Latest research in football - week 3 - 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 The key to success in elite athletes? Explicit and implicit motor learning in youth elite and non-elite soccer players
Reference: J Sports Sci. 2016 Jan 20:1-9. [Epub ahead of print]
Authors: Verburgh L, Scherder EJ, van Lange PA, Oosterlaan J
Summary: In sports, fast and accurate execution of movements is required. It has been shown that implicitly learned movements might be less vulnerable than explicitly learned movements to stressful and fast changing circumstances that exist at the elite sports level. The present study provides insight in explicit and implicit motor learning in youth soccer players with different expertise levels. Twenty-seven youth elite soccer players and 25 non-elite soccer players (aged 10-12) performed a serial reaction time task (SRTT). In the SRTT, one of the sequences must be learned explicitly, the other was implicitly learned. No main effect of group was found for implicit and explicit learning on mean reaction time (MRT) and accuracy. However, for MRT, an interaction was found between learning condition, learning phase and group. Analyses showed no group effects for the explicit learning condition, but youth elite soccer players showed better learning in the implicit learning condition. In particular, during implicit motor learning youth elite soccer showed faster MRTs in the early learning phase and earlier reached asymptote performance in terms of MRT. Present findings may be important for sports because children with superior implicit learning abilities in early learning phases may be able to learn more (durable) motor skills in a shorter time period as compared to other children.

#2 The within-match patterns of locomotor efficiency during professional soccer match play: Implications for injury risk?
Reference: J Sci Med Sport. 2015 Dec 29. pii: S1440-2440(15)00763-X. doi: 10.1016/j.jsams.2015.12.514. [Epub ahead of print]
Authors: Barrett S, Midgley A, Reeves M, Joel T, Franklin E, Heyworth R, Garrett A, Lovell R
Summary: The principle aim of the current study was to examine within-match patterns of locomotor efficiency in professional soccer, determined as the ratio between tri-axial accelerometer data (PlayerLoad™) and locomotor activities. Between match variability and determinants of PlayerLoad™ during match play were also assessed. Tri-axial accelerometer data (PlayerLoad™) was recorded during 86 competitive soccer matches in 63 English championship players (574 match observations). Accelerometer data accumulated (PlayerLoad Vector Magnitude [PLVM]) from the individual-component planes of PlayerLoad™ (anterior-posterior PlayerLoad™ [PLAP], medial-lateral PlayerLoad™ [PLML] and vertical PlayerLoad™ [PLV]), together with locomotor activity (Total Distance Covered [TDC]) were determined in 15-min segments. Locomotor efficiency was calculated using the ratio of PLVM and TDC (PlayerLoad™ per metre). The proportion of variance explaining the within-match trends in PLVM, PLAP, APML, APv, and TDC was determined owing to matches, individual players, and positional role. PLVM, PLAP, APML, APv and TDC reduced after the initial 15-min match period (p=0.001; η2=0.22-0.43, large effects). PL:TDC increased in the last 15min of each half (p=0.001; η2=0.25, large effect). The variance in PLVM during soccer match-play was explained by individual players (63.9%; p=0.001) and between-match variation (21.6%; p=0.001), but not positional role (14.1%; p=0.364). Locomotor efficiency is lower during the latter stages of each half of competitive soccer match-play, a trend synonymous with observations of increased injury incidence and fatigue in these periods. Locomotor efficiency may be a valuable metric to identify fatigue and heightened injury risk during soccer training and match-play.

#3 Effects of plyometric training and creatine supplementation on maximal-intensity exercise and endurance in female soccer players
Reference: J Sci Med Sport. 2015 Nov 6. pii: S1440-2440(15)00205-4. doi: 10.1016/j.jsams.2015.10.005. [Epub ahead of print]
Authors: Ramírez-Campillo R, González-Jurado JA, Martínez C, Nakamura FY, Peñailillo L, Meylan CM, Caniuqueo A, Cañas-Jamet R, Moran J, Alonso-Martínez AM, Izquierdo M
Summary: The purpose of the study was to investigate the effects of a six-week plyometric training and creatine supplementation intervention on maximal-intensity and endurance performance in female soccer players during in-season training. Young (age 22.9±2.5y) female players with similar training load and competitive background were assigned to a plyometric training group receiving placebo (PLACEBO, n=10), a plyometric training group receiving creatine supplementation (CREATINE, n=10) or a control group receiving placebo without following a plyometric program (CONTROL, n=10). Athletes were evaluated for jumping, maximal and repeated sprinting, endurance and change-of-direction speed performance before and after six weeks of training. After intervention the CONTROL group did not change, whereas both plyometric training groups improved jumps (ES=0.25-0.49), sprint (ES=0.35-0.41), repeated sprinting (ES=0.48-0.55), endurance (ES=0.32-0.34) and change-of-direction speed performance (ES=0.46-0.55). However, the CREATINE group improved more in the jumps and repeated sprinting performance tests than the CONTROL and the PLACEBO groups. Adaptations to plyometric training may be enhanced with creatine supplementation.

#4 Do Australian Football players have sensitive groins? Players with current groin pain exhibit mechanical hyperalgesia of the adductor tendon
Reference: J Sci Med Sport. 2016 Jan 7. pii: S1440-2440(15)00765-3. doi: 10.1016/j.jsams.2015.12.516. [Epub ahead of print]
Authors: Drew MK, Lovell G, Palsson TS, Chiarelli PE, Osmotherly PG
Summary: This is the first study to evaluate the mechanical sensitivity, clinical classifications and prevalence of groin pain in Australian football players. Professional (n=66) and semi-professional (n=9) Australian football players with and without current or previous groin injuries were recruited. Diagnoses were mapped to the Doha Agreement taxonomy. Point and career prevalence of groin pain was calculated. Pressure pain thresholds (PPTs) were assessed at regional and distant sites using handheld pressure algometry across four sites bilaterally (adductor longus tendon, pubic bone, rectus femoris, tibialis anterior muscle). To assess the relationship between current groin pain and fixed effects of hyperalgesia of each site and a history of groin pain, a mixed-effect logistic regression model was utilised. Receiver Operator Characteristic (ROC) curve were determined for the model. Point prevalence of groin pain in the preseason was 21.9% with a career prevalence of 44.8%. Adductor-related groin pain was the most prevalent classification in the pre-season period. Hyperalgesia was observed in the adductor longus tendon site in athletes with current groin pain (OR=16.27, 95% CI 1.86 to 142.02). The ROC area under the curve of the regression model was fair (AUC=0.76, 95% CI 0.54 to 0.83). Prevalence data indicates that groin pain is a larger issue than published incidence rates imply. Adductor-related groin pain is the most common diagnosis in pre-season in this population. This study has shown that hyperalgesia exists in Australian football players experiencing groin pain indicating the value of assessing mechanical pain sensitivity as a component of the clinical assessment.

#5 Change of Direction Ability Performance in Cerebral Palsy Football Players According to Functional Profiles
Reference: Front Physiol. 2016 Jan 6;6:409. doi: 10.3389/fphys.2015.00409. eCollection 2015.
Authors: Reina R, Sarabia JM, Yanci J, García-Vaquero MP, Campayo-Piernas M
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Summary: The aims of the present study were to evaluate the validity and reliability of the two different change of direction ability (CODA) tests in elite football players with cerebral palsy (CP) and to analyse the differences in performance of this ability between current functional classes (FT) and controls. The sample consisted of 96 international cerebral palsy football players (FPCP) and 37 football players. Participants were divided into four different groups according to the International Federation of Cerebral Palsy Football (IFCPF) classes and a control group (CG): FT5 (n = 8); FT6 (n = 12); FT7 (n = 62); FT8 (n = 14); and CG (n = 37). The reproducibility of Modified Agility Test (MAT) and Illinois Agility Test (IAT) (ICC = 0.82-0.95, SEM = 2.5-5.8%) showed excellent to good values. In two CODA tests, CG performed faster scores compared with FPCP classes (p < 0.01, d = 1.76-3.26). In IAT, FT8 class comparisons regarding the other classes were: FT5 (p = 0.047, d = 1.05), FT6 (p = 0.055, d = 1.19), and FT7 (p = 0.396, d = 0.56). With regard to MAT, FT8 class was also compared with FT5 (p = 0.006, d = 1.30), FT6 (p = 0.061, d = 0.93), and FT7 (p = 0.033, d = 1.01). No significant differences have been found between FT5, FT6, and FT7 classes. According to these results, IAT and MAT could be useful and reliable and valid tests to analyse CODA in FPCP. Each test (IAT and MAT) could be applied considering the cut point that classifiers need to make a decision about the FT8 class and the other FT classes (FT5, FT6, and FT7).

#6 Impairment of Sprint Mechanical Properties in an Actual Soccer Match: A Pilot Study
Reference: Int J Sports Physiol Perform. 2016 Jan 18. [Epub ahead of print]
Authors: Nagahara R, Morin JB, Koido M
Summary: This study aimed to assess soccer-specific impairment of mechanical properties in accelerated sprinting and its relation with activity profiles during an actual match. Thirteen male field players completed four sprint measurements, wherein running speed was obtained using a laser-distance-measurement system, before and after the respective halves of two soccer matches. Macroscopic mechanical properties (theoretical maximal horizontal force, F0; maximal horizontal sprinting power, Pmax; theoretical maximal sprinting velocity, V0) during the 35-m sprint acceleration were calculated from speed-time data. Players' activity profiles during the matches were collected using global-positioning-system units. After the match, while F0 and Pmax did not significantly change, V0 was reduced (P = .038), and the magnitude of this reduction correlated with distance (positive) and number (negative) of high-speed running, number of running (negative) and other low intensity activity distance (negative) during the match. Moreover, Pmax decreased immediately before the second half (P = .014). The results suggest that soccer-specific fatigue probably impairs more the maximal velocity capabilities of players rather than their maximal horizontal force production abilities at initial acceleration. Furthermore, a long distance running, especially at high speed, during the match may induce relatively large impairment of the maximal velocity capabilities. In addition, the capability of producing maximal horizontal power during sprinting is presumably impaired during half-time of a soccer match with passive recovery. These findings could be useful for players and coaches aiming at training effectively to maintain sprinting performance throughout a soccer match when planning a training program.

#7 Hot and Hypoxic Environments Inhibit Simulated Soccer Performance and Exacerbate Performance Decrements When Combined
Reference: Front Physiol. 2016 Jan 12;6:421. doi: 10.3389/fphys.2015.00421. eCollection 2015.
Authors: Aldous JW, Chrismas BC, Akubat I, Dascombe B, Abt G, Taylor L
Summary: The effects of heat and/or hypoxia have been well-documented in match-play data. However, large match-to-match variation for key physical performance measures makes environmental inferences difficult to ascertain from soccer match-play. Therefore, the present study aims to investigate the hot (HOT), hypoxic (HYP), and hot-hypoxic (HH) mediated-decrements during a non-motorized treadmill based soccer-specific simulation. Twelve male University soccer players completed three familiarization sessions and four randomized crossover experimental trials of the intermittent Soccer Performance Test (iSPT) in normoxic-temperate (CON: 18°C 50% rH), HOT (30°C; 50% rH), HYP (1000 m; 18°C 50% rH), and HH (1000 m; 30°C; 50% rH). Physical performance and its performance decrements, body temperatures (rectal, skin, and estimated muscle temperature), heart rate (HR), arterial blood oxygen saturation (SaO2), perceived exertion, thermal sensation (TS), body mass changes, blood lactate, and plasma volume were all measured. Performance decrements were similar in HOT and HYP [Total Distance (-4%), High-speed distance (~-8%), and variable run distance (~-12%) covered] and exacerbated in HH [total distance (-9%), high-speed distance (-15%), and variable run distance (-15%)] compared to CON. Peak sprint speed, was 4% greater in HOT compared with CON and HYP and 7% greater in HH. Sprint distance covered was unchanged (p > 0.05) in HOT and HYP and only decreased in HH (-8%) compared with CON. Body mass (-2%), temperatures (+2-5%), and TS (+18%) were altered in HOT. Furthermore, SaO2 (-8%) and HR (+3%) were changed in HYP. Similar changes in body mass and temperatures, HR, TS, and SaO2 were evident in HH to HOT and HYP, however, blood lactate (p < 0.001) and plasma volume (p < 0.001) were only significantly altered in HH. Perceived exertion was elevated (p < 0.05) by 7% in all conditions compared with CON. Regression analysis identified that absolute TS and absolute rise in skin and estimated muscle temperature (r = 0.82, r = 0.84 r = 0.82, respectively; p < 0.05) predicted the hot-mediated-decrements in HOT. The hot, hypoxic, and hot-hypoxic environments impaired physical performance during iSPT. Future interventions should address the increases in TS and body temperatures, to attenuate these decrements on soccer performance.

#8 Relationship Between External and Internal Load of Professional Soccer Players During Full-Matches in Official Games Using GPS and Heart Rate Technology
Reference: Int J Sports Physiol Perform. 2016 Jan 27. [Epub ahead of print]
Authors: Torreño N, Munguía-Izquierdo D, Coutts AJ, Sáez de Villarreal E, Asian-Clemente J, Suarez-Arrones L.
Summary: The purpose of the study was to analyze the match running profile, distance travelled over successive 15 minutes of match-play, heart rates and effindex of professional soccer players with Global Positioning System (GPS) and heart rate (HR) in official competition. Twenty-six professional players were investigated during full-matches in competitive club level matches (n=223). Time-motion data and HR were collected using GPS and HR technology. The relative total distance was 113±11 m·min-1 with substantial differences between halves. For all the playing positions, a substantial decrease in total distance and distance covered >13.0 km·h-1 was observed in the second half in comparison with the first. The decrease during the second half in distance covered >13.0 km·h-1 was substantially higher than in total distance. The average HR recorded was 86.0% HRmax and the relationship between external and internal load value (effindex) was 1.3, with substantial differences between halves in all playing positions, except strikers for effindex. Wide-midfielders reflected substantially the lowest mean HR and highest effindex, while CB showed substantially the lowest effindex than any other playing position. The current study confirmed the decrement in player's performance toward the end of match in all playing positions. Wide-midfielders performed the highest and fittest levels of physical and physiological demands, respectively, whereas centre-backs performed the lowest and unfittest levels of physical and physiological demands, respectively. The relationship between external and internal load measures among position-specific confirms that players with more overall running performance during the full-match were the best in effindex.

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