Latest research in football - week 47 - 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 Plantar pressure asymmetry and risk of stress injuries in the foot of young soccer players
Reference: Phys Ther Sport. 2016 Oct 24. pii: S1466-853X(16)30129-8. doi: 10.1016/j.ptsp.2016.10.001. [Epub ahead of print]
Authors: Azevedo RR, da Rocha ES, Franco PS, Carpes FP
Summary: Asymmetries in the magnitude of plantar pressure are considered a risk factor for stress fracture of the fifth metatarsal in soccer athletes. The objective was to investigate the presence of plantar pressure asymmetries among young soccer athletes. Thirty young adolescents divided into a soccer player group (n = 15) or a matched control group (n = 15) participated in this study. Mean plantar pressure was determined for seven different regions of the foot. Data were compared between the preferred and non-preferred foot, and between the groups, during barefoot standing on a pressure mat system. Higher pressure was found in the hallux, 5th metatarsal and medial rearfoot of the non-preferred foot in the young soccer players. These asymmetries were not observed in the control group. Magnitudes of plantar pressure did not differ between the groups. Young soccer players present asymmetries in plantar pressure in the hallux, 5th metatarsal and medial rearfoot, with higher pressure observed in the non-preferred foot.

#2 The acute:chonic workload ratio in relation to injury risk in professional soccer
Reference: J Sci Med Sport. 2016 Nov 9. pii: S1440-2440(16)30230-4. doi: 10.1016/j.jsams.2016.10.014. [Epub ahead of print]
Authors: Malone S, Owen A, Newton M, Mendes B, Collins KD, Gabbett TJ
Summary: The objective was to examine the association between combined sRPE measures and injury risk in elite professional soccer. Forty-eight professional soccer players (mean±SD age of 25.3±3.1 yr) from two elite European teams were involved within a one season study. Players completed a test of intermittent-aerobic capacity (Yo-YoIR1) to assess player's injury risk in relation to intermittent aerobic capacity. Weekly workload measures and time loss injuries were recorded during the entire period. Rolling weekly sums and week-to-week changes in workload were measured, allowing for the calculation of the acute:chronic workload ratio, which was calculated by dividing the acute (1-weekly) and chronic (4-weekly) workloads. All derived workload measures were modelled against injury data using logistic regression. Odds ratios (OR) were reported against a reference group. Players who exerted pre-season 1-weekly loads of ≥1500 to ≤2120AU were at significantly higher risk of injury compared to the reference group of ≤1500AU (OR=1.95, p=0.006). Players with increased intermittent-aerobic capacity were better able to tolerate increased 1-weekly absolute changes in training load than players with lower fitness levels (OR=4.52, p=0.011). Players who exerted in-season acute:chronic workload ratios of >1.00 to <1.25 (OR=0.68, p=0.006) were at significantly lower risk of injury compared to the reference group (≤0.85). These findings demonstrate that an acute:chronic workload of between 1.00 and 1.25 is protective for professional soccer players. A higher intermittent-aerobic capacity appears to offer greater injury protection when players are exposed to rapid changes in workload in elite soccer players. Moderate workloads, coupled with moderate-low to moderate-high acute:chronic workload ratios, appear to be protective for professional soccer players.

#3 The Relationship Between Coach and Player Training Load Perceptions in Professional Soccer
Reference: Percept Mot Skills. 2016 Nov 17. pii: 0031512516678727. [Epub ahead of print]
Authors: Redkva PE, Gregorio da Silva S, Paes MR, Dos-Santos JW
Summary: The training load imposed and perceived by coaches and soccer players, respectively, was compared for three weeks of the basic preparatory period of a professional soccer team through session ratings of perceived exertion (S-RPE). Participants were 24 professional Brazilian soccer players (all males, age: 24.1 ± 3.4 years) and their coaches. Athletes responded to the scale of perceived exertion (scores from 0 to10) after the training, while the coaches completed the scale prior to the training session, based on prior planning. The t-test for independent samples was used to compare S-RPE responses, and the Pearson correlation test was used to examine possible correlations between the parameters analyzed. There were no statistical differences between perceptions of prescribed (coaches) and experienced (players) S-RPE, and moderate correlations were found between these parameters (r = .60; p = .003). No statistically significant group differences were found in the perceived exertion during any of three types of training: physical, technical, or tactical. The results suggest that the S-RPE prescribed during the preseason period (by coaches) was not different from that perceived by professional soccer players.

#4 The Independent Influence of Concussive and Sub-concussive Impacts on Soccer Players' Neurophysiological and Neuropsychological Function
Reference: Int J Psychophysiol. 2016 Nov 17. pii: S0167-8760(16)30795-4. doi: 10.1016/j.ijpsycho.2016.11.011. [Epub ahead of print]
Authors: Moore RD, Lepine J, Ellemberg D
Summary: Accumulating research demonstrates that repetitive sub-concussive impacts can alter the structure, function and connectivity of the brain. However, the functional significance of these alterations as well as the independent contribution of concussive and sub-concussive impacts to neurophysiological and neuropsychological health are unclear. Accordingly, we compared the neurophysiological and neuropsychological function of contact athletes with (concussion group) and without (sub-concussion group) a history of concussion, to non-contact athletes. We evaluated event-related brain potentials (ERPs) elicited during an oddball task and performance on a targeted battery of neuropsychological tasks. Athletes in the sub-concussion and concussion groups exhibited similar amplitude reductions in the ERP indices of attentional resource allocation (P3b) and attentional orienting (P3a) relative to non-contact athletes. However, only athletes in the concussion group exhibited reduced amplitude in the ERP index of perceptual attention (N1). Athletes in the sub-concussion and concussion groups also exhibited deficits in memory recall relative to non-contact athletes, but athletes in the concussion group also exhibited significantly more recall errors than athletes in the sub-concussion group. Additionally, only athletes in the concussion group exhibited response delays during the oddball task. The current findings suggest that sub-concussive impacts are associated with alterations in the neurophysiological and neuropsychological indices of essential cognitive functions, albeit to a lesser degree than the combination of sub-concussive and concussive impacts.

#5 Incidence, Mechanisms, and Severity of Match-Related Collegiate Men's Soccer Injuries on FieldTurf and Natural Grass Surfaces: A 6-Year Prospective Study
Reference: Am J Sports Med. 2016 Nov 21. pii: 0363546516671715. [Epub ahead of print]
Authors: Meyers MC
Summary: Numerous injuries have been attributed to playing on artificial turf. More recently, newer generations of artificial turf have been developed to duplicate the playing characteristics of natural grass. Although artificial turf has been deemed safer than natural grass in some studies, few long-term studies have been conducted comparing match-related collegiate soccer injuries between the 2 playing surfaces. The authors hypothesize that Collegiate male soccer athletes do not experience any difference in the incidence, mechanisms, or severity of match-related injuries between FieldTurf and natural grass. Male soccer athletes from 11 universities were evaluated over 6 seasons. Demographic features and predictors included player position, cleat design, player weight, turf age, and environmental factors. Outcomes of interest included injury incidence, injury category, time loss, injury mechanism and situation, type of injury, injury grade and anatomic location, injury severity, head and lower extremity trauma, and elective medical procedures. All match-related injuries were evaluated by the attending head athletic trainer and team physicians on site and subsequently in the physician's office when further follow-up and treatment were deemed necessary. In sum, 765 collegiate games were evaluated for match-related soccer injuries sustained on FieldTurf or natural grass during 6 seasons. Overall, 380 team games (49.7%) were played on FieldTurf versus 385 team games (50.3%) played on natural grass. A total of 722 injuries were documented, with 268 (37.1%) occurring on FieldTurf and 454 (62.9%) on natural grass. Multivariate analysis per 10 team games indicated a significant playing surface effect: F2,720 = 7.260, P = .001. A significantly lower total injury incidence rate (IIR) of 7.1 (95% CI, 6.6-7.5) versus 11.8 (95% CI, 11.3-12.2; P < .0001) and lower rate of substantial injuries, 0.7 (95% CI, 0.5-1.0) versus 1.9 (95% CI, 1.5-2.3; P < .03), were documented on FieldTurf versus natural grass, respectively. Analyses also indicated significantly less trauma on FieldTurf when comparing injury category, time loss, player position, injury mechanism and situation, injuries under various environmental conditions, cleat design, turf age, anatomic location, and elective medical procedures. No significant difference (F11,710 = 0.822, P = .618) between surfaces by knee injury was observed, with the majority of knee injuries involving patellar tendinopathies/syndromes followed by medial collateral ligament injuries on both surfaces. Although similarities existed between FieldTurf and natural grass during competitive match play, FieldTurf is, in many cases, safer than natural grass when comparing injuries in collegiate men's soccer. The findings of this study, however, may not be generalizable to other levels of competition or to other artificial surfaces.

#6 Changes in lumbopelvic rhythm during trunk extension in adolescent soccer players
Reference: Gait Posture. 2016 Nov 15;52:72-75. doi: 10.1016/j.gaitpost.2016.11.026. [Epub ahead of print]
Authors: Tojima M, Torii S
Summary: Many adolescent athletes experience low back pain (LBP). Its causative factors include lower limb muscle tightness and hip-spine in coordination. Hip-spine coordination [or lumbopelvic rhythm, LPR] can be used to assess lower-limb and spine functions. We assessed the presence/absence of LBP in adolescent soccer players before and after a six-month period and divided them into four groups: no LBP both before and after the period (NBP group); LBP before but not after (PN group); LBP after but not before (NP group); and LBP both before and after (LBP group). We used a 3D motion analysis system during trunk extension to measure the lumbar spine and hip ranges of motion (ROMs). On comparing the results obtained before and after the six-month period, lumbar spine ROM decreased in the NP group, hip ROM increased in the LBP group. From before to after the period, the linear prediction indicated that, when the hip extends by 1°, the lumbar spine extends by 3.5°-3.2° for the PN group and by 3.4°-2.8° for the NP group. The NP group extended their lumbar spine excessively compared with the hip before the period, which could cause LBP, but decreased the extension after the period. Lumbar extension relative to hip extension decreased in the PN group, which could decrease excessive load on the lumbar spine and eliminate LBP. These findings suggest that to prevent LBP in adolescent soccer players, it is important to restrict lumbar spine extension relative to hip extension.

#7 Reliability, Validity and Usefulness of 30-15 Intermittent Fitness Test in Female Soccer Players
Reference: Front Physiol. 2016 Nov 17;7:510. eCollection 2016.
Authors: Čović N, Jelešković E, Alić H, Rađo I, Kafedžić E, Sporiš G, McMaster DT, Milanović Z
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Summary: The aim of this study was to examine the reliability, validity and usefulness of the 30-15IFT in competitive female soccer players. Seventeen elite female soccer players participated in the study. A within subject test-retest study design was utilized to assess the reliability of the 30-15 intermittent fitness test (IFT). Seven days prior to 30-15IFT, subjects performed a continuous aerobic running test (CT) under laboratory conditions to assess the criterion validity of the 30-15IFT. End running velocity (VCT and VIFT), peak heart rate (HRpeak) and maximal oxygen consumption (VO2max) were collected and/or estimated for both tests. VIFT (ICC = 0.91; CV = 1.8%), HRpeak (ICC = 0.94; CV = 1.2%), and VO2max (ICC = 0.94; CV = 1.6%) obtained from the 30-15IFT were all deemed highly reliable (p > 0.05). Pearson product moment correlations between the CT and 30-15IFT for VO2max, HRpeak and end running velocity were large (r = 0.67, p = 0.013), very large (r = 0.77, p = 0.02) and large (r = 0.57, p = 0.042), respectively. Current findings suggest that the 30-15IFT is a valid and reliable intermittent aerobic fitness test of elite female soccer players. The findings have also provided practitioners with evidence to support the accurate detection of meaningful individual changes in VIFT of 0.5 km/h (1 stage) and HRpeak of 2 bpm. This information may assist coaches in monitoring "real" aerobic fitness changes to better inform training of female intermittent team sport athletes. Lastly, coaches could use the 30-15IFT as a practical alternative to laboratory based assessments to assess and monitor intermittent aerobic fitness changes in their athletes.

#8 Do Elite and Amateur Soccer Players Outperform Non-Athletes on Neurocognitive Functioning? A Study Among 8-12 Year Old Children
Reference: PLoS One. 2016 Dec 1;11(12):e0165741. doi: 10.1371/journal.pone.0165741. eCollection 2016.
Authors: Verburgh L, Scherder EJ, Van Lange PA, Oosterlaan J
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Summary: Research suggested a positive association between physical fitness and neurocognitive functioning in children. Aim of the present study is to investigate possible dose-response relationships between diverse daily physical activities and a broad range of neurocognitive functions in preadolescent children. Furthermore, the relationship between several sedentary behaviours, including TV-watching, gaming and computer time, and neurocognitive functioning will be investigated in this group of children. A total of 168 preadolescent boys, aged 8 to 12 years, were recruited from various locations, including primary schools, an amateur soccer club, and a professional soccer club, to increase variability in the amount of participation in sports. All children performed neurocognitive tasks measuring inhibition, short term memory, working memory, attention and information processing speed. Regression analyses examined the predictive power of a broad range of physical activities, including sports, active transport to school, physical education (PE), outdoor play, and sedentary behaviour such as TV-watching and gaming, for neurocognitive functioning. Time spent in sports significantly accounted for the variance in inhibition, short term memory, working memory and lapses of attention, where more time spent in sports was associated with better performance. Outdoor play was also positively associated with working memory. In contrast, time spent on the computer was negatively associated with inhibition. Results of the current study suggest a positive relationship between participation in sports and several important neurocognitive functions. Interventions are recommended to increase sports participation and to reduce sedentary behaviour in preadolescent children.

#9 Sleep quality and high intensity interval training at two different times of day: A crossover study on the influence of the chronotype in male collegiate soccer players

Reference: Chronobiol Int. 2016 Dec 1:1-9. [Epub ahead of print]
Authors: Vitale JA, Bonato M, Galasso L, La Torre A, Merati G, Montaruli A, Roveda E, Carandente F
Summary: The influence of the chronotype on the sleep quality in male collegiate soccer players in response to acute high intensity interval training (HIIT) performed at two different times of day was evaluated. The sleep quality was poorer in the morning-type than in the evening-type players after the evening HIIT session, whereas no significant changes in the sleep quality of the two chronotypes after the morning HIIT session was observed. The results suggest that an athlete's chronotype should be taken into account when scheduling training sessions and to promote faster recovery processes.

#10 The efficacy, and characteristics, of warm-up and re-warm-up practices in soccer players: a systematic review
Reference: J Sports Med Phys Fitness. 2016 Nov 30. [Epub ahead of print]
Authors: Hammami A, Zois J, Slimani M, Russel M, Bouhlel E
Summary: This review aimed (i) to evaluate the current research that examines the efficacy of warm-up (WU) and re-warm-up (RWU) on physical performance, and (ii) to highlight the WU and RWU characteristics that optimise subsequent performance in soccer players. A computerized search was performed in the PubMed, ScienceDirect and Google Scholar (from 1995 to December 2015) for English-language, peer- reviewed investigations using the terms "soccer" OR "football" AND "warm-up" OR "stretching" OR "post-activation potentiation" OR "pre-activity" OR "re-warm-up" AND "performance" OR "jump" OR "sprint" OR "running". Twenty seven articles were retrieved. Particularly, 22 articles examined the effects of WU on soccer performance and 5 articles focused on the effects of RWU. Clear evidence exists supporting the inclusion of dynamic stretching or postactivation potentiation-based exercises within a WU as acute performance enhancements were reported (pooled estimate changes of +3.46% and +4.21%, respectively). The FIFA 11+ WU also significantly increases strength, jump, speed and explosive performances (changes from 1 to 20%). At half-time, active RWU protocols including postactivation potentiation practices and multidirectional speed drills attenuate temperature and performance reductions induced by habitual practice. The data obtained in the present review showed that the level of play did not moderate the effectiveness of WU and RWU on soccer performance. This review demonstrated that a static stretching WU reduced acute subsequent performance, while WU activities that include dynamic stretching, PAP-based exercises, and the FIFA 11+ can elicit positive effects in soccer players. The efficacy of an active RWU during half-time is also justified.

#11 Cardiac parasympathetic reactivation after small-sided soccer games and repeated sprints in untrained healthy adolescents
Reference: J Sports Med Phys Fitness. 2016 Nov 30. [Epub ahead of print]
Authors: Hammami A, Kasmi S, Yousfi N, Bouamra M, Tabka Z, Bouhlel E
Summary: It has been shown that recreational soccer was a highly motivating and social activity which produces large improvements in health-related indices in sedentary healthy and unhealthy subjects. The purpose of this study was to compare the acute parasympathetic reactivation after small-sided soccer games (SSG) and repeated sprints training (RST) sessions. Eight post-pubertal untrained adolescents (age 15.8 ± 0.6 years, body mass 59.1 ± 3.7 kg, height 1.7 ± 0.1 m) performed a RST, SSG and a control session in a counterbalanced order. Heart rate variability (HRV) indices in time and frequency domain, heart rate recovery and rating of perceived exertion (RPE) were evaluated. RPE was significantly lower after SSGs compared with RST (P = 0.02, ES = 1.1). There was a significant decrease in mean R-R intervals after RST (difference: -19.6%, P < 0.01, ES = 1.7) and after SSG (-19.2%, P < 0.01, ES = 2.3). A significant decrease was also noted in SDNN after RST (-26.6%, P = 0.02, ES = 1.8) and SSG (-37.8%, P = 0.01, ES = 1.1). For RMSSD, a significant decrease was observed only after SSG (48%, P = 0.01, ES = 1.3). No significant change in all HRV indices after the control condition. SSG and RST elicited high and similar heart rates responses. A low parasympathetic reactivation during early recovery was noted after both RST and SSG. These results were important especially for clinician looking to prescribe repeated sprint or small-sided game for sedentary subjects.

#12 Elastin: a possible genetic biomarker for more severe ligament injuries in elite soccer. A pilot study
Reference: Muscles Ligaments Tendons J. 2016 Sep 17;6(2):188-192.
Authors: Artells R, Pruna R, Dellal A, Maffulli N
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Summary: The study of new genetic biomarkers in genes related to connective tissue repair and regeneration may help to identify individuals with greater predisposition to injury, who may benefit from targeted preventive measures, and those who require longer recovery time following a muscle, ligament or tendon injury. The present study investigated whether single nucleotide polymorphisms of the Elastin gene could be related to MCL injury. 60 top class football players were studied to identify single nucleotide polymorphisms for the Elastin (ELN) gene using Allelic Discrimination analysis. Each player was followed for 7 seasons, and each MCL injury was noted. Ligament injury rate, severity and recovery time are related to specific genotypes observed in the elastin gene, especially the ELN-AA (16 MCL) and the ELN-AG (3 MCL). Players with the ELN-GG genotype sustained no MCL injury during the 7 seasons of the study. The identification of polymorphisms in the ELN gene may be used as a novel tool to better define an athlete's genotype, and help to plan training and rehabilitation programmes to prevent or minimize MCL ligament injuries, and optimize the therapeutic and rehabilitation process after soft tissue injuries, and manage the workloads during trainings and matches.

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