taraborelli M, Zeppetella A, Padulo J, D'Ottavio S.
Summary: The purpose was to investigate the acute effects of two different initial heart rates intensities when testing the repeated sprint ability (RSA) performances in young soccer players. Since there are many kinds of pre--match warm--ups, we chose to take as an absolute indicator of internal load the heart rate reached at the end of two different warm--up protocols (~90 vs. ≈60% HRmax) and to compare the respective RSA performances. The RSA tests were performed on fifteen male soccer players (Age: 17.9±1.5 yrs) with two sets of ten shuttle--sprints (15+15m) with a 1:3 exercise to rest ratio, in different days (randomized order) with different HR% (60 & 90% HRmax). In order to compare the different sprint performances a Fatigue Index (FI%) was computed, while the blood lactate concentrations (BLa--) were measured before and after testing, to compare metabolic energy. Significant differences among trials within each sets (P<0.01) were found. Differences between sets were also found, especially comparing the last five trials for each set (Factorial ANOVA;; P<0.01), effect size values confirming the relevance of these differences. Although the BLa-- after warm--up was higher (36%) between 90% vs. 60% HRmax, after the RSA test the differences were considerably low (7%). Based on physiological information's this methodological approach (testing with initial 90%HRmax) reflects more realistically the metabolic background in which a soccer player operates during a real match. This background may be partially reproduced by warming up protocols that, by duration and metabolic commitment, can reproduce conveniently the physiological conditions encountered in a real game (e.g. HRmax≈85--95%; BLa--> 4 mmol/L).


#4 Characteristics of high-level youth soccer players: variation by playing position
Reference: J Sports Sci. 2014 Jul 7:1-12. [Epub ahead of print]
Authors: Deprez D, Fransen J, Boone J, Lenoir M, Philippaerts R, Vaeyens R.
Author information
Summary:  The present study aimed to investigate positional differences in 744 high-level soccer players, aged 8 to 18 years. Players were assigned to six age groups (U9-U19) and divided into four playing positions (goalkeeper (GK), defender (DEF), midfielder (MF) and attacker (ATT)). MANOVA and effect sizes were used to examine anthropometrical and functional characteristics between all positions in all age groups. The main findings of the study were that GKs and DEFs were the tallest and heaviest compared with MFs and ATTs in all age groups. Further, between U9-U15, no significant differences in functional characteristics were found, except for dribbling skill, which MFs performed the best. In the U17-U19 age groups, ATTs seemed to be the most explosive (with GKs), the fastest and the more agile field players. These results suggest that inherent physical capacities (i.e., speed, power, agility) might select players in or reject players from an attacking position, which is still possible from U15-U17. Apparently, players with excellent dribbling skills at younger age are more likely to be selected to play as a MF, although, one might conclude that the typical physical characteristics for different positions at senior level are not yet fully developed among young soccer players between 8 and 14 years.


#5 Vitamin d and exercise performance in professional soccer players
Reference: PLoS One. 2014 Jul 3;9(7):e101659. doi: 10.1371/journal.pone.0101659. eCollection 2014.
Authors: Koundourakis NE, Androulakis NE, Malliaraki N, Margioris AN
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4081585/pdf/pone.0101659.pdf
Summary: The current study had two aims. The primary purpose was to examine the association between serum vitamin D levels and the ergometric evaluation of muscle strength, aerobic capacity, and speed in professional soccer players. The secondary aim was to evaluate the effects of the soccer off-season period on serum vitamin D levels. Sixty-seven Caucasian male soccer players (age 25.6±6.2 and height 1.81±0.08 m), members of two Greek Superleague Soccer teams and one Football-league championship team participated in this study. Exercise performance testing for the determination of squat jump (SJ), countermovement jump (CMJ), 10 (10 m) and 20 meters (20 m) sprint performance, maximal oxygen consumption (VO2max), anthropometry, and blood sampling were performed before (pre) and after (post) the six-week off-season period. Analysis of our results showed the following: (a) a significant correlations between serum vitamin D levels and performance parameters in both pre (SJ; P<0.001, CMJ; P<0.001, VO2max; P<0.001, 10 m; P<0.001, and 20 m; P<0.001) and post (SJ; P<0.001, CMJ; P<0.001, VO2max; P = 0.006, 10 m; P<0.001, and 20 m; P<0.001) experimental sessions. (b) Vitamin D concentration increased significantly (P<0.001) following the six-week off-season period compared to baseline, while at the same time all measured performance parameters decreased (SJ; P<0.001, CMJ; P<0.001, 10 m; P<0.001, 20 m; P<0.001, VO2max; P<0.001). Our findings suggest that vitamin D levels are associated with the ergometric evaluation of muscle strength, as expressed by SJ and CMJ, sprinting capacity, and VO2max in professional soccer players, irrespective the levels of performance. Furthermore, our data reaffirm the importance of UVB on serum vitamin D levels. Moreover, reductions in exercise training stress may also have beneficial effects on vitamin D levels, suggesting a possible association of its levels and the training-induced stress. Our results indicate a possibly bidirectional interaction between soccer performance indices and vitamin D levels.


#6 Creatine monohydrate supplementation on lower-limb muscle power in Brazilian elite soccer players
Reference: J Int Soc Sports Nutr. 2014 Jun 18;11:32. doi: 10.1186/1550-2783-11-32. eCollection 2014.
Authors: Claudino JG, Mezêncio B, Amaral S, Zanetti V, Benatti F, Roschel H, Gualano B, Amadio AC, Serrão JC
Summary: Studies involving chronic creatine supplementation in elite soccer players are scarce. Therefore, the aim of this study was to examine the effects of creatine monohydrate supplementation on lower-limb muscle power in Brazilian elite soccer players (n = 14 males) during pre-season training. This was a randomized, double-blind, placebo-controlled parallel-group study. Brazilian professional elite soccer players participated in this study. During the pre-season (7 weeks), all the subjects underwent a standardized physical and specific soccer training. Prior to and after either creatine monohydrate or placebo supplementation, the lower-limb muscle power was measured by countermovement jump performance. The Jumping performance was compared between groups at baseline (p = 0.99). After the intervention, jumping performance was lower in the placebo group (percent change = - 0.7%; ES = - 0.3) than in the creatine group (percent change = + 2.4%; ES = + 0.1), but it did not reach statistical significance (p = 0.23 for time x group interaction). Fisher's exact test revealed that the proportion of subjects that experienced a reduction in jumping performance was significantly greater in the placebo group than in the creatine group (5 and 1, respectively; p = 0.05) after the training. The magnitude-based inferences demonstrated that placebo resulted in a possible negative effect (50%) in jumping performance, whereas creatine supplementation led to a very likely trivial effect (96%) in jumping performance in the creatine group.


#7 Increase in upper extremity fractures in young male soccer players in the Netherlands, 1998-2009
Reference: Scand J Med Sci Sports. 2014 Jul 2. doi: 10.1111/sms.12287. [Epub ahead of print]
Authors: de Putter CE, van Beeck EF, Burdorf A, Borsboom GJ, Toet H, Hovius SE, Selles RW.
Summary: Young male soccer players have been identified as a target group for injury prevention, but studies addressing trends and determinants of injuries within this group are scarce. The goal of this study was to analyze age-specific trends in hospital-treated upper extremity fractures (UEF) among boys playing soccer in the Netherlands and to explore associated soccer-related factors. Data were obtained from a national database for the period 1998-2009. Rates were expressed as the annual number of UEF per 1000 soccer players. Poisson's regression was used to explore the association of UEF with the number of artificial turf fields and the number of injuries by physical contact. UEF rates increased significantly by 19.4% in boys 5-10 years, 73.2% in boys 11-14 years, and 38.8% in boys 15-18 years old. The number of injuries by physical contact showed a significant univariate association with UEF in boys 15-18 years old. The number of artificial turf fields showed a significant univariate association with UEF in all age groups, and remained significant for boys aged 15-18 years in a multivariate model. This study showed an increase of UEF rates in boys playing soccer, and an independent association between artificial turf fields and UEF in the oldest boys.


#8 High Injury Incidence in Adolescent Female Soccer
Reference: Am J Sports Med. 2014 Jul 2. pii: 0363546514541224. [Epub ahead of print]
Authors: Clausen MB, Zebis MK, Møller M, Krustrup P, Hölmich P, Wedderkopp N, Andersen LL, Christensen KB, Thorborg K
Summary: Previous studies report varying rates of time-loss injuries in adolescent female soccer, ranging from 2.4 to 5.3 per 1000 athlete-exposures or 2.5 to 3.7 per 1000 hours of exposure. However, these studies collected data using traditional injury reports from coaches or medical staff, with methods that significantly underestimate injury rates compared with players' self-reports. The primary aim was to investigate the injury incidence in adolescent female soccer using self-reports via mobile telephone text messaging. The secondary aim was to explore the association between soccer exposure, playing level, and injury risk. During a full adolescent female soccer season in Denmark (February-June 2012), a population-based sample of 498 girls aged 15 to 18 years was included in the prospective registration of injuries. All players were enrolled on a team participating in Danish Football Association series. Soccer injuries and exposure were reported weekly by answers to standardized text message questions, followed by individual injury interviews. Soccer exposure and playing levels were chosen a priori as the only independent variables of interest in the risk factor analyses. Injury rates and relative risks were estimated using Poisson regression. Generalized estimation equations were used to take into account that players were clustered within teams. There were 498 players who sustained a total of 424 soccer injuries. The incidence of injuries was 15.3 (95% CI, 13.1-17.8), the incidence of time-loss injuries was 9.7 (95% CI, 8.2-11.4), and the incidence of severe injuries was 1.1 (95% CI, 0.7-1.6) per 1000 hours of soccer exposure. Higher average exposure in injury-free weeks was associated with a lower injury risk (P value for trend <.001), and players with low exposure (≤1 h/wk) were 3 to 10 times more likely to sustain a time-loss injury compared with other players (P < .01). Playing level was not associated with the risk of time-loss injuries (P = .18). The injury incidence in adolescent female soccer is high, and this includes many severe injuries. Players with low soccer participation (≤1 h/wk) have a significantly higher injury risk compared with players participating more frequently.


#9 Metabolomics of salivary fatigue markers in soccer players after consecutive games
Reference: Appl Physiol Nutr Metab. 2014 Jul 2:1-7. [Epub ahead of print]
Authors: Ra SG, Maeda S, Higashino R, Imai T, Miyakawa S.
Summary: Strenuous and consecutive exercise leads to fatigue symptoms in athletes. Metabolomics is a comprehensive method to assess metabolites that involves the measurements of the overall metabolic signature of biological samples. Using metabolomic analysis, we investigated the identification of salivary fatigue markers in soccer players after 3 consecutive days of a game program. One hundred twenty-two male soccer players participated in 3 consecutive days of a game program. To detect fatigued athletes, we measured indices of traditional fatigue symptoms, i.e., heart rate, body mass and mood, before and after the program. We detected 37 fatigued players throughout the program. Before and after the program, the saliva in these players was analyzed using capillary electrophoresis and time-of-flight mass spectrometry (CE-TOFMS) and a multivariate statistical technique, principal component analysis, was used to process the data. CE-TOFMS was used to identify 144 metabolites in the saliva of fatigued players. A significant metabolomic difference was observed before and after 3 consecutive days of a soccer game program. Interestingly, metabolites were all increased after the program (P < 0.001). The identified metabolites, including 3-methylhistidine, glucose 1- and 6-phosphate, taurine, and some amino acids, were involved in skeletal muscle catabolism, glucose metabolism, lipid metabolism, amino acid metabolism, and energy metabolism. Our work demonstrated some salivary metabolites were significantly increased in the fatigued players after consecutive days of short soccer matches. We propose that the detected salivary metabolites may be new fatigue markers in athletes.


#10 Acceleration and sprint profiles of a professional elite football team in match play
Reference: Eur J Sport Sci. 2014 Jul 8:1-10. [Epub ahead of print]
Authors: Ingebrigtsen J, Dalen T, Hjelde GH, Drust B, Wisløff U.
Summary: The aim of this study was to characterise the acceleration and sprint profiles of elite football match play in one Norwegian elite football team (Rosenborg FC). Fifteen professional players in five playing positions took part in the study (n = 101 observations). Player movement was recorded during every domestic home game of one full season (n = 15) by an automatic tracking system based on microwave technology. Each player performed 91 ± 21 accelerations per match, with a lower number in the second compared with the first half (47 ± 12 vs. 44 ± 12). Players in lateral positions accelerated more often compared to players in central positions (98.3 ± 20.5 vs. 85.3 ± 19.5, p < 0.05). Average sprint distance was 213 ± 111 m distributed between 16.6 ± 7.9 sprints, with no differences between first (106 ± 60 m, 8.2 ± 4.2 sprints) and second halves (107 ± 72 m, 8.3 ± 4.8 sprints). Players in lateral positions sprinted longer distances (287 ± 211 m vs. 160 ± 76 m, p < 0.05) and tended to sprint more often (21.6 ± 7.8 vs. 13.0 ± 5.7, p = 0.064) compared to players in central positions. We found more walking and less of the more intense activities during the last third of the season compared to the first. The main finding in this study was that Norwegian elite players had substantially less number of accelerations and fewer but longer sprints than previous studies reported for higher-ranked leagues. Also, less high-intensity activity was found towards the end of the season. Ultimately, these data provide useful information for the fitness coach (1) in planning of position-specific football training and (2) to avoid the decline in high-intensity activities the last third of the competitive season.


#11 Comments on Bruun, d.m. Et Al. Community-based recreational football: a novel approach to promote physical activity and quality of life in prostate cancer survivors
Reference: Int J Environ Res Public Health. 2014 Jul 2;11(7):6842-3. doi: 10.3390/ijerph110706842.
Authors: Parnell D, Pringle A, McKenna J, Zwolinsky S.
Download link: http://www.mdpi.com/1660-4601/11/7/6842


#12 First aid on field management in youth football
Reference: Arch Orthop Trauma Surg. 2014 Jul 2. [Epub ahead of print]
Authors: Krutsch W, Voss A, Gerling S, Grechenig S, Nerlich M, Angele P.
Summary: Sufficient first aid equipment is essential to treat injuries on football fields. Deficits in first aid on field are still present in youth football. Injury pattern in youth football over one season and first aid equipment in youth football were analyzed, retrospectively. PRICE and ABC procedure served as basic principles in emergency management to assess the need for first aid equipment on field. Considering financial limits and adapted on youth football injuries, sufficient first aid equipment for youth football was configured. 84 % of 73 participating youth football teams had their own first aid kit, but the majority of them were insufficiently equipped. Team coaches were in 60 % of all youth teams responsible for using first aid equipment. The injury evaluation presented 922 injuries to 1,778 youth players over one season. Frequently presented types of injury were contusions and sprains of the lower extremity. Based on the analyzed injury data in youth football, first aid equipment with 90 <euro> is sufficient for 100 % of all occurred youth football injuries. Current first aid equipment in youth football is insufficient. Scientific-based first aid equipment with 90 <euro> is adequate to serve all injuries. Football coaches need education in first aid management.


#13 Structural deformation of longitudinal arches during running in soccer players with medial tibial stress syndrome
Reference: Eur J Sport Sci. 2014 Jul 11:1-9. [Epub ahead of print]
Authors: Noh B, Masunari A, Akiyama K, Fukano M, Fukubayashi T, Miyakawa S.
Summary: The purpose of this study was to compare angular change and translational motion from the medial longitudinal arch (MLA) and lateral longitudinal arch (LLA) during running between medial tibial stress syndrome (MTSS) and non-MTSS subjects. A total of 10 subjects volunteered, comprising 5 subjects with MTSS and 5 subjects without injury (non-MTSS) as the control group. All subjects performed the test movement that simulated running. Fluoroscopic imaging was used to investigate bone movement during landing in running. Sagittal motion was defined as the angular change and translational motion of the arch. A Mann-Whitney U-test was performed to determine the differences in the measured values between the MTSS and non-MTSS groups. The magnitude of angular change for the MLA and LLA was significantly greater for subjects with MTSS than for control subjects. Translational motion of the MLA and LLA of the MTSS group was also significantly greater than that of the non-MTSS group (all p < 0.05). Soccer players with MTSS have an abnormal structural deformation of foot during support (or stance) phase of running, with a large decrease in both the MLA and LLA. This abnormal motion could be a risk factor for the development of MTSS in these subjects.