Latest research in football - week 33 - 2015

#1 Respiratory and Muscular Perceived Exertion During Official Games in Professional Soccer Players
Reference: Int J Sports Physiol Perform. 2015 Jul 27. [Epub ahead of print]
Authors: Los Arcos A, Méndez-Villanueva A, Yanci J, Martínez-Santos R
Summary: The aim of this study was to assess the respiratory and muscular sRPEs after official soccer matches over an extended period of time (i. e., two competition seasons) in relation to playing time (>20, 20-45, 45-70 and >70 min groups) and to determine the between-match variability of both scores in young professional soccer players. Forty players belonging to the same reserve team of a Spanish La Liga club participated in this study. Respiratory and muscular perceived exertion (PE) was collected 10 min after every game. A total of 841 individual PE ratings were undertaken on outfield players. The differences between match respiratory and muscular load differ depending on the playing time, being the respiratory PE greater for the players that competed less than 45 min (Effect Size = -.45 ± .45 for the 20-45 min group) and the muscular PE greater for players that played more than 45 min (Effect Size = .23 ± .30, for the 45-70 min group). Match-to-match PE variability was considerable (CV = 14-54%) for all the level of participation groups but it was lower the longer the players participated. Playing time influenced the relative exertion that players' respiratory and leg musculature were exposed during a game, suggesting that differential PE scores might provide a more accurate evaluation of match-imposed internal load. However, the small magnitude differences between sRPEmus and sRPEres observed in the present study might question the practical relevance of assessing both scores.


#2 Effects of a 12-day maximal shuttle-run shock microcycle in hypoxia on soccer specific performance and oxidative stress
Reference: Appl Physiol Nutr Metab. 2015 Apr 2:1-4. [Epub ahead of print]
Authors: Gatterer H, Klarod K, Heinrich D, Schlemmer P, Dilitz S, Burtscher M
Summary: The purpose of this study was to investigate the effect of a maximal shuttle-run shock microcycle in hypoxia on repeated sprint ability (RSA, 6 × 40-m (6 × 20 m back and forth, 20″ rest in between)), Yo-Yo-intermittent-recovery (YYIR) test performance, and redox-status. Fourteen soccer players (age: 23.9 ± 2.1 years), randomly assigned to hypoxia (∼3300 m) or normoxia training, performed 8 maximal shuttle-run training sessions within 12 days. YYIR test performance and RSA fatigue-slope improved independently of the hypoxia stimulus (p < 0.05). Training reduced the oxidative stress level (-7.9%, p < 0.05), and the reduction was associated with performance improvements (r = 0.761, ΔRSA; r = -0.575, ΔYYIR, p < 0.05).


#3 Chronic Exertional Compartment Syndrome in a High School Soccer Player
Reference: Case Rep Orthop. 2015;2015:965257. doi: 10.1155/2015/965257. Epub 2015 Jul 1.
Authors: Bresnahan JJ, Hennrikus WL
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502308/pdf/CRIOR2015-965257.pdf
Summary: Chronic exertional compartment syndrome (CECS) is a relatively rare condition that affects young adult athletes and often causes them to present to the emergency department. If left untreated, those who continue to compete at high levels may experience debilitating leg pain. Physicians may have difficulty differentiating CECS from other syndromes of the lower leg such as medial tibial stress syndrome, stress fractures, and popliteal artery entrapment. The gold standard for diagnosing CECS is intramuscular compartment pressure monitoring before and/or after 10 minutes of exercise. Some patients may choose to stop participation in sports in order to relieve their pain, which otherwise does not respond well to nonoperative treatments. In patients who wish to continue to participate in sports and live an active life, fasciotomy provides relief in 80% or more. The typical athlete can return to training in about 8 weeks. This is a case of a high school soccer player who stopped competing due to chronic exertional compartment syndrome. She had a fascial hernia, resting intramuscular pressure of 30 mmHg, and postexercise intramuscular pressure of 99 mmHg. Following fasciotomy she experienced considerable life improvement and is once again training and playing soccer without symptoms.


#4 Analysis on the serum levels of the biomarker CTX-II in professional indoor soccer players over the course of one season
Reference: Rev Bras Ortop. 2015 Apr 16;50(3):331-5. doi: 10.1016/j.rboe.2015.04.001.
Authors: Severino RM, Jorge PB, Martinelli MO, de Lima MV, Severino NR, Duarte Junior A
Dowload link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4519574/pdf/main.pdf
Summary: The aim of this study was to analyze the blood serum levels of CTX-II in professional indoor soccer players, at three different times during one season: at the start of the pre-season, four months later (a time that marks the middle of the season) and at the end of the season. Fourteen male soccer players of mean age 19 years were included. Blood samples of 3 mL were collected from each individual. The samples were analyzed by means of Elisa tests. There was a significant increase in the serum level of CTX-II in the indoor soccer players, from the beginning to the end of the season (p < 0.01). These data suggest that joint degradation had occurred in these soccer players, by the end of this period. It is evident that further studies are needed, with methodological rigor, so as to make an effective contribution toward precise elucidation of the etiology of this osteoarthritis and its relationship with the biomarkers, as a tool for early diagnosis.


#5 Age and gender differences in kinematics of powerful instep kicks in soccer
Reference: Sports Biomech. 2015 Jul 25:1-13. [Epub ahead of print]
Authors: Katis A, Kellis E, Lees A.
Summary: Soccer kicking training should be adjusted to the characteristics of the athletes. Therefore, examination of differences in kicking kinematics of females and pubertal players relative to males is worthwhile. The purpose of the study was to compare kicking kinematics and segmental sequence parameters between male, female, and pubertal players. Ten adult male, ten adult female, and ten male pubertal players participated in the study. Participants performed five consecutive kicking trials of a stationary ball, as powerful as they could. Analysis of variance showed significantly higher ball velocity, higher joint linear velocities for the knee and the hip, and higher angular velocities of the knee and the ankle for males compared to female and pubertal players (p < 0.05). Similarly, the peak joint velocity was achieved significantly closer to ball impact in males compared to other groups (p < 0.05). Males also showed a more plantarflexed ankle immediately before ball impact (p < 0.05). Females and pubertal players may benefit from skill training aiming to increase ankle plantarflexion and hip flexion prior to ball impact, and to adjust thigh and shank motion, such that the shank-foot segment travels through a higher range of motion and with a greater velocity.


#6 Is Recreational Soccer Effective for Improving [Formula: see text]? A Systematic Review and Meta-Analysis
Reference: Sports Med. 2015 Jul 26. [Epub ahead of print]
Authors: Milanović Z, Pantelić S, Čović N, Sporiš G, Krustrup P.
Summary: Soccer is the most popular sport worldwide, with a long history and currently more than 500 million active participants, of whom 300 million are registered football club members. On the basis of scientific findings showing positive fitness and health effects of recreational soccer, FIFA (Fédération Internationale de Football Association) introduced the slogan "Playing football for 45 min twice a week-best prevention of non-communicable diseases" in 2010. The objective of this paper was to perform a systematic review and meta-analysis of the literature to determine the effects of recreational soccer on maximal oxygen uptake ([Formula: see text]). Six electronic databases (MEDLINE, PubMed, SPORTDiscus, Web of Science, CINAHL and Google Scholar) were searched for original research articles. A manual search was performed to cover the areas of recreational soccer, recreational physical activity, recreational small-sided games and [Formula: see text] using the following key terms, either singly or in combination: recreational small-sided games, recreational football, recreational soccer, street football, street soccer, effect, maximal oxygen uptake, peak oxygen uptake, cardiorespiratory fitness, [Formula: see text]. The inclusion criteria were divided into four sections: type of study, type of participants, type of interventions and type of outcome measures. Probabilistic magnitude-based inferences for meta-analysed effects were based on standardised thresholds for small, moderate and large changes (0.2, 0.6 and 1.2, respectively) derived from between-subject standard deviations for baseline fitness. Seventeen studies met the inclusion criteria and were included in the systematic review and meta-analysis. Mean differences showed that [Formula: see text] increased by 3.51 mL/kg/min (95 % CI 3.07-4.15) over a recreational soccer training programme in comparison with other training models. The meta-analysed effects of recreational soccer on [Formula: see text] compared with the controls of no exercise, continuous running and strength training were most likely largely beneficial [effect size (ES) = 1.46; 95 % confidence interval (CI) 0.91, 2.01; I 2 = 88.35 %], most likely moderately beneficial (ES = 0.68; 95 % CI 0.06, 1.29; I 2 = 69.13 %) and most likely moderately beneficial (ES = 1.08; 95 % CI -0.25, 2.42; I 2 = 71.06 %), respectively. In men and women, the meta-analysed effect was most likely largely beneficial for men (ES = 1.22) and most likely moderately beneficial for women (ES = 0.96) compared with the controls. After 12 weeks of recreational soccer with an intensity of 78-84 % maximal heart rate (HRmax), healthy untrained men improved their [Formula: see text] by 8-13 %, while untrained elderly participants improved their [Formula: see text] by 15-18 %. Soccer training for 12-70 weeks in healthy women resulted in an improvement in [Formula: see text] of 5-16 %. Significant improvements in [Formula: see text] have been observed in patients with diabetes mellitus, hypertension and prostate cancer. Recreational soccer produces large improvements in [Formula: see text] compared to strength training and no exercise, regardless of the age, sex and health status of the participants. Furthermore, recreational soccer is better than continuous endurance running, albeit the additional effect is moderate. This kind of physical activity has great potential for enhancing aerobic fitness, and for preventing and treating non-communicable diseases, and is ideal for addressing lack of motivation, a key component in physical (in)activity.


#7 Health markers in obese adolescents improved by a 12-week recreational soccer program: a randomised controlled trial
Reference: J Sports Sci. 2015 Jul 24:1-12. [Epub ahead of print]
Authors: Vasconcellos F, Seabra A, Cunha F, Montenegro R, Penha J, Bouskela E, Nogueira Neto JF, Collett-Solberg P, Farinatti P
Summary: The effects of a recreational soccer program (RSP) upon body composition, heart rate variability (HRV), biochemical markers, cardio-respiratory fitness, and endothelial function in obese adolescents were investigated. A randomised controlled clinical trial was conducted with 30 adolescents aged 12-17 years and body mass index (BMI) >2 standard deviations of WHO reference values, which were assigned to RSP (n = 10, 2 girls) and obese control (n = 10, 4 girls) groups. The 12-week RSP included 60-min sessions performed 3 times/week. BMI, waist circumference, blood pressure, blood glucose, lipid profile, insulin, C-reactive protein, HRV, and maximal oxygen consumption (VO2peak) were evaluated following standardised procedures. Body composition was determined by dual-energy X-ray absorptiometry and endothelial function by venous occlusion plethysmography. After intervention, RSP exhibited significant reductions in BMI (-0.7 ± 0.2 kg · m-2), waist circumference (-8.2 ± 1.4 cm), %body fat (-2.2 ± 0.4%), systolic blood pressure (-5.0 ± 2.3 mmHg), total cholesterol (-16.2 ± 5.8 mg · dL-1), triglycerides (-20.5 ± 12.9 mg · dL-1), C-reactive protein (-0.06 ± 0.01 mg · dL-1), insulin resistance (HOMA-IR, -1.4 ± 0.6), and sympathetic activity (LF, -13.9 ± 6.6 un) vs. controls (P < 0.05). Significant increase was observed in parasympathetic activity (HF, 13.9 ± 6.6 un), VO2peak (7.9 ± 2.8 ml · kg-1 · min-1), and high-density lipoprotein cholesterol (11.0 ± 6.3 mg · dL-1) (P < 0.05). Vascular conductance (19.5 ± 8.1 ml · min-1 · 100 ml, P = 0.005) increased and vascular resistance (-5.9 ± 2.4 ml · min-1 · 100 ml, P = 0.041) decreased in RSP, but not in controls. A 12-week recreational soccer intervention was effective to improve biochemical, cardiovascular, and fitness health markers in obese adolescents.


#8 Can the natural turf pitch be viewed as a risk factor for injury within Association Football?
Reference: J Sci Med Sport. 2015 Jul 10. pii: S1440-2440(15)00144-9. doi: 10.1016/j.jsams.2015.07.009. [Epub ahead of print]
Authors: Rennie DJ, Vanrenterghem J, Littlewood M, Drust B
Summary: A review of the current literature is used to propose a 'conceptual model for relative pitch hardness' and how this may affect incidence of injury within Association Football. Based upon the injury risk and causation model of Meeuwisse et al. (Clin J Sport Med 2007; 17(3):215), it may provide researchers a necessary framework to guide future research investigations. A comprehensive search of electronic databases available until October 2014, and supplemental hand searching was conducted to identify relevant studies. Studies were deemed relevant if they met the following criteria: published in English, presented or referenced in an epidemiological study or provided data directly and/or related to the surface of the football pitch, ball or boot to surface interaction and injury. Further information was sourced on surface hardness, players' movement patterns and physiological demands within football. Papers varied in methodological quality, with comparative studies examining injury rates on artificial versus natural turf pitches being most prevalent. No prospective studies were found that objectively measured the relationship between hardness of natural turf and injury risk within football. The literature review into natural turf pitches and injury within football has largely been unable to confirm that pitch hardness can be viewed as a significant extrinsic risk factor. Methodological concerns, including objectivity in pitch assessment and uniformity in defining injuries undermine the efficacy of available work. Future studies are needed utilising objective assessment tools to draw more definitive conclusions regarding pitch hardness as an extrinsic factor for injury within football.


#9 Room for Improvement in Nutrition Knowledge and Dietary Intake of Male Football (Soccer) Players in Australia
Reference: Int J Sport Nutr Exerc Metab. 2015 Aug 3. [Epub ahead of print]
Authors: Andrews MC, Itsiopoulos C
Summary: Athletes require sufficient nutrition knowledge and skills to enable appropriate selection and consumption of food and fluids to meet their health, body composition and performance needs. This paper reports the nutrition knowledge and dietary habits of male football (soccer) players in Australia. Players aged 18 years of age and older were recruited from one A-League club (professional) and four National Premier League clubs (semi-professional). No significant difference in general nutrition knowledge (GNK) (54.1 ± 13.4%; 56.8 ± 11.7%; t(71)=-0.91, p=0.37) or sports nutrition knowledge (SNK) (56.9 ± 15.5%; 61.3 ± 15.9%; t(71)=-1.16, p=0.25) were noted between professional (n=29) and semi-professional (n=44) players. In general, players lacked knowledge in regards to food sources and types of fat. While nutrition knowledge varied widely among players (24.6-82.8% correct responses), those who had recently studied nutrition answered significantly more items correctly than those who reported no recent formal nutrition education (62.6 ± 11.9%; 54.0 ± 11.4%; t(67)=2.88, p=0.005). Analysis of three-day estimated food diaries revealed both professionals (n=10) and semi-professionals (n=31) consumed on average less carbohydrate (3.5 ± 0.8gC/kg; 3.9 ± 1.8gC/kg) per day than football specific recommendations (F-MARC: 5-10gC/kg). There was a moderate, positive correlation between SNK and carbohydrate intake (n=41, rho=0.32, p=0.04), indicating that players who exhibited greater SNK had higher carbohydrate intakes. Based on these findings male football players in Australia would benefit from nutrition education targeting carbohydrate and fat in an attempt to improve nutrition knowledge and dietary practices.