Latest research in football - week 28 - 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 Match physical performance of elite female soccer players during international competition
Reference: J Strength Cond Res. 2016 Jul 26. [Epub ahead of print]
Authors: Datson N, Drust B, Weston M, Jarman I, Lisboa P, Gregson W
Summary: The purpose of the present study was to provide a detailed analysis of the physical demands of competitive international female soccer match-play. A total of 148 individual match observations were undertaken on 107 outfield players competing in competitive international matches during the 2011-2012 and 2012-2013 seasons, using a computerized tracking system (Prozone Sports Ltd., Leeds, England). Total distance (TD) and total high-speed running distances (THSR) were influenced by playing position, with central midfielders (CM) completing the highest (10985±706 m and 2882±500 m) and central defenders (CD) the lowest (9489±562 m and 1901±268 m) distances, respectively. Greater total very high-speed running (TVHSR) distances were completed when a team was without (399±143 m) compared to with (313±210 m) possession of the ball. The majority of sprints were over short distances with 76 % and 95 % being less than 5 m and 10 m, respectively. Between half reductions in physical performance were present for all variables, independent of playing position. The current study provides novel findings regarding the physical demands of different playing positions in competitive international female match-play and provides important insights for physical coaches preparing elite female players for competition.

#2 Relationships Between Training Load Indicators and Training Outcomes in Professional Soccer
Reference: Sports Med. 2016 Jul 26. [Epub ahead of print]
Authors: Jaspers A, Brink MS, Probst SG, Frencken WG, Helsen WF
Summary: In professional senior soccer, training load monitoring is used to ensure an optimal workload to maximize physical fitness and prevent injury or illness. However, to date, different training load indicators are used without a clear link to training outcomes. The aim of this systematic review was to identify the state of knowledge with respect to the relationship between training load indicators and training outcomes in terms of physical fitness, injury, and illness. A systematic search was conducted in four electronic databases (CINAHL, PubMed, SPORTDiscus, and Web of Science). Training load was defined as the amount of stress over a minimum of two training sessions or matches, quantified in either external (e.g., duration, distance covered) or internal load (e.g., heart rate [HR]), to obtain a training outcome over time. A total of 6492 records were retrieved, of which 3304 were duplicates. After screening the titles, abstracts and full texts, we identified 12 full-text articles that matched our inclusion criteria. One of these articles was identified through additional sources. All of these articles used correlations to examine the relationship between load indicators and training outcomes. For pre-season, training time spent at high intensity (i.e., >90 % of maximal HR) was linked to positive changes in aerobic fitness. Exposure time in terms of accumulated training, match or combined training, and match time showed both positive and negative relationships with changes in fitness over a season. Muscular perceived exertion may indicate negative changes in physical fitness. Additionally, it appeared that training at high intensity may involve a higher injury risk. Detailed external load indicators, using electronic performance and tracking systems, are relatively unexamined. In addition, most research focused on the relationship between training load indicators and changes in physical fitness, but less on injury and illness. HR indicators showed relationships with positive changes in physical fitness during pre-season. In addition, exposure time appeared to be related to positive and negative changes in physical fitness. Despite the availability of more detailed training load indicators nowadays, the evidence about the usefulness in relation to training outcomes is rare. Future research should implement continuous monitoring of training load, combined with the individual characteristics, to further examine their relationship with physical fitness, injury, and illness.

#3 Effects of recovery mode on physiological and psychological responses and performance of specific skills in young soccer players
Reference: J Sports Med Phys Fitness. 2016 Jul 22. [Epub ahead of print]
Authors: Gharbi A, Masmoudi L, Chtourou H, Chaari N, Tabka Z
Summary: The ability to perform repeated sprints is likely influenced by the mode of the recovery. Despite performance time, peak power, and mean power measured in most of studies, there are other specific sport abilities that should be examined after different recovery strategies.The aim of this study was to examine the effects of recovery modes (active [AR] vs passive [PR]) on physiological performance (lactate, HR, and blood pressure), psychological performance (perceived exertion rating [RPE] and feeling scale [FS]), and specific skills (kicking accuracy [KA] and repeated dribbling) in young soccer players. Ten male children (age 14.6 ± 0.8 yr; experience 5.3 ± 0.4 yr; body height 1.63 ± 0.4 m; body mass 52.5 ± 4.9 kg) who were soccer players performed two kicking accuracy tests on two separate occasions that involved ten 20-m dribbling speed tests with 20 s of PR or AR in a random order. The dribbling speed performance, total dribbling time (TT), best dribbling time (BT), mean time (MT), RPE, FS, blood pressure (BP), HR, lactate concentration ([La]), and KA were recorded. In addition, the fatigue index (FI) was calculated from the repeated dribbling sprint test (RDST). The results showed that performing the RDST with PR between exercise bouts resulted in a shorter dribbling sprint time, as compared with AR during the last six repetitions. TT, MT, and FI (p < 0.001) were higher in AR than PR. However, BT, kicking accuracy, and the physiological parameters (i.e., [La], systolic blood pressure, and diastolic blood pressure) were not affected by the recovery type. Conversely, the present study demonstrated a better feeling score and lower perception of effort during passive recovery than during the active mode. The results of the present study demonstrate that PR is better than AR for RDST performance and for subjective fatigue estimation. Therefore, coaches and athletes are advised to utilize PR during competitions and training sessions requiring repeated high intensity exercises.

#4 Head Injuries in Soccer
Reference: Phys Sportsmed. 1989 Jan;17(1):69-73. doi: 10.1080/00913847.1989.11709682.
Authors: Fields KB
Summary: In brief: Although soccer is considered a safe sport, fatal head injuries have occurred on rare occasion. Mechanisms of injury include heading the ball improperly and making head-to-head contact; injury may also occur when a forcefully kicked ball strikes a player's head. Goalkeepers most commonly sustain collision injuries when the head strikes the goalpost, the playing field, or another player's elbow, foot, or head. The author reviews the medical literature on soccer injuries and contends that rule changes and other measures may be more appropriate than the use of helmets to prevent head injuries.

#5 Effects of plyometric training on soccer players
Reference: Exp Ther Med. 2016 Aug;12(2):550-554. Epub 2016 Jun 3.
Authors: Wang YC, Zhang N
Summary: Plyometric training (PT) is a technique used to increase strength and explosiveness. It consists of physical exercises in which muscles exert maximum force at short intervals to increase dynamic performances. In such a training, muscles undergo a rapid elongation followed by an immediate shortening (stretch-shortening contraction), utilizing the elastic energy stored during the stretching phase. There is consensus on the fact that when used, PT contributes to improvement in vertical jump performance, acceleration, leg strength, muscular power, increase of joint awareness and overall sport-specific skills. Consequently, PT which was primarily used by martial artists, sprinters and high jumpers to improve performances has gained in popularity and has been used by athletes in all types of sports. However, although PT has been shown to increase performance variables in many sports, little scientific information is currently available to determine whether PT actually enhances skill performance in soccer players, considering that soccer is an extremely demanding sport. Soccer players require dynamic muscular performance for fighting at all levels of training status, including rapid movements such as acceleration and deceleration of the body, change of direction, vertical and horizontal jumps, endurance, speed as well as power for kicking and tackling. In this review we discussed the effects of PT on soccer players by considering gender and age categories.

#6 Longitudinal Changes in Hip Strength and Range of Motion in Female Youth Soccer Players: Implications for ACL Injury. A Pilot Study
Reference: J Sport Rehabil. 2016 Jul 21. [Epub ahead of print]
Authors: Nguyen AD, Zuk EF, Baellow AL, Pfile KR, DiStefano LJ, Boling MC
Summary: Risk of ACL injuries in young female athletes increases with age, appearing to peak during maturation. Changes in hip muscle strength and range of motion (ROM) during this time may contribute to altered dynamic movement patterns that are known to increase risk of ACL injuries. Understanding the longitudinal changes in hip strength and ROM is needed in order to develop appropriate interventions to reduce the risk of ACL injuries. The aim of the study was to examine the longitudinal changes in hip strength and ROM in female youth soccer players. Fourteen female youth soccer athletes (14.1± 1.1yrs, 165.8± 5.3cm, 57.5± 9.9kg) volunteered as part of a multi-year risk factor screening project. Clinical measures of hip strength and ROM were collected annually over three consecutive years. Passive hip internal rotation (IR), external rotation (ER), abduction (ABD), and adduction (ADD) ROM were measured with a digital inclinometer. Isometric hip ABD and extension (EXT) strength were evaluated using a hand-held dynamometer. Separate repeated measures ANOVAs compared hip strength and ROM values across 3 consecutive years (P<0.05). As youth female soccer players increased in age, there were no changes in normalized hip ABD (P=0.830) or EXT strength (P=0.062) across three consecutive years. Longitudinal changes in hip ROM were observed with increases in hip IR (P=0.001) and ABD (P<0.001), while hip ADD (P=0.009) and ER (P<0.001) decreased. Anatomical changes at the hip occur as youth female soccer players increase in age. While there are no changes in hip strength, there is an increase in hip IR and ABD ROM with a concomitant decrease in hip ER and ADD ROM. The resulting asymmetries in hip ROM may decrease the activation and force producing capabilities of the hip muscles during dynamic activities, contributing to altered lower extremity mechanics known to increase the risk of ACL injuries.

#7 Associations between Functional and Isolated Performance Measures in Collegiate Women's Soccer Players
Reference: J Sport Rehabil. 2016 Jul 21. [Epub ahead of print]
Authors: McCann RS, Kosik KB, Terada M, Beard MQ, Buskirk GE, Gribble PA
Summary: The Star Excursion Balance Test (SEBT) and Functional Movement Screen (FMS) are functional performance measures capable of predicting lower extremity injury risk. While suboptimal SEBT and FMS performances are influenced by multiple factors, the contribution of hip strength and flexibility to these tests is mostly unknown. Examination of hip strength and flexibility influences on the SEBT and FMS may direct clinicians to better methods of correcting functional deficits. Determine the relationships of isometric hip strength and hip passive range of motion (PROM) with functional performance measures. Forty-three NCAA Division I women's soccer players (19.65±1.12yrs; 166.93±3.84cm; 60.99±4.31kg) volunteered. All participants were tested bilaterally in the SEBT; the deep squat, in-line lunge, hurdle step, and straight leg raise, comprising a lower extremity FMS (FMS-LE); hip internal and external rotation PROM; and isometric hip extension strength (HEXT). The mean of the three averaged, normalized SEBT scores was used as a composite score. Pearson product moment correlations assessed relationships of SEBT and FMS-LE scores with PROM and HEXT. Significance was set a priori at P<0.05. Pearson correlations revealed anterior (ANT) SEBT scores had a low negative association with HEXT (r=-0.33,P=0.004) and a low positive association with hip internal rotation PROM (PROM-IR) (r=0.43,P=0.0032). All other correlations were negligible. Flexibility training aimed at PROM-IR may contribute to improved ANT scores. Targeting HEXT and hip external rotation PROM are likely not preferred means of correcting deficits in SEBT and FMS-LE performance.

#8 Injury Patterns among Elite Football Players: A Media-based Analysis over 6 Seasons with Emphasis on Playing Position
Reference: Int J Sports Med. 2016 Jul 28. [Epub ahead of print]
Authors: Leventer L, Eek F, Hofstetter S, Lames M
Summary: The study objective was to describe the types, localizations and severity of injuries among first division Bundesliga football players, and to study the effect of playing position on match and training injury incidence and severity, based on information from the public media. Exposure and injuries data from 1 448 players over 6 consecutive seasons were collected from a media-based register. In total, 3 358 injuries were documented. The incidence rate for match and training injuries was 11.5 per 1 000 match-hours (95% confidence interval [CI]: 10.9-12.2), and 61.4 per 100 player-seasons (95% CI: 58.8-64.1), respectively. Strains (30.3%) and sprains (16.7%) were the major injury types, with the latter causing significantly longer lay-off times than the former. Significant differences between the playing positions were found regarding injury incidence and injury burden (lay-off time per incidence-rate), with wing-defenders sustaining significantly lower incidence-rates of groin injuries compared to forwards (rate ratio: 0.43, 95% CI: 0.17-0.96). Wing-midfielders had the highest incidence-rate and injury burden from match injuries, whereas central-defenders sustained the highest incidence-rate and injury burden from training injuries. There were also significant differences in match availability due to an injury across the playing positions, with midfielders sustaining the highest unavailability rates from a match and training injury. Injury-risk and patterns seem to vary substantially between different playing positions. Identifying positional differences in injury-risk may be of major importance to medical practitioners when considering preventive measures.

#9 Death in Community Australian Football: A Ten Year National Insurance Claims Report
Reference: PLoS One. 2016 Jul 28;11(7):e0159008. doi: 10.1371/journal.pone.0159008. eCollection 2016.
Authors: Fortington LV, Finch CF
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Summary: While deaths are thought to be rare in community Australian sport, there is no systematic reporting so the frequency and leading causes of death is unknown. The aim of this study was to describe the frequency and cause of deaths associated with community-level Australian Football (AF), based on insurance-claims records. Retrospective review of prospectively collected insurance-claims for death in relation to community-level AF activities Australia-wide from 2004 to 2013. Eligible participants were aged 15+ years, involved in an Australian football club as players, coaches, umpires or supporting roles. Details were extracted for: year of death, level of play, age, sex, anatomical location of injury, and a descriptive narrative of the event. Descriptive data are presented for frequency of cases by subgroups. From 26,749 insurance-claims relating to AF, 31 cases were in relation to a death. All fatalities were in males. The initial event occurred during on-field activities of players (football matches or training) in 16 cases. The remainder occurred to people outside of on-field football activity (n = 8), or non-players (n = 7). Road trauma (n = 8) and cardiac conditions (n = 7) were the leading identifiable causes, with unconfirmed and other causes (including collapsed or not yet determined) comprising 16 cases. Although rare, fatalities do occur in community AF to both players and people in supporting roles, averaging 3 per year in this setting alone. A systematic, comprehensive approach to data collection is urgently required to better understand the risk and causes of death in participants of AF and other sports.

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