Latest research in football - week 44 - 2014

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Multilevel Development Models of Explosive Leg Power in High-Level Soccer Players
Reference: Med Sci Sports Exerc. 2014 Oct 9. [Epub ahead of print]
Authors: Deprez D, Valente-Dos-Santos J, Silva MJ, Lenoir M, Philippaerts R, Vaeyens R.
Summary: The aim of the present study was to model developmental changes in explosive power based on the contribution of chronological age, anthropometrical characteristics, motor coordination parameters and flexibility. Two different longitudinal, multilevel models were obtained to predict countermovement jump (CMJ) and standing broad jump (SBJ) performance in 356 high-level, youth soccer players, aged 11 to 14 years at baseline. Biological maturity status was estimated (age at peak height velocity, APHV) and variation in the development of explosive power was examined based on three maturity groups (APHV; earliest<P33, P33<average<P66, latest>P66). The best fitting model for the CMJ performance of the latest maturing players could be expressed as: 8.65 + 1.04 x age + 0.17 x age + 0.15 x leg length + 0.12 x fat-free mass + 0.07 x sit-and-reach + 0.01 x moving sideways. The best models for average and earliest maturing players were the same as for the latest maturing players, minus 0.73 and 1.74 cm, respectively. The best fitting model on the SBJ performance could be expressed as follows: 102.97 + 2.24 x age + 0.55 x leg length + 0.66 x fat-free mass + 0.16 x sit-and-reach + 0.13 jumping sideways. Maturity groups had a negligible effect on SBJ performance. These findings suggest that different jumping protocols (vertical vs. long jump) highlight the need for special attention in the evaluation of jump performance. Both protocols emphasized growth, muscularity, flexibility and motor coordination as longitudinal predictors. The use of the SBJ is recommended in youth soccer identification and selection programs, as biological maturity status has no impact on its development through puberty.

#2 Changes in hydration, body-cell mass and endurance performance of professional soccer players through a competitive season
Reference: J Sports Med Phys Fitness. 2014 Oct 10. [Epub ahead of print]
Authors: Mascherini G, Gatterer H, Lukaski H, Burtscher M, Galanti G.
Summary: The purpose was to determine changes of the bioelectrical impedance vector (BIVA) throughout a soccer season and to ascertain whether vector changes are associated with endurance performance changes. Eighteen professional male soccer players (age = 21.8±3.0 yr, height = 1.8±0.07 m, mass =7.2±6.5 kg) participated in the study. BIVA was conducted serially on 8 occasions throughout one soccer season. Endurance performance (Yo--Yo test) was assessed before the first training session of the pre--season training, after the pre--season training and at the end of the season. Vector length shortened (p<0.05) during pre--season training and was associated with improvements in endurance performance (r=0.569, p=0.034). Vector length and phase--angle increased at mid--season compared to post pre--season training (p<0.05). Vector length at end--season was lower compared to mid--season (p<0.05). No further changes in endurance performance occurred. Bioimpedance vector variations from baseline indicate that fluid--gains occur during the pre--season training, possibly due to plasma volume expansion and enhanced glycogen storage, accompanied by improvements in endurance performance. The vector migration and the increase in phase angle during the competitive season indicate fluid--loss and an increase in body cell mass without effects on performance. At the very end of the season, when training volume and intensity are reduced, body fluid increases again.

#3 Evaluation of the Zachery Lystedt Law among female youth soccer players
Reference: Phys Sportsmed. 2014 Sep;42(3):39-44. doi: 10.3810/psm.2014.09.2074.
Authors: O'Kane JW, Levy MR, Neradilek M, Polissar NL, Schiff MA.
Summary: Despite recent increased awareness about sports concussions, few studies have evaluated the effect of concussion laws on concussion outcomes among young athletes. The purpose of our study was to evaluate the effect of the Washington State Zachery Lystedt Concussion Law on playing with concussion symptoms and being evaluated by a health care provider. We performed a prospective cohort study of 351 elite female soccer players, aged 12 to 15 years, from 33 randomly selected youth soccer teams in the Puget Sound region of Washington State from 2008 to 2012. The Washington State Zachery Lystedt Concussion Law went into effect on July 1, 2009. Among concussed players (N = 59), we assessed the risk of playing with symptoms, the evaluation by a health care professional, and receiving a concussion diagnosis before and after the law was passed using logistic regression to estimate odds ratios and 95% CIs. The majority of concussed players (59.3%) continued to play with symptoms, and we found no statistically significant difference in the proportion of players who played with symptoms before and after the law was passed. Only 44.1% of concussed players were evaluated by a health care provider, with no difference before and after the law was passed. Among those evaluated by a health care professional, players were 2.1-fold (95% CI, 1.0-10.1) more likely to receive a concussion diagnosis after the law was passed. The majority of concussed female youth soccer players report playing with symptoms. Legislation mandating concussion education and evaluation prior to returning to play was not associated with an increase in concussion evaluations by health care providers.

#5 The Effect of Different Environmental Conditions on the Decision-making Performance of Soccer Goal Line Officials
Reference: Res Sports Med. 2014;22(4):425-37. doi: 10.1080/15438627.2014.948624.
Authors: Watkins SL, Castle P, Mauger AR, Sculthorpe N, Fitch N, Aldous J, Brewer J, Midgley AW, Taylor L.
Summary: Goal line officials (GLO) are exposed to extreme environmental conditions when employed to officiate in professional European soccer cup competitions. The present study aimed to investigate the effect of such environments on GLO decision-making ability. Thirteen male participants were exposed to three conditions: cold (-5°C, 50% relative humidity (RH)); temperate (18°C, 50% RH); and hot (30°C, 50% RH) for 90 min per condition, with a 15 min half-time break after 45 min. Decision-making ability was assessed throughout the 90 min exposure. Core and skin temperatures were recorded throughout. Decision making was improved during exposure to the temperate condition when compared with the cold (mean difference = 12.5%; 95% CI = 1.1%, 23.9%; P = 0.031). Regression analysis indicated that as skin temperature increases so does decision-making ability. Exposure to cold conditions diminished the decision-making ability of GLO.

#6 Physical growth and changes in intermittent endurance run performance in young male basque soccer players
Reference: Res Sports Med. 2014;22(4):408-24. doi: 10.1080/15438627.2014.944301.
Authors: Carvalho HM, Bidaurrazaga-Letona I, Lekue JA, Amado M, Figueiredo AJ, Gil SM.
Summary: The present 4-year longitudinal study examined physical growth and development of intermittent endurance run performance in young Basque soccer players aged 10-15 years applying multilevel regression modeling. Anthropometry, predicted adult stature and Yo-Yo Intermittent Recovery level 1 test (Yo-Yo IR1) of players from the under-11 teams from the Athletic Club of Bilbao were measured at pre- and end-season (two measurements per year of study, n = 33 considered for analysis). A non-linear effect of age on intermittent endurance run was observed, with significantly higher increases in Yo-Yo IR1 between 10-11 year-old and 14-15 year-old players. The development of Yo-Yo IR1 performance in all the years of the study was influenced positively by training exposure during the seasons (P < 0.01) and independent of maturity status and body size (P > 0.05). The steady development of intermittent endurance run performance during pubertal years in adolescent Basque soccer players is partially influenced by training exposure.

#7 The Biological Age of 14-year-old Boys and Success in Adult Soccer: Do Early Maturers Predominate in the Top-level Game?
Reference: Res Sports Med. 2014;22(4):398-407. doi: 10.1080/15438627.2014.944303.
Authors: Ostojic SM, Castagna C, Calleja-González J, Jukic I, Idrizovic K, Stojanovic M.
Summary: Talent identification and development in soccer is often biased by maturation-related differences of young athletes. However, there is no information available about success rates for youth maturing at different tempos to achieve success in elite adult soccer. The purposes of this study were to determine the prevalence of different maturational groups among boys playing soccer, and to track them for competence in adult performance. A prospective cohort study design was used to follow 55, 14-year-old boys playing in Serbian youth soccer Division I over eight years. At the age of 14, biological age using skeletal age rates was determined, and participants were categorized as early maturers (EaM), normal maturers (NoM), and late maturers (LaM). Game competence for adult soccer at age 22 was described as elite if an individual played for clubs competing in top-five international soccer leagues (La Liga, Premier League, Bundesliga, Serie A, and Ligue 1), and/or has become a member of an adult National team. Among boys in our study group, 43.8% were categorized as EaM, 35.4% as NoM, and 20.8% as LaM (P = 0.11). A significant difference in biological age was found among maturational groups at age 14, with EaM > NoM > LaM (P > 0.0001). When assessed for adult soccer competence, 33.3% of participants (16 out of 48 players) succeed in achieving elite level. Elite soccer competence acquired 60.1% players from the group of LaM, 38.1% from NoM, and 11.8% from EaM (P > 0.0001). Our comparative analysis suggests that soccer excludes early maturing boys and favors late maturing boys as level of performance increases.

#8 Acute Effects of the Number of Players and Scoring Method on Physiological, Physical, and Technical Performance in Small-sided Soccer Games
Reference: Res Sports Med. 2014;22(4):380-97. doi: 10.1080/15438627.2014.951761.
Authors: Clemente FM, Wong del P, Martins FM, Mendes RS.
Summary: This study aims to examine the effect of differences in the number of players and scoring method on heart rate responses, time-motion characteristics, and technical/tactical performance during small-sided soccer games. Ten male amateur soccer players (26.4 ± 5.3 years old, 8.4 ± 3.2 years of practice, 179.3 ± 5.2 cm body height, 71.2 ± 7.1 kg body weight, 45.8 ± 2.6 from the Portuguese regional league played nine different small-sided games (i.e., 3 formats × 3 scoring methods). The study used two-way MANOVA, two-away ANOVA, and one-way ANOVA, depending on the specific procedure for the analysis. Compared with other formats, 2v2 induced significantly greater values of technical/tactical indexes (p = 0.001), 3v3 induced significantly higher %HRreserve values (p = 0.001), and 4v4 led to significantly greater distance coverage and speed (p = 0.001). The study provided evidence for coaches to set different small-sided game conditions depending on the training purpose in terms of physiological, physical, and technical performance.

#9 Soccer-specific Fatigue Decreases Reactive Postural Control with Implications for Ankle Sprain Injury
Reference: Res Sports Med. 2014;22(4):368-79. doi: 10.1080/15438627.2014.944300.
Authors: Greig M, McNaughton L.
Summary: The purpose of the study was to quantify the influence of soccer-specific fatigue on reactive dynamic balance, ten male professional soccer players (age 24.7 ± 4.4 yr, body mass 77.1 ± 8.3 kg, VO2max 63.0 ± 4.8 ml·kg·min(-1)) completed an exercise protocol replicating the activity profile of match-play. Pre-exercise, and at 15 min intervals, players completed three balance tasks requiring response to a system perturbed to induce either plantar flexion of the ankle or inversion of the ankle (by rotation or translation). ANOVA revealed a significant main effect for exercise duration in each task, with both reaction time and total centre of gravity displacement tending to increase during each half. In all three trials there was a significant increase in medio-lateral and anterior-posterior displacement, the planar perturbation of the platform evoking a multi-angular response. Dynamic balance performance decreased as a function of time during each half, suggesting a greater risk of injuries at these specific times, in accord with epidemiological observations of ankle sprain injury.

#10 Characterization of static balance abilities in elite soccer players by playing position and age
Reference: Res Sports Med. 2014;22(4):355-67. doi: 10.1080/15438627.2014.944302.
Authors: Pau M, Ibba G, Leban B, Scorcu M.
Summary: In this study, we investigated the static balance of adult and adolescent elite soccer players to understand how expertise and playing position influence postural control. Seventy-one national level players were tested using a force platform to acquire Center-of-Pressure (COP) data in uni- and bipedal stance and calculate sway area (SA), COP path length, velocity and displacements. The results show significant differences in postural sway related to age and playing position only for single-limb stance. In particular, midfielders exhibited significantly lower values of SA with respect to defenders (-48%, p = 0.001) and the under-15 players exhibited SA 42-64% higher than all the others (p = 0.001). In the light of planning training or rehabilitation programs specific for each player's role and age, sway measurements may supply useful, objective and reliable information only for the unipedal test as the bipedal standing appears not challenging enough to let differences in balance abilities emerge.

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