Latest research in football - week 12 - 2016

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 Influence of Skeletal Maturity on Size, Function and Sport-specific Technical Skills in Youth Soccer Players
Reference: Int J Sports Med. 2016 Mar 18. [Epub ahead of print]
Authors: Gouvea M, Cyrino ES, Ribeiro AS, da Silva DR, Ohara D, Valente-Dos-Santos J, Coelho-E-Silva MJ, Ronque E
Summary: This study compared variation in size, function and sport-specific technical skills of youth soccer players associated with differences in biological maturity status. 60 male soccer players of under-14 (U14) and under-17 (U17) categories were submitted to anthropometric and body composition measurements as well as motor and soccer-specific technical skill tests. Skeletal maturity was determined by skeletal age. Athletes of both categories were classified as early, on-time or late-maturing, according to the difference between chronological age and skeletal age. Body mass and height were lower in the late athletes, independent of category (P<0.01). Differences in adiposity were found only between athletes of the U14 (late<early, P<0.05). Statistically significant differences were identified on aerobic endurance in U14 (early<on time, P<0.01), upper limbs muscular strength (late<early, P<0.01) and flexibility in U17 (late<on time, P<0.05). Players in each age group of contrasting maturity status do not differ in soccer-specific skills. The results suggest that the maturational development influences body mass, height, body fat, flexibility, muscular strength of upper limbs and cardiorespiratory fitness, whereas the specific technical skills and other functional capabilities do not seem to be affected.

#2 Quantifying Head Impact Exposure in Collegiate Women's Soccer
Reference: Clin J Sport Med. 2016 Mar 8. [Epub ahead of print]
Authors: Press JN, Rowson S
Summary: The aim of this study was to quantify head impact exposure for a collegiate women's soccer team over the course of the 2014 season. Twenty-six collegiate level women's soccer players with a mean player age of 19 ± 1 participated in this study. Players were instrumented with head impact sensors for biomechanical analysis. Video recordings of each event were used to manually verify each impact sustained. The sensors collected data from a total of 17 865 accelerative events, 8999 of which were classified as head impacts. Of these, a total of 1703 impacts were positively identified (19% of total real impacts recorded by sensor), 90% of which were associated with heading the ball. The average number of impacts per player per practice or game was 1.86 ± 1.42. Exposure to head impact varied by player position. Head impact exposure was quantified through 2 different methods, which illustrated the challenges associated with autonomously collecting acceleration data with head impact sensors. Users of head impact data must exercise caution when interpreting on-field head impact sensor data.

#3 Yo-Yo Intermittent Recovery Test Performance in Sub-Elite Gaelic Football Players from Under 13 to Senior Age Groups
Reference: J Strength Cond Res. 2016 Mar 12. [Epub ahead of print]
Authors: Roe M, Malone S
Summary: Gaelic football is indigenous to Ireland and has similar locomotion profiles to soccer and Australian Football. Given the increasing attention on long-term player development, investigations into age-related variation in Yo-YoIR1 performance may provide useful information in talent identification, programme design, and player monitoring. Therefore, the aim of this study was to evaluate Yo-YoIR1 performance across Gaelic football age groups. Male participants (n = 355) were recruited from division one, Gaelic football teams. Participants were allocated to one of seven groups according to respective age groups from under 13 (U13), under 14, under 15 (U15), under 16 (U16), minor, under 21 (U21), to senior age groups. Total Yo-YoIR1 distance (m) increased progressively from U13 (885 ± 347 m) to U16 (1595 ± 380 m) equating to a rate of change of 180.2%. In comparison to U13, total distance at minor (1206 ± 327 m) increased by 136.4%. Subsequent increases were observed in U21 (1585 ± 445 m) and senior players (2365 ± 489). Minimum (800-880 m) and maximum (2240-2280 m) total distances were comparable for U15, U16, and U21 players. Differences in total distance (m) for all age groups were statistically significant when compared to U13 players (p<0.002). In comparison to U13 players the magnitude of differences between age groups for total distance were deemed to be large (ES >0.8). Similar trends were observed for maximum velocity and estimated VO2max. The evolution of Yo-YoIR1 performance in Gaelic football players from adolescents to adulthood highlights how maturation may influence sport-related running ability. Changes in Yo-YoIR1 performance should be closely monitored to optimise interventions for individuals transitioning across age groups.

#4 Physical and physiological responses of amateur football players on 3rd generation artificial turf systems during simulated game situations.
Reference: J Strength Cond Res. 2016 Mar 12. [Epub ahead of print]
Authors: Sánchez-Sánchez J, García-Unanue J, Felipe JL, Jiménez-Reyes P, Viejo-Romero D, Gómez-López M, Hernando E, Burillo P, Gallardo L.
Summary: The aim of this study is to evaluate the physical and physiological load imposed on amateur football players in a simulated game situation on different artificial turf systems. For that purpose, 20 football players (21.65±3.10 years old) were monitored with Global Positioning Systems and heart rate bands during 45 minute games on four selected artificial turf systems. The results show more covered distance in highintensity ranges on the system with lower levels of damping and higher rates of rotational traction (p<0.05). Likewise, this system of artificial turf demonstrated a high number of sprints (12.65±5.67), as well as more elevated maximum speed peaks during the last part of the game (28.16±2.90 km/h) in contrast to the systems with better damping capacity (p<0.05). On the other hand, the physiological load was similar across the four artificial turf systems (p>0.05). Finally, the regression analysis demonstrated a significant influence of the mechanical properties of the surface on global distance (15.4%), number (12.6%) and maximum speed (16.6%) of the sprints. To conclude, the mechanical variability of the artificial turf systems resulted in differences in the activity profiles and the players' perceptions during simulated football games.

#5 Sudden cardiac death while playing Australian Rules football: a retrospective 14 year review
Reference: Forensic Sci Med Pathol. 2016 Mar 14. [Epub ahead of print]
Authors: Parsons S, Lynch M
Summary: Australian Rules football is a sport which evolved from Gaelic football and which is played by a large number of predominantly male participants in a number of countries. The highest participation rates are in the southern states of Australia. A retrospective review over a period of 14 years identified 14 cases of sudden cardiac death that occurred in individuals while playing the sport. All were male and ranged in age from 13 to 36 years with a mean and median age of 23 years. A spectrum of cardiac causes was identified including coronary artery atherosclerosis, myocarditis, anomalous coronary artery anatomy, arrhythmogenic right ventricular cardiomyopathy, and healed Kawasaki disease. In 5 cases the heart was morphologically normal raising the possibility of a channelopathy. No traumatic deaths were identified. Some of the individuals had experienced symptoms prior to the fatal episode and the role of pre participation screening in reducing mortality is discussed.

#6 The Effects of a 6-Week Strength Training on Critical Velocity, Anaerobic Running Distance, 30-M Sprint and Yo-Yo Intermittent Running Test Performances in Male Soccer Players.
Reference: PLoS One. 2016 Mar 25;11(3):e0151448. doi: 10.1371/journal.pone.0151448. eCollection 2016.
Authors: Karsten B, Larumbe-Zabala E, Kandemir G, Hazir T, Klose A, Naclerio F
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Summary: The objectives of this study were to examine the effects of a moderate intensity strength training on changes in critical velocity (CV), anaerobic running distance (D'), sprint performance and Yo-Yo intermittent running test (Yo-Yo IR1) performances. Two recreational soccer teams were divided in a soccer training only group (SO; n = 13) and a strength and soccer training group (ST; n = 13). Both groups were tested for values of CV, D', Yo-Yo IR1 distance and 30-m sprint time on two separate occasions (pre and post intervention). The ST group performed a concurrent 6-week upper and lower body strength and soccer training, whilst the SO group performed a soccer only training. After the re-test of all variables, the ST demonstrated significant improvements for both, YoYo IR1 distance (p = 0.002) and CV values (p<0.001) with no significant changes in the SO group. 30-m sprint performance were slightly improved in the ST group with significantly decreased performance times identified in the SO group (p<0.001). Values for D' were slightly reduced in both groups (ST -44.5 m, 95% CI = -90.6 to 1.6; SO -42.6 m, 95% CI = -88.7 to 3.5). Combining a 6-week moderate strength training with soccer training significantly improves CV, Yo-Yo IR1 whilst moderately improving 30-m sprint performances in non-previously resistance trained male soccer players. Critical Velocity can be recommended to coaches as an additional valid testing tool in soccer.

#7 Neuromuscular demand of a soccer match assessed by a continuous electromyographic recording.
Reference: J Sports Med Phys Fitness. 2016 Mar 25. [Epub ahead of print]
Authors: Montini M, Felici F, NICOLò A, Sacchetti M, Bazzucchi I.
Summary: The bulk of research investigating soccer player's performance has been concentrated on the metabolic demand, while only few studies focused on the neuromuscular activation. The present study aimed at investigating the activation profile of the leg muscles throughout a 90- minute soccer match. Fifteen football players (18.3±0.7 years) performed: 1) an isometric maximal voluntary contraction (MVC) before the game [MVCpre]; 2) a 90-minute soccer match (composed of two 45-minute periods separated by a 15-minute rest); 3) a second MVC after the match [MVCpost]. Electromyographic (EMG) activity of the Vastus Lateralis (VL) muscle of the dominant leg was recorded during the match. The root mean square (RMS) of the EMG signals was normalized for the maximal RMS obtained during the MVCpre (100%RMSmax) and six intensity classes were created in order to represent the %RMS distribution during the match (1st: 0-20%RMSmax; 2nd: 20-40%RMSmax; 3rd: 40-60%RMSmax; 4th : 60-80%RMSmax; 5th: 80-100%RMSmax; 6th: 100-120%RMSmax). After the 90-minute soccer match, knee extensor MVC failed to show any statistical difference from pre-game values (-4.2%; p>0.05) whilst the neuromuscular activation demonstrated a significant reduction (-26.3%, p<0.01). During the game, the mean total distribution of RMS of the players was: 84.8±7.1% of total time in the 1th class, 8.5±3.9% in the 2th, 3.6±1.6% in the 3th, 1.7±1.0% in the 4th, 0.9±0.6% in the 5th and 0.4±0.5% in the 6th class of intensity. There was a significant difference (p<0.05) between the first versus the second half for the classes 1th, 3th and 4th. This represents the first attempt to characterize the neuromuscular activation profile during a 90-minute soccer match. Integrating this approach with more traditional ones may help further our understanding of the physiological demand of competitive soccer.

#8 Correction: Analysis of Jumping-Landing Manoeuvers after Different Speed Performances in Soccer Players.
Reference: PLoS One. 2016 Mar 24;11(3):e0152630. doi: 10.1371/journal.pone.0152630.
Authors: Daneshjoo A, Abu Osman NA, Sahebozamani M, Yusof A. [This corrects the article DOI: 10.1371/journal.pone.0143323.].
Erratum for Analysis of Jumping-Landing Manoeuvers after Different Speed Performances in Soccer Players. [PLoS One. 2015]
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#9 Mental Fatigue Impairs Technical Performance in Small-Sided Soccer Games.
Reference: Int J Sports Physiol Perform. 2016 Mar 22. [Epub ahead of print]
Authors: Badin OO, Smith MR, Conte D, Coutts AJ.
Summary: The purpose of the study was to assess the effects of mental fatigue on physical and technical performance in small-sided soccer games. Twenty soccer players (age 17.8 ± 1.0 y, height 179 ± 5 cm, body mass 72.4 ± 6.8 kg, playing experience 8.3 ± 1.4 y) from an Australian National Premier League soccer club volunteered to participate in this randomised crossover investigation. Participants played 15-min 5 vs 5 small-sided games (SSG) without goalkeepers on two occasions, separated by 1 wk. Prior to the SSG, one team watched a 30-min emotionally neutral documentary (control), while the other performed 30 min of a computer-based Stroop task (mental fatigue). Subjective ratings of mental and physical fatigue were recorded before and after treatment and following the SSG. Motivation was assessed prior to treatment and SSG; mental effort was assessed after treatment and SSG. Player activity profiles and heart rate (HR) were measured throughout the SSG, while ratings of perceived exertion (RPE) were recorded prior to the SSG, and immediately following each half. Video recordings of the SSG allowed for notational analysis of technical variables. Subjective ratings of mental fatigue and effort were higher following the Stroop task, while motivation for the upcoming SSG was similar between conditions. HR during the SSG was possibly higher in the control condition, while RPE was likely higher in the mental fatigue condition. Mental fatigue had an unclear effect on most physical performance variables, but impaired most technical performance variables. Mental fatigue impairs technical, but not physical performance in small-sided soccer games.

#10 Certification of competitive sports participation of a professional soccer player with hypertrophic cardiomyopathy and implanted ICD.
Reference: Clin Res Cardiol. 2016 Mar 22. [Epub ahead of print]
Authors: Laszlo R, Steinacker JM
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#11 [Injury of the Obturator Internus Muscle - a Rare Differential Diagnosis in a Soccer Player].
Reference: Sportverletz Sportschaden. 2016 Mar;30(1):50-3. doi: 10.1055/s-0042-100959. Epub 2016 Mar 22.  [Article in German]
Authors: Kelm J, Ludwig O, Schneider G, Hopp S
Summary: Lesions/irritations of the obturator internus muscle (OIM) are rare, several differential diagnoses are possible. This paper describes the case of an OIM injury in a professional football player. On clinical examination, painful internal rotation of the hip joint was an indication for a lesion/irritation of the OIM. MRI was the procedure of choice for imaging. Movement analysis served to detect a functional malposition. A short recovery time requires functional treatment as well as the use of orthopaedic aids to correct possible deformities.

#12 [Effects of Complex Versus Block Strength Training on the Athletic Performance of Elite Youth Soccer Players]
Reference: Sportverletz Sportschaden. 2016 Mar;30(1):31-7. doi: 10.1055/s-0041-106949. Epub 2016 Mar 22.  [Article in German]
Authors: Wallenta C, Granacher U, Lesinski M, Schünemann C, Mühlbauer T
Summary:  Muscle strength and speed are important determinants of soccer performance. It has previously been shown that complex training (CT, combination of strength and plyometric exercises within a single training session) is effective to enhance strength and speed performance in athletes. However, it is unresolved whether CT is more effective than conventional strength training that is delivered in one single block (BT) to increase proxies of athletic performance. Thus, the aim of the present study was to investigate the effects of CT versus BT on measures of muscle strength/power, speed, and agility in elite youth soccer players. Eighteen male elite youth soccer players conducted six weeks (2 sessions/week, 30 min. each) of progressive CT (n = 10, age: 18.5 ± 2.2 years) or BT (n = 8, age: 18.1 ± 1.6 years) in addition to their regular soccer training (approx. 6 sessions/week, 60 - 90 min. each). Before and after training, tests were conducted for the assessment of strength (one-repetition maximum [1RM] squat), power (countermovement jump [CMJ]), speed (30-m linear sprint), and agility (T test). Non-parametric analyses were used to calculate differences within (Wilcoxon test) and between (Mann-Whitney-U test) groups. Both CT and BT proved to be safe (i.e. no training-related, but six match-related injuries reported) and feasible (i.e. attendance rate of ≥ 80% in both groups) training regimens when implemented in addition to regular soccer training. The statistical analysis revealed significant improvements from pre-training to post-training tests for the CT group in 1 RM squat (p = 0.043) and CMJ height (p = 0.046). For the BT-group, significantly enhanced sprint times were observed over 5 m (p = 0.039) and 10 m (p = 0.026). Furthermore, both groups significantly improved their t test time (CT: p = 0.046; BT: p = 0.027). However, group comparisons (CT vs. BT) over time (post-training minus pre-training test) did not show any significant differences. Six weeks of CT and BT resulted in significant improvements in proxies of athletic performance. Yet CT did not produce any additional effects compared to BT. Future research is needed to examine whether the observed test-specific changes, i.e. improvements in strength/power for the CT-group and improvements in speed for the BT-group, are due to the applied configuration of strength, plyometric, and sprint exercises or if they rather indicate a general training response.

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