Latest research in football - week 20 - 2015

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 A longitudinal study investigating the stability of anthropometry and soccer-specific endurance in pubertal high-level youth soccer players
Reference: J Sports Sci Med. 2015 May 8;14(2):418-26. eCollection 2015.
Authors: Deprez D, Buchheit M, Fransen J, Pion J, Lenoir M, Philippaerts RM, Vaeyens R
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Summary: We investigated the evolution and stability of anthropometric and soccer-specific endurance characteristics of 42 high-level, pubertal soccer players with high, average and low yo-yo intermittent recovery test level 1 (YYIR1) baseline performances over two and four years. The rates of improvement were calculated for each performance group, and intra-class correlations were used to verify short- and long-term stability. The main finding was that after two and four years, the magnitudes of the differences at baseline were reduced, although players with high YYIR1 baseline performance still covered the largest distance (e.g., low from 703 m to 2126 m; high from 1503 m to 2434 m over four years). Furthermore, the YYIR1 showed a high stability over two years (ICC = 0.76) and a moderate stability over four years (ICC = 0.59), due to large intra-individual differences in YYIR1 performances over time. Anthropometric measures showed very high stability (ICCs between 0.94 to 0.97) over a two-year period, in comparison with a moderate stability (ICCs between 0.57 and 0.75) over four years. These results confirm the moderate-to-high stability of high-intensity running performance in young soccer players, and suggest that the longer the follow-up, the lower the ability to predict player's future potential in running performance. They also show that with growth and maturation, poor performers might only partially catch up their fitter counterparts between 12 and 16 years. Key pointsYoung, high-level soccer players with a relatively low intermittent-endurance capacity are capable to catch up with their better performing peers after four years.Individual development and improvements of anthropometric and physical characteristics should be considered when evaluating young soccer players.

#2 Negative Associations between Perceived Training Load, Volume and Changes in Physical Fitness in Professional Soccer Players
Reference: J Sports Sci Med. 2015 May 8;14(2):394-401. eCollection 2015.
Authors: Arcos AL, Martínez-Santos R, Yanci J, Mendiguchia J, Méndez-Villanueva A
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Summary: The purpose of this study was to examine the usefulness of the rating of perceived exertion training load for monitoring changes in several aerobic fitness and neuromuscular performance variables during 9 weeks of soccer training in young professional players. Nineteen male soccer players (20.2 ± 1.9 years) belonging to the same reserve team of a Spanish La Liga Club participated in this study. Countermovement jump (CMJ), CMJ arm swing, single leg CMJ, a sprint running test (i.e., 5 m and 15 m times) and an aerobic fitness running test were performed at the start of the pre-season (Test 1) and 9 weeks later (Test 2). During 9 weeks, after each training session and match, players reported their rating of perceived exertion (RPE) separately for respiratory (RPEres) and leg musculature (RPEmus) effort. The training load (TL) was calculated by multiplying the RPE value by the duration in minutes of each training session or match. Accumulated RPEmus, and associated TL, as well as accumulated training volume were negatively correlated with the changes in most physical fitness attributes after 9 weeks of training (r = -0.51 to -0.64). Present results suggest that a high perception of leg muscular effort associated with training sessions and matches, as well as an excessive accumulation of training volume (time), can impair the improvement in several physical fitness variables believed to be relevant for on-field soccer performance. Therefore, the independent assessment of leg muscular effort to quantify TL can be an interesting additional monitoring measure in soccer training. Key pointsThe purpose of this study was to examine the usefulness of the perceived exertion-derived TL for monitoring changes in several aerobic fitness and neuromuscular parameters during 9 weeks of soccer training in young professional players.A high perception of leg muscular effort associated with training and matches, as well as an excessive accumulation of training volume (time), can impair several physical fitness factors believed to be relevant for on-field soccer performance.The independent assessment of muscular effort to quantify TL can be an interesting additional monitoring measure in soccer training.

#3 Adropin and apelin fluctuations throughout a season in professional soccer players: Are they related with performance?
Reference: Peptides. 2015 May 14. pii: S0196-9781(15)00146-1. doi: 10.1016/j.peptides.2015.05.001. [Epub ahead of print]
Authors: Sanchis-Gomar F, Alis R, Rampinini E, Bosio A, Ferioli D, La Torre A, Xu J, Sansoni V, Perego S, Romagnoli M, Lombardi G
Summary: Myokines are likely to be involved in the whole-body metabolic adaptive changes that occur in response to regular exercise. We aimed to investigate the association of the two myokines (adropin and apelin) with physical performance in professional soccer players. To this purpose, we analyzed the fluctuations of circulating levels of both adropin and apelin in professional soccer players during a season and evaluated the possible association of these myokines with the performance level. Creatine kinase (CK) and lactate dehydrogenase (LDH) activity as well as iron, transferrin and high-sensitivity C-Reactive protein (hsCRP), ferritin, soluble transferrin receptor (sTfR), free testosterone/cortisol ratio (FTCR), total iron binding capacity (TIBC) were also determined. Fifteen male professional soccer players from an Italian Serie A team were included in this study. Regarding the results of the biochemical analyses, the patterns of changes in the biomarkers of fatigue and inflammation, i.e., HsCRP, CK and LDH reflected the effects of the training throughout the season. No significant changes were observed in adropin, while apelin exhibited variations that seem not to be related with performance. In addition, both adropin and apelin did not represent valuable strategy to assist in the performance assessment of professional soccer players.

#4 Evidence-based hamstring injury prevention is not adopted by the majority of Champions League or Norwegian Premier League football teams: the Nordic Hamstring survey
Reference: Br J Sports Med. 2015 May 20. pii: bjsports-2015-094826. doi: 10.1136/bjsports-2015-094826. [Epub ahead of print]
Authors: Bahr R, Thorborg K, Ekstrand J
Summary: The Nordic hamstring (NH) exercise programme was introduced in 2001 and has been shown to reduce the risk of acute hamstring injuries in football by at least 50%. Despite this, the rate of hamstring injuries has not decreased over the past decade in male elite football. The purpose was to examine the implementation of the NH exercise programme at the highest level of male football in Europe, the UEFA Champions League (UCL), and to compare this to the Norwegian Premier League, Tippeligaen, where the pioneer research on the NH programme was conducted. 50 professional football teams, 32 from the UCL and 18 from Tippeligaen participated in this study. A questionnaire, based on the Reach, Efficacy, Adoption, Implementation and Maintenance framework, addressing key issues related to the implementation of the NH programme during three seasons from 2012 through 2014, was distributed to team medical staff using electronic survey software. The response rate was 100%. Of the 150 club-seasons covered by the study, the NH programme was completed in full in 16 (10.7%) and in part in an additional 9 (6%) seasons. Consequently, 125 (83.3%) club-seasons were classified as non-compliant. There was no difference in compliance between the UCL and Tippeligaen in any season (χ2: 0.41 to 0.52). Adoption and implementation of the NH exercise programme at the highest levels of male football in Europe is low; too low to expect any overall effect on acute hamstring injury rates.

#5 Recreational football is effective in the treatment of non-communicable diseases
Reference: Br J Sports Med. 2015 May 19. pii: bjsports-2015-094955. doi: 10.1136/bjsports-2015-094955. [Epub ahead of print]
Authors: Krustrup P, Bangsbo J
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#6 Professional football can be considered a healthy sport?
Reference: Knee Surg Sports Traumatol Arthrosc. 2015 May 17. [Epub ahead of print]
Authors: Arliani GG, Astur DC, Yamada RK, Yamada AF, da Rocha Corrêa Fernandes A, Ejnisman B, de Castro Pochini A, Cohen M.
Summary: This study aimed to compare the results of knee MRIs of former football players with no previous knee surgeries with non-regular practitioners of impact sports, matched by age and sex, and combine these results with other variables such as current quality of life and pain in the knees. The study participants were 16 male former professional football players and 21 male volunteers from different non-sports professional areas. All participants underwent bilateral magnetic resonances. Specific knee evaluations with regard to osteoarthritis and quality of life were performed in both groups by applying the Knee Injury and Osteoarthritis Outcome Score (KOOS) subjective questionnaires and SF-36, respectively. The between-group comparison revealed significant differences on: pain, symptoms, and quality of life related to the knee in KOOS subscales; physical aspects and vitality subscale of SF-36; and former soccer players had worst magnetic resonances scores than controls. Results of this study indicate probable specific adverse effects associated with participating in professional football.

#7 Somatotype and body composition analysis of Korean youth soccer players according to playing position for sports physiotherapy research
Reference: J Phys Ther Sci. 2015 Apr;27(4):1013-7. doi: 10.1589/jpts.27.1013. Epub 2015 Apr 30.
Authors: Noh JW, Kim MY, Lee LK, Park BS, Yang SM, Jeon HJ, Lee WD, Kim JH, Lee JU, Kwak TY, Lee TH, Kim JY, Kim J
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Summary: The purpose of this study was to investigate the somatotype and physical characteristic differences among elite youth soccer players. [Subjects and Methods] In the present study, we evaluated twenty-two Korean youth soccer players in different playing positions. The playing positions were divided into forward (FW), midfielder (MF), defender (DF), and goalkeeper (GK). The participants' lean body mass (LBM), fat free mass (FFM), fat mass (FM), and basal metabolic rate (BMR) were measured and their somatotype determined according to the Heath-Carter method. [Results] The youth soccer players had twelve ectomorphic, eight mesomorphic, and two central predominant types. The DFs were taller than, but otherwise similar in physical characteristics to the FWs and MFs. The GKs were taller and heavier than the other players; however, their somatotype components were not significantly different. LBM, FFM, and BMR were significantly higher in GKs than in FWs and MFs. Although LBM, FFM, and BMR values between GKs and DFs showed large differences, they were not statistically significant. [Conclusion] The present study may contribute to our understanding of the differences in somatotype and body composition of Korean youth soccer players involved in sports physiotherapy research.

#8 Effect of Ambient Temperature on Pacing in Soccer depends on Skill Level
Reference: J Strength Cond Res. 2015 May 16. [Epub ahead of print]
Authors: Link D, Weber H.
Summary: This study examines the influence ambient temperature has on the distances covered by players in soccer matches. For this purpose, 1211 games from the top German professional leagues were analysed over the course of the seasons 2011/12 and 2012/13 using an optical tracking system. The data shows a) significant differences in the total distance covered (TDC, in m/10 min) between the 1. Bundesliga (M = 1225) and 2. Bundesliga (M = 1201) and b) a significant decrease in TDC from NEUTRAL (-4 to 13° C, M = 1229) to WARM (≥ 14° C, M = 1217) environments. The size of the temperature effect is greater in the 1. Bundesliga (d=.30 vs. d=.16), even though these players presumably have a higher level of fitness. This suggests that better players reduce their exertion level to a greater extent, thus preserving their ability to undertake the high intensity activities when called upon. No reduction in running performance due to COLD (≤ 5° C) temperatures was observed.

#9 The effect of combined sensorimotor-resistance training on strength, balance and jumping performance of soccer players
Reference: J Strength Cond Res. 2015 May 16. [Epub ahead of print]
Authors: Manolopoulos K, Gissis I, Galazoulas C, Manolopoulos E, Patikas D, Gollhofer A, Kotzamanidis C.
Summary: The purpose of the study was to investigate the effects of resistance training (RT) and sensorimotor training combined with RT (SM-RT) on balance, 1 repetition maximum (RM), rate of force development (RFD) and squat jump (SJ) height. Twenty amateur soccer players were equally divided into two groups assigned as SM-RT group (age 22±1.7 years, body mass 79.9±6.3 kg, body height 1.81±0.06 m) and RT group (age 21.3±1.3 years, body mass 77.4±9.3 kg, body height 1.78±0.04 m). Both groups were trained over a 6-week period with two session units per week. SM-RT group performed sensorimotor training (balance on balance board) followed by a high intensity RT at 8-5 RM leg-press. The RT group performed the resistance program only. Both groups showed significantly increased 1 RM leg-press strength, RFD, SJ height and balance abilities (p<0.05), whereas no significant between-group differences were observed in any of the outcome variables (p>0.05). It was concluded, that SM-RT was not superior compared to RT for both balance and strength enhancement. These findings have implications in time management during training for soccer players

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