Latest research in football - week 29 - 2018

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 Influence of intense training cycle and psychometric status on technical and physiological aspects performed during the small-sided games in soccer players
Reference: Res Sports Med. 2018 Jul 3:1-12. doi: 10.1080/15438627.2018.1492398. [Epub ahead of print]
Authors: Selmi O, Marzouki H, Ouergui I, BenKhalifa W, Bouassida A
Summary: The study investigated the effect of intense training cycle (IT) of early season preparation period (SPP) and psychological status on technical and physiological parameters during small-sided games (SSG) and the relationships between these variables. Sixteen professional soccer players participated in the study (mean±SD: age: 24.5±4.1). Training load (TL), Total quality recovery (TQR) and well-being indices were performed daily. TL increased progressively (%TL=31.56 [AU]). Physiological variables did not change after IT and were not influenced by well-being indices and TQR. Technical aspects were negatively altered after IT (p<0.05). TL was significantly correlated with successful passes (r=-0.57, p=0.02), interceptions (r=-0.83, p<0.001) and lost balls (r=0.73, p=0.002). Well-being and TQR were related to successful passes, interceptions and lost passes [(r=-0.55, p=0.03; r=-0.75, p=0.001; r=-0.69, p=0.004); (r=0.54, p=0.03; r=-0.76, p=0.001; r=-0.69, p=0.004), respectively]. TL, Well-being indices and TQR represent a useful strategy for coaches to control technical aspects in soccer players during SPP.

#2 Effects of traditional balance and slackline training on physical performance and perceived enjoyment in young soccer players
Reference: Res Sports Med. 2018 Jul 2:1-12. doi: 10.1080/15438627.2018.1492392. [Epub ahead of print]
Authors: Trecroci A, Cavaggioni L, Lastella M, Broggi M, Perri E, Iaia FM, Alberti G
Summary: The aim of this study was to evaluate the effects of 12-week balance and slackline training programs on physical performance and perceived enjoyment scale in young soccer players. Forty-one preadolescent soccer players were assigned to two experimental groups performing traditional balance (BLT) or slackline training (SLT), and a control group. Pre-post assessment encompassed Balance Error Scoring System (BESS), Star Excursion Balance test (SEBT), sprint with 90° turns (S90), and countermovement jump (CMJ). The rate of perceived enjoyment scale (PACES) was applied at the end of the experimental period. SLT and BLT improved similarly in BESS, SEBT and S90. No changes were detected in the CMJ. Regarding PACES score, SLT presented significantly higher values than BLT. Young athletes may benefit from a motivating training approach, thus, a designed program based on slackline drills should be preferable to improve physical performance in terms of balance and change of direction ability in preadolescent soccer players.

#3 Contextual factors on physical demands in professional women's soccer: Female Athletes in Motion study
Reference: Eur J Sport Sci. 2018 Jul 1:1-6. doi: 10.1080/17461391.2018.1491628. [Epub ahead of print]
Authors: Vescovi JD, Falenchuk O
Summary: The aim of this study was to examine the impact of contextual factors on relative locomotor and metabolic power distances during professional female soccer matches. Twenty-eight players (forwards, n = 4; midfielders, n = 12; defenders, n = 12) that competed in a 90-min home and away match (regular season only). The generalised estimating equations (GEE) was used to evaluate relative locomotor and metabolic power distances for three contextual factors: location (home vs. away), type of turf (natural vs. artificial), and match outcome (win, loss and draw). No differences were observed for home vs. away matches. Moderate-intensity running (20.0 ± 1.0 m min-1 and 16.4 ± 0.9 m min-1), high-intensity running (8.6 ± 0.4 m min-1 and 7.3 ± 0.4 m min-1) and high-metabolic power (16.3 ± 0.5 m min-1 and 14.4 ± 0.5 m min-1) distances were elevated on artificial turf compared to natural grass, respectively. Relative sprint distance was greater during losses compared with draws (4.3 ± 0.4 m min-1 and 3.4 ± 0.3 m min-1). Overall physical demands of professional women's soccer were not impacted by match location. However, the elevation of moderate and high-intensity demands while playing on artificial turf may have implications on match preparations as well as recovery strategies.

#4 Exercise training in overweight and obese children: Recreational football and high-intensity interval training provide similar benefits to physical fitness
Reference: Scand J Med Sci Sports. 2018 Jul 6. doi: 10.1111/sms.13241. [Epub ahead of print]
Authors: Cvetković N, Stojanović E, Stojiljković N, Nikolić D, Scanlan AT, Milanović Z
Summary: This study compared the effects of recreational football and high-intensity interval training (HIIT) on body composition, muscular fitness, and cardiorespiratory fitness in overweight and obese children. Forty-two overweight/obese males aged 11-13 years [body mass index (BMI) >20.5 kg/m2 ] were randomly assigned to a recreational football training group (n = 14; 157.9 ± 5.8 cm; 63.7 ± 12.6 kg), HIIT group (n = 14; 163.8 ± 9.4 cm; 71.5 ± 10.5 kg), or nontraining control group (n = 14; 162.7 ± 9.3 cm; 67.4 ± 16.1 kg). Physical fitness components were measured at baseline and after 12 weeks of training at the same time of the day and under similar conditions, including body composition, muscular fitness (lower-body power, change-of-direction speed, and flexibility), and cardiovascular fitness (Yo-Yo Intermittent Endurance test distance, resting heart rate, and blood pressure). Lean body mass (4.3%, ES = 0.40; 95% CI: -0.48, 1.29; P = .382) and muscle mass 4.4% (ES = 0.40; 95% CI: -0.48, 1.29; P = .378) very likely increased in the recreational football group, while possible improvements were observed in the HIIT group (lean body mass: 2.5%, ES = 0.22; 95% CI: -0.62, 1.06; P = .607, muscle mass: 2.8%, ES = 0.23; 95% CI: -0.61, 1.07; P = .594). Only trivial increases were observed in the control group for lean body mass (0.5%, ES = 0.05; 95% CI: -0.70, 0.79; P = .906) and muscle mass (1.1%, ES = 0.09; 95% CI: -0.65, 0.83; P = .814). Significant differences were found between the recreational football and control groups in post-training body mass (P = .034) and body mass index (P = .017). Body fat very likely decreased in the recreational football group (-7.7%, ES = -0.41; 95% CI: -1.29, 0.48; P = .376) and possibly decreased in the HIIT group (-5.2%, ES = -0.22; 95% CI: -1.05, 0.62; P = .607), with a trivial reduction in the control group (-1.1%, ES = -0.04; 95% CI: -0.78, 0.70; P = .914). Very likely increases in lower-body power were evident in the recreational football (17.0%, ES = 0.76; 95% CI: -0.15, 1.66; P = .107) and control groups (16.1%, ES = 0.55; 95% CI: -0.20, 1.31; P = .156), while small improvements were observed in the HIIT group (6.0%, ES = 0.24; 95% CI: -0.60, 1.08; P = .580, possible). Likely to most likely improvements in Yo-Yo Intermittent Endurance test performance and change-of-direction speed were noted in the recreational football group (Yo-Yo: 79.8%, ES = 1.09; 95% CI: 0.16, 2.03; P = .025, change-of-direction speed: -10.6%, ES = -1.05; 95% CI: -1.98, -0.12; P = .031) and the HIIT group (Yo-Yo: 81.2%, ES = 1.03; 95% CI: 0.15, 1.92; P = .025, change-of-direction speed: -5.4%, ES = -0.91; 95% CI: -1.79, -0.04; P = .045). Diastolic blood pressure likely decreased in the recreational football (-8.6%, ES = -0.74; 95% CI: -1.64, 0.17; P = .116) and HIIT groups (-9.8%, ES = -0.57; 95% CI: -1.40, 0.30; P = .195), with a possible increase in the control group (1.2%, ES = 0.21; 95% CI: -0.53, 0.96; P = .068). Recreational football and HIIT elicited improvements in all muscular and cardiorespiratory fitness measures. In contrast, the control group, which performed only physical education classes, increased body mass, BMI, and fat mass. Therefore, additional activities such as recreational football or HIIT might counter the prevalence of overweight and obesity in children.

#5 Bowlegs and Intensive Football Training in Children and Adolescents
Reference: Dtsch Arztebl Int. 2018 Jun 15;115(24):401-408. doi: 10.3238/arztebl.2018.0401.
Authors: Thaller PH, Fürmetz J, Chen F, Degen N, Manz KM, Wolf F.
Summary: In many countries around the world, football (association football, or "soccer" predominantly in North America) is the sport most commonly played by children and adolescents. It is widely thought that football players are more likely to develop genu varum (bowlegs); an association with knee arthritis also seems likely. The goals of this systematic review and meta-analysis are to provide an overview of the available evidence on genu varum after intensive soccer training in childhood and adolescence, and to discuss the possible pathogenetic mechanisms. We systematically searched the PubMed, Medline, Embase, and Coch- rane Library databases for studies of the relation between leg axis development and intensive football playing during the growing years. Controlled studies employing the intercondylar distance (ICD) as the target variable were evaluated in a meta-analysis, with the mean difference as a measure of effect strength. This meta-analysis included 3 studies with a total of 1344 football players and 1277 control individuals. All three studies individually showed a signifi- cant difference in the mean ICD values of the two groups. The pooled effect esti- mator for the mean difference was 1.50 cm (95% confidence interval [0.53; 2.46]). Two further studies that could not be included in the meta-analysis had similar con- clusions. Asymmetrical, varus muscle forces and predominantly varus stress on the osseous growth plates neighboring the knee joint, especially during the prepubertal growth spurt, seem to be the cause of this phenomenon. Intensive soccer playing during the growing years can promote the devel- opment of bowlegs (genu varum) and, in turn, increase the risk of knee arthritis. Phy- sicians should inform young athletes and their parents of this if asked to advise about the choice of soccer as a sport for intensive training. It cannot be concluded, however, that football predisposes to bowlegs when played merely as a leisure activity.

#6 The Impact of an External Load of Football Equipment on Dynamic Balance as Assessed by the Modified Star Excursion Balance Test
Reference: Int J Exerc Sci. 2018 Jun 1;11(4):797-805. eCollection 2018.
Authors: Denehey T, Marshall T, Spaccarotella K, Andzel W
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Summary: Ankle sprains are common injuries, especially for football players, and may result in ankle instability, which can limit performance and increase injury risk. Ankle stability return to play criteria is often assessed under loaded conditions, even though previous research suggests loaded conditions affect dynamic balance. The purpose of this study was to evaluate dynamic balance under loaded conditions. A modified Star Excursion Balance Test (SEBT), incorporating anterior, posterior medial and posterior lateral reach directions under the loaded condition of NCAA Division III football equipment was evaluated. Thirty male collegiate football players completed the modified SEBT under loaded and non-loaded conditions. Scores for the three reach directions on the SEBT were computed for loaded and non-loaded conditions. Repeated measures ANOVA was used to compare reach directions under loaded and non-loaded. Under loaded conditions, participants had significantly shorter posterior lateral reach distances for the left (98.05 ± 12.73 cm vs. 89.30 ± 10.45 cm, p = 0.00) and right (103.77 ± 12.78 cm vs. 99.07 ± 13.50 cm, p = 0.00) legs and significantly shorter reach distances for the right leg in both the anterior direction (84.58 ± 5.64 cm vs. 80.57 ± 13.73 cm, p = 0.02) and composite dynamic balance score (105.99 ± 12.99 vs. 102.30 ± 14.28, p = 0.009). The addition of 6.2 kg of external load significantly affected dynamic balance assessed by the modified Star Balance Excursion Test. These findings suggest that return to support assessments should involve sport-specific conditions when determining readiness of return to play.

#7 Effects of Football Simulated Fatigue on Neuromuscular Function and Whole-body Response to Disturbances in Balance
Reference: Scand J Med Sci Sports. 2018 Jul 7. doi: 10.1111/sms.13261. [Epub ahead of print]
Authors: Behan FP, Willis S, Pain MTG, Folland JP
Summary: The effect of football specific fatigue on explosive neuromuscular performance and dynamic balance has received little attention in the literature despite the potential consequences for injury risk. This study aimed to investigate the effect of fatigue induced by simulated football match-play on maximal and explosive knee flexor (KF) and knee extensor (KE) torque, and thus the maximal and explosive KF/KE ratio, as well as the effect of fatigue induced by simulated football match-play on whole-body response to disturbances in balance. Fifteen male team sports players (mean ± SD: age 24.2±4.2 years; stature 1.79±0.09 m; body mass, 77.3±10.7 kg) underwent ~90 minutes of the modified Loughborough Intermittent Shuttle Test (LIST; fatiguing exercise condition) or seated rest (control condition) on separate days. Maximal and explosive isometric KF and KE voluntary torque (MVT/ EVT) were assessed pre and post condition. Maximal and explosive KF/KE ratios were calculated. Centre of mass (COM) response (displacement) to unexpected anterior and posterior platform perturbations were also assessed pre and post condition. Football simulated fatigue resulted in reduced KF (15%) and KE (12%) MVT (p≤0.002) but was not found to reduce EVT of either muscle group, or explosive KF/KE ratio. Football simulated fatigue resulted in impaired balance response (11% increase in COM displacement) to unexpected perturbation in the posterior (p=0.002) but not the anterior direction. Impaired response to dynamic disturbances in balance, rather than explosive torque or changes in muscle balance (H/Q ratios) may be a contributory factor towards increased injury risk in the latter portion of football games, and likely highlights the influence of fatigue on sensory/proprioceptive processes.

#8 Football training over 5 years is associated with preserved femoral bone mineral density in men with prostate cancer
Reference: Scand J Med Sci Sports. 2018 Jul 12. doi: 10.1111/sms.13242. [Epub ahead of print]
Authors: Uth J, Fristrup B, Haahr RD, Brasso K, Helge JW, Rørth M, Midtgaard J, Helge EW, Krustrup P
Summary: This study investigated the association between long-term adherence to football training and retaining bone mineralization and physical capacity in men with prostate cancer (PCa) managed with androgen deprivation therapy (ADT). Patients completing follow-up at 32 weeks in the FC Prostate Randomized Controlled Trial (RCT) in 2012 or 2013 were invited to 5-year follow-up assessments in May 2017 (n = 30). Changes in physiological outcomes over time between the football participants (FTG) and nonparticipants (CON) were examined. Twenty-two men accepted the invitation of which 11, aged 71.3 ± 3.8 years, had continued to play self-organized football 1.7 (SD 0.5) times per week for 4½ years (±8 months). At 5 years, right femoral neck bone mineral density (BMD) had improved significantly in the FTG compared to CON (P = .028). No other significant between-group differences were observed. In FTG, RHR decreased by 4.3 bpm (P = .009) with no changes in CON. Muscle mass, knee-extensor muscle strength, VO2 max, and postural balance decreased in both groups. In FTG, the fraction of training time with HR between 80%-90% or >90% of HRmax was 29.9% (SD 20.6) and 22.8% (SD 28.7), respectively. Average distance covered during 3 × 20 minutes of football training was 2524 m (SD 525). Football training over a 5-year period was associated with preserved femoral neck BMD in elderly men with PCa managed on ADT. Intensity during football training was >80% of HRmax for 51% of training time after 5 years. Body composition and physical capacity deteriorated over 5 years regardless of football participation.

#9 Heading and unintentional head impacts have opposing associations with Patient Reported Outcomes in amateur soccer players
Reference: Res Sports Med. 2018 Jul 13:1-11. doi: 10.1080/15438627.2018.1492396. [Epub ahead of print]
Authors: Hunter LE, Ifrah C, Zimmerman ME, Kim M, Lipton RB, Stewart WF, Lipton ML
Summary: The effects of soccer-related head impacts, beyond overt concussions, on Patient Reported Outcomes (PROs) have not been explored to date. Generalized estimating equations were employed to determine the association between soccer-related head impacts (headers in the prior 2 weeks, unintentional head impacts in the prior 2 weeks, headers in the prior 12 months and lifetime concussions) on PROs including depression, anxiety, sleep disturbance and sleep impairment. Compared to players with no unintentional head impacts in the prior 2 weeks, players with one unintentional exposure reported more symptoms of anxiety (p = 0.002) and players with 2+ exposures reported more symptoms of depression (p = 0.006) and anxiety (p < 0.001). In contrast, players in the 3rd Quartile of 12 mo. headers reported less anxiety (p = 0.001), sleep disturbance (p = 0.002) and sleep impairment (p < 0.001) compared to those in the 1st quartile. Unintentional head impacts are associated with worse PROs while more headers are paradoxically associated with better PROs.

#10 Development of an Educational Program for Non-Professional Soccer Coaches in Charge of Community-Based Soccer in Men with Prostate Cancer: a Qualitative Study
Reference: Sports Med Open. 2018 Jul 13;4(1):31. doi: 10.1186/s40798-018-0147-y.
Authors: Bjerre ED, Leth M, Hammer NM, Midtgaard J
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Summary: While clinical trials have demonstrated the benefits of structured exercise for prostate cancer survivors, few attempts have been made to investigate and implement sustainable community-based exercise programs supporting adoption of long-term physical activity behavior. Against this background, the aims of this study was to explore the perspectives of experts and stakeholders on the development of a training course and intervention manual used to support the delivery of community-based soccer training in men with prostate cancer (the FC Prostate Community [FCPC] trial). A two-step qualitative design including triangulation of methods, data sources, and researchers. Step 1 comprised key informant interviews with clinical and scientific experts (n = 4). Step 2 included stakeholder focus group interviews with nurses (n = 5), non-professional soccer coaches and club representatives (n = 5), and prostate cancer survivors (n = 7). Four themes emerged from the analysis of the key informant interviews: The Coach's Qualifications, Structure of the Training, Prevention of Injuries, and A Non-Patient Environment, which informed development of the training course and intervention manual. The stakeholders added the importance of clarifying the Responsibility of the Coach, the value of Positive Competition, and Social Inclusion of the prostate cancer survivors in the club. Based on these results, we present the final templates for the training course and intervention manual. No general set of rules or safety measures to promote or optimize the delivery of community-based exercise in cancer survivors is recommended. However, the general principles related to the necessary clarification of the coach's responsibility in relation to the prevention and management of injuries and participant adherence through a non-patient environment may be transferable to the training and education of other groups of lay persons in charge of delivering exercise interventions to other clinical subpopulations in a non-hospital setting.

#11 Association between knee-to-hip flexion ratio during single-leg vertical landings, and strength and range of motion in professional soccer players
Reference: Sports Biomech. 2018 Jul 12:1-10. doi: 10.1080/14763141.2018.1494207. [Epub ahead of print]
Authors: Leporace G, Tannure M, Zeitoune G, Metsavaht L, Marocolo M, Souto Maior A
Summary: The aim of this study was to test the correlation between knee-to-hip flexion ratio during a single leg landing task and hip and knee strength, and ankle range of motion. Twenty-four male participants from a professional soccer team performed a continuous single leg jump-landing test during 10s, while lower limb kinematics data were collected using a motion analysis system. After biomechanical testing, maximal isometric hip (abduction, extension, external rotation), knee extension and flexion strength were measured. Maximum ankle dorsiflexion range of motion was assessed statically using the weight bearing lunge test. Pearson correlation coefficients were calculated to determine the associations between the predictor variables (knee and hip strength, and ankle ROM) and the main outcome measure (knee-to-hip flexion ratio). Correlation between knee-to-hip flexion ratio and hip abductors strength was significant (r = -0.47; p = 0.019). No other significant correlations were observed among the variables (p > 0.05). These results demonstrated that a lower hip abductors strength in male soccer players was correlated with a high knee-to-hip flexion ratio during landing from a single leg jump, potentially increasing knee overload by decreasing energy absorption at the hip. The results provide a novel proposal for the functioning of hip muscles to control knee overload.

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