Latest research in football - week 23 - 2017

As previous literature updates, I 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 Effect of a Simulated Soccer Match on Anterior Cruciate Ligament Injury Risk Factors
Reference: Int J Sports Med. 2017 Jun 2. doi: 10.1055/s-0043-109238. [Epub ahead of print]
Authors: Wright M, Chesterton P, Wijnbergen M, O'Rourke A, Macpherson T
Summary: The purpose was to investigate the effect of within match fatigue on knee kinematics and jump kinetics in girls' soccer players, a quasi-experiment time series design was employed collecting data before, after and at 15-min intervals during a 90-min simulated soccer match. 15 girl players (age 13.1±1.4 years) performed a counter movement jump and a single-leg drop jump. Mean concentric force and flight time to contraction time ratio were derived from the counter movement jump. Knee valgus and flexion angles were calculated during the single-leg drop from 3-dimensional motion capture. Subjective ratings of perceived exertion (RPE) and readiness were collected at each time series. Small to large increases in RPE and reductions in readiness were observed throughout the match from baseline. Moderate to large improvements in mean concentric force were shown at 15, 75 and 90-min when compared to baseline. Flight time to contraction time ratio increased moderately at 15 min. Changes in kinematics were typically trivial or unclear however, small increases in knee valgus were shown after 30 min compared to baseline. Subjective measures may provide useful information to understand the physical response of young players to match play.

#2 Perceptions of the Coach-Athlete Relationship Predict the Attainment of Mastery Achievement Goals Six Months Later: A Two-Wave Longitudinal Study among F. A. Premier League Academy Soccer Players
Reference:  Front Psychol. 2017 May 18;8:684. doi: 10.3389/fpsyg.2017.00684. eCollection 2017.
Authors: Nicholls AR, Earle K, Earle F, Madigan DJ
Summary: All football teams that compete within the F. A. Premier League possess an academy, whose objective is to produce more and better home-grown players that are capable of playing professionally. These young players spend a large amount of time with their coach, but little is known about player's perception of the coach-athlete relationship within F. A. Premier League Academies. The objectives of this study were to examine whether perceptions of the coach-athlete relationship changed over six months and if the coach-athlete relationship predicted self-reported goal achievement among F. A. Premier League academy players. This study included cross-sectional (n = 104) and longitudinal (n = 52) assessments, in which academy soccer players completed a measure of the coach-athlete relationship and goal achievement across either one or two time periods. The cross-sectional data were subjected to bivariate correlations, whereas the longitudinal data were analyzed using multiple regressions. Perceptions of the coach-athlete relationship remained stable over time. The coach-athlete relationship predicted the achievement of mastery goals six months later. Enhancing the quality of the coach-athlete relationship among elite adolescent athletes appears to be a suitable way of maximizing mastery achievement goals, particularly among developmental athletes who participate in team sports.

#3 Soccer small-sided games in young players: rule modification to induce higher physiological responses
Reference: Biol Sport. 2017 Jun;34(2):163-168. doi: 10.5114/biolsport.2017.64590. Epub 2017 Jan 1.
Authors: Halouani J, Chtourou H, Dellal A, Chaouachi A, Chamari K
Summary: The aim of this study was to identify the physiological responses of 3 forms of players' numbers during two different games rules of small-sided games (SSG: stop-ball vs. small-goals rules). Eighteen youth amateur soccer players (age 13.5±0.7 years; height 168.9±6.1cm; body mass 63.1±7.7 kg) participated in this study and performed 3 SSGs with varying players' number (2vs.2; 3vs.3 and 4vs.4): stop-ball SSG (SB-SSG) vs. small-goals SSG (SG-SSG) in a randomized and counter-balanced order on a constant pitch dimension (20×25m). The players performed 4×4 min SSG with 2-min of passive recovery in-between. Heart rate (HR), (expressed in bpm and % HRmax), lactate ([La-]), and rating of perceived exertion (RPE) were collected during each session. SB-SSG induced the higher HR values in comparison with the SG-SSG for the 3 game formats (2vs.2; 3vs.3 and 4vs.4). Also, compared with SG-SSG, SB-SSG induced the higher HR values during 2vs.2 compared with 4vs.4 games rules (178 vs. 174 and 175 vs. 171 bpm, respectively). However, the SB-SSG was more intense compared with SG-SSG in the 2 vs. 2 game rule compared with the two others (3 vs.3 and 4 vs. 4) for [La-] and RPE (7.58 vs. 7; 7.25 vs. 6.75 and 6.5 vs. 6.16 mmol ∙ L-1, and 7.75 vs. 7.33; 7.41 vs. 7.08 and 7.16 vs. 6.83, respectively). Therefore, the use of 2 vs. 2 and 3 vs. 3 SSG with SB-SSG seems to represent an alternative to coaches to increase cardiovascular and metabolic demands in youth soccer players.

#4 In-season training periodization of professional soccer players
Reference: Biol Sport. 2017 Jun;34(2):149-155. doi: 10.5114/biolsport.2017.64588. Epub 2017 Jan 1.
Authors: Los Arcos A, Mendez-Villanueva A, Martinez-Santos R
Summary: The aim of this study was to quantify the seasonal perceived respiratory and muscular training loads (i.e., sRPEres-TL and sRPEmus-TL) completed by elite-oriented young professional soccer players. Twenty-four players (20.3 ± 2.0 years) belonging to the same reserve team of a Spanish La Liga club participated in this study. Only the players that were available to train for a whole week with the team and also to play the weekly game were considered: Starters, players that participated in the match for at least 45 min and Non-Starters, players that did not participate or played less than 45 minutes in the match. The competitive period was analysed after the division into 5x6-8 week blocks and 35x1 week microcycles. Data were also analysed with respect to number of days before the immediate match. Weekly TL variation across the in-season blocks was trivial-small for both groups except between Block 2 and Block 3 (ES= moderate). Substantial TL differences (ES= small-very likely) were found between training days, the TL pattern being a progressive increase up to MD-3 followed by a decrease until MD-1. Except for the match, sRPEres-/sRPEmus-TL was very similar between Starters and Non-Starters. In summary, perceived TL across the season displayed limited variation. Coaches periodized training contents to attain the highest weekly TL 72 hours before the match to progressively unload the players between MD-3 and the match day. The data revealed that the TL arising from the weekly game was solely responsible for the observed higher weekly TL of Starters in comparison with Non-Starters.

#5 Specific physical trainability in elite young soccer players: efficiency over 6 weeks' in-season training
Reference: Biol Sport. 2017 Jun;34(2):137-148. doi: 10.5114/biolsport.2017.64587. Epub 2017 Jan 1.
Authors: Chtara M, Rouissi M, Haddad M, Chtara H, Chaalali A, Owen A, Chamari K
Summary: The aim of the present study was to compare the effects of 3 training protocols (plyometric [PLYO], agility [AG], or repeated shuttle sprints [RS]) on physical performance in the same population of young soccer players. Forty-two youth-level male players (13.6±0.3-years; 1.65±0.07 m; 54.1±6.5 kg; body fat: 12.8±2.6%) participated in a short-term (6-week) randomized parallel fully controlled training study (pre-to-post measurements): PLYO group, n=10; AG group, n=10; RS group, n=12; and control group [CON] n=10. PLYO training = 9 lower limb exercises (2-3 sets of 8-12 repetitions). The AG group performed planned AG drills and direction changes. RS training consisted of 2-4 sets of 5-6x 20 to 30 m shuttle sprints (20 seconds recovery in between). Progressive overload principles were incorporated into the programme by increasing the number of foot contacts and varying the complexity of the exercises. Pre/post-training tests were: bilateral standing horizontal jump, and unilateral horizontal jumps, sprint (30 m with 10 m lap time), agility (20 m zigzag), and repeated sprint ability (RSA) (i.e. 6x30 m shuttle sprints: 2x15 m with 180° turns). Significant main effects for time (i.e. training application) and group (training type) were detected. Improvements in horizontal jumping were higher (p<0.01: ES=large) in PLYO. The RS group improved significantly more (p<0.01; ES=large) than other groups: 30 m sprint, RSAbest and RSAmean performances. Significantly greater increases in 20 m zigzag performance were observed following AG and RS training (4.0 and 3.8%, respectively) compared with PLYO (2.0%) and CON training (0.8%). No significant differences were reported in the RSAdec between groups. Elite young male soccer players' physical performances can be significantly and specifically improved either using PLYO or AG or RSA training over short-term in-season training.

#6 The influence of relative age on success and dropout in male soccer players
Reference: Am J Hum Biol. 1998;10(6):791-798. doi: 10.1002/(SICI)1520-6300(1998)10:6<791::AID-AJHB10>3.0.CO;2-1.
Authors: Helsen WF, Starkes JL, Van Winckel J
Summary: The consistent asymmetry in the birth-date distribution of senior professional soccer players has led us to investigate whether similar asymmetries emerge throughout youth categories in soccer. Birth dates were considered for professional players, national youth teams, youth players transferred to top teams, and regular youth league players. Kolmogorov Smirnov tests assessed differences between observed and expected birth-date distributions. Regression analyses examined the relationship between month of birth and number of participants at various levels of play in soccer. Results indicated that youth players born from August to October (the early part of the selection year), beginning in the 6-8 year age group, are more likely to be identified as talented and to be exposed to higher levels of coaching. Eventually, these players are more likely to be transferred to top teams, to play for national teams, and to become involved professionally. In comparison, players born late in the selection year tended to dropout as early as 12 years of age. Recommendations suggest a review of the 24-month age band and current methods for talent detection and selection.

#7 Infrared thermography applied to lower limb muscles in elite soccer players with functional ankle equinus and non-equinus condition
Reference: PeerJ. 2017 May 25;5:e3388. doi: 10.7717/peerj.3388. eCollection 2017.
Authors: Rodriguez-Sanz D, Losa-Iglesias ME, Lopez-Lopez D, Calvo-Lobo C, Palomo-Lopez P, Becerro-de-Bengoa-Vallejo R
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Summary: Gastrocnemius-soleus equinus (GSE) is a foot-ankle complaint in which the extensibility of the gastrocnemius (G) and soleus muscles (triceps surae) and ankle are limited to a dorsiflexion beyond a neutral ankle position. The asymmetric forces of leg muscles and the associated asymmetric loading forces might promote major activation of the triceps surae, tibialis anterior, transverses abdominal and multifidus muscles. Here, we made infrared recordings of 21 sportsmen (elite professional soccer players) before activity and after 30 min of running. These recordings were used to assess temperature modifications on the gastrocnemius, tibialis anterior, and Achilles tendon in GSE and non-GSE participants. We identified significant temperature modifications among GSE and non-GSE participants for the tibialis anterior muscle (mean, minimum, and maximum temperature values). The cutaneous temperature increased as a direct consequence of muscle activity in GSE participants. IR imaging capture was reliable to muscle pattern activation for lower limb. Based on our findings, we propose that non-invasive IR evaluation is suitable for clinical evaluation of the status of these muscles.

#8 Quantitative EEG evaluation for performance level analysis of professional female soccer players
Reference: Cogn Neurodyn. 2017 Jun;11(3):233-244. doi: 10.1007/s11571-017-9427-3. Epub 2017 Feb 24.
Authors: Tharawadeepimuk K, Wongsawat Y
Summary: Quantitative electroencephalography (QEEG) was used to investigate the brain activity of Thai professional female soccer team players who exhibit high performance. The QEEGs of 29 players were recorded three times: twice before a competition (once a week) and a week after a competition. The results of the brain topographic map (absolute power) in the alpha frequency band and the brain connectivity (coherence) in the delta frequency bands represented their anxiety and decision-making levels, respectively. These phenomena occurred in the brain activities of the athletes, which could be used to predict their performances during the competition. Moreover, the value of the correlation coefficient between the brain activity ranking and average performance score revealed a moderate to good relationship (rs = .586, p = .001). These results support the association between brain activity and performance level during competition.

#9 Decrements in neuromuscular performance and increases in creatine kinase impact training outputs in elite soccer players
Reference: J Strength Cond Res. 2017 May 23. doi: 10.1519/JSC.0000000000001997. [Epub ahead of print]
Authors: Malone S, Mendes B, Hughes B, Roe M, Devenney S, Collins K, Owen A.
Summary: The aim of the current investigation was to understand the impact of pre-training neuromuscular performance and creatine kinase status on subsequent training performance in elite soccer players. Thirty soccer players (age: 25.3 ± 3.1 years; height: 183 ± 7 cm; mass: 72 ± 7 kg) were involved in this observational study. Each morning prior to training, players completed assessments for neuromuscular performance (countermovement jump; CMJ) and creatine kinase (CK) levels. Global positioning technology provided external load: total distance, high-speed distance, sprint distance, accelerations, decelerations, average metabolic power, explosive distance, high metabolic power distance (>25.5 W·kg). Mixed-effect linear models revealed significant effects for CK and CMJ Z-score on total high speed distance, very high speed distance, accelerations, decelerations, explosive distance and maximal velocity. Effects are reported with 90% confidence limits. A CK Z-score of +1 corresponded to a -5.5 ± 1.1, -3.9 ± 0.5, -4.3 ± 2.9%, 4.1 ± 2.9%, 3.1 ± 2.9% and -4.6 ± 1.9%, reduction in total high-speed distance, very high-speed distance, accelerations, decelerations, explosive distance and maximal velocity respectively. CMJ Z-score of -1 corresponded to a -3.5 ± 1.1, -2.9 ± 0.5, -2.1 ± 1.4, -5.3 ± 2.9%, 3.8 ± 2.9%, 1.1 ± 2.9% and -5.6 ± 1.2% reduction in these external load measures. Magnitude-based analysis revealed that the practical size of the effect of a pre-training CMJ Z-score of -1 and CK Z-score of +1 would have on total high speed distance, very high speed distance, high metabolic power distance (>25.5 W·kg), accelerations, decelerations, explosive distance and maximal velocity was likely negative. The results of this study suggest that systematic pre-training monitoring of neuromuscular and muscle stress within soccer cohorts can provide coaches with information about the training output that can be expected from individual players during a training session.

#10 The effects of game types on intensity of small-sided games among pre-adolescent youth football players
Reference: Biol Sport. 2017 Jun;34(2):157-162. doi: 10.5114/biolsport.2017.64589. Epub 2017 Jan 1.
Authors: Halouani J, Chtourou H, Dellal A, Chaouachi A, Chamari K
Summary: The aim of this study was to examine the effects of variations in pitch dimensions on pre-adolescent youth soccer players' physiological responses during two different types of small-sided games (SSG). Sixteen young soccer players (age: 13.2 ± 0.6 years; body mass: 52.5 ± 7 kg; height: 163.4 ± 6 cm) participated in this study. They performed 4 vs. 4 stop-ball SSG (SB-SSG) vs. small-goals SSG (SG-SSG) with 4×4 min and 2 min of passive recovery in between, using 3 different pitch sizes (small: 10×15, medium: 15×20, and large: 20×25 m). Heart rate (HR), lactate concentration ([La-]), and rating of perceived exertion (RPE) were measured during each session. The results show that SB-SSG induced higher HR responses than SG-SSG for the 3 pitch sizes: for HR (167.2±3.0 vs. 164.5±3.0, 172.3±2.9 vs. 169.2±3.1, and 175.4±3.1 vs. 171.1±2.7 bpm; P<0.05, for small, medium, and large, respectively) and [La-] (7.1±1.0 vs. 6.5±1.04, 7.3±1.0 vs. 6.8±1.2, and 7.8±0.9 vs. 7.1±0.8 mmol·l-1; P<0.05 on small, medium, and large pitches, respectively), whereas RPE scores were significantly higher during SB-SSG compared to SG-SSG (6.2±1.0 vs. 5.8±0.9; P<0.05, respectively) on the small pitch. In the present study higher physiological responses were observed in SSG in pre-adolescent young soccer players when using the stop-ball conditions in comparison with the small-goal rule for all pitch sizes - small, medium, and large. Stop-ball conditions in comparison with the small-goal rule for all pitch sizes - small, medium, and large.

American Football
#1 Greater circadian disadvantage during evening games for the National Basketball Association (NBA), National Hockey League (NHL) and National Football League (NFL) teams travelling westward
Reference: J Sleep Res. 2017 Jun 1. doi: 10.1111/jsr.12565. [Epub ahead of print]
Authors: Roy J, Forest G
Summary: We investigated the effects of a circadian disadvantage (i.e. playing in a different time zone) on the winning percentages in three major sport leagues in North America: the National Basketball Association, the National Hockey League and the National Football League. We reviewed 5 years of regular season games in the National Basketball Association, National Hockey League and National Football League, and noted the winning percentage of the visiting team depending on the direction of travel (west, east, and same time zone) and game time (day and evening games). T-tests and analysis of variance were performed to evaluate the effects of the circadian disadvantage, its direction, the number of time zones travelled, and the game time on winning percentages in each major league. The results showed an association between the winning percentages and the number of time zones traveled for the away evening games, with a clear disadvantage for the teams travelling westward. There was a significant difference in the teams' winning percentages depending on the travelling direction in the National Basketball Association (F2,5908  = 16.12, P < 0.0001) and the National Hockey League (F2,5639  = 4.48, P = 0.011), and a trend was found in the National Football League (F2,1279  = 2.86, P = 0.058). The effect of the circadian disadvantage transcends the type of sport and needs to be addressed for greater equity among the western and eastern teams in professional sports. These results also highlight the importance of circadian rhythms in sport performance and athletic competitions.

#2 Return to Play After Shoulder Instability Surgery in National Collegiate Athletic Association Division I Intercollegiate Football Athletes
Reference: Am J Sports Med. 2017 May 1:363546517705635. doi: 10.1177/0363546517705635. [Epub ahead of print]
Authors: Robins RJ, Daruwalla JH, Gamradt SC, McCarty EC, Dragoo JL, Hancock RE, Guy JA, Cotsonis GA, Xerogeanes JW; ASP Collaborative Group, Greis PE, Tuman JM, Tibone JE, Javernick MA, Yochem EM, Boden SA, Pilato A, Miley JH
Summary: Recent attention has focused on the optimal surgical treatment for recurrent shoulder instability in young athletes. Collision athletes are at a higher risk for recurrent instability after surgery. The purpose was to evaluate variables affecting return-to-play (RTP) rates in Division I intercollegiate football athletes after shoulder instability surgery. Invitations to participate were made to select sports medicine programs that care for athletes in Division I football conferences (Pac-12 Conference, Southeastern Conference [SEC], Atlantic Coast Conference [ACC]). After gaining institutional review board approval, 7 programs qualified and participated. Data on direction of instability, type of surgery, time to resume participation, and quality and level of play before and after surgery were collected. There were 168 of 177 procedures that were arthroscopic surgery, with a mean 3.3-year follow-up. Overall, 85.4% of players who underwent arthroscopic surgery without concomitant procedures returned to play. Moreover, 15.6% of athletes who returned to play sustained subsequent shoulder injuries, and 10.3% sustained recurrent instability, resulting in reduction/revision surgery. No differences were noted in RTP rates in athletes who underwent anterior labral repair (82.4%), posterior labral repair (92.9%), combined anterior-posterior repair (84.8%; P = .2945), or open repair (88.9%; P = .9362). Also, 93.3% of starters, 95.4% of utilized players, and 75.7% of rarely used players returned to play. The percentage of games played before the injury was 49.9% and rose to 71.5% after surgery ( P < .0001). Athletes who played in a higher percentage of games before the injury were more likely to return to play; 91% of athletes who were starters before the injury returned as starters after surgery. Scholarship status significantly correlated with RTP after surgery ( P = .0003). The majority of surgical interventions were isolated arthroscopic stabilization procedures, with no statistically significant difference in RTP rates when concomitant arthroscopic procedures or open stabilization procedures were performed. Athletes who returned to play often played in a higher percentage of games after surgery than before the injury, and many played at the same or a higher level after surgery.

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