Latest research in football - week 46 - 2014

#1 Injury Characteristics in the German Professional Male Soccer Leagues After a Shortened Winter Break
Reference: J Athl Train. 2014 Nov 3. [Epub ahead of print]
Authors: Fünten KA, Faude O, Lensch J, Meyer T.
Summary: The winter break in the top 2 German professional soccer leagues was shortened from 6.5 to 3.5 weeks in the 2009-2010 season. The objective was to investigate whether this change affected injury characteristics by comparing the second half of the 2008-2009 (long winter break) with the equivalent period in the 2009-2010 season (short winter break). Seven professional German male soccer teams (184 players in the 2008-2009 season, 188 players in the 2009-2010 season) participated in this study. Injury incidences and injury characteristics (cause of injury, location, severity, type, diagnosis), including their monthly distribution, were recorded. A total of 300 time-loss injuries (2008-2009 n = 151, 2009-2010 n = 149) occurred. The overall injury incidence per 1000 soccer hours was 5.90 (95% confidence interval = 5.03, 6.82) in 2008-2009 and 6.55 (5.58, 7.69) in 2009-2010. Match injuries per 1000 hours were 31.5 (25.0, 38.0) in the first season and 26.5 (20.2, 32.7) in the second season; the corresponding training values were 2.67 (2.08-3.44) and 3.98 (3.19-4.95), respectively. The training injury incidence (incidence rate ratio = 1.49 [95% confidence interval = 1.07, 2.08], P = .02) and the risk of sustaining a knee injury (incidence rate ratio = 1.66 [1.00, 2.76], P = .049) were higher in 2009-2010 after the short winter break; the incidence of moderate and severe injuries (time loss >7 days) trended higher (incidence rate ratio = 1.34 [0.96,-1.86], P = .09). Shortening the winter break from 6.5 to 3.5 weeks did not change the overall injury incidence; however, a higher number of training, knee, and possibly more severe injuries (time loss >7 days) occurred.


#2 Two New Indexes for the Assessment of Autonomic Balance in Elite Soccer Players
Reference: Int J Sports Physiol Perform. 2014 Oct 29. [Epub ahead of print]
Authors: Naranjo Orellana J, de la Cruz Torres B, Sarabia Cachadiña E, Del Hoyo Lora M, Cobo SD.
Summary: The application of Poincaré plot analysis to Heart Rate Variability (HRV) is a common method for the assessment of autonomic balance. However, results obtained from the indexes provided by this analysis, tent to be difficult to interpret. In this study we aim to prove the usefulness of two new indexes: Stress Score (SS) and sympathetic/parasympathetic ratio (S/PS ratio). 25 professional Spanish soccer players from same team underwent 330 resting measurements of HRV. All subjects experienced 10 minutes of HRV monitoring through the RR-Interval recorder Firstbeat Bodyguard, Firstbeat Technologies Oy, Jyväskylä, Finland. The following parameters have been calculated: 1) Poincaré plot indexes: SD1 which is proportional to parasympathetic activity, SD2 which is inversely proportional to sympathetic activity and SD1/SD2 ratio); 2) time domain parameters: SDNN, rMSSD and pNN50;and 3) the proposed two new indexes: SS and S/PS ratio. The study found a high negative correlation between SS and SDNN (R2=0.94). S/PS ratio correlated inversely to rMMSD (R2=0.95), SDNN (R2=0.94) and pNN50 (R2=0.74). S/PS ratio showed a strong correlation with SD1 (R2=0.95) and SS (r=0.87 y R2=0.88). The application of SS as sympathetic activity index and the S/PS ratio as a representation of autonomic balance (SS/SD1) provides a better understanding of the Poincaré plot method in HRV.


#3 Effect of Training Session Intensity Distribution on Session-RPE in Soccer Players
Reference: Int J Sports Physiol Perform. 2014 Oct 28. [Epub ahead of print]
Authors: Fanchini M, Ghielmetti R, Coutts AJ, Schena F, Impellizzeri FM.
Summary: The aims of this study were to examine the effect of different exercise intensity distributions within a training session on the session-RPE and to examine the timing of measure on the rating. Nineteen junior players (age 16 ± 1 years, height 173 ± 5 cm, body mass 64 ± 6 kg) from a Swiss soccer team were involved in the study. Percentage of heart rate max (%HR) and rating of perceived exertion (RPE, Borg CR100©) were collected in four standardized training sessions (conditions). Total quality of recovery scale (TQR) and Visual Analogue Scale (VAS) for pain of lower limbs were used to control for the effect of pre-training fatigue. Every session consisted of three 20-min blocks of different intensities (i.e. low-moderate-high) performed in a random order. RPE was collected after every block (RPE5), immediately after the session (RPE-end) and 30 min after the session (RPE30). RPE5 of each block were different depending on the distribution sequence (p<0.0001). RPE-end, TQR and VAS values were not different between conditions (p=0.57, p=0.55 and p=0.96, respectively). The %HR was significantly different between conditions (p=0.008), with condition-3 higher than condition-2 (74.1 vs. 70.2%, p=0.02). Edward's training loads were not significantly different between conditions (p=0.09). RPE30 was not different compared to RPE-end (p>0.05). The present results show that coaches can design training sessions without concern about the influence of the within-session distribution of exercise intensity on session-RPE and that RPE can be collected at the end of the session or 30-min later.


#4 Reduced High Intensity Running Rate in Collegiate Women's Soccer When Games are Separated by 42-hours
Reference: Int J Sports Physiol Perform. 2014 Oct 28. [Epub ahead of print]
Authors: McCormack WP, Hoffman JR, Pruna GJ, Scanlon TC, Bohner JD, Townsend JR, Jajtner AR, Stout JR, Fragala MS, Fukuda DH.
Summary: During the competitive soccer season, women's intercollegiate matches are typically played on Friday evenings and Sunday afternoons. The efficacy of a 42-hour recovery period is not well understood. This investigation was conducted to determine performance differences between Friday and Sunday matches during a competitive season. Ten NCAA Division I female soccer players (20.5±1.0yr; 166.6±5.1cm; 61.1±5.8kg) were monitored with a 10-Hz GPS device across eight weekends with matches played on Friday evenings and Sunday afternoons. The players represented outside backs, midfielders, and forwards. All players had to participate in a minimum of 45 minutes per match to be included in the study. Average minutes played, total distance covered, total distance of high-intensity running (HIR) (defined as running at a velocity equal to or exceeding 3.61 m·sec-1 for greater than 1 second), the number of HIR efforts, and the number of sprints were calculated for each match. Data for Friday vs. Sunday matches were averaged and then compared utilizing dependent t-tests. No differences were seen in minutes played, distance rate, or number of sprints between Friday and Sunday matches. A significant (p=0.017) decrease in rate of HIR between Friday (25.37±7.22 m·min-1) and Sunday matches (22.90±5.70 m·min-1) was seen. In addition, there was a trend toward a difference (p=0.073) in the number of efforts of HIR between Friday (138.41±36.43) and Sunday (126.92±31.31). NCAA Division I female soccer players cover less distance of HIR in games played less than 48 hours after the first game. This could be due to various factors such as dehydration, glycogen depletion, or muscle damage.


#5 Extended stereopsis evaluation of professional and amateur soccer players and subjects without soccer background
Reference: Front Psychol. 2014 Oct 20;5:1186. doi: 10.3389/fpsyg.2014.01186. eCollection 2014.
Authors: Paulus J, Tong J, Hornegger J, Schmidt M, Eskofier B, Michelson G
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4202718/pdf/fpsyg-05-01186.pdf
Summary: Stereopsis is one of several visual depth cues. It has been evaluated for athletes of different types of sports in the past. However, most studies do not cover the full range of stereopsis performance. Therefore, we propose computer-supported stereopsis tests that provide an extended assessment and analysis of stereopsis performance including stereo acuity and response times. By providing stationary and moving stimuli they cover static and dynamic stereopsis, respectively. The proposed stereopsis tests were used to compare professional and amateur soccer players with subjects without soccer background. The soccer players could not perform significantly (p ≤ 0.05) superior than the subjects without soccer background. However, the soccer players showed significantly (p ≤ 0.01) superior choice reaction times for monocular stimuli. The results are in congruence with previous findings in literature.


#6 Reproducibility of running anaerobic sprint test (rast) for soccer players
Reference: J Sports Med Phys Fitness. 2014 Nov 6. [Epub ahead of print]
Authors: de Andrade VL, Pereira Santiago PR, Kalva Filho CA, Campos EZ, Papoti M.
Summary: Although the Running Anaerobic Sprint Test (RAST) presents reliability when performed on firmer surfaces (i.e. athletic track), its application on less rigid surfaces can compromise the measure determinations. The aim of the present study was to evaluate the RAST reliability for soccer players performing on grass, and wearing soccer cleats. Fourteen soccer players (16±1 years, 72.3±10.3 Kg, 177.2±8.4 cm, 14.5±5.3% of fat mass, and VO2MAX of 52.0±5.1 ml∙kg--1∙min--1) performed six maximal 35m effort interspersed by 10s of passive rest (RAST). After 48h the RAST was repeated to test the reliability. The main variables analyzed were the peak power (PP), mean power (MP), fatigue indexes (FI), and impulse (ImP). The reproducibility of test and re--test was tested through the Student's t Test to paired samples, intraclass correlation (ICC), typical error (TE), and coefficient of variation (CV%). The PP (test = 701.4±169.5 W; re--test 712.4±142.3 W), MP (test = 538.6±111.4 W; re--test = 551.9±101.1 W), and the ImP (test = 2841.2±461.8 N∙s; re--test = 2797.2±575.9 N∙s) were not different, presented significant correlation between the situations (ICC = 0.88; 0.96 e 0.93; respectively), and low values of TE (71.9 W; 30.6 W e 191.1 N∙s, respectively) and CV% (10.2%; 5.9% e 6.8%, respectively). The FI (test = 40.1±5.8; re--test = 38.7±7.7%) were not significantly related between the test and re--test, and presented high TE (5.7%) and CV% (14.4%). We can conclude that RAST presents high reliability when performed on grass with soccer cleats, just as rigid surfaces. Besides, the ImP is more robust than the usually assessed FI to evaluate the performance decay during RAST.


#7 Perceived Sources of Team Confidence in Soccer and Basketball
Reference: Med Sci Sports Exerc. 2014 Nov 6. [Epub ahead of print]
Authors: Fransen K, Vanbeselaere N, De Cuyper B, Broek GV, Boen F.
Summary: Although it is generally accepted that team confidence is beneficial for optimal team functioning and performance, little is known about the predictors of team confidence. The present study aims to shed light on the precursors of both high and low team confidence in two different sports. A distinction is made between sources of process-oriented team confidence (i.e., collective efficacy) and sources of outcome-oriented team confidence (i.e., team outcome confidence), which have often been confounded in previous research. In a first step, two qualitative studies were conducted to identify all possible sources of team confidence in basketball and in soccer. In a second step, three quantitative studies were conducted to further investigate the sources of team outcome confidence in soccer (N = 1,028) and in basketball (N =867), and the sources of collective efficacy in basketball (N = 825). Players perceived high-quality performance as the most important factor for their team outcome confidence. With regard to collective efficacy, team enthusiasm was perceived as most predictive determinant. Positive coaching emerged as second most decisive factor for both types of team confidence. In contrast, negative communication and expression by the players or the coach was perceived as the most decisive predictor of low levels of team confidence. At item level, all studies pointed to the importance of team confidence expression by the athlete leaders (i.e., leader figures within the team) and the coach. The present manuscript shed light on the precursors of high and low levels of team confidence. Athlete leaders and the coach emerged as key triggers of both upward and downward spirals of team confidence, thereby contaminating all team members.


#8 The Effect of 16-Week Plyometric Training on Explosive Actions in Early to Mid-Puberty Elite Soccer Players
Reference: Strength Cond Res 28(8): 2105–2114, 2014
Authors: Söhnlein Q, Müller E, Stöggl T,
Summary: Plyometric training (PT) programs are widely used to improve explosive actions in soccer players of various ages, although there is debate about optimal training duration and time course of improvement. Twenty-two early to mid-puberty elite soccer players were assigned to a control group (CG, n = 10, regular soccer training) or a plyometric training group (PTG, n = 12, regular soccer training substituted with 2 PT sessions each week). Both groups trained for 16 weeks during the in-season period. Control group performed only tests at baseline and after intervention, whereas PTG performed additional tests after 4, 8, and 12 weeks. During each test, subjects' performances in speed (10 and 30 m; 5 and 20 m), agility, shuttle run, multiple 5 bounds (MB5), and standing long jump (LJ) were recorded. The PTG showed improved performance in 20-m sprint time (−3.2%), agility time (−6.1%), MB5 distance (+11.8%), and LJ distance (+7.3%) (all, p ≤ 0.05) after 16 weeks. All these improvements were higher compared with CG (all, p ≤ 0.05). The time course of improvement in the PT group showed that 20-m sprint time improved after 16 weeks (p = 0.012); agility after 4 (p = 0.047) and 8 weeks (p = 0.004) but stopped after 12 weeks (p = 0.007); MB5 after 8 (p = 0.039), 12 (p = 0.028), and 16 weeks (p < 0.001); and LJ improved after 4 (p = 0.045), 12 (p = 0.008), and 16 weeks (p < 0.001). Plyometric training seems to be an appropriate training tool to enhance some but not all explosive actions. The results indicate that the duration of a PT program is highly dependent on what type of explosive actions should be improved, or whether several explosive actions should be improved at the same time.


#9 Multidirectional sprints and small-sided games training effect on agility and change of direction abilities in youth soccer
Reference: J Strength Cond Res 28(11): 3126–3132, 2014
Authors: Chaouachi A, Chtara M, Hammami R, Chtara H, Turki O, and Castagna C
Summary: The aim of this study was to compare the training effects of a small-sided game (SSG) and multidirectional sprint intervention on agility and change of direction (COD) ability in young male soccer players. Thirty-six soccer players (age: 14.2 ± 0.9 years; height: 167.2 ± 5.7 cm; body mass: 54.1 ± 6.3 kg, body fat: 12.5 ± 2.2%) participated in a short-term (6 weeks) randomized parallel fully controlled training study, with pre-to-post measurements. Players were randomly assigned to 2 experimental groups: training with preplanned COD drills (CODG, n = 12) or using SSGs (SSGG, n = 12) and to a control group (CONG, n = 12). Pre- and post-training players completed a test battery involving linear sprinting (15- and 30-m sprint), COD sprinting (COD: 15 m, ball: 15 m, 10-8-8-10 m, zigzag: 20 m), reactive agility test (RAT, RAT-ball), and vertical and horizontal jumping (countermovement jump and 5-jump, respectively). A significant (p ≤ 0.05) group × time effect was detected for all variables in CODG and SSGG. Improvements in sprint, agility without ball, COD, and jumping performances, were higher in CODG than in the other groups. The SSGG improved significantly more (p ≤ 0.05) than other groups in agility tests with the ball. The CONG showed significant improvements (p ≤ 0.05) on linear sprinting over a distance longer than 10 m and in all the agility and COD tests used in this study. It is concluded that in young male soccer players, agility can be improved either using purpose-built SSG or preplanned COD sprints. However, the use of specifically designed SSG may provide superior results in match-relevant variables.


#10 Reliability and validity of the Carminatti's test for aerobic fitness in youth soccer players
Reference: J Strength Cond Res 28(11): 3269–3278, 2014November 2014 - Volume 28 - Issue 11 - p 3264–3273
Authors: Teixeira AS, da Silva JF, Carminatti LJ, Dittrich N, Castagna C, and Guglielmo LGA
Summary: In this study, we examined the reliability and validity of peak velocity determined using the Carminatti's test (PVT-CAR) to evaluate the aerobic fitness of young soccer players (age = 13.4 ± 1.2 years; range, 10.3–15.4 years). To determine test-retest reliability of PVT-CAR, 34 adolescents (U-12, n = 13; U-14, n = 21) performed the Carminatti's test twice within 3–5 days. Validity was assessed in 43 adolescents (U-14, n = 20; U-16, n = 23) submitted to both the Carminatti's test and an incremental treadmill test to determine their aerobic fitness indicators. The intraclass correlation of PVT-CAR was 0.89, 0.93, and 0.81 with a coefficient of variation of 2.30% (0.33 km·h−1), 1.89% (0.26 km·h−1), and 2.66% (0.39 km·h−1) for the total sample (pooled data) or separately for the U-12 and U-14 groups, respectively. No significant difference was found between PVT-CAR and maximal aerobic speed (MAS) for the total sample (pooled data) or separately for the U-14 and U-16 groups. In addition, Bland and Altman plots evidenced acceptable agreement between them. The PVT-CAR was significantly related with peak velocity and MAS obtained in the incremental test for the total sample (r = 0.86 and 0.81, p < 0.01, respectively) and separately for the U-14 (r = 0.84 and 0.75, p < 0.01, respectively) and U-16 groups (r = 0.60 and 0.58, p < 0.01, respectively). Furthermore, the PVT-CAR was correlated with the V[Combining Dot Above]O2peak (r = 0.57, p < 0.01) and the velocity associated to the second ventilatory threshold (r = 0.69, p < 0.01) when the data were pooled (total sample). As a result, the Carminatti's test may be considered as a reliable and valid measure for assessing and monitoring the development of MAS of young soccer players during adolescence.


#11 Rating of Muscular and Respiratory Perceived Exertion in Professional Soccer Players
Reference: J Strength Cond Res 28(11): 3285–3293, 2014
Authors: Los Arcos A, Yanci J, Mendiguchia J, and Gorostiaga EM.
Summary: This study investigated, in male professional players: (a) fluctuations in rating of local-muscular (sRPEmus) and central-respiratory (sRPEres) perceived exertion measured after the completion of each training and competitive session, over a 9-week competitive period and (b) the influence of quantitative assessment of different training and competition modes on changes in physical performance. sRPEres, sRPEmus, and heart rate were measured in 21 players in 847 individual training and competitive sessions. Training load was calculated by multiplying sRPEmus or sRPEres by the duration of the training or competition sessions. A test battery (vertical jump, sprint, and endurance running) was performed before and after the studied period. At the end of official matches, average sRPEmus was higher (7.4 ± 0.6; p ≤ 0.05) than sRPEres (6.4 ± 1.3). Significant negative correlations were observed between the values of total training and competition time (r = −0.62; p < 0.01) or total added sRPEmus (r = −0.59; p ≤ 0.05), and vertical jump or sprint running velocity changes, respectively. This suggests that sRPEmus should be considered the main fatigue rating during a soccer match. Training and competition volume may have negative effects on the muscle power performance gains of the legs.

#12 Shuttle-run sprint training in hypoxia for youth elite soccer players: A pilot study
Reference: Journal of Sports Science and Medicine, 2014. 13: 731-735
Authors: Gatterer, H., et al.
Summary: The purposes of the present study were to investigate if a) shut- tle-run sprint training performed in a normobaric hypoxia cham- ber of limited size (4.75x2.25m) is feasible, in terms of produc- ing 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, per- formed 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 be- tween 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 re- stricted 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.