Latest research in football - week 50 part II - 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 Classifying young soccer players by training performances
Reference: Percept Mot Skills. 2014 Dec 2. [Epub ahead of print]
Authors: Abade EA, Gonçalves BV, Silva AM, Leite NM, Castagna C, Sampaio JE.
Summary: Players within the same age group may present different physical and physiological profiles. This study classified young soccer players according to their physical and physiological profiles obtained during the training sessions and compared classification by age and playing position criteria. 151 male elite Portuguese soccer players (under 15, under 17, and under 19 years old) participated. Time-motion and body acceleration and deceleration data were collected using GPS technology with heart rate monitored continuously across the selected training sessions. The data were grouped using two-step cluster analysis to classify athletes. A repeated-measures factorial ANOVA was performed to identify differences in the variables. Three clusters comprised 15.2%, 37.1%, and 47.7% of the total sample, respectively. Players of the same ages and playing experience had different performance profiles. Grouping players with similar physiological profiles during training sessions may allow coaches to balance oppositions and reduce the variability of the physiological outcomes.

#2 How important is it to score a goal? The influence of the score line on match performance
Reference: Percept Mot Skills. 2014 Dec 2. [Epub ahead of print]
Authors: Lago-Peñas C, Gómez-López M.
Summary: The goal of this study was to examine the effects of three different scorelines (1 Goal Up, Level Score, 1 Goal Down) on match performance indicators in elite soccer. Ball possession decreased when teams were 1 goal up. High Range Budget Clubs (HRBC) and Upper-Mid Range Budget Clubs (UMRBC) dominated possession against their opponents whether winning, losing, or drawing. Lower-Mid Range Budget Clubs (LMRBC) and Low Range Budget Clubs (LRBC) had less possession than HRBC. The probability of reaching the final one-third of the pitch decreased when teams were 1 goal up. LMRBC and LRBC had less match final third entries than HRBC. Similarly, shots on goal decreased when teams were 1 goal up. These findings could be used by coaches and match analysts when they evaluate performance and develop training drills.

#3 Measuring soccer technique with easy-to-administered field tasks in female soccer players from four different competitive levels
Reference: Percept Mot Skills. 2014 Dec 2. [Epub ahead of print]
Authors: Pedersen AV, Lorås H, Norvang OP, Asplund J.
Summary: Soccer is a multidimensional sport that requires skills in many different domains. Reports from competitions at the highest levels around the world suggest that a particularly decisive performance factor is a team's technical execution. Testing of technical skills in soccer has been infrequent compared with testing of physiological variables, and there has been a lack of consensus as to which tasks should be included in test batteries. In this study, the validity of four field tasks (heading, long pass, juggling, and hit-the-post) was examined by testing 108 female soccer players from four different competitive levels, representing a hierarchy of skill levels. Correlation analysis indicated that the tasks' results appeared statistically unrelated (Spearman's ρ ≤ .36). Statistical comparisons across competitive levels showed that task performance was closely correlated with players' competition level, with regression analysis indicating that 92% of the variance in mean rankings across tasks could be explained by competitive level. As the easily administered and low-cost tasks identified differences in technical skills across competitive levels, such tasks appear valid for inclusion in tests of technical skills.

#4 Anterior Cruciate Ligament and Knee Injury Prevention Programs for Soccer Players: A Systematic Review and Meta-analysis
Reference: Am J Sports Med. 2014 Dec 1. pii: 0363546514556737. [Epub ahead of print]
Authors: Grimm NL, Jacobs JC Jr, Kim J, Denney BS, Shea KG
Summary: Soccer has one of the highest incidences of anterior cruciate ligament (ACL) injuries for both males and females. Several injury prevention programs have been developed to address this concern. However, an analysis of the pooled effect has yet to be elicited. The purpose was to conduct a systematic review and meta-analysis of ACL and knee injury prevention programs for soccer players, assess the heterogeneity among the studies, and evaluate the reported effectiveness of the prevention programs. A systematic search of the literature was conducted on PubMed (Medline), Embase, CINAHL, and Central-Cochrane Database. Studies were limited to randomized controlled trials (RCTs) of injury prevention programs specific to the knee and/or ACL in soccer players. The Cochrane Q test and I2 index were independently used to assess heterogeneity among the studies. The pooled risk difference, assessing knee and/or ACL injury rates between intervention and control groups, was calculated by random-effects models with use of the DerSimonian-Laird method. Publication bias was assessed with a funnel plot and Egger weighted regression technique. Nine studies met the inclusion criteria as RCTs. A total of 11,562 athletes were included, of whom 7889 were analyzed for ACL-specific injuries. Moderate heterogeneity was found among studies of knee injury prevention (P = .041); however, there was insignificant variation found among studies of ACL injury prevention programs (P = .222). For studies of knee injury prevention programs, the risk ratio was 0.74 (95% CI, 0.55-0.89), and a significant reduction in risk of knee injury was found in the prevention group (P = .039). For studies of ACL injury prevention programs, the risk ratio was 0.66 (95% CI, 0.33-1.32), and a nonsignificant reduction in risk of ACL injury was found in the prevention group (P = .238). No evidence of publication bias was found among studies of either knee or ACL injury prevention programs. This systematic review and meta-analysis of ACL and knee injury prevention program studies found a statistically significant reduction in injury risk for knee injuries but did not find a statistically significant reduction of ACL injuries.

#5 Just how important is a good season start? Overall team performance and financial budget of elite soccer clubs
Reference: J Sports Sci. 2014 Dec 2:1-5. [Epub ahead of print]
Authors: Lago-Peñas C, Sampaio J.
Summary: The aim of the current study was (i) to identify how important is a good season start on elite soccer teams' performance and (ii) to examine whether this impact is related to the clubs' financial budget. The match performances and annual budgets of all teams were collected from the English FA Premier League, French Ligue 1, Spanish La Liga, Italian Serie A and German Bundesliga for three consecutive seasons (2010-2011 to 2012-2013). A k-means cluster analysis classified the clubs according to their budget as High Range Budget Clubs, Upper-Mid Range Budget Clubs, Lower-Mid Range Budget Clubs and Low Range Budget Clubs. Data were examined through linear regression models. Overall, the results suggested that the better the team performance at the beginning of the season, the better the ranking at the end of the season. However, the impact of the effect depended on the clubs' annual budget, with lower budgets being associated with a greater importance of having a good season start (P < 0.01). Moreover, there were differences in trends across the different leagues. These variables can be used to develop accurate models to estimate final rankings. Conversely, Lower-Mid and Lower Range Budget Clubs can benefit from fine-tuning preseason planning in order to accelerate the acquisition of optimal performances.

#6 Lower-extremity strength ratios of professional soccer players according to field position
Reference: J Strength Cond Res. 2014 Nov 26. [Epub ahead of print]
Authors: Ruas CV1, Minozzo F, Pinto MD, Brown LE, Pinto RS.
Summary: Previous investigators have proposed that knee strength, hamstrings to quadriceps and side-to-side asymmetries may vary according to soccer field positions. However, different results have been found in these variables, and a generalization of this topic could lead to data misinterpretation by coaches and soccer clubs. Thus, the aim of this study was to measure knee strength and asymmetry in soccer players across different field positions. One hundred and two male professional soccer players performed maximal concentric and eccentric isokinetic knee actions on the preferred and non-preferred legs at a velocity of 60°·s. Players were divided into their field positions for analysis: goalkeepers, side backs, central backs, central defender midfielders, central attacking midfielders, and forwards. Results demonstrated that only goalkeepers differed from most other field positions on players' characteristics, and concentric peak torque across muscles. Although all players presented functional ratios of the preferred (0.79 ± 0.14) and non-preferred (0.75 ± 0.13) legs below accepted normative values, there were no differences between positions for conventional or functional strength ratios or side-to-side asymmetry. The same comparisons were made only between field players, without inclusion of the goalkeepers, and no differences were found between positions. Therefore, the hamstrings to quadriceps and side-to-side asymmetries found here may reflect knee strength functional balance required for soccer skills performance and game demands across field positions. These results also suggest that isokinetic strength profiles should be considered differently in goalkeepers compared to other field positions due to their specific physiological and training characteristics.

#7 Comparison of inflammatory responses to a soccer match between elite male and female players
Reference: J Strength Cond Res. 2014 Nov 26. [Epub ahead of print]
Authors: Souglis A, Papapanagiotou A, Bogdanis GC, Travlos A, Apostolidis N, Geladas N.
Summary: The aim of this study was to compare the inflammatory responses between male and female soccer players for a period of 48 hours after an official match. Blood samples were taken from 83 subjects (22 elite male and 21 elite female soccer players and 20 male and 20 female inactive individuals) in the morning of the game day, immediately after the soccer game and 24h and 48h after the match. Average relative exercise intensity during the match was similar in male and female players, as indicated by mean heart rate that was 86.9±4.3 and 85.6±2.3 % of maximal HR (p=0.23), respectively. Interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) increased 2-4 fold above resting values, peaking immediately after the match. C-reactive protein (CRP) and creatine kinase (CK) peaked 24h after the match. IL-6, CRP and CK responses were similar in male and female players, but the peak in TNF-α was 18% higher in male players. IL-6, TNF-α and CRP at rest were lower in male and female players compared with the control subjects, suggesting a protective effect of regular exercise training regarding the inflammatory profile. The results of the present study show that a soccer match induces significant inflammatory responses in both male and female players, with only TNF-α peak values being lower in females. Due to the effects of inflammatory responses on performance and health of the players, it is suggested that coaches and trainers should adjust exercise training programs after a match, in order to promote recovery and protect the athletes' health.

#8 Seasonal Variation in Objectively Assessed Physical Activity among Young Norwegian Talented Soccer Players: A Description of Daily Physical Activity Level
Reference: J Sports Sci Med. 2014 Dec 1;13(4):964-968. eCollection 2014.
Authors: Sæther SA, Aspvik NP.
Download link:
Summary: 'Practise makes perfect' is a well-known expression in most sports, including top-level soccer. However, a high training and match load increases the risk for injury, overtraining and burnout. With the use of accelerometers and a self-report questionnaire, the aim of this study was to describe talented players' physical activity (PA) level. Data were collected three times during the 2011 Norwegian Football season (March, June and October). The accelerometer output, counts·min-1 (counts per unit time registered), reports the daily PA-level for young talented soccer players. Results showed a stable PA-level across the season (March: 901.2 counts·min-1, June: 854.9 counts·min-1, October: 861.5 counts·min-1). Furthermore, comparison of five different training sessions across the season showed that the PA-level ranged from 2435.8 to 3745.4 counts·min-1. A one-way ANOVA showed no significant differences between the three measured weeks during the soccer season (p≤0.814). However, the training sessions in January had a significantly higher PA-level than those in June and October (p≤0.001). Based on these results, we discuss how potential implications of PA-level affect factors such as risk of injury, overtraining and burnout. We argue that player development must be seen as part of an overall picture in which club training and match load should be regarded as one of many variables influencing players' PA-level. It is well established that to achieve a high performance level in sport, one must implement a high training and match load in childhood and youth.With the use of accelerometers and a self-reported questionnaire, the aim of this study was to describe talented players' total physical activity (PA) load.These results indicate that young talented soccer players must overcome large doses of PA on a weekly basis, exposing them to a high risk of injury, overtraining and burnout.

#9 Hydration Status and Fluid Balance of Elite European Youth Soccer Players during Consecutive Training Sessions
Reference: J Sports Sci Med. 2014 Dec 1;13(4):817-822. eCollection 2014.
Authors: Phillips SM, Sykes D, Gibson N
Download link:
Summary: The objective of the study was to investigate the hydration status and fluid balance of elite European youth soccer players during three consecutive training sessions. Fourteen males (age 16.9 ± 0.8 years, height 1.79 ± 0.06 m, body mass (BM) 70.6 ± 5.0 kg) had their hydration status assessed from first morning urine samples (baseline) and pre- and post-training using urine specific gravity (USG) measures, and their fluid balance calculated from pre- to post-training BM change, corrected for fluid intake and urine output. Most participants were hypohydrated upon waking (USG >1.020; 77% on days 1 and 3, and 62% on day 2). There was no significant difference between first morning and pre-training USG (p = 0.11) and no influence of training session (p = 0.34) or time (pre- vs. post-training; p = 0.16) on USG. Significant BM loss occurred in sessions 1-3 (0.69 ± 0.22, 0.42 ± 0.25, and 0.38 ± 0.30 kg respectively, p < 0.05). Mean fluid intake in sessions 1-3 was 425 ± 185, 355 ± 161, and 247 ± 157 ml, respectively (p < 0.05). Participants replaced on average 71.3 ± 64.1% (range 0-363.6%) of fluid losses across the three sessions. Body mass loss, fluid intake, and USG measures showed large inter-individual variation. Elite young European soccer players likely wake and present for training hypohydrated, when a USG threshold of 1.020 is applied. When training in a cool environment with ad libitum access to fluid, replacing ~71% of sweat losses results in minimal hypohydration (<1% BM). Consumption of fluid ad libitum throughout training appears to prevent excessive (≥2% BM) dehydration, as advised by current fluid intake guidelines. Current fluid intake guidelines appear applicable for elite European youth soccer players training in a cool environment. Key PointsThe paper demonstrates a notable inter-participant variation in first morning, pre- and post-training hydration status and fluid balance of elite young European soccer players.On average, elite young European soccer players are hypohydrated upon waking and remain hypohydrated before and after training.Elite young European soccer players display varied fluid intake volumes during training, but on average do not consume sufficient fluid to offset fluid losses.Consecutive training sessions do not significantly impair hydration status, suggesting that elite young European soccer players consume sufficient fluid between training to maintain a stable hydration status and prevent excessive (≥2% body mass) dehydrationCurrent fluid intake guidelines appear applicable to this population when training in a cool environment.

#10 Shuttle-Run Sprint Training in Hypoxia for Youth Elite Soccer Players: A Pilot Study
Reference: J Sports Sci Med. 2014 Dec 1;13(4):731-735. eCollection 2014.
Authors: Gatterer H, Philippe M, Menz V, Mosbach F, Faulhaber M, Burtscher M.
Summary: The purposes of the present study were to investigate if a) shuttle-run sprint training performed in a normobaric hypoxia chamber of limited size (4.75x2.25m) is feasible, in terms of producing the same absolute training load, when compared to training in normoxia, and b) if such training improves the repeated sprint ability (RSA) and the Yo-Yo intermittent recovery (YYIR) test outcome in young elite soccer players. Players of an elite soccer training Centre (age: 15.3 ± 0.5 years, height: 1.73 ± 0.07 m, body mass: 62.6 ± 6.6 kg) were randomly assigned to a hypoxia or a normoxia training group. Within a 5-week period, players, who were not informed about the hypoxia intervention, performed at least 7 sessions of identical shuttle-run sprint training either in a normal training room (FiO2 = 20.95%) or in a hypoxic chamber (FiO2 = 14.8%; approximately 3300m), both equipped with the same floor. Each training session comprised 3 series of 5x10s back and forth sprints (4.5m) performed at maximal intensity. Recovery time between repetitions was 20s and between series 5min. Before and after the training period the RSA (6 x 40m shuttle sprint with 20 s rest between shuttles) and the YYIR test were performed. The size of the chamber did not restrict the training intensity of the sprint training (both groups performed approximately 8 shuttles during 10s). Training in hypoxia resulted in a lower fatigue slope which indicates better running speed maintenance during the RSA test (p = 0.024). YYIR performance increased over time (p = 0.045) without differences between groups (p > 0.05). This study showed that training intensity of the shuttle-run sprint training was not restricted in a hypoxic chamber of limited size which indicates that such training is feasible. Furthermore, hypoxia compared to normoxia training reduced the fatigue slope during the RSA test in youth soccer players. Key PointsShuttle-run sprint training is feasible in hypoxic chambers of limited size (i.e., 4.75x2.25m).Hypoxia sprint training (RSH), in comparison to normoxia training, might lead to better running speed maintenance during the repeated sprint ability test.

The Training Manager -