Latest research in football - week 6 - 2014

#1 The Effectiveness of Preventive Programs in Decreasing the Risk of Soccer Injuries in Belgium: National Trends Over a Decade
Authors: Bollars P, Claes S, Vanlommel L, Van Crombrugge K, Corten K, Bellemans J.
Reference: Am J Sports Med. 2014 Jan 30. [Epub ahead of print]
Summary: Although characterized by a relatively high injury rate, soccer is the world's most popular sport. In Belgium, the national Royal Belgian Football Association involves about 420,000 licensed players, whose injury reports are collected in a nationwide registry. Over a period of 10 years, the association has introduced the Fédération Internationale de Football Association preventive programs and has initiated a stringent postponement policy of competition in case of nonoptimal weather conditions. HYPOTHESIS:The authors questioned whether these preventive programs effectively decreased the incidence of soccer-related injuries. STUDY DESIGN:Descriptive epidemiology study. METHODS:The authors compared the incidence, location, timing, and severity of all registered soccer injuries in Belgium during 2 complete seasons separated by a decade (1999-2000 vs 2009-2010). RESULTS:A total of 56,364 injuries were reported, with an average of 6.8 injuries per 100 players per season. There was a 21.1% reduction in injury rate in the second season (rate ratio = 0.789; 95% confidence interval, 0.776-0.802), predominantly caused by a significant reduction in injuries during the winter period. In both seasons, an injury peak was noted during the first 3 months of the season. Recreational players had a higher risk for injury than national-level players (7.2 vs 4.4 injuries per 100 players per season; rate ratio = 1.64; 95% confidence interval, 1.59-1.69). The relative proportion of severe injuries was higher for female players and male youth players in general. CONCLUSION:The introduction of injury preventive programs has led to a significant reduction of soccer-related injuries, especially during the winter period. However, there is still room for improvement, and preventive programs can become more effective when specific parameters are targeted, such as adequate conditioning of players in the preseason.

#2 Practice and play as determinants of self-determined motivation in youth soccer players
Authors: Hendry DT, Crocker PR, Hodges NJ.
Reference: J Sports Sci. 2014 Jan 30. [Epub ahead of print]
Summary: Based upon predictions derived from the Developmental Model of Sports Participation, we tested whether hours in domain-specific play (self-led activities) and practice (coach-led activities) during childhood (~5-12 year) in an elite group of youth soccer players from the UK (N = 144) were related to motivation. Independent analysis of three different age groups (Under 13, 15 and 17 year) did not show relations between play and practice activities during childhood and global measures of motivation. However, secondary analysis showed that when controlling for years in soccer, years in the UK Academy system were negatively related to global indices of self-determined motivation (SDI) and positively related to controlled motivation for the oldest players. Despite predictions, there was no evidence that play during childhood was positively related to more SDI. Prospective research is recommended to enable more robust conclusions about the role of early developmental practice activities, especially early specialisation in a high-performance system, on both skill and psychosocial development.


#3 An atraumatic turf toe in an elite soccer player - A stress related phenomenon?
Authors: Roche AJ1, Calder JD2.
Reference: Foot Ankle Surg. 2014 Mar;20(1):71-3. doi: 10.1016/j.fas.2013.09.003. Epub 2013 Oct 5.
Summary: Plantar plate injuries to the hallux in elite athlete could potentially be career threatening. Reports in the literature are invariably linked to a significant traumatic episode. The occurrence of an atraumatic severe plantar plate injury in the presence of a bipartite sesamoid may suggest a stress related phenomenon. We present a case in an elite soccer player who was treated surgically and returned to top-level competition. The case is reported in detail and differences to other reports in the literature discussed.


#4 Reliability and validity of the Yo-Yo intermittent recovery test level 1 in young soccer players
Authors: Deprez D, Coutts AJ, Lenoir M, Fransen J, Pion J, Philippaerts R, Vaeyens R.
Reference: J Sports Sci. 2014 Jan 30. [Epub ahead of print]
Summary: The present study investigated the test-retest reliability from the Yo-Yo IR1 (distance and heart rate responses), and the ability of the Yo-Yo IR1 to differentiate between elite and non-elite youth soccer players. A total of 228 youth soccer players (11-17 years) participated: 78 non-elite players to examine the test-retest reliability within 1 week, added with 150 elite players to investigate the construct validity. The main finding was that the distance covered was adequately reproducible in the youngest age groups (U13 and U15) and highly reproducible in the oldest age group (U17). Also, the physiological responses were highly reproducible in all age groups. Moreover, the Yo-Yo IR1 test had a high-discriminative ability to distinguish between elite and non-elite young soccer players. Furthermore, age-related standards for the Yo-Yo IR1 established for elite and non-elite groups in this study may be used for comparison of other young soccer players.


#5 The effect of 16 weeks plyometric training on explosive actions in early to mid-puberty elite soccer players
Authors: Söhnlein Q, Müller E, Stöggl T.
Reference: J Strength Cond Res. 2014 Jan 27. [Epub ahead of print]
Summary: Plyometric training (PT) programs are widely used to improve explosive actions in soccer players of various ages, although there is debate about optimal training duration and time course of improvement. Twenty-two early to mid-puberty elite soccer players were assigned to a control (CG, n=10, regular soccer training) or plyometric training group (PTG, n=12, regular soccer training substituted with two PT sessions each week). Both groups trained for 16 weeks during the in-season period. CG performed only tests at baseline and post-intervention, whereas PTG performed additional tests after 4, 8 and 12 weeks. During each test, subjects' performances in speed (10-m&30-m; 5-m&20-m), agility, shuttle run (SR), multiple 5 bounds (MB5) and standing long jump (LJ) were recorded. The PTG showed improved performance in 20-m sprint time (-3.2%), agility time (-6.1%), MB5 distance (+11.8%) and LJ distance (+7.3%) (all, p<0.05) after 16 weeks. All these improvements were higher compared with CG (all, p<0.05). The time course of improvement in the PT group showed that 20-m sprint time improved after 16 weeks (p=0.012), agility after 4 (p=0.047) and 8 weeks (p=0.004), but stopped after 12 weeks (p=0.007); MB5 after 8 (p=0.039), 12 (p=0.028) and 16 weeks (p<0.001), and LJ improved after 4 (p=0.045), 12 (p=0.008) and 16 weeks (p<0.001). PT seems to be an appropriate training tool to enhance some, but not all explosive actions. The results indicate that the duration of a PT program is highly dependent on what type of explosive actions should be improved or whether several explosive actions should be improved at the same time.


#6 Physiological characteristics of international female soccer players
Authors: Manson SA, Brughelli M, Harris NK.
Reference: J Strength Cond Res. 2014 Feb;28(2):308-18. doi: 10.1519/JSC.0b013e31829b56b1.
Summary: The purpose of this study was to investigate the physiological characteristics of Fédération Internationale de Football Association (FIFA) eligible international female soccer players aged 14-36 years and to determine if measures were significantly different for players selected (i.e., starters) to the starting line up for an FIFA tournament as compared with those not selected (i.e., nonstarters). Fifty-one (N = 18 Under 17; N = 18 Under 20; N = 15 Senior) international female soccer players participated in this study. The subjects underwent measurements of anthropometry (height and body mass), lower body strength (isokinetic testing), sprint kinetics and kinematics (nonmotorized treadmill), leg power (unilateral jumping), and maximal aerobic velocity (30:15 intermittent fitness test) during the final preparatory stage for an FIFA event. Outcomes of the age group data indicate that differences in physiological capacities are evident for the Under 17 players as compared with those for the Under 20 and Senior capped international players, suggesting a plateau in the acquisition of physical qualities as players mature. Starters tended to be faster (effect size [ES] = 0.55-1.0, p < 0.05) and have a higher maximal aerobic velocity (ES = 0.78-2.45, p < 0.05), along with greater eccentric leg strength (ES = 0.33-1.67, p < 0.05). Significant differences were detected between starters and nonstarters for isokinetic leg strength (ES = 0.54-1.24, p < 0.05) and maximal aerobic velocity (ES = 0.87, p < 0.05) for Under 17 players, where maximal aerobic velocity was the primary difference between starters and nonstarters (ES = 0.83-2.45, p < 0.05) for the Under 20 and Senior players. Coaches should emphasize the development of speed, maximal aerobic velocity, and leg strength in developing female soccer players.


#7 Concussions and heading in soccer: A review of the evidence of incidence, mechanisms, biomarkers and neurocognitive outcomes
Authors: Maher ME, Hutchison M, Cusimano M, Comper P, Schweizer TA.
Reference: Brain Inj. 2014 Jan 29. [Epub ahead of print]
Summary: Soccer is currently the most popular and fastest-growing sport worldwide. Similar to many sports, soccer carries an inherent risk of injury, including concussion. Soccer is also unique in the use of 'heading'. The present paper provides a comprehensive review of the research examining the incidence, mechanisms, biomarkers of injury and neurocognitive outcomes of concussions and heading in soccer. Seven databases were searched for articles from 1806 to 24 May 2013. Articles obtained by the electronic search were reviewed for relevance, with 229 selected for review. Ultimately, 49 articles met criteria for inclusion in the present review. Female soccer players have a higher incidence of concussions than males. The most frequent injury mechanism is player-to-player contact for both genders. Few studies examined the effects of concussion in soccer players; however, neurocognitive outcomes were similar to those reported in the larger sport concussion literature, while the effect of heading is less clear. Despite variation in research designs and study characteristics, the outcomes of concussions in soccer align with the greater concussion literature. This review makes recommendations for future research to increase standardization of research for improved understanding of concussions in soccer as well as the effects of heading.


#8  Salivary IgA response and upper respiratory tract infection symptoms during a 21-week competitive season in young soccer players
Authors: Moreira A, Mortatti AL, Arruda AF, Freitas CG, de Arruda M, Aoki MS.
Reference: J Strength Cond Res. 2014 Feb;28(2):467-73. doi: 10.1519/JSC.0b013e31829b5512.
Summary: Sports training and competition are significant sources of stress, especially for young athletes. It is well known that physiological and psychological stressors induce neuroendocrine responses that could modulate immune system function. However, to date, little is known about the immune responses of young soccer players during a competitive season. Therefore, this study examined the effects of a 21-week competitive season divided into preseason, competitive season, and detraining on salivary immunoglobulin A (SIgA), upper respiratory tract infection (URTI) symptoms, and salivary cortisol in preadolescent male soccer players. Thirty-four young soccer players agreed to participate, and 26 (12.9 ± 0.2 years) completed the entire study. The investigation period was structured as follows: a 12-week preparatory training phase (preseason training), a 7-week competitive and a 2-week detraining phase. Resting saliva samples were taken to determine cortisol and SIgA responses. The players were required to complete a weekly log during the entire investigation reporting every sign or symptoms consistent with URTI. A significant increase in SIgA secretion rate and a decrease in URTI symptoms were observed after the 2-week detraining period (p < 0.05). No change was observed for cortisol during the study. These results indicate that training and competition demands affect the mucosal immune responses of young athletes. In addition, a short-prophylactic period (2-week detraining period) after a competitive period may attenuate mucosal immunosuppression related to URTI symptoms. Sport coaches should monitor markers of mucosal immune function to minimize illness that ultimately might lead to a decrease in performance.


#9 Effect of strength and high-intensity training on jumping, sprinting, and intermittent endurance performance in prepubertal soccer players
Authors: Ferrete C, Requena B, Suarez-Arrones L, de Villarreal ES.
Reference: J Strength Cond Res. 2014 Feb;28(2):413-22. doi: 10.1519/JSC.0b013e31829b2222.
Summary: The purpose of this study was to examine the effects of a 26-week on-field combined strength and high-intensity training on the physical performance capacity among prepubertal soccer players who were undertaking a competitive phase of training. Twenty-four prepubertal soccer players between the age of 8 and 9 years were randomly assigned to 2 groups: a control (C; n = 13) and an experimental group (S; n = 11). Both groups performed an identical soccer-training program, whereas the S group also performed combined strength and high-intensity training before the soccer-specific training. The 15-m sprint time (seconds), countermovement jump (CMJ) displacement, Yo-Yo intermittent endurance test (Yo-Yo IE), and Sit and Reach flexibility were each measured before (baseline) and after 9 (T2), 18 (T3), and 26 weeks (posttest) of training. There were no significant differences between the groups in any of the variables tested at baseline. After 26 weeks, significant improvements were found in the CMJ (6.72%; effect size [ES] = 0.37), Yo-Yo IE (49.57%, ES = 1.39), and Flexibility (7.26%; ES = 0.37) variables for the S group. Conversely, significant decreases were noted for the CMJ (-10.82%; ES = 0.61) and flexibility (-13.09%; ES = 0.94) variables in the C group. A significant negative correlation was found between 15-m sprint time and CMJ (r = -0.77) and Yo-Yo IE (r = -0.77) in the S group. Specific combined strength and high-intensity training in prepubertal soccer players for 26 weeks produced a positive effect on performance qualities highly specific to soccer. Therefore, we propose modifications to current training methodology for prepubertal soccer players to include strength and high-intensity training for athlete preparation in this sport.


#10  The Scandinavian athlete's heart; echocardiographic characteristics of male professional football players
Authors: Gjerdalen GF, Hisdal J, Solberg EE, Andersen TE, Radunovic Z, Steine K.
Reference: Scand J Med Sci Sports. 2014 Jan 29. doi: 10.1111/sms.12178. [Epub ahead of print]
Summary: This investigation explores the cardiac four-chamber remodeling response to training in male players in Norwegian professional football league, and ethnicity as determinants in the development of athlete's heart. Standard 2D echocardiographic examination and analysis of all four cavities were performed in 504 football players of Caucasian origin, 49 of African origin, and 47 matched Caucasian controls (<3 h training /week). All results were indexed to body surface area (BSA). Most athletes exhibited BSA-indexed values within normal ranges. Left ventricle (LV) mass was equally enlarged in both groups of athletes, but LV relative wall thickness and right ventricular (RV) relative wall thickness were increased in Africans compared with Caucasian athletes (0.37 ± 0.06 vs 0.33 ± 0.06 and 0.25 ± 0.06 vs 0.22 ± 0.04, respectively). Both LV and RV were smaller in Africans than in Caucasian athletes (67.8 ± 12.0 ml/m2 vs 73.6 ± 13.2 ml/m2 and 12.8 ± 2.1 vs 13.7 ± 2.4 cm2 /m2 , respectively, both P < 0.05), while left and right atria increased similarly. This first large-scale echocardiographic survey of elite football players in a Scandinavian league suggests use of BSA-indexed upper normal limits for both LV and RV in athletes. African athletes had significantly more concentric remodeled LV and RV than the Caucasian athletes.