Latest research in football - week 33 - 2017

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 Effects of Inhaled Salbutamol on Sport-Specific Fitness of Non-Asthmatic Football Players
Reference: Acta Med Iran. 2017 May;55(5):324-332.
Authors: Halabchi F, Abarashi M, Mansournia MA, Seifbarghi T
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Summary: In this article, we investigated the effectiveness of inhaled salbutamol withtherapeutic dose on the sport-specific performance of non-asthmatic young football players. In a double-blinded, randomised placebo controlled trial with 2-treatment, 2-period crossover design, twenty participants who were non-asthmatic junior professional football players were randomly allocated to two groups. Fifteen minutes before sport-specific fitness testing, each group randomly received 2 inhalations (200 micrograms) of salbutamol or placebo, respectively. After 1 week wash-out period, each participant has tested again, this time with the alternative inhaler. The primary outcomes were the differences between salbutamol and placebo groups in six tests of 7×30-m repeated sprint, Loughborough soccer dribbling, vertical jump, agility, Loughborough soccer passing, 20-m multistage shuttle run. A total of twenty players did two test batteries completely. There was no significant difference between salbutamol and placebo users in the tests [Treatment effect (CI95%); 7×30 sprint: -2.4 (-7.6-2.9), dribbling: -3.8 (-12.2-4.5), vertical jump: -1.2 (-3.7-1.3), agility: -0.4 (-0.9-0.1), passing: 0.2 (-12-12.4), shuttle run distance: -112 (-503.2-279.2)]. Furthermore, no period or carry-over effects were detected. It seems that single therapeutic dose of inhaled salbutamol (200 micrograms) does not appear to improve football related performance.

#2 Heading for trouble: is dementia a game changer for football?
Reference: Br J Sports Med. 2017 Jul 20. pii: bjsports-2017-097627. doi: 10.1136/bjsports-2017-097627. [Epub ahead of print]
Authors: Rutherford A, Stewart W, Bruno D

#3 Infographics: Injury prevention exercise programmes: what are the perceptions of programme deliverers in the academy football setting?
Reference: Br J Sports Med. 2017 Jul 22. pii: bjsports-2017-097774. doi: 10.1136/bjsports-2017-097774. [Epub ahead of print]
Authors: Bekker S, Finch CF, O Brien J

#4 Fixture congestion modulates post-match recovery kinetics in professional soccer players
Reference: Res Sports Med. 2017 Aug 10:1-13. doi: 10.1080/15438627.2017.1365296. [Epub ahead of print]
Authors: Lundberg TR, Weckstrom K
Summary: This study examined the influence of fixture congestion on physical performance and biochemical variables in professional male footballers. After 3 competitive matches within a week (3M cycle), 16 players underwent blood sampling and field testing 72 h after the last match. The same tests were performed after a regular 1 match-week cycle (1M cycle). The 1M vs. 3M change scores were compared between Congested (high match exposure) and non-selected Control players. The change score in muscle soreness was greater (effect size 1.0; CI 0.0-1.9) in the Congested players than Controls, indicating a possible negative effect of fixture congestion. There were no effects on sprint and jump performance. The change in plasma (P)-Urea was greater in Congested players than controls (effect size 1.3; CI 0.3-2.2). The effects on other blood variables were either non-existing/trivial, or unclear. Altogether, physical fitness and immune function were not compromised by match congestion, yet some indices of physiological stress and muscle damage were still evident.

#5 Patellar tendinopathy in young elite soccer- clinical and sonographical analysis of a German elite soccer academy
Reference: BMC Musculoskelet Disord. 2017 Aug 8;18(1):344. doi: 10.1186/s12891-017-1690-2.
Authors: Bode G, Hammer T, Karvouniaris N, Feucht MJ, Konstantinidis L, Sudkamp NP, Hirschmuller A
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Summary: The prevalence of patellar tendinopathy is elevated in elite soccer compared to less explosive sports. While the burden of training hours and load is comparably high in youth elite players (age < 23 years), little is known about the prevalence of patellar tendinopathy at this age. There is only little data available on the influence of age, the amount of training, the position on the field, as well as muscular strength, range of motion, or sonographical findings in this age group. The purpose of the present study was to examine the above-mentioned parameters in all age groups of a German youth elite soccer academy. One hundred nineteen male youth soccer players (age 15,97 ± 2,24 years, height 174, 60 ± 10,16 cm, BMI 21, 24 ± 2,65) of the U-13 to U-23 teams were part of the study. Data acquisition included sport specific parameters such as footwear, amount of training hours, leg dominance, history of tendon pathologies, and clinical examination for palpatory pain, indurations, muscular circumference, and range of motion. Subjective complaints were measured with the Victorian Institute of Sport Assessment Patellar (VISA-P) Score. Furthermore, sonographical examinations (Aplio SSA-770A/80; Toshiba, Tokyo, Japan) with 12-MHz multifrequency linear transducers (8-14 MHz) of both patellar tendons were performed with special emphasis on hyper- and hypo echogenic areas, diameter and neovascularization. The prevalence of patellar tendinopathies was 13.4%. Seventy-five percent of the players complained of pain of their dominant leg with onset of pain at training in 87.5%. The injured players showed a medium amount of 10.34 ± 3.85 training hours and a medium duration of symptoms of 11.94 ± 18.75 weeks. Two thirds of players with patellar tendinopathy were at the age of 15-17 (Odds ratio 1.89) while no differences between players of the national or regional league were observed. In case of patellar tendinopathy, VISA-P was significantly lower in comparison to healthy players (mean ± SD 76.80 ± 28.56 points vs. 95.85 ± 10.37). The clinical examination revealed local pain at the distal patella, pain at stretching, and thickening of the patellar tendon (p = 0.02). The mean tendon diameter measured 2 cm distally to the patella was 4.10 ± 0.68 mm with a significantly increased diameter of 0.15 mm in case of an underlying tendinopathy (p = 0.00). The incidence of hypo-echogenic areas and neovascularizations was significantly elevated in players with patellar tendon syndrome (PTS) (p = 0.05). The prevalence of patellar tendinopathy in youth elite soccer is relatively high in comparison to available data of adult players. Especially players at the age of 15 to 17 are at considerable risk. Tendon thickening, hypo-echogenic areas, and neovascularization are more common in tendons affected by PTS.

#6 The Effects of Maturation on Measures of Asymmetry During Neuromuscular Control Tests in Elite Male Youth Soccer Players
Reference: Pediatr Exerc Sci. 2017 Aug 8:1-23. doi: 10.1123/pes.2017-0081. [Epub ahead of print]
Authors: Read PJ, Oliver JL, Myer GD, De Ste Croix MBA, Lloyd RS
Summary: Asymmetry is a risk factor for male youth soccer players. There is a paucity of data confirming the presence of asymmetry using practically viable screening tasks in players at different stages of maturation. A cross sectional sample (N = 347) of elite male youth soccer players who were either (pre-, circa- or post-peak height velocity (PHV)) completed the following single leg assessments: Y-Balance anterior reach (Y-Bal); hop for distance (SLHD); 75% hop and stick (75%Hop) and countermovement jumps (SLCMJ). SLCMJ landing force asymmetry was higher in both circa and post-PHV groups, (p < 0.001; d = 0.41 - 0.43). 75%Hop landing force asymmetries were also highest in circa PHV players but between group comparisons were not statistically significant and effect sizes were small. SLHD and Y-Bal asymmetries reduced with maturation; however, no group differences were significant, with small to trivial effect sizes (d = ≤ 0.25). Stage of maturation did not have a profound effect on asymmetry. Between-limb differences in functional performance seem to be established in early childhood; thus, targeted interventions to reduce this injury risk factor should commence in pre-PHV athletes and be maintained throughout childhood and adolescence to ensure asymmetry does not increase.

#7 Characteristics of the Foot Static Alignment and the Plantar Pressure Associated with Fifth Metatarsal Stress Fracture History in Male Soccer Players: a Case-Control Study
Reference: Sports Med Open. 2017 Dec;3(1):27. doi: 10.1186/s40798-017-0095-y. Epub 2017 Aug 7.
Authors: Matsuda S, Fukubayashi T, Hirose N
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Summary: There is a large amount of information regarding risk factors for fifth metatarsal stress fractures; however, there are few studies involving large numbers of subjects. This study aimed to compare the static foot alignment and distribution of foot pressure of athletes with and without a history of fifth metatarsal stress fractures. The study participants comprised 335 collegiate male soccer players. Twenty-nine with a history of fifth metatarsal stress fractures were in the fracture group and 306 were in the control group (with subgroups as follows: 30 in the fracture foot group and 28 in the non-fracture group). We measured the foot length, arch height, weight-bearing leg-heel alignment, non-weight-bearing leg-heel alignment, forefoot angle relative to the rearfoot, forefoot angle relative to the horizontal axis, and foot pressure. The non-weight-bearing leg-heel alignment was significantly smaller and the forefoot angle relative to the rearfoot was significantly greater in the fracture foot group than in the control foot group (P = 0.049 and P = 0.038, respectively). With regard to plantar pressure, there were no significant differences among the groups. Midfield players had significantly higher rates of fifth metatarsal stress fracture in their histories, whereas defenders had significantly lower rates (chi-square = 13.2, P < 0.05). There were no significant differences in the frequency of fifth metatarsal stress fractures according to the type of foot (kicking foot vs. pivoting foot) or the severity of ankle sprain. Playing the midfield position and having an everted rearfoot and inverted forefoot alignment were associated with fifth metatarsal stress fractures. This information may be helpful for preventing fifth metatarsal stress fracture recurrence. More detailed load evaluations and a prospective study are needed in the future.

#8 The psycho-hormonal influence of anaerobic fatigue on semi-professional female soccer players
Reference: Physiol Behav. 2017 Aug 4;180:8-14. doi: 10.1016/j.physbeh.2017.07.031. [Epub ahead of print]
Authors: Broodryk A, Pienaar C, Edwards D, Sparks M
Summary: Globally it is assumed that high-intensity activities are the general cause of fatigue experienced during a soccer match. However, little is known about the hormonal and psychological effects of fatigue due to these activities on semi-professional female soccer players. Forty-seven female players (22.0±2.7y) from a tertiary education institution volunteered for the study. Their cortisol values (saliva sample), anxiety [Spielberger State-trait anxiety inventory questionnaire (STAI)] and mood scores [Incredible Short Profile of Mood states questionnaire (ISP)] were taken an hour and immediately prior to, and 15min after an anaerobic fatiguing test (AFT). During the AFT, subjects completed a 5-m multiple shuttle run test and their HRmax, blood lactate (BLa-) and rate of perceived exertion (RPE) taken afterwards. Anxiety scores were divided into three categories and mood scores into the Total Mood Disturbances (TMD) and six subscales. The results indicated an increase in cortisol, psychological fatigue and TMD from baseline and/or pre- to post-AFT (p<0.05). Vigour and confusion decreased from baseline and/or pre- to post-AFT (p<0.05). A relationship was seen between state-anxiety and TMD (r≥0.63, p<0.05) at all three time points, as well as between state-anxiety and HRmax (r=0.37, p=0.03). Cortisol and RPE (r=-0.34, p=0.03) demonstrated a correlation post-AFT. This is the first study to evaluate the effects of anaerobic fatigue on the hormonal and psychological states of female soccer players. The results suggest that an AFT can be perceived as a physiological and psychological stressor by female players, hence has the ability to influence performance. Altering a player's awareness and anaerobic fitness level might therefore influence both the hormonal and psychological consequences of the stressor, subsequently reducing the experience of fatigue and thereby enhancing performance.

#9 Pubertal development of body size and soccer-specific functional capacities in adolescent players
Reference: Res Sports Med. 2017 Aug 17:1-16. doi: 10.1080/15438627.2017.1365301. [Epub ahead of print]
Authors: Carvalho HM, Lekue JA, Gil SM, Bidaurrazaga-Letona I
Summary: Pubertal growth in body size and functional capacities were examined in adolescent soccer players (n = 33). The average age at baseline was 10.9 (9.8-11.8 years). Peak height velocity (PHV) and growth curves for body mass and functional performance (countermovement jump, 15-m sprint, agility and Yo-Yo intermittent recovery test - level 1) were determined with Bayesian multilevel models. Estimates for PHV and age at PHV were 8.1 cm/year (95% credible interval: 4.2-18.5 cm/year) and 12.9 years (95% credible interval: 11.8-15.5 years), respectively. Peak body mass velocity occurred 0.48 year after PHV. Jump performance maximum velocity occurred about 2 years after PHV and peak sprint performance maximum velocity was coincident with PHV. Agility and intermittent endurance run performance showed a quadratic trend of improvement of performance, starting to level off at about 3-4 years after PHV. The modelling procedures were efficient to determine pubertal growth curves aligned for chronological age and age at PHV, considering individual differences in maturation when interpreting the development of performance in youth soccer.

#10 Effect of Changes in Artificial Turf on Sports Injuries in Male University Soccer Players
Reference: Orthop J Sports Med. 2017 Aug 2;5(8):2325967117719648. doi: 10.1177/2325967117719648. eCollection 2017 Aug.
Authors: Fujitaka K, Taniguchi A, Kumai T, Otuki S, Okubo M, Tanaka Y
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Summary: Studies comparing the types and severity of trauma and injuries caused by different types of field surfaces have been conducted. However, there have been no studies on sports injuries caused by temporal deterioration of long-pile artificial turf fields and related decreases in the rubber chip and silica sand infill. The purpose was to investigate the influence of an artificial turf field on sports injuries in a university soccer team. A total of 397 male soccer players who were members of a single university soccer team were surveyed over a 12-year period, from April 2003 to March 2015. During this period, the team played for 4 years on a soil field (2003-2006) and 8 years on artificial turf (2007-2014). We analyzed the effect of changes in the artificial turf on the incidence rate of sports injuries (injury rate per 1000 athlete-exposures). We calculated the incidence rate of injuries sustained by the team and compared the results for each year of the study. After conversion of the field to artificial turf, there was a significant increase in the incidence of upper extremity trauma (P < .05). There was a significant increase in lower extremity sprains from 2007 to 2008, 1 year after the conversion from soil to artificial turf (P < .05). Analysis of the incidence of lower extremity muscle strain indicated that although the injury rate increased progressively, it decreased significantly after the insertion of additional rubber chips in 2014 (P < .05). After conversion to artificial turf, there was a significant increase in the incidence of upper extremity trauma. After the refurbishing with additional rubber chips, the incidence of lower extremity muscle strain significantly declined. When analyzing measures that could prevent sports injuries related to soccer, it is necessary to take into consideration the changes that occur to the artificial turf over time.

#11 The influence of speed abilities and technical skills in early adolescence on adult success in soccer: A long-term prospective analysis using ANOVA and SEM approaches
Reference: PLoS One. 2017 Aug 14;12(8):e0182211. doi: 10.1371/journal.pone.0182211. eCollection 2017.
Authors: Honer O, Leyhr D, Kelava A
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Summary: Several talent development programs in youth soccer have implemented motor diagnostics measuring performance factors. However, the predictive value of such tests for adult success is a controversial topic in talent research. This prospective cohort study evaluated the long-term predictive value of 1) motor tests and 2) players' speed abilities (SA) and technical skills (TS) in early adolescence. The sample consisted of 14,178 U12 players from the German talent development program. Five tests (sprint, agility, dribbling, ball control, shooting) were conducted and players' height, weight as well as relative age were assessed at nationwide diagnostics between 2004 and 2006. In the 2014/15 season, the players were then categorized as professional (n = 89), semi-professional (n = 913), or non-professional players (n = 13,176), indicating their adult performance level (APL). The motor tests' prognostic relevance was determined using ANOVAs. Players' future success was predicted by a logistic regression threshold model. This structural equation model comprised a measurement model with the motor tests and two correlated latent factors, SA and TS, with simultaneous consideration for the manifest covariates height, weight and relative age. Each motor predictor and anthropometric characteristic discriminated significantly between the APL (p < .001; η2 ≤ .02). The threshold model significantly predicted the APL (R2 = 24.8%), and in early adolescence the factor TS (p < .001) seems to have a stronger effect on adult performance than SA (p < .05). Both approaches (ANOVA, SEM) verified the diagnostics' predictive validity over a long-term period (≈ 9 years). However, because of the limited effect sizes, the motor tests' prognostic relevance remains ambiguous. A challenge for future research lies in the integration of different (e.g., person-oriented or multilevel) multivariate approaches that expand beyond the "traditional" topic of single tests' predictive validity and toward more theoretically founded issues.

American Football
#1 The Effects of Cardiovascular Fitness and Body Composition on Maximal Core Temperature in Collegiate Football Players During Pre-season
Reference: J Strength Cond Res. 2017 Jul 14. doi: 10.1519/JSC.0000000000002027. [Epub ahead of print]
Authors: McClelland JM, Godek SF, Chlad PS, Feairheller DL, Morrison KE
Summary: This study evaluated the effects of BMI and aerobic fitness (VO2max) on maximal core temperature values (Tcmax) in 17 NCAA Division III football players during pre-season. The subjects included nine backs (BKs) and eight linemen (LM). VO2max testing was performed one week prior to pre-season. Core temperature was monitored via ingestible sensor every 10 min during practices on day 4(D1), day 5(D2), day 7(D3), and post-acclimatization on day 14(D4). Wet bulb globe temperature (WBGT) was recorded on each collection day. Independent, paired t-tests and Pearson's correlations were performed (α=0.05). There were no significant correlations between VO2max and Tcmax on D1 (WBGT=29.07°C) or D2 (WBGT=30.93°C), but on D3 (WBGT=31.39 °C) there was a non-significant moderate negative correlation (r=-0.564, P=0.090). There were no significant correlations between BMI and Tcmax on D1or D2, but on D3 there was a non-significant moderate positive correlation (r=0.596, P=0.069). Paired t-tests revealed that overall Tcmax (D1-3) (38.56±0.32°C) was statistically higher (P=0.002) than D4 (38.16±0.30 °C). Independent t-tests between groups showed the Tcmax values during pre-acclimatization (D1-D3) were significantly higher in LM (38.50±0.37°C) than BKs (38.16±0.35°C) (P=0.007). VO2max was significantly lower (P=0.006) in LM [36.89±6.40 ml/kg•min] than BKs [47.44±7.09 ml/kg•min] and BMI was significantly higher (P=0.019) in LM (35.59±4.00 kg/m) than BKs (28.68±3.38 kg/m). The results of this study demonstrate that LM are significantly less fit than BKs and have a greater BMI. When WBGT was the highest on D3, the results suggest that those with lower VO2max and higher BMI experienced a higher Tcmax.

#2 Temperate-Water Immersion as a Treatment for Hyperthermic Humans Wearing American Football Uniforms
Reference: J Athl Train. 2017 Jul 17. doi: 10.4085/1062-6050-52.5.05. [Epub ahead of print]
Authors: Miller KC, Truxton T, Long B
Summary: Cold-water immersion (CWI; 10°C) can effectively reduce body core temperature even if a hyperthermic human is wearing a full American football uniform (PADS) during treatment. Temperate-water immersion (TWI; 21°C) may be an effective alternative to CWI if resources for the latter (eg, ice) are unavailable. The purpose was to measure rectal temperature (Trec) cooling rates, thermal sensation, and Environmental Symptoms Questionnaire (ESQ) scores of participants wearing PADS or shorts, undergarments, and socks (NOpads) before, during, and after TWI. Thirteen physically active, unacclimatized men (age = 22 ± 2 years, height = 182.3 ± 5.2 cm, mass = 82.5 ± 13.4 kg, body fat = 10% ± 4%, body surface area = 2.04 ± 0.16 m2). Participants exercised in the heat (40°C, 50% relative humidity) on 2 days while wearing PADS until Trec reached 39.5°C. Participants then underwent TWI while wearing either NOpads or PADS until Trec reached 38°C. Thermal sensation and ESQ responses were collected at various times before and after exercise. Temperate-water immersion duration (minutes), Trec cooling rates (°C/min), thermal sensation, and ESQ scores were used as outcome measures. Participants had similar exercise times (NOpads = 38.1 ± 8.1 minutes, PADS = 38.1 ± 8.5 minutes), hypohydration levels (NOpads = 1.1% ± 0.2%, PADS = 1.2% ± 0.2%), and thermal sensation ratings (NOpads = 7.1 ± 0.4, PADS = 7.3 ± 0.4) before TWI. Rectal temperature cooling rates were similar between conditions (NOpads = 0.12°C/min ± 0.05°C/min, PADS = 0.13°C/min ± 0.05°C/min; t12 = 0.82, P = .79). Thermal sensation and ESQ scores were unremarkable between conditions over time. Temperate-water immersion produced acceptable (ie, >0.08°C/min), though not ideal, cooling rates regardless of whether PADS or NOpads were worn. If a football uniform is difficult to remove or the patient is noncompliant, clinicians should begin water-immersion treatment with the athlete fully equipped. Clinicians should strive to use CWI to treat severe hyperthermia, but when CWI is not feasible, TWI should be the next treatment option because its cooling rate was higher than the rates of other common modalities (eg, ice packs, fanning).

#3 Influence of Body Composition on Functional Movement Screen™ Scores in Collegiate Football Players
Reference: J Sport Rehabil. 2017 Jul 17:1-21. doi: 10.1123/jsr.2015-0080. [Epub ahead of print]
Authors: Nicolozakes CP, Schneider DK, Rower B, Borchers J, Hewett TE
Summary: The Functional Movement Screen (FMS™) is used to identify movement asymmetries and deficiencies. While obesity has been reported to impede movement, the correlation between body mass index (BMI), body fat percentage (BF%), and FMS™ in athletes is unknown. The objective was to determine if there is a relationship between BMI, BF%, and FMS™ scores in a sample of National Collegiate Athletic Association (NCAA) Division I football athletes. 38 male freshman football players (18.0 ± 0.7 y, 185.3 ± 5.5 cm, 103.9 ± 20.3 kg) participated in this study.  Height, weight, and BF% were collected, and subjects underwent the FMS™ conducted by a certified athletic trainer. The dependent variables were BMI, BF%, composite FMS™ score, and seven individual FMS™ test scores. Subjects were grouped as normal BMI (BMI < 30 kg/m2) or obese (BMI ≥ 30 kg/m2). A composite FMS™ score of ≤14 and an individual FMS™ score of ≤1 were classified as cut-offs for poor movement performance. A negative correlation between composite FMS™ score and BMI approached significance (p = 0.07, ρ = -0.296). A negative correlation between composite FMS™ score and BF% was significant (p = 0.010, ρ = -0.449). There was a significant difference in the number of obese subjects scoring below the composite FMS™ cut-off (χ2 = 5.179, p = 0.023) and the individual FMS™ cut-off on the deep squat (χ2 = 6.341, p = 0.012), hurdle step (χ2 = 9.870, p = 0.002), and in-line lunge (χ2 = 5.584, p = 0.018) when compared to normal BMI subjects. Increased BF% and BMI relate to lower composite FMS™ and individual FMS™ test scores, indicating potentially poor movement patterns in larger NCAA football athletes. Future research should focus on examining lower extremity-specific FMS™ tasks individually from composite FMS™ scores.

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