Latest research in football - week 12 - 2015

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 Rotational Stiffness Of Football Shoes Affects Ankle Biomechanics And Injury Severity
Reference: J Biomech Eng. 2015 Mar 1. doi: 10.1115/1.4029979. [Epub ahead of print]
Authors: Button KD, Braman JE, Davison MA, Wei F, Schaeffer MC, Haut R.
Summary: While previous studies have investigated the effect of shoe-surface interaction on injury risk, few studies have examined the effect of shoe rotational stiffness. The hypothesis of the current study was that ankles externally rotated to failure in shoes with low rotational stiffness would allow more talus eversion than those in shoes with a higher rotational stiffness, resulting in less severe injury. Twelve (six pairs) of cadaver lower extremities were externally rotated to gross failure while positioned in 20 degrees of pre-eversion and 20 degrees of pre-dorsiflexion. One ankle in each pair was constrained by a football shoe with a stiff upper while the other was constrained by a football shoe with a flexible upper. Experimental bone motions were input into specimen-specific computational models to measure ligament strains at failure. Ankles in flexible shoes failed at 97.4 ± 47.0 Nm which was greater than the failure torque for ankles in stiff shoes (89.2 ± 44.9 Nm) in addition to allowing 6.7 ± 2.4 degrees of talus eversion during rotation, significantly greater than the 1.7 ± 1.0 degrees for ankles in stiff shoes. All ankles failed by either medial ankle injury or syndesmotic injury, or a combination of both. Complex (more than one ligament or bone) injuries were noted in 4 of 6 ankles in stiff shoes and 1 of 6 ankles in flexible shoes. Models of ankles in flexible shoes showed significantly less strain in the deltoid at failure, but significantly more strain in three of four subtalar ligaments. The current study suggests flexibility (or rotational stiffness) of the shoe may play an important role in both the risk and severity of ankle injuries in athletes.

#2 Negative health implications of sickle cell trait in high income countries: from the football field to the laboratory
Reference: Br J Haematol. 2015 Mar 7. doi: 10.1111/bjh.13363. [Epub ahead of print]
Authors: Key NS, Connes P, Derebail VK.
Summary: Worldwide, sickle cell trait is a highly prevalent gene carrier state. While generally a benign condition with a normal life expectancy, it is becoming increasingly clear that the sickle trait is associated with certain adverse outcomes. This article will focus on three of these outcomes, namely exertional rhabdomyolysis and sudden death, chronic renal dysfunction, and venous thromboembolism. In each case, the epidemiological evidence for the association is reviewed, together with the existing data on potential underlying mechanisms. Because newborn screening programmes for sickle cell anaemia also identify those with sickle cell trait, it is imperative that further studies determine what, if any, preventive measures can be taken to reduce the burden of these uncommon but potentially morbid complications in affected individuals.

#3 Influence of carbohydrate mouth rinsing on running and jumping performance during early morning soccer scrimmaging
Reference: Eur J Sport Sci. 2015 Mar 20:1-7. [Epub ahead of print]
Authors: Přibyslavská V, Scudamore EM, Johnson SL, Green JM, Stevenson Wilcoxson MC, Lowe JB, O'Neal EK.
Summary: Carbohydrate mouth rinse (CMR) is a novel method proposed to enhance endurance performance lasting ≤ 60 min. The current study examined the influence of CMR on anaerobic performance tasks in 11 collegiate female soccer players after an overnight fast. Athletes completed two experimental sessions, during which carbohydrate (CHO; 6% maltodextrin) or taste- and colour-matched placebo (PLA) mouth-rinse solutions were administered in a counterbalanced, double-blinded design. Three rounds of a 5-min scrimmage bout and series of performance tests including a single countermovement vertical jump (1VJ), a set of four consecutive vertical jumps, a 72-m shuttle run (SR72) and 18-m sprint comprised each trial. Thirst sensation (TS), session TS, ratings of perceived exertion (RPE) and session RPE were assessed as secondary outcomes. The first SR72 approached significance (p = 0.069), but no significant between-trials differences were observed for any of the mean performance tasks. The highest 1VJ scores did not differ for the first (CHO = 47.3 ± 3.4, PLA = 47.7 ± 3.5 cm; p = 0.43), second (CHO = 48.0 ± 4.1, PLA = 47.9 ± 3.5 cm; p = 0.82) or third bout (CHO = 47.4 ± 3.9, PLA = 48.1 ± 3.9 cm; p = 0.26). TS approached significance (p = 0.053) during the first bout. No significant differences (p > 0.05) were found for any of the perceptual variables. Current results fail to support ergogenic influence of CMR on anaerobic performance tasks in collegiate female athletes.

#4 Kinesio Taping effects on knee extension force among soccer players
Reference: Braz J Phys Ther. 2015 Mar 13:0. [Epub ahead of print]
Authors: Serra MV, Vieira ER, Brunt D, Goethel MF, Gonçalves M, Quemelo PR
Summary: Kinesio Taping (KT) is widely used, however the effects of KT on muscle activation and force are contradictory. The purpose of the study was to evaluate the effects of KT on knee extension force in soccer players. Thirty-four subjects performed two maximal isometric voluntary contractions of the lower limbs pre, immediately post, and 24 hours after tape application on the lower limbs. Both lower limbs were taped, using K-Tape and 3M Micropore tape randomly on the right and left thighs of the participants. Isometric knee extension force was measured for dominant side using a strain gauge. The following variables were assessed: peak force, time to peak force, rate of force development until peak force, time to peak rate of force development, and 200 ms pulse. There were no statistically significant differences in the variables assessed between KT and Micropore conditions (F=0.645, p=0.666) or among testing sessions (pre, post, and 24h after) (F=0.528, p=0.868), and there was no statistical significance (F=0.271, p=0.986) for interaction between tape conditions and testing session. KT did not affect the force-related measures assessed immediately and 24 hours after the KT application compared with Micropore application, during maximal isometric voluntary knee extension.

#5 Visual and skill effects on soccer passing performance, kinematics, and outcome estimations
Reference: Front Psychol. 2015 Mar 2;6:198. doi: 10.3389/fpsyg.2015.00198. eCollection 2015
Authors: Basevitch I, Tenenbaum G, Land WM, Ward P
Summary: The role of visual information and action representations in executing a motor task was examined from a mental representations approach. High-skill (n = 20) and low-skill (n = 20) soccer players performed a passing task to two targets at distances of 9.14 and 18.29 m, under three visual conditions: normal, occluded, and distorted vision (i.e., +4.0 corrective lenses, a visual acuity of approximately 6/75) without knowledge of results. Following each pass, participants estimated the relative horizontal distance from the target as the ball crossed the target plane. Kinematic data during each pass were also recorded for the shorter distance. Results revealed that performance on the motor task decreased as a function of visual information and task complexity (i.e., distance from target) regardless of skill level. High-skill players performed significantly better than low-skill players on both the actual passing and estimation tasks, at each target distance and visual condition. In addition, kinematic data indicated that high-skill participants were more consistent and had different kinematic movement patterns than low-skill participants. Findings contribute to the understanding of the underlying mechanisms required for successful performance in a self-paced, discrete and closed motor task.

#6 Effect of foot type on knee valgus, ground reaction force, and hip muscle activation in female soccer players
Reference: J Sports Med Phys Fitness. 2015 Mar 17. [Epub ahead of print]
Authors: Rath ME, Walker CR, Cox JG, Stearne DJ.
Summary: The purpose of this study was to determine the degree to which subtalar joint pronation resulting from a SP foot affects knee alignment, hip muscle activation and ground reaction force attenuation in female athletes during a broad jump-to-cut maneuver. Twelve National Collegiate Athletic Association (NCAA) Division II female soccer players (age=19.4 ± 1.4 years, height=1.64±0.05 m, mass=64.10±4.8 kg) were identified as having either supple planus (SP) or rigid feet (RF). Participants completed three broad jump-tocut trials onto a force plate while EMG and motion data were collected. Muscle activation levels (%MVC) in the gluteus maximus, gluteus medius, biceps femoris, and rectus femoris were calculated, and peak vertical and medial shear force, rate of loading, and valgus angle were collected for each trial. Mann-Whitney U tests revealed no statistical significance between foot-type groups, however, effect size statistics revealed practical significance for between-group %MVC biceps femoris (d=1.107), %MVC gluteus maximus (d=1.069), and vertical ground reaction force (d=1.061). Athletes with a SP foot type may experience decreased hip muscle activation associated with increased vertical ground reaction force during a broad jump-to-cut maneuver. This might result in reduced dynamic stability and neuromuscular control during deceleration, potentially increasing the risk of non-contact ACL injury in female soccer players.

#7 Seasonal DXA-measured body composition changes in professional male soccer players
Reference: J Sports Sci. 2015 Mar 16:1-10. [Epub ahead of print]
Authors: Milanese C, Cavedon V, Corradini G, De Vita F, Zancanaro C.
Summary: This work investigated changes in body composition of professional soccer players attending an Italian Serie A club across the competitive season; it is original insofar as body composition was assessed at multiple time points across the season using the accurate three-compartment model provided by Dual-Energy X-Ray Absorptiometry (DXA). Thirty-one players (4 goalkeepers, 13 defenders, 8 midfielders, 6 forwards) underwent DXA and anthropometry at pre-, mid- and end-season. One operator measured whole body and regional body composition (fat mass, FM; fat-free soft tissue mass, FFSTM; mineral mass). Two players were excluded from analysis due to serious injury. Data were analysed with repeated measures ANOVA; factors were season time point and playing position. Results showed that whole-body FM and %FM significantly (P < 0.001) decrease at mid-season (-11.9%; -1.3%, respectively) and end-season (-8.3%; -0.8%, respectively) whereas FFSTM significantly (P < 0.001) increase at mid-season (+1.3%) and end-season (+1.5%). Limited, but significant changes took place in bone mineral content. Some regional (upper and lower limbs, trunk) differences in the pattern of body composition changes across the season were also found. Changes were similar for all playing positions. It was concluded that professional soccer players undergo changes in their FM, FFSTM, and mineral mass across the season with some regional variations, irrespective of the playing position. Changes are mostly positive at mid-season, possibly due to difference in training between the first and second phase of the season.

#8 Half-squat or jump squat training under optimum power load conditions to counteract power and speed decrements in Brazilian elite soccer players during the preseason
Reference: J Sports Sci. 2015 Mar 16:1-10. [Epub ahead of print]
Authors: Loturco I, Pereira LA, Kobal R, Zanetti V, Gil S, Kitamura K, Abad CC, Nakamura FY.
Summary: The purpose of this study was to test which specific type of exercise (i.e., jump squat (JS) or half-squat (HS)) is more effective at maintaining speed and power abilities throughout a preseason in soccer players. Twenty-three male soccer players were randomly allocated into two groups: JS and HS. The mean propulsive power, vertical jumping ability, and sprinting performance were evaluated before and after 4 weeks of a preseason period. The optimum power loads for the JS and HS exercises were assessed and were used as load-references. The soccer players performed 10 power oriented training sessions in total. Both JS and HS maintained power in JS and speed abilities (P > 0.05, for main effects and interaction effect) as indicated by ANCOVA. Both groups demonstrated reduced power during HS (ES = -0.76 vs. -0.78, for JS and HS, respectively); both groups improved acceleration (ACC) from 5 to 10 m (ES = 0.52). JS was more effective at reducing the ACC decrements over 0-5 m (ES = -0.38 vs. -0.58, for JS and HS, respectively). The HS group increased squat jump height (ES = 0.76 vs. 0.11, for HS and JS, respectively). In summary, JS is more effective in reducing the ACC capacity over very short sprints while HS is more effective in improving squat jump performance. Both strategies improve ACC over longer distances. New training strategies should be implemented/developed to avoid concurrent training effects between power and endurance adaptations during professional soccer preseasons.

#9 The older, the wider: On-field tactical behavior of elite-standard youth soccer players in small-sided games
Reference: Hum Mov Sci. 2015 Mar 10;41:92-102. doi: 10.1016/j.humov.2015.02.004. [Epub ahead of print]
Authors: Olthof SB, Frencken WG, Lemmink KA
Summary: Young soccer players need excellent tactical skills to reach the top. Tactical behavior emerges through interactions between opposing teams. However, few studies have focused on on-field tactical behavior of teams with talented soccer players. Therefore, this study aimed to determine teams' tactical behavior during small-sided games in two age categories, Under-17 and Under-19. Positional data of thirty-nine elite-standard soccer players were collected during twenty-four small-sided games to calculate longitudinal and lateral inter-team distances, stretch indices and length per width ratios. Corresponding interaction patterns and game-to-game variability were also determined. Under-19 showed a significantly larger lateral stretch index and a significantly lower length per width ratio compared with Under-17. Furthermore, teams of both age groups showed similar large proportions of in-phase behavior. Variability of tactical performance measures within and between games was similar for Under-17 and Under-19. Variability within games seems to be functional for attacking teams for creating goal-scoring opportunities. In conclusion, the main difference was that Under-19 adopted a wider pitch dispersion than Under-17, represented by a larger lateral stretch index and smaller length per width ratio. Coach instructions and training exercises should be directed at exploiting pitch width to increase the pursuit of goal-scoring.

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