Latest research in football - week 49 - 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 Yo-Yo Intermittent Recovery Test Level 2 and its Relationship to other Typical Soccer Field Tests in Female Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Nov 19. [Epub ahead of print]
Authors: Lockie RG, Jalilvand F, Moreno MR, Orjalo AJ, Risso FG, Nimphius S
Summary: The ability to complete high-intensity running is essential for soccer. The Yo-Yo Intermittent Recovery Test Level 2 (YYIRT2) can measure this capacity, but there is limited information regarding this assessment in collegiate female soccer players. This study investigated the YYIRT2 as a measure of high-intensity running in this population, and its relationship to other soccer field tests. Twenty-one players from a Division I team were recruited. In addition to the YYIRT2, subjects completed linear (0-5, 0-10, 0-30 m sprint intervals) and change-of-direction (pro-agility and 60-yard shuttle) speed tests, as well as the YYIRT Level 1 (YYIRT1), to assess relationships with YYIRT2 via correlations (p < 0.05). The correlation of YYIRT1 with the speed tests was also assessed. YYIRT1 and YYIRT2 were standardized via z-scores for comparison to elite benchmarks to investigate relative performance on each test. YYIRT2 and YYIRT1 distance did not significantly correlate with the speed tests (r = -0.251-0.274). There was a large relationship between YYIRT2 and YYIRT1 distance (r = 0.582), although the explained variance was low (33.87%). Mean YYIRT2 z-scores (-4.29 ± 1.66) indicated a performance further from elite benchmarks than the YYIRT1 (-1.92 ± 1.61), and 90.5% (19 of 21) subjects performed relatively better in the YYIRT1 than YYIRT2. The YYIRT2 provided a more specific measure of high-intensity running to that of the YYIRT1 in collegiate female soccer players. Coaches may consider using the YYIRT2 to gauge and track progress of high-intensity running capabilities, and create training programs to improve this ability in female players.

#2 Enhancing Collegiate Women's Soccer Psychosocial and Performance Outcomes by Promoting Intrinsic Sources of Sport Enjoyment
Reference: J Sports Sci Med. 2016 Dec 1;15(4):678-687. eCollection 2016.
Authors: Barnicle SP, Burton D
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Summary: This study examined the effectiveness of an applied mental skills training (MST) intervention utilizing mental skills to enhance intrinsic sources of enjoyment (ISOEs) as a means of promoting self-confidence, motivational style, and athletic performance, while also decreasing trait anxiety. The intervention project was designed to increase intrinsic SOE using a systematic and individualized mental training protocol, and then examine its relationships to mental skills and soccer performance. A Division 1 collegiate women's soccer team was randomly assigned to treatment (n = 8) and control (n = 11) groups, equally distributed by academic year, position, and pre-season coach-evaluated starters and non-starts. Results revealed that the MST intervention significantly increased intrinsic enjoyment targeted psychological and competitive outcomes, both in practice and competition within the treatment group as compared to the control group. This study's support for the impact mental skills training may have had on ISOEs, as well as other psychosocial outcomes and athletic performance can serve to highlight a mental skill often overlooked by consultants and coaches.

#3 Effects of a Whole-Body Electrostimulation Program on Strength, Sprinting, Jumping, and Kicking Capacity in Elite Soccer Players
Reference: J Sports Sci Med. 2016 Dec 1;15(4):639-648. eCollection 2016.
Authors: Filipovic A, Grau M, Kleinöder H, Zimmer P, Hollmann W, Bloch W
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Summary: The aim of the present study was to investigate the effect of a 14-week dynamic Whole-Body Electrostimulation (WB-EMS) training program on muscular strength, soccer relevant sprint, jump and kicking velocity performance in elite soccer players during competitive season. Twenty-two field-players were assigned to 2 groups: WB-EMS group (EG, n = 12), jump-training group (TG, n = 10). The training programs were conducted twice a week concurrent to 6-7 soccer training sessions during the 2nd half of the season. Participants were tested before (baseline), during (wk-7) and after (wk-14). Blood serum samples for analyzing IGF-1 and CK were taken before each testing, 15-30min post and 24h post the training program. Our findings of the present study were that a 14-week in-season WB-EMS program significant increased one-leg maximal strength (1RM) at the leg press machine (1.99 vs. 1.66 kg/kg, p = 0.001), and improved linear sprinting (5m: 1.01 vs. 1.04s, p=0.039), sprinting with direction changes (3.07 vs. 3.25s, p = 0.024), and vertical jumping performance (SJ: 38.8 vs. 35.9cm p = 0.021) as well as kicking velocity (1step: 93.8 vs. 83.9 km·h-1, p < 0.001). The TG showed no changes in strength and performance. The EG revealed significantly increased CK levels 24h post training and yielded significantly higher CK levels compared to the TG. IGF-1 serum levels neither changed in the EG nor in the TG. The results give first hints that two sessions of a dynamic WB-EMS training in addition to 6-7 soccer sessions per week can be effective for significantly enhancing soccer relevant performance capacities in professional players during competitive season.

#4 Subjective well-being and training load predict in-season injury and illness risk in female youth soccer players
Reference: Br J Sports Med. 2016 Dec 5. pii: bjsports-2016-096584. doi: 10.1136/bjsports-2016-096584. [Epub ahead of print]
Authors: Watson A, Brickson S, Brooks A, Dunn W
Summary: The purpose of this study was to evaluate the effects of training load (TL) and well-being on injury and illness risk in youth soccer players. Throughout a 20-week season, 75 female adolescent soccer players reported mood, fatigue, stress, soreness, sleep quality, sleep hours, TL, injuries and illnesses. Well-being measures were recorded from -3 (worst) to +3 (best). TL was expressed as daily, weekly and monthly, as well as an acute:chronic workload ratio (weekly divided by monthly). Variables were compared between days with and without an injury, and with or without an illness. Poisson regression models were developed to predict daily injuries and illnesses using well-being and TL (z-scores) as predictors. 36 injuries and 52 illnesses were recorded. Days with an injury had lower (worse) daily mood (1.24±0.2 vs 1.16±0.1, p=0.012) and higher daily TL (517±138 vs 440±158, p=0.010). Average monthly TL was higher preceding days with an illness (12 442 ±409 vs 12 627 ±403, p=0.043), while no differences were found with respect to other measures of TL or well-being. Worse daily mood (p=0.011, OR=0.012), higher daily TL (p<0.001, OR=1.98), and higher prior day TL (p=0.040, OR=1.34) were independent predictors of injury, while weekly (p=0.005, OR=1.50) and monthly TL (p=0.007, OR=1.54) were predictors of illness. Lower mood and higher acute TL are associated with increased injury risk, while higher chronic TL increases the risk of illness. Monitoring well-being and TL may facilitate intervention to reduce in-season injury and illness.

#5 The Influence of Changes in Acute Training Load on Daily Sensitivity of Morning-measured Fatigue Variables in Elite Soccer Players
Reference: Int J Sports Physiol Perform. 2016 Dec 5:1-23. [Epub ahead of print]
Authors: Thorpe RT, Strudwick AJ, Buchheit M, Atkinson G, Drust B, Gregson W
Summary: The purpose was to determine the sensitivity of a range of potential fatigue measures to daily training load accumulated over the previous two, three and four days during a short in-season competitive period in elite senior soccer players (n=10). Total high-speed running distance, perceived ratings of wellness (fatigue, muscle soreness, sleep quality), counter-movement jump height (CMJ), submaximal heart rate (HRex), post-exercise heart rate recovery (HRR) and heart rate variability (HRV: Ln rMSSD) were analysed during an in-season competitive period (17 days). General linear models were used to evaluate the influence of two, three and four day total high-speed running distance accumulation on fatigue measures. Fluctuations in perceived ratings of fatigue were correlated with fluctuations in total high-speed running distance accumulation covered on the previous 2-days (r=-0.31; small), 3 -days (r=-0.42; moderate) and 4-days (r=-0.28; small) (p<0.05). Changes in HRex (r=0.28; small; p= 0.02) were correlated with changes in 4-day total high-speed running distance accumulation only. Correlations between variability in muscle soreness, sleep quality, CMJ, HRR% and HRV and total high-speed running distance were negligible and not statistically significant for all accumulation training loads. Perceived ratings of fatigue and HRex were sensitive to fluctuations in acute total high-speed running distance accumulation, although, sensitivity was not systematically influenced by the number of previous days over which the training load was accumulated. The present findings indicate that the sensitivity of morning-measured fatigue variables to changes in training load is generally not improved when compared with training loads beyond the previous days training.

#6 Relationships Between Internal and External Match Load Indicators in Soccer Match Officials
Reference: Int J Sports Physiol Perform. 2016 Dec 5:1-21. [Epub ahead of print]
Authors: Castillo D, Weston M, McLaren SJ, Cámara J, Yanci J
Summary: The aims of this study were to describe the internal and external match load (ML) of refereeing activity during official matches and also to investigate the relationship among the methods of ML quantification across a competitive soccer season. A further aim was to examine the usefulness of differential perceived exertion (dRPE) as a tool for monitoring internal ML in soccer referees. Twenty field referees (FR) and 43 assistant referees (AR) participated in this study. Data were collected from 30 competitive matches (FR = 20 observations, AR = 43 observations) and included measures of internal (Edwards' heart rate derived training impulse [TRIMPEDW]), external (total distance covered [TD], distance covered at high speeds [HSR] and player load [PL]) ML, differentiated ratings of perceived respiratory [sRPEres ML] and leg muscle [sRPEmus ML] exertion). Internal and external ML were all greater for FR when compared to AR (-19.7 to -72.5); with differences ranging from very likely very large to most likely extremely large. The relationships between internal ML and external ML indicators were, in most cases, unclear for FR (r < .35) and small to moderate for AR (r < .40). We found substantial differences between RPEres and RPEmus scores in both FR (.6 AU; ±90% confidence limits .4 AU) and AR (.4; ±.3 AU). These data demonstrate the multifaceted demands of soccer refereeing and thereby highlight the importance of monitoring both internal and external ML. Moreover, dRPE represent distinct dimensions of effort and may be useful in monitoring soccer referees ML during official matches.

#7 Seasonal changes in soccer players' body composition and dietary intake practices
Reference: J Strength Cond Res. 2016 Nov 29. [Epub ahead of print]
Authors: Devlin BL, Kingsley M, Leveritt MD, Belski R
Summary: The aims of this study were two-fold: to determine seasonal changes in dietary intake and body composition in elite soccer players and to evaluate the influence of self-determined individual body composition goals on dietary intake and body composition. This longitudinal, observational study assessed body composition (total mass, fat-free soft tissue mass and fat mass) using dual-energy x-ray absorptiometry and dietary intake (energy and macronutrients) via multiple pass 24-hour recalls, at four time points over a competitive season in elite soccer players from one professional club in the Australian A-League competition. Self-reported body composition goals were also recorded. Eighteen elite male soccer players took part (25 ± 5 years, 180.5 ± 7.4 cm, 75.6 ± 6.5 kg). Majority (≥67%) reported the goal to maintain weight. Fat-free soft tissue mass increased from the start of preseason (55278 ± 5475 g) to the start of competitive season (56784 ± 5168 g; p<0.001) and these gains were maintained until the end of the season. Fat mass decreased over the preseason period (10072 ± 2493 g to 8712 ± 1432 g; p<0.001), but increased during the latter part of the competitive season. Dietary intake practices on training days were consistent over time and low compared to sport nutrition recommendations. The self-reported body composition goals did not strongly influence dietary intake practices or changes in body composition. This study has demonstrated that body composition changes over the course of a soccer season are subtle in elite soccer players despite relatively low self-reported intakes of energy and carbohydrate.

#8 Assessing the effectiveness of the Functional Movement Screen (FMS™) in predicting non-contact injury rates in soccer players
Reference: J Strength Cond Res. 2016 Dec 7. [Epub ahead of print]
Authors: Smith PD, Hanlon M
Summary: This study assessed if the Functional Movement Screen (FMS™) can accurately predict non-contact injury in adult soccer players when normalizing non-contact injury occurrence against match exposure levels. Senior male players (n=89) from five League of Ireland semi-professional clubs participated in the study (mean age=23.2 ± 4.4 years; mean height=179.5 ± 6.6 cm; mean body mass=77.5 ± 7.8 kg). Participants performed the FMS™ during preseason and their injury occurrence rates and match minutes were tracked throughout one season. In total, 66 non-contact injuries were recorded. No significant difference was found in FMS™ composite scores between players receiving non-contact injuries and players not suffering a non-contact injury (p=0.96). There was no significant difference in exposure-normalized non-contact injury incidence between those scoring 14 or below and those scoring above 14 on the FMS™ (0.36 vs. 0.29 non-contact injuries per player per 1000 match minutes). Players scoring 14 or below on the FMS™ had an odds ratio of 0.63 (p=0.45; CI 95%=0.19- 2.07) of receiving a non contact injury. Despite previous research showing links between low FMS™ composite scores and subsequent injury, these results suggest the FMS™ cannot accurately predict a male soccer player's likelihood of receiving a non-contact injury and that a lower FMS™ composite score does not significantly increase their non-contact injury incidence rate per 1000 match minutes. Caution should therefore be used when employing the FMS™ as a predictor of non-contact injury, and pain prevalence during the FMS™, previous injuries, and training/match exposure levels should also be taken into account.

#9 Intra-articular injections of HYADD4-G in male professional soccer players with traumatic or degenerative knee chondropathy. A pilot, prospective study
Reference: J Sports Med Phys Fitness. 2016 Dec;56(12):1534-1539.
Authors: Tamburrino P, Castellacci E
Summary: Knee injuries are very common in some sports and particularly in soccer due to the highly repetitive loading of the mechanical stress involved in this practice. Knee-joint injuries account for 40% of all different kinds of lesions. Traumatic or degenerative patellofemoral or tibialfemoral chondropaties of knee cause disabling symptoms, joint pain and/or dysfunctions. The aim of the study was to evaluate the effects of HYADD4-G, a hydrogel based on a hyaluronic acid derivative, in professional soccer players affected by traumatic or degenerative knee chondropathy. Thirty male professional soccer players participants in the Italian League 2014-2015, affected by traumatic or degenerative knee patellofemoral (N.=12) or tibiofemoral (N.=18) chondropathy assessed through MRI and/or arthroscopy of knee joints and the ICRS staging (International Cartilage Repair Society ≤3a), were enrolled in this pilot prospective study. Patients underwent 2 intra-articular (IA) injections of HYADD4-G (3 mL of 8 mg/mL) at one week interval. Patients were prospectively evaluated at baseline and then at 1, 3 and 6 months after the treatment by the Osteoarthritis Outcome Score (KOOS) Score (main outcome) and by the Visual Analog Scale (VAS) to evaluate pain. A significant improvement in all clinical endpoints from pretreatment to different times of evaluation was found in all patients. ANOVA with repeated measure using the SPSS has showed significantly better results in term of KOOS and VAS scores at 1, 3 and 6 months compared to the pre-injection value (P<0.05). IA HYADD4-G is highly effective to improve resting and walking pain in professional male soccer players with traumatic or degenerative knee chondropathy.

#10 Sex-Based Differences in Cognitive Deficits and Symptom Reporting Among Acutely Concussed Adolescent Lacrosse and Soccer Players
Reference: Am J Sports Med. 2016 Dec 9. pii: 0363546516677246. [Epub ahead of print]
Authors: Sandel NK, Schatz P, Goldberg KB, Lazar M
Summary: Research on the acute effects of a concussion among lacrosse players is limited, and postconcussion patterns between male and female athletes have yet to be clearly established. Differences in the style of play and protective gear worn among male and female lacrosse players potentially confound a direct comparison of sex-based differences in this population. The purpose was to explore sex-based differences in postconcussive neurocognitive functioning and symptom reporting outcomes in concussed adolescent male and female lacrosse players compared with a group of soccer players. A total of 224 adolescent lacrosse players (112 male, 112 female) aged 13 to 17 years (mean [±SD] age, 15.43 ± 1.09 years) were included in this study. A comparison group of soccer players was added and matched to lacrosse players based on age and sex to address confounding sport differences in male and female versions of lacrosse. All athletes underwent baseline and postinjury testing within 3 days of an injury using the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) tool. Data were analyzed at baseline using a multivariate analysis of variance (MANOVA) with sport and sex as between-participant factors. A 2 × 2 × 2 mixed-factorial MANOVA was also conducted for sex and sport comparisons at baseline versus after a concussion. Ancillary analyses evaluated sex-based differences in exceeded reliable change indices (RCIs) using an independent-samples t test and established postinjury cutoff scores reflective of a protracted recovery using chi-square tests. All athletes had a significantly worse cognitive profile and greater endorsement of symptoms after an injury (F5,216 = 30.30, P < .001, ηρ2 = .41). Sport yielded a significant main effect (F5,216 = 2.36, P = .04, ηρ2 = .05), but subsequent univariate analyses were nonsignificant (P > .05) across all neurocognitive and symptom outcome variables. Likewise, there were no significant interaction effects for sport × time (F5,216 = 1.46, P = .21, ηρ2 = .03) or sport × sex × time (F5,216 = 2.09, P = .07, ηρ2 = .05), indicating that lacrosse and soccer players respond similarly on neurocognitive testing and symptom reporting after sustaining a concussion. Regarding sex-based differences, female athletes had a significantly greater neurocognitive decline and increased symptoms after a concussion relative to male athletes, regardless of the sport type (sex × time interaction effect: F5,216 = 3.86, P = .002, ηρ2 = .08), with the relationship between concussions and sex demonstrating a medium- to large-sized effect. Female athletes demonstrated a significantly greater number of exceeded RCIs (t(216.16) = -3.732, P < .001), with 59% of male and 74% of female athletes with at least 1 RCI decline. Approximately 13% of male athletes, compared with 30% of female athletes, demonstrated scores indicative of protracted recovery at a 75% sensitivity (χ2 (1, N = 224) = 9.43, P = .002). Athletes performed more poorly on computerized cognitive screening tools and reported greater symptoms after an acute concussion relative to their baseline performance. Female sex may be a modifier of an acute concussion outcome, given that female athletes in this study performed significantly worse than male athletes across all neurocognitive measures and reported greater symptoms relative to their baseline testing compared with male athletes, regardless of the sport played. Female athletes were also more likely than male athletes to demonstrate scores on neurocognitive testing that exceeded reliable change cutoffs and were predictive of a protracted recovery. The practical significance of these findings should be further verified by prospective longitudinal research given the medium- to large-sized effect demonstrated for the overall relationship between sex and concussions.

#11 Identification of Sensitive Measures of Recovery Following External Load From Football Match Play
Reference: Int J Sports Physiol Perform. 2016 Dec 14:1-25. [Epub ahead of print]
Authors: Rowell AE, Aughey RJ, Hopkins WG, Stewart AM, Cormack SJ
Summary: Objective measures of recovery from football match-play could be useful for assessing athletes' readiness to train, if sensitive to preceding match load. The purpose of the study was to identify the sensitivity of countermovement-jump (CMJ) performance and concentration of salivary testosterone and cortisol relative to elite football match load. CMJ performance and salivary hormones were measured in 18 elite football players before (27-, 1-h) and after (0.5-, 18-, 42-, 66-, 90-h) three consecutive matches. Match load was determined via accelerometer derived PlayerLoad™ and praised into tertiles. Sensitivity of CMJ performance and hormone concentrations to match load was quantified with t-statistics and magnitude-based inferences (change in mean as % ± 90% confidence interval (CI)) derived with a linear mixed model. Jump height was reduced in medium- and high-load at 0.5-h (10% ± 7% and 16% ± 8%) and 18-h (7% ± 4% and 9% ± 5%) post match. There was a 12% ± 7% reduction in Flight time:contraction time (FT:CT) ratio in high-load at 0.5-h post, with reductions in medium- and high-load at 18-h. Reductions in FT:CT persisted at later post-match time-points than changes in Jump height. Increased cortisol (range: 55% to 165%) and testosterone (range: 17% to 20%) was observed in all match loads at 0.5-h post with individual variability thereafter. Measures of CMJ performance and hormonal concentrations were sensitive to levels of A-League football match load. Although jump height was reduced immediately post-match, FT:CT provided a more sensitive measure of recovery. Football match play induces an acute hormonal response with substantial individual variability thereafter.

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