Latest research in football - week 49 - 2013

#1 Injury surveillance during a 2-day national female youth football tournament in Kenya
Reference: Br J Sports Med. 2013 Nov 22. doi: 10.1136/bjsports-2013-092307. [Epub ahead of print]
Authors: Lislevand M, Andersen TE, Junge A, Dvorak J, Steffen K.
Summary: The purpose was to analyse the incidence, characteristics and circumstances of injuries during a female youth amateur football tournament in Kenya. 14 injury recorders prospectively registered and classified all injuries during all matches. Four physiotherapists and two doctors supported the injury recorders. A 2-day Mathare Youth Sports Association (MYSA) inter-provincial football tournament for female players in Nairobi, Kenya. The tournament is organised by a non-governmental organisation (NGO). 938 females divided into three age groups (under 13 years (U13), under 16 years (U16) and over 16 years (O16)). 123 injuries occurred in 106 matches. The incidence of all injuries was 93.3 injuries/1000 h. Players in the U13 (relative risk (RR)=2.16, 95% CI 1.3 to 3.5; p=0.002) and U16 (RR=2.17, 95% CI 1.3 to 3.5; p=0.002) age groups had an increased risk of injury compared to the O16 group. Most injuries allowed the players to continue to play (n=98 of 121; 81%). For 15 (12%) of the injuries the player did not continue to play but was expected to fully participate in the following match, and eight of the injuries (6.1 injuries/1000 h) were expected to result in the player's absence from play for 1-7 days. The injuries most commonly affected the lower limb (n=100; 82%); contusions to the ankle (n=15; 12%) and foot/toe (n=15; 12%) were the most common specific injury types. Most acute injuries (89 of 113, 79%) were caused by player contact. The incidence of injuries among female youth football players in a national tournament in Kenya was high, but time-loss injuries were rare. Playing football in a tournament organised by an NGO at the inter-provincial level was safe.


#2 Control of dynamic foot-ground interactions in male and female soccer athletes: Females exhibit reduced dexterity and higher limb stiffness during landing
Reference: J Biomech. 2013 Nov 7. pii: S0021-9290(13)00530-7. doi: 10.1016/j.jbiomech.2013.10.038. [Epub ahead of print]
Authors: Lyle MA, Valero-Cuevas FJ, Gregor RJ, Powers CM.
Summary: Controlling dynamic interactions between the lower limb and ground is important for skilled locomotion and may influence injury risk in athletes. It is well known that female athletes sustain anterior cruciate ligament (ACL) tears at higher rates than male athletes, and exhibit lower extremity biomechanics thought to increase injury risk during sport maneuvers. The purpose of this study was to examine whether lower extremity dexterity (LED) - the ability to dynamically control endpoint force magnitude and direction as quantified by compressing an unstable spring with the lower limb at submaximal forces - is a potential contributing factor to the "at-risk" movement behavior exhibited by female athletes. We tested this hypothesis by comparing LED-test performance and single-limb drop jump biomechanics between 14 female and 14 male high school soccer players. We found that female athletes exhibited reduced LED-test performance (p=0.001) and higher limb stiffness during landing (p=0.008) calculated on average within 51ms of foot contact. Females also exhibited higher coactivation at the ankle (p=0.001) and knee (p=0.02) before landing. No sex differences in sagittal plane joint angles and center of mass velocity at foot contact were observed. Collectively, our results raise the possibility that the higher leg stiffness observed in females during landing is an anticipatory behavior due in part to reduced lower extremity dexterity. The reduced lower extremity dexterity and compensatory stiffening strategy may contribute to the heightened risk of ACL injury in this population.


#3 The influence of athletic status on the passive properties of the muscle-tendon unit and traditional performance measures in division I female soccer players and non-athlete controls
Authors: Palmer TB, Thompson BJ, Hawkey MJ, Conchola EC, Adams BM, Akehi K, Thiele RM, Smith DB.
Reference: J Strength Cond Res. 2013 Nov 22. [Epub ahead of print]
Summary: The purpose of the present study was to determine if passive muscle-tendon properties of the posterior muscles of the hip and thigh and lower-body muscle power could discriminate between athletic status in Division I female soccer athletes and non-athlete controls. Ten athletes (mean±SE: age=18.70±0.34years; mass=64.61±2.16kg; height=165.99±1.46cm; thigh muscle cross-sectional area=94.08±2.58cm) and eleven non-athletes (19.64±0.51years; 62.81±2.60kg; 162.44±2.20cm; 86.33±2.81cm) performed two instrumented straight-leg raise (iSLR) assessments using an isokinetic dynamometer programmed in passive mode to move the foot toward the head at 5°·s. During each iSLR, passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curve and maximum range of motion (ROM) was determined as the point of discomfort but not pain, as indicated by the participant. Lower-body power characteristics were assessed via a countermovement vertical jump (CMJ) test. The results indicated that phase 1 and 2 slopes, CMJ height, and peak power (Pmax) were significantly higher (P=0.004-0.036) for the athletes compared to the non-athletes; however, maximum ROM was not different (P=0.601) between groups. Significant relationships were also observed between phase 1 and 2 slopes and CMJ height and Pmax (r=0.483-0.827; P≤0.001-0.027). These findings suggest that in addition to traditional power characteristics, passive stiffness may also be a sensitive and effective measure for discriminating athletes from non-athletes. Coaches and practitioners may use these findings when designing training programs aimed at increasing musculotendinous stiffness of the posterior hip and thigh muscles and to help identify athletes with high overall athletic potential.


#4 Caffeine Supplementation and Reactive Agility in Elite Youth Soccer Players
Authors: Jordan JB, Korgaokar A, Farley RS, Coons JM, Caputo JL.
Reference: Pediatr Exerc Sci. 2013 Nov 25. [Epub ahead of print]
Summary: This study examined the effects of caffeine supplementation (6 mg·kg-1) on performance of a reactive agility test (RAT) in 17 elite, male, youth (M = 14 yrs) soccer players. Using a double-blind, repeated-measures design, players completed 4 days of testing on the RAT after a standardized warm-up. On Day 1, anthropometric measurements were taken and players were accommodated to the RAT. On Day 2, baseline performance was established. Caffeine or placebo conditions were randomly assigned on Day 3 and the condition was reversed on Day 4. Players completed 3 randomized trials of the RAT on Days 2, 3, and 4 with at least one trial to the players' dominant and non-dominant sides. There were no significant differences among conditions in reaction time (RT) to the dominant side, heart rates at any point of measurement, or ratings of perceived exertion (RPE) after completion of the warm-up. Caffeine produced faster RT to the non-dominant side (P = .041), higher RPE at the conclusion of the RAT (P = .013). The effect on the Total Time (TT) to complete the agility test to the non-dominant side approached significance (P = .051). Sprint time and TT to either side did not differ. Caffeine supplementation may provide ergogenic benefit to elite, male, youth soccer players.


#5 Tuberculosis of testis and prostate that mimicked testicular cancer in young male soccer player
Authors: Cho YS, Joo KJ, Kwon CH, Park HJ.
Reference: J Exerc Rehabil. 2013 Jun 30;9(3):389-393.
Summary: Staphylococcus infection was the most common organism found in infection of athletics, and tuberculosis (TB) was rare. Although genitourinary tuberculosis (GUTB) was the most common subtype of extrapulmonary tuberculosis (EPTB) in the past, it was recently reported to account for less than 0.5% of all patients with EPTB and 1.5% of all patients with pulmonary tuberculosis (TB). And, there are few cases reported about concomitant tuberculous infection of testis and prostate. Pubic pain is a common symptom in soccer player and its cause can be difficult to determine. A 25-yr-old male soccer player presented with persistent pubic pain of unknown origin. Incidentally, right testicular mass was detected on physical examination. Computed tomography revealed a multiple enlarged retroperitoneal lymph nodes. Under the clinical diagnosis of a right testicular tumor, right radical inguinal orchiectomy was performed. And prostate biopsy was performed due to elevated serum prostate specific antigen (PSA). Pathologic examination confirmed concomitant TB of testis and prostate.


#6 Mechanisms of Injury for Concussions in University Football, Ice Hockey, and Soccer
Authors: Delaney JS, Al-Kashmiri A, Correa JA.
Reference: Clin J Sport Med. 2013 Nov 26. [Epub ahead of print]
Summary: The purpose of this study was to examine the mechanisms of injury for concussions in university football, ice hockey, and soccer. Male and female athletes participating in varsity football, ice hockey, and soccer were of interest.  Athletes were followed prospectively over a 10-year period to determine the mechanisms of injury for concussions and whether contact with certain areas of the body or individual variables predisposed to longer recovery from concussions. For soccer, data were collected on whether concussions occurred while attempting to head the ball. There were 226 concussions in 170 athletes over the study period. The side/temporal area of the head or helmet was the most common area to be struck resulting in concussion in all 3 sports. Contact from another player's head or helmet was the most probable mechanism in football and soccer. In hockey, concussion impacts were more likely to occur from contact with another body part or object rather than another head/helmet. Differences in mechanisms of injuries were found between males and females in soccer and ice hockey. Athletes with multiple concussions took longer to return to play with each subsequent concussion. Half of the concussions in soccer were related to attempting to head the soccer ball. The side of the head or helmet was the most common area to be struck resulting in concussion in all 3 sports. In ice hockey and soccer, there are differences in the mechanisms of injury for males and females within the same sport.


#7 Relationships between field performance tests in high-level soccer players
Authors: Ingebrigtsen J, Brochmann M, Castagna C, Bradley P, Ade J, Krustrup P, & Holtermann A.
Reference: Journal of Strength and Conditioning Research 2013
Summary: In order to reduce athlete testing time, the aim of this study was to investigate the relationship between the Yo-Yo intermittent recovery test level 1 (IR1) and 2 (IR2) test performances, maximal sprinting speed (10, 20 and 35 m), repeated sprint ability (RSA) (7x35 m), and sub- maximal heart rates after two and four minutes of the Yo-Yo IR tests by testing 57 high-level soccer players. All players played regularly in one of the three highest levels of Norwegian soccer and were tested during three sessions on three consecutive days. Large correlations were observed between Yo-Yo IR1 and IR2 test performances (r=0.753 p≤0.05). Small and moderate correlations were found between 20 and 35 m sprinting speed and Yo-Yo IR1 performance (r=-0.289 and -0.321, respectively, p≤0.05), while 35 m sprinting speed correlated moderately to Yo-Yo IR2 performance (r=-0.371, p≤0.05). RSA at 10, 20 and 35 m all showed moderate to large correlations to Yo-Yo IR1 performance (r=-0.337 to -0.573, p≤0.05). RSA at 20 m (r = -0.348, p≤0.05) and 35 m (r=-0.552, p≤0.01) correlated moderately and largely to Yo-Yo IR2 performance. Also, moderate and large correlations were found between sub-maximal Yo-Yo IR1 heart rates after 2 (r=-0.483, p≤0.01) and 4 min (r=-0.655, p≤0.01) and Yo-Yo IR1 performance, and 2 min Yo-Yo IR2 heart rate and Yo-Yo IR2 performance (r=-0.530, p≤0.01). ICC measures of sub-maximal HR after 2 and 4 min of Yo-Yo IR1 test, and after 2 min of the Yo-Yo IR2 were 0.92 (CV=4.1%, n=33), 0.93 (CV=3.8%, n=33) and 0.72 (CV=2.9%, n=10). Adjusted ordinary least square (OLS) regressions revealed associations (p≤0.05) between sprint speed at 20 m and 35 m and Yo-Yo IR1 test performance, but only between 35 m and IR2 test performance (p≤0.05). Further, OLS showed that RSA at 35 m was related to both levels of the Yo-Yo IR test (p≤0.01), and that sub-maximal heart rates after 2 and 4 min were independently associated to Yo-Yo IR1 and IR2 performances (p≤0.01). In conclusion, Yo-Yo IR1 and 2 test performances, as well as sprint and RSA performances, correlated very largely, and it may therefore be considered using only one of the Yo-Yo tests and a RSA test, in a general soccer-specific field test protocol. The sub-maximal heart rate measures during Yo-Yo tests are reproducible and may be utilized for frequent, time-efficient and non-exhaustive testing of intermittent exercise capacity of high-level soccer players


#8 Inspiratory muscle training improves exercise tolerance in recreational soccer players without concomitant gain in soccer specific fitness
Authors: Guy JH, Edwards AM, Deakin GB.
Reference: J Strength Cond Res. 2013. [Epub ahead of print]
Summary: This study investigated whether the addition of inspiratory muscle training (IMT) to an existing programme of pre-season soccer training would augment performance indices such as exercise tolerance and sports-specific performance beyond the use of pre-season training alone. Thirty one adult males were randomised across three groups: experimental (EXP: n=12), placebo (PLA: n=9), and control (CON: n=10). EXP and PLA completed a 6-week pre-season programme (two x weekly sessions) in addition to concurrent IMT with either a IM training load (EXP) or negligible (PLA) inspiratory resistance. CON did not use an IMT device or undertake soccer training. All participants performed the following tests before and after the 6-week period: Standard spirometry; maximal inspiratory mouth pressure (MIP); multi stage fitness test (MSFT) and a soccer specific fitness test (SSFT). Following 6-weeks training, EXP significantly improved: MIP (P=0.002); MSFT distance covered (P=0.02); and post SSFT blood lactate (BLa) (P=0.04). No other outcomes from the SSFT were changed. Pre to post training performance outcomes for PLA and CON were unchanged. These findings suggest the addition of IMT to pre-season soccer training improved exercise tolerance (MSFT distance covered) but had little effect on soccer specific fitness indices beyond a slightly reduced post-training SSFT BLa. In conclusion, there may be benefit for soccer players to incorporate IMT to their pre-season training but the effect is not conclusive. It is likely that a greater pre-season training stimulus would be particularly meaningful for this population if fitness gains are a priority and also evoke a stronger IMT response.


#9 Match Analysis of U9 and U10 English Premier League Academy Soccer Players using a Global Positioning System: Relevance for Talent Identification and Development
Authors: Goto H, Morris JG, Nevill ME.
Reference: J Strength Cond Res. 2013 [Epub ahead of print]
Summary: The purpose of this study was to examine the match activity profile of U9 and U10 elite soccer players and to establish if there were any differences between players who were subsequently retained or released by their clubs. Such information should prove valuable in the design of training programs for these very young players and in the talent identification and development process. A Global Positioning System was used to analyze 2-4 inter-academy 6-a-side matches of English Premier League Academy players (U9: N = 22 and U10: N = 12) who trained three times a week (4.5 h) . Speed zones were created based on 5 and 10 m sprint times and an independent sample t-test was employed for a statistical analysis.Both squads covered ∼4000 m in total or ∼4700 m·h during a match (NS between squads), with the U10s tending to cover a greater distance at moderate (p = 0.10) and high speeds (p = 0.08) than the U9s. Retained group covered a greater distance than released group (retained vs. released: 4478 ± 513 m vs. 4091 ± 462 m, p < 0.05) during a match and covered a greater distance during low speed running in absolute (1226 ± 259 m vs. 1005 ± 221 m, p < 0.05) and relative (1325 ± 235 m vs. 1132 ± 210 mh, p < 0.05) terms. Thus, U9 and U10 players cover over 4000 m in match play and those players who are retained by academies cover a greater distance in total and at low speeds (2.1-3.1 m·s). This information may support the preparation of squad training programs and the talent identification and development process.