Latest research in football - week 44 - 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 The Transition Period in Soccer: A Window of Opportunity
Reference: Sports Med. 2015 Nov 3. [Epub ahead of print]
Authors: Silva JR, Brito J, Akenhead R, Nassis GP
Summary: The aim of this paper is to describe the physiological changes that occur during the transition period in soccer players. A secondary aim is to address the issue of utilizing the transition period to lay the foundation for the succeeding season. We reviewed published peer-reviewed studies if they met the following three selection criteria: (1) the studied population comprised adult soccer players (aged >18 years), (2) time points of physiological and performance assessments were provided, and (3) appropriate statistics for the calculation of effect sizes were reported. Following two selection phases, 12 scientific publications were considered, involving a total sample of 252 players. The transition period elicits small to moderate negative changes in body composition, a moderate decline in sprint performance with and without changes of direction, and small to moderate decrements in muscle power. Detraining effects are also evident for endurance-related physiological and performance outcomes: large decrements in maximal oxygen consumption ([Formula: see text]O2max) and time to exhaustion, and moderate to very large impairments have been observed in intermittent-running performance. Off-season programs should be characterized by clear training objectives, a low frequency of training sessions, and simple training tools in order to facilitate compliance. The program suggested here may constitute the 'minimum effective dose' to maintain or at least attenuate the decay of endurance- and neuromuscular-related performance parameters, as well as restore an adequate strength profile (reduce muscle strength imbalances). This periodization strategy may improve the ability of players to cope with the elevated training demands of pre-season training and therefore reduce the risk of injury. Moreover, this strategy will favor a more efficient development of other relevant facets of performance during the pre-competition phase (e.g., tactical organization). We contend that the transition period needs to be perceived as a 'window of opportunity' for players to both recover and 'rebuild' for the following season.

#2 Pathogenesis of Fifth Metatarsal Fractures in College Soccer Players
Reference: Orthop J Sports Med. 2015 Sep 18;3(9):2325967115603654. doi: 10.1177/2325967115603654. eCollection 2015.
Authors: Fujitaka K, Taniguchi A, Isomoto S, Kumai T, Otuki S, Okubo M, Tanaka Y
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Summary: The purpose of the study was to test the study hypothesis, physical characteristics and environmental factors, which have received limited attention in the literature thus far, might be involved in the development of fifth metatarsal stress fractures a medical examination and survey of the living environment of collegiate soccer players was conducted and correlated with the existence of fifth metatarsal stress fractures. The survey and measurements were conducted in 273 male athletes from the same college soccer team between 2005 and 2013. A medical examination comprising assessment of stature, body weight, body mass index, foot-arch height ratio, toe-grip strength, quadriceps angle, leg-heel angle, functional reach test, single-leg standing time with eyes closed, straight-leg raise angle, finger-floor distance, heel-buttock distance, ankle joint range of motion, and a general joint laxity test were performed once a year, along with a questionnaire survey. The survey was also repeated when a fifth metatarsal stress fracture was diagnosed. The study participants were separated into a fifth metatarsal stress fracture injury group and a noninjury group. The measurement items and survey items were compared, and the association between the factors and the presence or absence of injuries was analyzed. Toe-grip strength was significantly weaker in the injury group compared with the noninjury group, suggesting that weak toe-grip is associated with fifth metatarsal stress fracture (P < .05). In addition, fifth metatarsal stress fractures were more common in the nondominant leg (P < .05). Between-group comparisons of the other items showed no statistically significant differences. The association between weak toe-grip strength and fifth metatarsal fracture suggests that weak toe-grip may lead to an increase in the load applied onto the lateral side of the foot, resulting in stress fracture. The finding of stress fracture being more common in the nondominant leg needs further study.

#3 Sports injuries profile of a first division Brazilian soccer team: a descriptive cohort study
Reference: Braz J Phys Ther. 2015 Oct;19(5):390-7. doi: 10.1590/bjpt-rbf.2014.0120. Epub 2015 Oct 6.
Authors: Reis GF, Santos TR, Lasmar RC, Oliveira Júnior O, Lopes RF, Fonseca ST
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Summary: The purpose of the study was to establish the injury profile of soccer players from a first division Brazilian soccer team. In addition, we investigated the association between the characteristics of the injuries and the player's age and position. Forty-eight players from a Brazilian first division soccer team were followed during one season. Descriptive statistics were used to characterize the injury profile. Spearman's tests were used to verify the association between the number and severity of injuries and the player's age. Chi-square test was used to verify the association between type of injury and player's position. Fisher's exact test was used to verify the association between the severity of injuries and player's position. The incidence of injuries was 42.84/1000 hours in matches and 2.40/1000 hours in training. The injury severity was 19.5±34.4 days off competition or training. Lower limb was the most common location of injury and most injuries were muscular/tendinous, overuse, non-recurrent, and non-contact injuries. Player's age correlated with the amount and severity of muscle and tendon injuries. Defenders had more minimal injuries (1-3 days lost), while forwards had more moderate (8-28 days lost) and severe injuries (>28 days lost). Furthermore, wingbacks had more muscle and tendon injuries, while midfielders had more joint and ligament injuries. The injury profile of the Brazilian players investigated in this study reflected regional differences in soccer practices. Results confirm the influence of the player's age and position on the soccer injuries profile.

#4 Effect of clenching with a mouthguard on head acceleration during heading of a soccer ball
Reference: Gen Dent. 2015 Nov-Dec;63(6):41-6.
Authors: Narimatsu K, Takeda T, Nakajima K, Konno M, Ozawa T, Ishigami K.
Summary: Concussions are acceleration-deceleration injuries that occur when biomechanical forces are transmitted to the cerebral tissues. By limiting acceleration of the head, enhanced cervical muscle activity derived from clenching with a mouthguard (MG) may reduce the incidence or severity of concussions following impact. The purpose of this study was to investigate the effect of voluntary clenching with a proper MG on acceleration of the head during "heading" of a soccer ball. Eleven male high school soccer players (mean age, 16.8 years) participated in the study. Each player was given a customized MG. An automated soccer machine was used to project the ball at the participants at a constant speed. The participants headed the ball under 3 different oral conditions: drill 1, heading freely performed without instruction and without the MG; drill 2, heading performed as the subject was instructed to clench the masseter muscles tightly while not wearing the MG; drill 3, heading performed as the subject was instructed to clench tightly while wearing the MG. Each participant repeated each drill 5 times. Linear acceleration of the head was measured with a 3-axis accelerometer. Activity of the masseter and sternocleidomastoid muscles was measured by wireless electromyography. Weak masseter and sternocleidomastoid muscle activity was observed during drill 1. After the soccer players had been instructed to clench their masseter muscles (drills 2 and 3), statistically significant decreases in head acceleration and increases in masseter and sternocleidomastoid muscle activity were observed (P < 0.05; paired t test). The effect was stronger when the players wore the MG. Dentists should encourage soccer players to habitually clench while wearing a proper mouthguard to strengthen cervical muscle resistance as a way to mitigate the damage caused by heading.

#5 Controlled Laboratory Comparison Study of Motion With Football Equipment in a Destabilized Cervical Spine: Three Spine-Board Transfer Techniques
Reference: Orthop J Sports Med. 2015 Sep 8;3(9):2325967115601853. doi: 10.1177/2325967115601853. eCollection 2015.
Authors: Prasarn ML, Horodyski M, DiPaola MJ, DiPaola CP, Del Rossi G, Conrad BP, Rechtine GR 2nd
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Summary: Numerous studies have shown that there are better alternatives to log rolling patients with unstable spinal injuries, although this method is still commonly used for placing patients onto a spine board. No previous studies have examined transfer maneuvers involving an injured football player with equipment in place onto a spine board. To test 3 different transfer maneuvers of an injured football player onto a spine board to determine which method most effectively minimizes spinal motion in an injured cervical spine model. Five whole, lightly embalmed cadavers were fitted with shoulder pads and helmets and tested both before and after global instability was surgically created at C5-C6. An electromagnetic motion analysis device was used to assess the amount of angular and linear motion with sensors placed above and below the injured segment during transfer. Spine-boarding techniques evaluated were the log roll, the lift and slide, and the 8-person lift. The 8-person lift technique resulted in the least amount of angular and linear motion for all planes tested as compared with the lift-and-slide and log-roll techniques. This reached statistical significance for lateral bending (P = .031) and medial-lateral translation (P = .030) when compared with the log-roll maneuver. The lift-and-slide technique was significantly more effective at reducing motion than the log roll for axial rotation (P = .029) and lateral bending (P = .006). The log roll resulted in the most motion at an unstable cervical injury as compared with the other 2 spine-boarding techniques examined. The 8-person lift and lift-and-slide techniques may both be more effective than the log roll at reducing unwanted cervical spine motion when spine boarding an injured football player. Reduction of such motion is critical in the prevention of iatrogenic injury.

#6 Poor oral health including active caries in 187 UK professional male football players: clinical dental examination performed by dentists
Reference: Br J Sports Med. 2015 Nov 2. pii: bjsports-2015-094953. doi: 10.1136/bjsports-2015-094953. [Epub ahead of print]
Authors: Needleman I, Ashley P, Meehan L, Petrie A, Weiler R, McNally S, Ayer C, Hanna R, Hunt I, Kell S, Ridgewell P, Taylor R
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Summary: The few studies that have assessed oral health in professional/elite football suggest poor oral health with minimal data on impact on performance. The aim of this research was to determine oral health in a representative sample of professional footballers in the UK and investigate possible determinants of oral health and self-reported impact on well-being, training and performance. Clinical oral health examination of senior squad players using standard methods and outcomes carried out at club training facilities. Questionnaire data were also collected. 8 teams were included, 5 Premier League, 2 Championship and 1 League One. 6 dentists examined 187 players who represented >90% of each senior squad. Oral health was poor: 37% players had active dental caries, 53% dental erosion and 5% moderate-severe irreversible periodontal disease. 45% were bothered by their oral health, 20% reported an impact on their quality of life and 7% on training or performance. Despite attendance for dental check-ups, oral health deteriorated with age. This is the first large, representative sample study in professional football. Oral health of professional footballers is poor, and this impacts on well-being and performance. Successful strategies to promote oral health within professional football are urgently needed, and research should investigate models based on best evidence for behaviour change and implementation science. Furthermore, this study provides strong evidence to support oral health screening within professional football.

#7 Reliability of the tuck jump injury risk screening assessment in elite male youth soccer players
Reference: J Strength Cond Res. 2015 Nov 7. [Epub ahead of print]
Authors: Read P, Oliver JL, DE Ste Croix MB, Myer GD, Lloyd RS
Summary: Altered neuromuscular control has been suggested as a mechanism for injury in soccer players. Ligamentous injuries most often occur during dynamic movements, such as decelerations from jump-landing maneuvers where high risk movement patterns are present. The assessment of kinematic variables during jump-landing tasks as part of a pre-participation screen is useful in the identification of injury risk. An example of a field-based screening tool is the repeated tuck jump assessment. The purpose of this study was to analyze the within-subject variation of the tuck jump screening assessment in elite male youth soccer players. 25 pre and 25 post-peak height velocity (PHV) elite male youth soccer players from the academy of a professional English soccer club completed the assessment. A test, re-test design was used to explore the within-subject inter-session reliability. Technique was graded retrospectively against the 10-point criteria set out in the screening protocol using two-dimensional video cameras. The typical error range reported for tuck jump total score (0.90 - 1.01 in pre and post-PHV players respectively) was considered acceptable. When each criteria was analyzed individually, Kappa coefficient determined that knee valgus was the only criterion to reach substantial agreement across the two test sessions for both groups. The results of this study suggest that although tuck jump total score may be reliably assessed in elite male youth soccer players, caution should be applied in solely interpreting the composite score due to the high within-subject variation in a number of the individual criteria. Knee valgus may be reliably used to screen elite youth male soccer players for this plyometric technique error and for test, re-test comparison.

#8 Relationship between reactive agility and change of direction speed in amateur soccer players
Reference: J Strength Cond Res. 2015 Nov 7. [Epub ahead of print]
Authors: Matlák J, Tihanyi J, Rácz L.
Summary: The aim of the study was to assess the relationship between reactive agility and change of direction speed among amateur soccer players using running tests with four directional changes. Sixteen amateur soccer players (24.1 ± 3.3 years; 72.4 ± 7.3 kg; 178.7 ± 6 cm) completed change of direction speed (CODS) and reactive agility tests with four changes of direction using the SpeedCourt™ system (Globalspeed GmbH, Hemsbach, Germany). Counter-movement jump height and maximal foot tapping count (completed in 3 seconds) were also measured with the same device. In the reactive agility test, participants had to react to a series of light stimuli projected onto a screen. Total time was shorter in the CODS test than in the reactive agility test (p<0.001). Nonsignificant correlations were found among variables measured in the CODS, reactive agility, and counter-movement jump tests. Low common variance (r = 0.03 - 0.18) was found between CODS and reactive agility test variables. The results of this study underscore the importance of cognitive factors in reactive agility performance and suggest that specific methods may be required for training and testing reactive agility and change of direction speed.

#9 Acute effects of loaded half-squat jumps on sprint running speed in track and field athletes and soccer players
Reference: J Strength Cond Res. 2015 Nov 7. [Epub ahead of print]
Authors: Vanderka M, Krčmár M, Longová K, Walker S.
Summary: The purpose of the study was to determine the acute responses to a jump squat protocol designed to induce post-activation potentiation (PAP) on sprint running performance in experienced track & field athletes and soccer players. Twenty five regional level athletes (12 track and field: ∼17 year, ∼177 cm, ∼73 kg and 13 soccer: ∼18 year, ∼175 cm, ∼72 kg) performed 2 test sessions assessing 40 m sprint running performance in a balanced, cross-over design. Dual-beam light timing gates measured 0-20 m and 20-40 m sprint times before and after either 9 min of sitting (control) or 2 sets of 6 repetition half-squat jump with the load eliciting maximum power (experimental) conditions. Sprint performance was significantly enhanced over both 0-20 m (3.09 ± 0.07 to 3.04 ± 0.08 s, Δ ∼1.5 %, P < 0.05) and 20-40 m (2.42 ± 0.09 to 2.39 ± 0.09 s, Δ ∼1 %, P < 0.05) in track and field athletes only. Also, the magnitude of enhanced sprint performance was related to baseline 0-20 m sprint performance (r = 0.44, p = 0.028, n = 25). It appears that using loaded half-squat jumps to enhance sprint performance could be utilized in training of high level young athletes.

#10 Changes in muscle damage, inflammation, and fatigue-related parameters in young elite soccer players after a match
Reference: J Sports Med Phys Fitness. 2015 Nov 11. [Epub ahead of print]
Authors: Romagnoli M, Sanchis-Gomar F, Alis R, Risso-Ballester J, Bosio A, Graziani RL, Rampinini E.
Summary: Professional soccer players are subjected to substantial physical loads during competitive seasons. We aimed to explore the changes induced by a soccer match on muscle damage and inflammation biomarkers, and their relationship with fatigue parameters. Twenty young male professional in-field soccer players from an Italian Serie A team (age 17-20 years, weight 73.0±7.0 kg, height 1.81±0.05m) played a 90-minute soccer match. Players' distances and velocities were recorded during the match. Before the match and 30 minutes, 24 and 48 hours after the match, blood samples were drawn and a full blood cell count was determined, along with serum creatine kinase (CK), interleukin 6 (hsIL-6), cortisol and testosterone. At the same time intervals, counter-movement jump (CMJ) performance was recorded. The players covered fewer meters at low velocities in the second period while the meters covered at higher intensity remained unchanged. CMJ height was lower at all post-game time-points compared to the pre-game measurement. Immediately after the match, CK, hs-IL6 and neutrophil counts were elevated. 24 and 48 hours after the match, CK and neutrophil counts remained significantly elevated. The distance covered during the game was found to be correlated with the values for post-match hsIL-6 (ρ=0.521, p=0.027), post 24-hour cortisol (r=0.502, p=0.034) and the increase in cortisol at 48 hours with respect to pre-match values (r=0.515, p=0.029). A soccer match provokes a transient systemic imbalance that results in muscle damage and inflammatory and performance- related parameter changes. HsIL-6 and cortisol could be used to monitor recovery processes and as fatigue markers, even for short time periods.

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