Latest research in football - week 24 - 2013

Latest research in football

As previous literature 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 Neuromuscular efficiency of the vastus medialis obliquus and postural balance in professional soccer athletes after anterior cruciate ligament reconstruction
Authors: Chaves SF, Marques NP, Silva RL, Rebouças NS, de Freitas LM, de Paula Lima PO, de Oliveira RR.
Reference: Muscles Ligaments Tendons J. 2012 Sep 10;2(2):121-6. Print 2012 Apr.
Summary: The purpose of this study was to evaluate the neuromuscular efficiency of the vastus medialis obliquus and postural balance in high-performance soccer athletes after anterior cruciate ligament (ACL) reconstruction, compared to the uninvolved leg. A cross-sectional study was conducted with 22 male professional soccer players after ACL reconstruction (4-12 months postoperatively). The athletes were submitted to functional rehabilitation with an accelerated protocol on the soccer team. They were evaluated using isokinetic dynamometer, surface electromyography and electronic baropodometer. There was no decrease or difference between neuromuscular efficiency of the VMO when comparing both the limbs after ACL reconstruction in the professional soccer athletes under treatment. The same result was found in postural balance. It can be concluded that the NME of the VMO in the involved member and postural balance were successfully re-established after the reconstruction procedure of the ACL in the sample group studied.

#2 Thicker Achilles tendons are a risk factor to develop Achilles tendinopathy in elite professional soccer players
Authors: Jhingan S, Perry M, O'Driscoll G, Lewin C, Teatino R, Malliaras P, Maffulli N, Morrissey D.
Reference: Muscles Ligaments Tendons J. 2011 Dec 29;1(2):51-6. Print 2011 Apr.
Summary: The primary aim of this prospective cohort study was to compare the incidence of Achilles tendinopathy symptoms in elite soccer players with and without baseline asymptomatic ultrasound abnormalities. This study also investigated the relationship between baseline tendon thickness and development of symptoms. Using ultrasonography, 18 players were examined in 2009 for the existence of hypoechoicity, paratenon blurring, focal thickening and/or neovascularisation, and anteroposterior tendon thickness was measured. Symptom development during the follow-up period was assessed by interview one year later. Baseline mid-tendon thickness was greater (p=0.041) in tendons that experienced symptoms [median (IQR): 0.53 (0.51-0.55) cm] in the following year than tendons remaining asymptomatic [0.48 (0.45-0.52) cm]. No association between the existence of baseline ultrasound signs and development of symptoms in the following year was observed (Chi-Square: 1.180, p=0.277). A thicker baseline mid-tendon thickness was identified as a risk indicator for the development of Achilles tendinopathy in elite soccer players.

#3 Ad libitum fluid intake does not prevent dehydration in suboptimally hydrated young soccer players during a training session of a summer cAMP
Authors: Arnaoutis G, Kavouras SA, Kotsis YP, Tsekouras YE, Makrillos M, Bardis CN.
Reference: Int J Sport Nutr Exerc Metab. 2013 Jun;23(3):245-51.
Summary: There is a lack of studies concerning hydration status of young athletes exercising in the heat. The purpose of the study was to assess pre-exercise hydration status in young soccer players during a summer sports camp and to evaluate body-water balance after soccer training sessions. Initial hydration status was assessed in 107 young male soccer players (age 11-16 yr) during the 2nd day of the camp. Seventy-two athletes agreed to be monitored during 2 more training sessions (3rd and 5th days of the camp) to calculate dehydration via changes in body weight, while water drinking was allowed ad libitum. Hydration status was assessed via urine specific gravity (USG), urine color, and changes in total body weight. Mean environmental temperature and humidity were 27.2 ± 2 °C and 57% ± 9%, respectively. According to USG values, 95 of 107 of the players were hypohydrated (USG ≥ 1.020) before practice. The prevalence of dehydration observed was maintained on both days, with 95.8% and 97.2% of the players being dehydrated after the training sessions on the 3rd and 5th days, respectively. Despite fluid availability, 54 of the 66 (81.8%) dehydrated players reduced their body weight (-0.35 ± 0.04 kg) as a response to training, while 74.6% (47 out of the 63) further reduced their body weight (-0.22 ± 0.03 kg) after training on the 5th day. Approximately 90% of the young soccer players who began exercising under warm weather conditions were hypohydrated, while drinking ad libitum during practice did not prevent further dehydration in already dehydrated players.

#4 Warm-up strategies of professional soccer players: practitioners' perspectives
Authors: Towlson C, Midgley AW, Lovell R.
Reference: J Sports Sci. 2013 Jun 4. [Epub ahead of print]
Summary: Recent research has challenged the typical pre-match and half-time (HT) interval warm-up (WU) routines currently used by professional soccer players. This study surveyed 2010/11 season WU strategies and their underpinning scientific reasoning and situational factors via an internet-based questionnaire, which was distributed to English Premier League and Championship practitioners, of which 43% responded. The pre-match WU duration was 30.8 (8.2) min, ranging between 15-45 min, and 89% of practitioners administered a WU of ≥ 25 min. Respondents also reported a 12.4 (3.8) min period between the end of the WU and match kick-off. Eighty-nine per cent recognised the physiological benefits of re-WUs during this "down-time" period, with 63% instructing players to engage in such activity. During HT, 58% instructed players to re-WU either on the pitch or within stadia facilities, but "unwillingness of the coach/manager" (42%) and a "lack of time" (63%) were major constraints. Practitioners reported that 2.6 (1.6) min might be available for HT re-WUs. Factors such as match regulations, league policy, and stadia facilities were not generally considered as major barriers to the delivery of WUand re-WU strategies. We suggest that researchers consider the time-demands and barriers faced by practitioners when developing experimental designs to examine WU regimens.

#5 Effective learning among elite football players: The development of a football-specific self-regulated learning questionnaire
Authors: Toering T, Jordet G, Ripegutu A.
Reference: J Sports Sci. 2013 Jun 4. [Epub ahead of print]
Summary: The present study aimed to develop a football-specific self-report instrument measuring self-regulated learning in the context of daily practice, which can be used to monitor the extent to which players take responsibility for their own learning. Development of the instrument involved six steps: 1. Literature review based on Zimmerman's ( 2006 ) theory of self-regulated learning, 2. Item generation, 3. Item validation, 4. Pilot studies, 5. Exploratory factor analysis (EFA), and 6. Confirmatory factor analysis (CFA). The instrument was tested for reliability and validity among 204 elite youth football players aged 13-16 years (Mage = 14.6; s = 0.60; 123 boys, 81 girls). The EFA indicated that a five-factor model fitted the observed data best (reflection, evaluation, planning, speaking up, and coaching). However, the CFA showed that a three-factor structure including 22 items produced a satisfactory model fit (reflection, evaluation, and planning; non-normed fit index [NNFI] = 0.96, comparative fit index [CFI] = 0.95, root mean square error of approximation [RMSEA] = 0.067). While the self-regulation processes of reflection, evaluation, and planning are strongly related and fit well into one model, other self-regulated learning processes seem to be more individually determined. In conclusion, the questionnaire developed in this study is considered a reliable and valid instrument to measure self-regulated learning among elite football players.

#6 Geometric indices of hip bone strength in young female football players
Author: El Hage R.
Reference: J Musculoskelet Neuronal Interact. 2013 Jun;13(2):206-12.
Summary: The aim of this study was to compare geometric indices of hip bone strength in female football players and controls. 18 adult female football players and 18 adult sedentary females participated in this study. The two groups were paired for age, weight and body mass index (BMI). Daily calcium intake (DCI) and daily protein intake (DPI) were evaluated by questionnaires. Total hip bone mineral density (BMD) and femoral neck BMD were measured by DXA. Cross-sectional area (CSA), an index of axial compression strength, section modulus (Z), an index of bending strength and cortical thickness (CT) were evaluated at the femoral neck (FN), the intertrochanteric (IT) and the femoral shaft (FS) regions by the hip structure analysis (HSA) program. Age, weight, height, BMI, DCI and DPI were not different between the two groups. TH BMD, FN BMD, FN CSA, FN Z, FN CT, IT CSA, IT Z, IT CT, FS CSA and FS Z were significantly higher in football players compared to controls (crude percentage differences between the two groups varied between 8 and 19%; P<0.05). After adjusting for body weight using a one-way analysis of covariance (ANCOVA), TH BMD, FN BMD, FN CSA, FN Z, FN CT, IT CSA, IT Z, IT CT, FS CSA and FS Z remained significantly higher in football players compared to controls (adjusted percentage differences between the two groups varied between 7 and 17%; P<0.05). This study suggests that, in adult females, football practice is associated with greater geometric indices of hip bone strength.

#7 High intensity interval training vs. high-volume running training during pre-season conditioning in high-level youth football: a cross-over trial
Authors: Faude O, Schnittker R, Schulte-Zurhausen R, Müller F, Meyer T.
Reference: J Sports Sci. 2013 May 31. [Epub ahead of print]
Summary: We aimed at comparing the endurance effects of high-intensity interval training (HIIT) with high-volume running training (HVT) during pre-season conditioning in 20 high-level youth football players (15.9 (s 0.8) years). Players either conducted HVT or HIIT during the summer preparation period. During winter preparation they performed the other training programme. Before and after each training period several fitness tests were conducted: multi-stage running test (to assess the individual anaerobic threshold (IAT) and maximal running velocity (Vmax)), vertical jumping height, and straight sprinting. A significant increase from pre- to post-test was observed in IAT velocity (P < 0.001) with a greater increase after HVT (+0.8 km · h-1 vs. +0.5 km · h-1 after HIIT, P = 0.04). Maximal velocity during the incremental exercise test also slightly increased with time (P = 0.09). Forty per cent (HIIT) and 15% (HVT) of all players did not improve IAT beyond baseline variability. The players who did not respond to HIIT were significantly slower during 30 m sprinting than responders (P = 0.02). No further significant differences between responders and non-responders were observed. Jump heights deteriorated significantly after both training periods (P < 0.003). Both training programmes seem to be promising means to improve endurance capacity in high-level youth football players during pre-season conditioning.

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