Latest research in football - week 49 - 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 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 ml.kg(-1)min(-1)VO2max) 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.

#2 Caffeine supplementation and reactive agility in elite youth soccer players
Reference: Pediatr Exerc Sci. 2014 May;26(2):168-76. doi: 10.1123/pes.2013-0134. Epub 2013 Nov 25.
Authors: Jordan JB, Korgaokar A, Farley RS, Coons JM, Caputo JL
Summary: This study examined the effects of caffeine supplementation (6 mg·kg-1) on performance of a reactive agility test (RAT) in 17 elite, male, youth (M = 14 y) soccer players. Using a double-blind, repeated-measures design, players completed 4 days of testing on the RAT after a standardized warm-up. On day 1, anthropometric measurements were taken and players were accommodated to the RAT. On day 2, baseline performance was established. Caffeine or placebo conditions were randomly assigned on day 3 and the condition was reversed on day 4. Players completed 3 randomized trials of the RAT on days 2, 3, and 4 with at least 1 trial to the players' dominant and nondominant sides. There were no significant differences among conditions in reaction time (RT) to the dominant side, heart rates at any point of measurement, or ratings of perceived exertion (RPE) after completion of the warm-up. Caffeine produced faster RT to the nondominant side (P = .041) and higher RPE at the conclusion of the RAT (P = .013). The effect on the total time (TT) to complete the agility test to the nondominant side approached significance (P = .051). Sprint time and TT to either side did not differ. Caffeine supplementation may provide ergogenic benefit to elite, male, youth soccer players.

#3 Talent identification and selection process of outfield players and goalkeepers in a professional soccer club
Reference: J Sports Sci. 2014 Nov 28:1-9. [Epub ahead of print]
Authors: Gil SM, Zabala-Lili J, Bidaurrazaga-Letona I, Aduna B, Lekue JA, Santos-Concejero J, Granados C.
Summary: The aim of this study was to analyse the talent identification process of a professional soccer club. A preselection of players (n = 64) aged 9-10 years and a final selection (n = 21) were performed by the technical staff through the observation during training sessions and matches. Also, 34 age-matched players of an open soccer camp (CampP) acted as controls. All participants underwent anthropometric, maturity and performance measurements. Preselected outfield players (OFs) were older and leaner than CampP (P < 0.05). Besides, they performed better in velocity, agility, endurance and jump tests (P < 0.05). A discriminant analysis showed that velocity and agility were the most important parameters. Finally, selected OFs were older and displayed better agility and endurance compared to the nonselected OFs (P < 0.05). Goalkeepers (GKs) were taller and heavier and had more body fat than OFs; also, they performed worse in the physical tests (P < 0.05). Finally, selected GKs were older and taller, had a higher predicted height and advanced maturity and performed better in the handgrip (dynamometry) and jump tests (P < 0.05). Thus, the technical staff selected OFs with a particular anthropometry and best performance, particularly agility and endurance, while GKs had a different profile. Moreover, chronological age had an important role in the whole selection process.

#4 Longitudinal Field Test Assessment in a Basque Soccer Youth Academy: A Multilevel Modeling Framework to Partition Effects of Maturation
Reference: Int J Sports Med. 2014 Nov 27. [Epub ahead of print]
Authors: Bidaurrazaga-Letona I, Carvalho HM, Lekue JA, Santos-Concejero J, Figueiredo AJ, Gil SM
Summary: The purpose of the study was to examine the effect of age on short-term performance indicators applying multilevel regression modeling, and whether changes induced by age were affected by maturation. The study applied a mixed longitudinal approach with 8 measurement points over a period of 4 years. Anthropometry, predicted adult stature, countermovement jump, 15-m sprint and agility test from 38 under-11 young soccer players were considered. Early maturing players were 3% taller compared to late maturers. A substantial effect of age was present in all performance indicators (P<0.05). Parameters showed improvements in performance, even when accounting for interindividual variation in somatic maturity. Vertical jump tended to be stable in early maturers during the first year, presenting an exponential increase thereafter (16%, P<0.05). Additionally, early maturing boys had lower vertical jump scores but a substantial higher rate of development with age (3% per year). Performance tends to plateau during the first 3 years following the improvements in agility (9.1%, P<0.05). In the running tests, early maturers had better performances (19%, P<0.05), while a higher rate of improvement of 1% was observed for the late maturers. Young soccer players should be expected to have substantial improvements in short-term performance, influenced by independent variation between players in maturity status.

#5 Hamstrings strength imbalance in professional football (soccer) players in Australia
Reference: J Strength Cond Res. 2014 Nov 25. [Epub ahead of print]
Authors: Ardern CL, Pizzari T, Wollin M, Webster KE
Summary: The aim of this study was to describe the isokinetic thigh muscle strength profile of professional male football players in Australia. Concentric (60° and 240°/second) and eccentric (30° and 120°/second) hamstrings and quadriceps isokinetic strength was measured with a HUMAC NORM dynamometer. The primary variables were bilateral concentric and eccentric hamstring and quadriceps peak torque ratios, concentric hamstring-quadriceps peak torque ratios, and mixed ratios (eccentric hamstring 30°/second ÷ concentric quadriceps 240°/second). Hamstring strength imbalance was defined as deficits in any two of: bilateral concentric hamstring peak torque ratio < 0.86, bilateral eccentric hamstring peak torque ratio < 0.86, concentric hamstring-quadriceps ratio < 0.47, mixed ratio < 0.80. Fifty-five strength tests involving 42 players were conducted. Ten players (24%) were identified as having hamstring strength imbalance. Athletes with strength imbalance had significantly reduced concentric and eccentric bilateral hamstring peak torque ratios at all angular velocities tested; and reduced eccentric quadriceps peak torque (30°/second) in their stance leg, compared to those without strength imbalance. Approximately one in four players had preseason hamstring strength imbalance; and all strength deficits were observed in the stance leg. Concentric and eccentric hamstrings strength imbalance may impact in-season football performance, and could have implications for the future risk of injury.

#6 Post-effort chances in C-reactive protein level among soccer players at the end of the training season
Reference: J Strength Cond Res. 2014 Nov 25. [Epub ahead of print]
Authors: Kostrzewa-Nowak D, Nowak R, Chamera T, Buryta R, Moska W, Cięszczyk P.
Summary: Numerous literature data point out the differences in immunological parameters as a result of physical effort and the relation of those changes to the subject's fitness level.This study was aimed at the assessment of soccer players' condition and adaptation to physical effort based on the changes in C-reactive protein (CRP) blood level.CRP, total protein and albumin plasma levels before and after 60-minute-long outdoor were determined among sixteen (8 men and 8 women) soccer players.Statistically significant increase in total blood protein level was observed in both studied groups. However, there were no statistically significant changes in albumin level in soccer players' blood. Determination of CRP showed that the exercise test caused changes in its level among both women and men, yet statistically significant increase in CRP level was found only in women's blood.The different influence of effort on CRP plasma level may be explained by the involvement of various mechanisms in regulation of acute phase responses in different conditions. It was found in our study that CRP level could be a valuable tool to assess the metabolic response to aerobic exercise.

#7 Core temperature changes and sprint performance of elite female soccer players after a 15-minute warm-up in a hot-humid environment
Reference: J Strength Cond Res. 2014 Nov 25. [Epub ahead of print]
Authors: Somboonwong J, Chutimakul L, Sanguanrungsirikul S.
Summary: Warm-up session should be modified according to the environmental conditions. However, there is limited evidence regarding the proper soccer warm-up time for female players in the heat. The purpose of the present study was to examine the rise in core body temperature and the sprint performance after a 15-minute warm-up in a hot-humid environment using female soccer players during different phases of their menstrual cycle. Thirteen eumenorrheic national female soccer players (aged 18.8±1.3years, VO2max53.05±6.66 mL·kg·min) performed a 15-minute warm-up protocol at an ambient temperature of 32.5±1.6C with a relative humidity of 53.6±10.2% during their early follicular and mid-luteal phases of their cycle. The warm-up protocol is composed of jogging, skipping by moving the legs in various directions, and sprinting alternated with jogging, followed by a 45-minute recovery period. Rectal temperatures were recorded during the rest period and every 5 minutes throughout the warm-up and recovery phases of the study. Heart rate was monitored at rest and every 5 minutes during warm-up. Forty-yard sprint time was assessed immediately after the completion of warm-up which was later compared to the time at baseline. The value for the baseline was obtained at least 2 days prior to the experiment. During the early follicular and mid-luteal phases, the rectal temperatures obtained at the end of the warm-up period were significantly (P<0.05) higher by 1.26C (95% CI = +0.46 to +2.06C) and 1.18 C (95% CI = +0.53 to +1.83C) whereas the heart rates increased to 153.67±20.34 and 158.38±15.19 beats per mins, respectively. After 20 minutes of the recovery period, the rectal temperature decreased by approximately 50%. The sprint times were significantly (P<0.05) faster post-warm-up during both the early follicular (5.52 s; 95% CI = 5.43-5.60 s) and mid-luteal phases (5.51 s; 95% CI = 5.41-5.60 s) compared to the baseline time (5.66 s; 95% CI = 5.58-5.74 s). There were no significant differences in any parameters assessed following warm-up between the two phases. In conclusion, a 15-minute warm-up increased the core temperature by approximately 1C and improved the 40-yard sprint time for elite female soccer players in a hot environment regardless of menstrual phase.

#8 Effect of psychological skill training as a psychological intervention for a successful rehabilitation of a professional soccer player: single case study
Reference: J Exerc Rehabil. 2014 Oct 31;10(5):295-301. eCollection 2014.
Authors: Yoon I, Yoon YJ
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4237845/pdf/jer-10-5-295.pdf
Summary: The purpose of this study is developing and applying psychological skill training (PST) program as one of the methods of intervention for psychological rehabilitation in order for a successful recovery of the professional soccer player (K). He is currently on rehabilitation training after an injury, and we tried to see the results of this program. It was designed as a program of 17 sessions including 3 interviews and diagnostic checks (psychological skill questionnaire: PSQ, profiles of mood states: POMS) and 14 sessions of PST (goal setting, anxiety reduction, concentration, confidence). After the application of the program, the levels of anxiety reduction, goal setting, concentration, and confidence were visibly increased, and in POMS, which is an indicator of physical rehabilitation process of K, vigor was increased. Meanwhile negative emotions, such as tension, depression, and fatigue were decreased. This program was developed for K, and therefore it has some difficulties in applying it to other players. However, the significance of this study is that it could serve as a basis on developing programs for other players in the rehabilitation process. In addition, it has also proven that PST can be used as a successful method for psychological rehabilitation intervention.

#9 Dynamic peripheral visual performance relates to alpha activity in soccer players
Reference: Front Hum Neurosci. 2014 Nov 11;8:913. eCollection 2014.
Authors: Nan W, Migotina D, Wan F, Lou CI, Rodrigues J, Semedo J, Vai MI, Pereira JG, Melicio F, Da Rosa AC
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4227514/pdf/fnhum-08-00913.pdf
Summary: Many studies have demonstrated the relationship between the alpha activity and the central visual ability, in which the visual ability is usually assessed through static stimuli. Besides static circumstance, however in the real environment there are often dynamic changes and the peripheral visual ability in a dynamic environment (i.e., dynamic peripheral visual ability) is important for all people. So far, no work has reported whether there is a relationship between the dynamic peripheral visual ability and the alpha activity. Thus, the objective of this study was to investigate their relationship. Sixty-two soccer players performed a newly designed peripheral vision task in which the visual stimuli were dynamic, while their EEG signals were recorded from Cz, O1, and O2 locations. The relationship between the dynamic peripheral visual performance and the alpha activity was examined by the percentage-bend correlation test. The results indicated no significant correlation between the dynamic peripheral visual performance and the alpha amplitudes in the eyes-open and eyes-closed resting condition. However, it was not the case for the alpha activity during the peripheral vision task: the dynamic peripheral visual performance showed significant positive inter-individual correlations with the amplitudes in the alpha band (8-12 Hz) and the individual alpha band (IAB) during the peripheral vision task. A potential application of this finding is to improve the dynamic peripheral visual performance by up-regulating alpha activity using neuromodulation techniques.

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