Latest research in football - week 13 - 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 The effects of congested fixtures period on tactical and physical performance in elite football
Reference: J Sports Sci. 2015 Mar 13:1-10. [Epub ahead of print]
Authors: Folgado H, Duarte R, Marques P, Sampaio J
Summary: The aim of this study was to examine the physical and tactical performances of a professional football team under congested and non-congested fixture periods. Six home matches of an English professional football team were analysed during competitive season (3 matches distancing three days from the previous fixture and 3 matches distancing six or more days from the previous fixture). Players' physical performances were measured by the total distance covered and distance covered at different speed categories. Tactical performances were measured by the percentage of time of players' movement synchronisation of lateral and longitudinal displacements. This variable was calculated considering all the possible pairs of outfield players, for the overall match and at different speed categories. Results showed no differences in the physical performance, although players' spent more time synchronised during the non-congested fixtures compared to congested fixtures, both for lateral (41.26% to 38.51%, ES: -0.3, P < 0.001) and longitudinal displacements (77.22% to 74.48%, ES: -0.5, P < 0.001). These coordination differences were particularly evident at the lower speed categories and in dyads composed by positions that tend to be further apart during the match, typically central and wing positioned players. Tactical performance seems to be affected by fixtures distribution, with players' spending more time synchronised during the non-congested fixtures. As players' cover the same amount of distance at similar intensities in both fixtures distribution, this reduction of synchronisation may be associated with an increased perception of fatigue and consequent adaptation strategies.

#2 Effects of seven weeks of static hamstring stretching on flexibility and sprint performance in young soccer players according to their playing position
Reference: J Sports Med Phys Fitness. 2015 Mar 13. [Epub ahead of print]
Authors: Rodiguez A, Sanchez J, Rodriguez-Marroyo JA, Villa JG
Summary: The aim of this study was to investigate the effect of 7 weeks of static hamstring stretching on flexibility and sprint performance in young soccer players. One hundred and three healthy soccer players voluntarily participated in this study. Subjects were assigned to a control group (n=22, 16.5±0.7 years, 174.0±5.4 cm and 68.0±6.8 kg) and an experimental group (n=81, 18.9±1.8 years, 176.0±5.8 cm and 68.2±8.4 kg). All subjects performed a sit-and-reach and a 30-m sprint test to assess their flexibility performance and sprinting ability, respectively, before and after a 7 weeks of static hamstring stretching program. The static stretching program consisted of 4 stretching exercises performed at the end of the training session during 6 days per week. Each stretch was held for 30-s and performed twice with a 15-s rest between. Flexibility was significantly (p<0.05) improved for the experimental group. This improvement was analyzed in all playing positions studied. There were significant differences (p<0.05) between pre and post 30-m sprint test in both groups. All soccer positions significantly (p<0.05) improved their performance in the experimental group. However, in the control group only defenders improved significantly (p<0.05) the sprint time. The use of static stretching at the end of the training sessions prevents the negative effect of the load on hamstring flexibility and it can influence improvement in flexibility.

#3 Typical weekly workload of under 15, under 17, and under 19 elite Portuguese football players
Reference: J Sports Sci. 2015 Mar 19:1-9. [Epub ahead of print]
Authors: Coutinho D, Gonçalves B, Figueira B, Abade E, Marcelino R, Sampaio J
Summary: This study aims to describe the time-motion and physiological performance profiles of footballers whose ages are under 15 (U15), under 17 (U17), and under 19 (U19) during a typical week of a competitive season. A total of 151 elite Portuguese players U15 (age 14.0 ± 0.2; n = 56), U17 (age 15.8 ± 0.4; n = 66), and U19 (age 17.8 ± 0.6; n = 19) were monitored during 33 training sessions (TSs) (U15 n = 12; U17 n = 11; and U19 n = 10 TSs). The TS data were captured at 15 Hz by global positioning systems devices and divided into post-match (session after the match), prematch (session before the match), and middle week (average of remaining sessions). The U15 middle week showed a higher number of sprints, distance covered in intermediate speed zones, and time spent above 90% HRmax, while the prematch presented a higher distance covered above 18 km · h-1 and time spent below 75% HRmax. In U17, both prematch and post-match data presented lower values than middle-week data in most of the variables. The post-match data in U19 presented higher values of distance covered above 13 km · h-1, body impacts above 10 G, and time spent above 85% HRmax, while middle week showed higher values in body impacts in most of the zones. In addition, the prematch data presented 35% to 100% less values than the middle-week data. Understanding the weekly workload variations according to the competition and the developmental ages of the players can contribute to optimising short- and mid-term planning.

#4 The Landing Error Scoring System as a Screening Tool for an Anterior Cruciate Ligament Injury-Prevention Program in Elite-Youth Soccer Athletes
Reference: J Athl Train. 2015 Mar 26. [Epub ahead of print]
Authors: Padua DA, DiStefano LJ, Beutler AI, de la Motte SJ, DiStefano MJ, Marshall SW
Summary: Identifying neuromuscular screening factors for anterior cruciate ligament (ACL) injury is a critical step toward large-scale deployment of effective ACL-injury-prevention programs. The Landing Error Scoring System (LESS) is a valid and reliable clinical assessment of jump-landing biomechanics. The purpose of this study was to investigate the ability of the LESS to identify individuals at risk for ACL injury in an elite-youth soccer population. A total of 829 elite-youth soccer athletes (348 boys, 481 girls; age = 13.9 ± 1.8 years, age range = 11 to 18 years), of whom 25% (n = 207) were less than 13 years of age. Baseline preseason testing for all participants consisted of a jump-landing task (3 trials). Participants were followed prospectively throughout their soccer seasons for diagnosis of ACL injuries (1217 athlete-seasons of follow-up). Landings were scored for "errors" in technique using the LESS. We used receiver operator characteristic curves to determine a cutpoint on the LESS. Sensitivity and specificity of the LESS in predicting ACL injury were assessed. Seven participants sustained ACL injuries during the follow-up period; the mechanism of injury was noncontact or indirect contact for all injuries. Uninjured participants had lower LESS scores (4.43 ± 1.71) than injured participants (6.24 ± 1.75; t1215 = -2.784, P = .005). The receiver operator characteristic curve analyses suggested that 5 was the optimal cutpoint for the LESS, generating a sensitivity of 86% and a specificity of 64%. Despite sample-size limitations, the LESS showed potential as a screening tool to determine ACL injury risk in elite-youth soccer athletes.

#5 Training-induced dynamic changes in left atrial reservoir, conduit, and active volumes in professional soccer players
Reference: Eur J Appl Physiol. 2015 Mar 26. [Epub ahead of print]
Authors: D'Ascenzi F, Pelliccia A, Natali BM, Cameli M, Lisi M, Focardi M, Padeletti M, Palmitesta P, Corrado D, Bonifazi M, Mondillo S, Henein M
Summary: Although left atrial (LA) enlargement is a recognized component of athlete's heart, dynamic cavity changes occurring during the training period remain to be elucidated. We aimed to investigate the adaptive changes of LA reservoir, conduit, and active volumes in elite athletes vs. controls and their response to different training loads. LA maximum, pre-P, and minimum volumes were assessed in 26 top-level athletes and 23 controls. In athletes, LA volumes were measured at pre-, mid-, end-training, and post-detraining time points using conventional 2D echocardiography. Athletes had larger maximum (27.5 ± 3.2 vs. 20.3 ± 5.8 mL/m2, p = 0.001), pre-P (11.5 ± 0.9 vs. 9.8 ± 2.2 mL/m2, p = 0.001), and minimum (6.6 ± 0.9 vs. 5.0 ± 1.2 mL/m2, p < 0.001) LA indexed volumes, compared with controls. Total and passive emptying volume indices were also larger in athletes compared with controls (18.7 ± 3.1 vs. 15.3 ± 4.9 mL/m2, p < 0.05 and 13.8 ± 2.9 vs. 10.5 ± 4.6 mL/m2, p < 0.05, respectively), while active emptying volume was similar (p = 0.74). During training, LA maximum (p < 0.0001), pre-P (p < 0.0001), minimum (p < 0.0001), total (p < 0.005), and passive (p < 0.05) emptying volume indices progressively increased, while active emptying volume (p = 0.10) and E/e' ratio (p = 0.32) remained unchanged. After detraining, LA volume measurements were not different from pre-training ones. End-training left ventricular mass index was the only independent predictor of the respective maximum LA volume (β = 0.74, p < 0.005). Top-level athletes exhibit a dynamic morphological and functional LA remodeling, induced by training, with an increase in reservoir and conduit volumes, but stable active volume. LA remodeling is closely associated with left ventricular adaptation to exercise and both completely regress after detraining.

#6 Geometric indices of hip bone strength in male professional soccer players
Reference: J Med Liban. 2014 Oct-Nov;62(4):207-12.
Authors: El Hage R, Zakhem E, Zunquin G, Theunynck D.
Summary: The aim of this study was to compare geometric indices of hip bone strength in male professional soccer players and controls. Twenty-three male professional soccer players and 21 male sedentary subjects whose ages range between 18 and 30 years participated in this study. Weight and height were measured, and body mass index (BMI) was calculated. Daily calcium intake and physical activity were evaluated using validated questionnaires. Hip bone mineral density was measured by dual-energy X-ray absorptiometry (DXA). To evaluate hip bone geometry, DXA scans were analyzed at the narrow-neck (NN), the intertrochanteric (IT) region and the femoral shaft (FS) by the Hip Structure Analysis (HSA) program. Cross sectional area (CSA), an index of axial compression strength, cross sectional moment of inertia (CSMI), an index of structural rigidity, section modulus (Z), an index of bending strength, cortical thickness (CT) and buckling ratio (BR) were measured from bone mass profiles. CSA, CSMI, Z and CT of the three regions (NN, IT and FS) were higher in soccer players compared to controls. After adjustment for either age, body weight, height or physical activity duration (h/week), CSA, CSMI, Z and CT of the three regions remained higher in soccer players compared to controls. This study suggests that, in young adult males, soccer practice is associated with greater axial strength, bending strength and structural rigidity indices at the hip.

#7 Training for power and speed: Effects of increasing or decreasing jump-squat velocity in elite young soccer players
Reference: J Strength Cond Res. 2015 Mar 23. [Epub ahead of print]
Authors: Loturco I, Nakamura FY, Kobal R, Gil S, Cal Abad CC, Cuniyochi R, Pereira LA, Roschel H
Summary: The aim of this study was to test the effects of two different velocity-oriented power-training regimens by either increasing or decreasing the jump-squat velocity during jump training sessions applied three times a week for 6 weeks in soccer players. Twenty-four elite under-20 soccer players were randomly assigned to an increased bar-velocity group (IVG) or a reduced bar-velocity group (RVG). Athletes had their countermovement jump heights, mean propulsive velocities (MPV) in jump squat, leg-press maximum dynamic strength (1RM), 20 m sprint times and zig-zag change of direction (COD) abilities assessed before and after the intervention. Performance in all tests improved after training in both groups. However, greater gains in 1RM and MPV using 50-90% of body mass (BM) were noted for the RVG. The IVG demonstrated greater improvements in speed at 5, 10, and 20m and MPV with no additional external load and with 40% BM. Both groups improved similarly in countermovement jumps and COD. To conclude, both velocity-oriented power-training regimens were effective in eliciting neuromechanical adaptations leading to better strength/power/speed performances and the choice as to the most suitable method should be tailored according to players' needs/deficiencies.

#8 Assessing the Energy Expenditure of Elite Female Soccer Players; A Preliminary Study
Reference: J Strength Cond Res. 2015 Mar 23. [Epub ahead of print]
Authors: Mara JK, Thompson KG, Pumpa KL
Summary: The aim of this study was to assess the total and exercise energy expenditure of elite female soccer players during a training week. Eight elite female soccer players wore SenseWear Mini Armbands (SWA) for seven consecutive days during the preseason phase of a national league competition. In addition, players wore 15Hz GPSports tracking devices during four training sessions and a friendly game. Total energy expenditure, exercise energy expenditure and training and game demands were collected from the SWA and GPSports devices. Mean daily energy expenditure for the game day, training days and rest days were 12,242kJ (SD = 603kJ), 11,692 (SD = 274kJ) and 9,516 (SD = 369kJ), respectively, with significant differences shown between activities (p < 0.001, partial η = 0.357), as well as between individual days (p < 0.001, partial η = 0.517). Mean values for energy expenditure during the friendly game (mean = 2,695kJ, SD = 301kJ) and training sessions (mean = 2,538kJ, SD = 316kJ) were similar (p = 0.278, Cohen's d = 0.5). However, there were significant differences found between individual training sessions (p = 0.001 - 0.035). Total and exercise energy expenditure differs throughout the week in female soccer players. Nutritional intake should be adjusted accordingly to avoid energy imbalances for optimal performance and recovery.

#9 Sprint conditioning of junior soccer players: effects of training intensity and technique supervision
Reference: PLoS One. 2015 Mar 23;10(3):e0121827. doi: 10.1371/journal.pone.0121827. eCollection 2015.
Autors: Haugen T, Tønnessen E, Øksenholt Ø3, Haugen FL, Paulsen G, Enoksen E, Seiler S
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Summary: The aims of the present study were to compare the effects of 1) training at 90 and 100% sprint velocity and 2) supervised versus unsupervised sprint training on soccer-specific physical performance in junior soccer players. Young, male soccer players (17 ±1 yr, 71 ±10 kg, 180 ±6 cm) were randomly assigned to four different treatment conditions over a 7-week intervention period. A control group (CON, n=9) completed regular soccer training according to their teams' original training plans. Three training groups performed a weekly repeated-sprint training session in addition to their regular soccer training sessions performed at A) 100% intensity without supervision (100UNSUP, n=13), B) 90% of maximal sprint velocity with supervision (90SUP, n=10) or C) 90% of maximal sprint velocity without supervision (90UNSUP, n=13). Repetitions x distance for the sprint-training sessions were 15x20 m for 100UNSUP and 30x20 m for 90SUP and 90UNSUP. Single-sprint performance (best time from 15x20 m sprints), repeated-sprint performance (mean time over 15x20 m sprints), countermovement jump and Yo-Yo Intermittent Recovery Level 1 (Yo-Yo IR1) were assessed during pre-training and post-training tests. No significant differences in performance outcomes were observed across groups. 90SUP improved Yo-Yo IR1 by a moderate margin compared to controls, while all other effect magnitudes were trivial or small. In conclusion, neither weekly sprint training at 90 or 100% velocity, nor supervised sprint training enhanced soccer-specific physical performance in junior soccer players.

#10 Response to regarding sudden cardiac death in soccer players
Reference: Phys Sportsmed. 2015 Mar 22:1-3. [Epub ahead of print]

Authors: Davogustto G, Higgins JP

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