Latest research in football - week 9 - 2013

Latest research in football

As previous 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 A comparison of methods to quantify the in-season training load of professional soccer players.
Authors: Scott BR, Lockie RG, Knight TJ, Clark AC, Janse de Jonge X AK.
Reference: Int J Sports Physiol Perform. 2013 Mar;8(2):195-202.
Summary: The purpose of the investigation was to compare various measures of training load (TL). Variables were a) physiological (heart rate (HR)), b) perceptual (rating of perceived exertion [RPE]), and c) physical (global positioning system (GPS) and accelerometer) data from in-season field-based training for professional soccer. Fifteen professional male soccer players participated in 97 in-season individual training sessions and measure of external TL (total distance (TD), the volume of low-speed activity (LSA; <14.4 km/h), high-speed running (HSR; >14.4 km/h), very high-speed running (VHSR; >19.8 km/h), and player load, HR and session-RPE (sRPE) were recorded. Internal TL scores (HR-based and sRPE-based) were calculated, and their relationships with measures of external TL were correlated. TD, LSA volume, and player load provided significant large correlations with the HR-based and sRPE-based methods. Volume of HSR and VHSR were moderately correlated with internal TL. The authors concluded that  volume of HSR and VHSR provided significant relationships with internal TL, physical-performance measures of TD, LSA volume, and player load appear to be more acceptable indicators of external TL, due to the greater magnitude of their correlations with measures of internal TL.

#2 Anaerobic performance testing of professional soccer players 1995-2010
Authors: Haugen TA, Tønnessen E, Seiler S.
Reference: Int J Sports Physiol Perform. 2013 Mar;8(2):148-56.
Summary: The purpose of the study was to compare sprint and countermovement-jump (CMJ) performance among competitive soccer players as a function of performance level, field position, and age. Additionally, the authors wanted to quantify the evolution of these physical characteristics among professional players over a 15-y period. Highly trained athletes (N = 939) were tested for 40-m sprint time and CMJ at the Norwegian Olympic Training Center between 1995 and 2010. National-team and 1st-division players were significant faster than 2nd-division (1.0-1.4%), 3rd- to 5th-division (3.0-3.8%), junior national-team (1.7-2.2%), and junior players (2.8-3.7%). Forwards were significant faster than defenders (1.4%), midfielders (2.5%), and goalkeepers (3.2%) over 0-20 m. Midfielders showed significant lower jumping performance (~2.0 cm) than the other playing positions. Sprinting running performance was highest in the age range 20-28 years and declined significantly thereafter. Players from 2006-2010 had 1-2% faster 0-20 m and peak velocity than players from the 1995-1999 and 2000-2005 years. However there were no differences in CMJ performance from those players. The authors concluded that CMJ performance has remained stable over time, there has been a small but positive development in sprinting velocity among professional players.

#3 Repeated High-Intensity Running and Sprinting in Elite Women's Soccer Competition
Authors: Gabbett TJ, Wiig H, Spencer M.
Reference: Int J Sports Physiol Perform. 2013 Mar;8(2):130-8.
Summary: The purpose of this study was to report on the RSA of elite women's football competition. Additionally, to describe the nature of RHIA (eg, striding and sprinting activities) that involve a high energy cost and are associated with short (i.e. ≤20 s) recovery periods.  The video-based time-motion analysis on 34 occasions during national and international standard matches of elite women soccer players (N = 13) were evaluated for data analysis. RSA and RHIA were defined as successive (i.e., 2) sprints or striding and sprinting efforts that occurred with ≤20 s between efforts. The results showed no differences of first half and second half RSA and RHIA bouts. However, recovery duration between efforts increased in the second half, when a greater number of efforts were performed per bout. The authors concluded that there is no reductions in RHIA and RSA  from the first to the second half in in elite women's soccer competition. However, players increase the amount of low-intensity recovery undertaken between RHIA and RSA efforts.

#4 Changes in immune functions during a peaking period in male university soccer players.
Authors: Ueno Y, Umeda T, Takahashi I, Iwane K, Okubo N, Kuroiwa J, Miyazawa M, Osato R, Yoneda K, Nakaji S.
Reference: Luminescence. 2013 Feb 21. doi: 10.1002/bio.2496. [Epub ahead of print]
Summary: The concept of peaking ensures that athletes have trained to attain their absolute peak performance levels prior to a competition. This study investigates the effects of peaking on the functions of neutrophils and lymphocytes in university soccer players during a five-day soccer training camp followed by two weeks of tapering. The study subjects were 22 soccer players who were members of a university soccer club. We carried out our investigation during a five-day training camp and two weeks after the training camp (i.e. the tapering period). We measured body composition, immune-related parameters (leukocyte count, neutrophil count, lymphocyte count, immunoglobulins and complements), myogenic enzymes, superoxide dismutase activity (SOD) and neutrophil functions [reactive oxygen species (ROS) production, phagocytic activity, serum opsonic activity and lymphocyte subtypes]. Leukocyte and neutrophil counts tend to increase after the training camp compared with values before the training camp, and recovered during the conditioning period, although the final values were still lower than those before the training camp. The amount of ROS production per neutrophil and level of SOD decreased significantly during the conditioning period compared with before the training camp (p < 0.05, p < 0.01, respectively). Levels of Th1 cells decreased significantly during the conditioning period compared with the training camp (p < 0.05). In conclusion, the period of two weeks for the tapering period was considered insufficient to allow the athletes' immune function to recover completely after an intensive training camp.

#5 Abnormal Frontal Plane Knee Mechanics During Sidestep Cutting in Female Soccer Athletes After Anterior Cruciate Ligament Reconstruction and Return to Sport.
Authors: Stearns KM, Pollard CD
Reference: Am J Sports Med. 2013 Feb 20. [Epub ahead of print]
Summary: Soccer players are prone for re-injuries upon the return to sports participation, especially players who suffered from anterior cruciate ligament reconstruction (ACLR). While the mechanisms are unknown, it has been suggested that altered knee biomechanics during sports-specific activities may be a contributing factor. The purpose of the study was to compare frontal plane knee joint angles and moments during a sidestep cutting maneuver in female soccer athletes who have undergone ACLR with those in athletes with no history of knee injury. Players (N = 12) with a history of ACLR served as the experimental group, and equal amount of female soccer players with no history of knee injury constituted as the control group. Three-dimensional kinematics and ground-reaction forces were collected while each participant performed a sidestep cutting maneuver. Participants in the ACLR group exhibited a significant increase in average knee abduction angles (ACLR: 3.8° vs control: 1.8°) and peak knee adductor moments (ACLR: 1.33 N•m/kg vs control: 0.80 N•m/kg) compared with the control group. The authors concluded that female soccer players who have undergone ACLR and returned to sports participation exhibited increased knee abduction angles and knee adductor moments during the early deceleration phase of cutting compared with their healthy counterparts with no history of knee injury.

#6 The effects of a congested fixture period on physical performance, technical activity and injury rate during matches in a professional soccer team.
Authors: Dellal A, Lago-Peñas C, Rey E, Chamari K, Orhant E.
Reference: Br J Sports Med. 2013 Feb 19. [Epub ahead of print]
Summary: The purpose was to investigate the influence of playing multiple games with a short recovery time between matches on physical activity, technical performance and injury rates. The variation of physical (overall distance, light-intensity, low-intensity, moderate-intensity and high-intensity running) and technical performance (successful passes, balls lost, number of touches per possession and duels won) of 16 international players was examined during three different congested periods of matches (six games in 18 days) from the French League and Cup (n=12), and the UEFA Champions' League (n=6) during the 2011-2012 season and compared with that reported in matches outside these periods. Data were collected using Amisco. Injury rate, time loss injuries, as well as the mechanism, circumstances and severity of the injury were also analyzed. There were no differences were found across the six successive games in the congested period, and between no congested and the three congested periods for all the physical and technical activities. The total incidence of injury (matches and training) across the prolonged congested periods did not differ significantly to that reported in the non-congested periods. However, the injury rate during match-play was significantly higher during the congested period compared with the non-congested period. The injury rate during training time was significantly lower during the congested period compared with the non-congested periods. The mean lay-off duration for injuries was significant shorter during the congested periods compared with the non-congested periods. The authors concluded that despite being active, the technical performance and injury incidence were unaffected during a prolonged period of fixture congestion. However, the congested period affects injury rates during training and match-play and the lay-off duration.

#7 Preventive exercises reduced injury-related costs among adult male amateur soccer players: a cluster-randomised trial.
Authors: Krist MR, van Beijsterveldt AM, Backx FJ, Ardine de Wit G.
Reference: J Physiother. 2013;59(1):15-23. doi: 10.1016/S1836-9553(13)70142-5.
Summary: The purpose of the study was to investigate the efficacy and the cost efficacy of an injury prevention program consisting of 10 exercises designed to improve stability, muscle strength, co-ordination, and flexibility of the trunk, hip and leg muscles (known as The11+) in adult male amateur soccer players. Adult male soccer players (N = 479) participated in this study and the intervention group was instructed to perform the exercises at each training session, 2-3 times per week over a soccer season. The control group continued their routine warm-up. Variables measured were all injuries and costs associated with these injuries and were compared between groups after bootstrapping (5000 replications). The results showed no significant differences in the proportion of injured players and injury rate between the two groups. Average overall costs in the 11+ group were €161 per athlete and €256 per injured athlete. Mean overall costs in the control group were €361 per athlete and €606 per injured athlete. While intervention players showed significant lower costs the exercises failed to significantly reduce the number of injuries in male amateur soccer players within one season, however, seemed to significantly reduce injury-related costs. The authors concluded that the savings might be the result of a preventive effect on knee injuries, which often have substantial costs due to lengthy rehabilitation and lost productivity.

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