Latest research in football - week 36 - 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 King-Devick test normative reference values and internal consistency in youth football and soccer athletes
Reference: Scand J Med Sci Sports. 2018 Aug 28. doi: 10.1111/sms.13286. [Epub ahead of print]
Authors: Moran RN, Covassin T
Summary: The King-Devick (K-D) test has gained popularity as a sideline concussion assessment tool, comprising of visual tracking and saccadic eye movements. However, limited normative data exists for youth athletes under the age of 13. The purpose of this study was to establish normative reference values and examine the internal consistency of the K-D test in youth athletes. The K-D test was administered to 422 youth football and soccer athletes prior to their respective season. The average K-D score was 54.29±11.5 seconds. Across the two trials, 55% of participants committed at least one error. Overall, the K-D test demonstrated a high internal consistency (Cronbach α = 0.92) when administered at baseline. Inter-item correlations revealed a moderate to strong relationship between test cards and trials (r range= 0.71 to 0.95; p<0.001), along with test cards and baseline K-D time (r range= 0.85 to 0.94; p<0.001). Although the K-D test was consistent during baseline testing, the high percentage of errors at baseline makes the K-D test questionable for post-concussion comparisons.

#2 Epidemiological Findings of Soccer Injuries During the 2017 Gold Cup
Reference: Orthop J Sports Med. 2018 Aug 20;6(8):2325967118791754. doi: 10.1177/2325967118791754. eCollection 2018 Aug.
Authors: Chahla J, Sherman B, Cinque M, Miranda A, Garrett WE, Chiampas G, O'Malley H, Gerhardt MB, Mandelbaum BR
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Summary: Surveillance programs are vital to analyze the cause and nature of lesions and ultimately establish protocols of action to lower injury rates. The purpose of the study was to evaluate the adherence of team doctors to an electronic surveillance system and determine the incidence and characteristics of injuries among soccer players participating in the 2017 Gold Cup.All data were collected from the electronic medical reports submitted during each match of the 2017 Gold Cup. Twelve teams participated in the tournament (each with 23  the team physician after each injury. Each report contained the player's number, the exact time of injury (minute of play), the location and diagnosis of injury as indicated by a previously defined code, and its severity in terms of the number of days of absence from training and match play. The electronic reporting system had a response rate of 100.0%, with 97.2% of questions answered completely. The mean age of injured players was 27 years (range, 21-35 years) and was not statistically significantly different from the overall mean player age (P > .05). There were no significant differences in the frequency of injuries when analyzed by player position (P = .743). The overall rate of injuries was 1.04 per match, with the most common injuries being contusions (42.3%), sprains (7.7%), strains (7.7%), and fractures (7.7%). These injuries were more commonly the result of contact (75.0%) than noncontact (25.0%) mechanisms (P < .001). Injuries most commonly occurred between the 60th and 75th minute of play when comparing all 15-minute time intervals (P = .004). This study supports the use of electronic injury reporting, which demonstrated a high level of adherence among an international cohort of team physicians and has significant potential for improving injury surveillance and tracking responses to prevention programs. Injury rates in the Gold Cup were similar to those in previous studies and demonstrated the highest rates late in the second half of the game, specifically between the 60th and 75th minute of play.

#3 Altered lower limb kinematics and muscle activities in soccer players with chronic ankle instability
Reference: Phys Ther Sport. 2018 Aug 9;34:28-35. doi: 10.1016/j.ptsp.2018.08.003. [Epub ahead of print]
Authors: Kunugi S, Masunari A, Koumura T, Fujimoto A, Yoshida N, Miyakawa S
Summary: The purpose was to examine the lower limb kinematics and muscle activities in diagonal single-leg rebound jump in soccer players with chronic ankle instability (CAI). Thirty male collegiate soccer players participated: 15 with CAI were compared with 15 without CAI, matched by physical description. In the diagonal single-leg rebound jump, participants stood on one leg on a 30-cm high box, hopped down diagonally (45°) onto a force plate, and jumped vertically as high as possible with hands on their hips. Hip, knee, and ankle kinematics were acquired using a motion capture system. The activity of the gluteus medius, hip adductor, and lower leg muscles was recorded using electromyography. Jump performance was calculated using a force plate. The CAI group had (i) decreased hip adduction, knee flexion, external rotation, and dorsiflexion angle; (ii) reduced hip adductor and peroneus muscle activations; and (iii) reduced jump height and short flight time. Male collegiate soccer players with CAI showed altered kinematics and muscle activities during a diagonal single-leg rebound jump; this may adversely affect rebound jump performance.

#4 Match-Play and Performance Test Responses of Soccer Goalkeepers: A Review of Current Literature
Reference: Sports Med. 2018 Aug 24. doi: 10.1007/s40279-018-0977-2. [Epub ahead of print]
Authors: White A, Hills SP, Cooke CB, Batten T, Kilduff LP, Cook CJ, Roberts C, Russell M
Summary: Goalkeepers are typically the last defensive line for soccer teams aiming to minimise goals being conceded, with match rules permitting ball handling within a specific area. Goalkeepers are also involved in initiating some offensive plays, and typically remain in close proximity to the goal line while covering ~ 50% of the match distances of outfield players; hence, the competitive and training demands of goalkeepers are unique to their specialised position. Indeed, isolated performance tests differentiate goalkeepers from outfield players in multiple variables. With a view to informing future research, this review summarised currently available literature reporting goalkeeper responses to: (1) match play (movement and skilled/technical demands) and (2) isolated performance assessments (strength, power, speed, aerobic capacity, joint range of motion). Literature searching and screening processes yielded 26 eligible records and highlighted that goalkeepers covered ~ 4-6 km on match day whilst spending ~ 98% of time at low-movement intensities. The most decisive moments are the 2-10 saves·match-1 performed, which often involve explosive actions (e.g. dives, jumps). Whilst no between-half performance decrements have been observed in professional goalkeepers, possible transient changes over shorter match epochs remain unclear. Isolated performance tests confirm divergent profiles between goalkeepers and outfield players (i.e. superior jump performance, reduced [Formula: see text]2max values, slower sprint times), and the training of soccer goalkeepers is typically completed separately from outfield positions with a focus primarily on technical or explosive drills performed within confined spaces. Additional work is needed to examine the physiological responses to goalkeeper-specific training and match activities to determine the efficacy of current preparatory strategies.

#5 Return to Competition After Surgery for Herniated Lumbar Disc in Professional Football Players
Reference: Clin J Sport Med. 2018 Aug 28. doi: 10.1097/JSM.0000000000000662. [Epub ahead of print]
Authors: Tencone F, Minetto MA, Tomaello L, Giannini A, Roi GS
Summary: The purpose was to investigate the prevalence and outcomes of surgery for lumbar disc herniation in professional football players. A period of 10 seasons of the Italian Football First League (Serie A) was retrospectively investigated. Thirty-three teams (for a total of 1960 players) took turns in the 10 seasons, and 42 team doctors were requested to provide information about the number of players who underwent surgery for lumbar disc herniation. Prevalence and match incidence of the lumbar discectomy, proportion of players returning to competition after surgery, recovery time and preintervention and postintervention number of appearances in official matches were analyzed. Eleven players underwent the surgical intervention during the considered period. The prevalence of the surgical treatment was 0.6%, whereas the match incidence was 0.09 cases/1000 match hours. All players returned to competitions 6.0 (3.5-7.7) months after surgery, with no significant difference between different roles. The number of appearances in official matches was comparable during the seasons before and after surgery. The lumbar discectomy must be considered a rare surgical procedure performed in professional football players. All players returned to competitions after surgery. The postintervention number of appearances in official matches was comparable with the preintervention one.

#6 Early return to playing professional football following fixation of 5th metatarsal stress fractures may lead to delayed union but does not increase the risk of long-term non-union
Reference: Knee Surg Sports Traumatol Arthrosc. 2018 Aug 28. doi: 10.1007/s00167-018-5104-2. [Epub ahead of print]
Authors: Miller D, Marsland D, Jones M, Calder J
Summary: 5th metatarsal stress fractures are frequently encountered in professional football. There is concern that early return to play following intra-medullary screw fixation may lead to an increased risk of delayed union. The purpose of the study was to assess whether an early return to play after surgical fixation of 5th metatarsal fractures in professional football players is a risk factor for delayed union and the effect of this on the ultimate clinical outcome. Retrospective review of prospectively collected data of a series of 37 professional football players following intramedullary screw fixation of 5th metatarsal stress fractures. End points included time of return to play and to radiological union of the fracture. At a minimum follow-up of 24 months the mean return to play was 10.5 weeks and mean time to complete radiological union was 12.7 weeks. Return to play at 8 weeks or less resulted in a higher risk of delayed radiological union (24% at 3 months), but this neither prevented the athlete from continuing to play football nor did it affect the ultimate risk of non-union (3% overall). A re-fracture occurred in 1 patient (3%) at 10 months who previously had complete radiographic union at 9 weeks. Intramedullary screw fixation of 5th metatarsal stress fractures leads to a predictable time of return to play and a low rate of non-union. If players return to play at 8 weeks or less a persistent line may be expected in up to a quarter of patients. However, if asymptomatic this radiological finding does not mean that athletes must avoid playing football as ultimately a good outcome is expected with low rates of non-union and refracture.

#7 Injury incidence in semi-professional football claims for increased need of injury prevention in elite junior football
Reference: Knee Surg Sports Traumatol Arthrosc. 2018 Aug 25. doi: 10.1007/s00167-018-5119-8. [Epub ahead of print]
Authors: Loose O, Fellner B, Lehmann J, Achenbach L, Krutsch V, Gerling S, Jansen P, Angele P, Nerlich M, Krutsch W
Summary: Injuries are a common occurrence in football. Sufficient epidemiological data are available in professional football but not in salaried semi-professional football. This study investigates the injury incidence at different levels of semi-professional football with focus on junior football. The data were based on injury reports provided by players and medical staff over the 2015-2016 season, which corresponded to the consensus statement for data samples in football. This study investigated the injury incidence and prevalence of five skill levels of semi-professional football (the fourth to the seventh league and elite junior football). 1130 players had sustained 2630 injuries over the 2015-2016 season. The overall injury incidence was 9.7 per 1000 h football exposure; prevalence with at least one injury was 79%. The highest overall injury incidence in elite junior football was 10.4 in 1000 h football exposure. The fifth league had the lowest incidence with 9.0 in 1000 h football (p < 0.05). Traumatic injuries most often occurred in the fourth league (3.9 in 1000 h football). The body areas most affected by traumatic injury were knees, ankles and thighs. Elite junior players had a significantly higher incidence of overuse complaints (7.4 in 1000 h football) than the fourth league (5.4, p = 0.005). The body areas most affected by overuse complaints were the lower back, thigh and groin. No differences were found between the different positions on field. Salaried semi-professional football involves a high overall injury incidence. The highest incidence, particularly of overuse injuries, was seen in elite junior football. These findings should be incorporated in specific injury prevention training or screenings beginning in junior football.

#8 Neurocognitive Performance of 425 Top-Level Football Players: Sport-specific Norm Values and Implications
Reference: Arch Clin Neuropsychol. 2018 Aug 25. doi: 10.1093/arclin/acy056. [Epub ahead of print]
Authors: Prien A, Junge A, Brugger P, Straumann D, Feddermann-Demont N
Summary: Concussion diagnosis and management in sports largely relies on neurocognitive testing. In the absence of baseline assessment, only norm values of the general population are available for comparison with scores of concussed athletes. To evaluate whether (elite) sport specific norm values are needed, cognitive performance was compared between top-level football players and the general population. Cognitive performance of 425 top-level football players was evaluated using the computerized test battery CNS Vital Signs. Players were split into two age groups (15-19 and 20-29 years) and test results were compared with a norm sample (n = 268) by means of age-standardized scores using Cohen's d effect size statistics. The younger age group outperformed the norm sample in all domains, with small to moderate effects on tests of processing speed (d = 0.58, 95% CI = 0.31,0.85), cognitive flexibility (d = 0.27, 95% CI = 0.01,0.53) and psychomotor speed (d = 0.97, 95% CI = 0.69,1.24). In the older age group, no differences were found on four out of six domains; a moderate positive effect was found for psychomotor speed (d = 0.74, 95% CI = 0.54,0.93), a small negative effect for reaction time (d = -0.47, 95% CI = -0.66,-0.28). Relative to the norm, older football players scored lower than younger football players on all test domains. Cognitive performance of elite football players may be different from the general population. It is recommended to use football-specific norm scores for comparison with test results of concussed players, and to choose an adequate control group when investigating effects of contact sport on cognition. Studies with older/retired football players are needed to further analyze potential sport-specific age effects.

#9 Match Related Time Course of Perceived Recovery in Youth Football Players
Reference: Int J Sports Physiol Perform. 2018 Aug 30:1-16. doi: 10.1123/ijspp.2017-0521. [Epub ahead of print]
Authors: Paul DJ, Tomazoli G, Nassis GP
Summary: The aim of the study was to i) examine the reproducibility of the perceived recovery scale (PRS) in football players ii) describe the time course of the PRS in response to a football match. Methods Twenty trained youth players (mean ± SD; age 16.2 ± 1.2 y, height 1.75 ± 0.07 m, body mass 64.0 ± 7.8 kg) took part in the study. PRS was collected - 2 hrs, - 30 mins before and +15 mins, +3 hrs and +24 hrs after an international football match. Players were categorised into two groups based on their playing time (≤45 and 90 mins). Reproducibility of the PRS was high (ICC = 0.83, TE = 0.59, CV = 9.9%) between the two pre-match measures. Overall, PRS was lower at +15 mins (4.0 ± 1.5, p< 0.01; ES=2.2) and + 3 hrs (4.7 ± 1.6, p< 0.01; ES=1.5) compared to -30 mins (7.1 ± 1.3), while +15 mins was lower than +24 hrs (6.1 ± 1.3, p<0.01; ES=1.5). No differences between groups for PRS scores at any of the time points. The perceived recovery scale is a reproducible method for monitoring perceptions of recovery to football activity and sensitive to time course changes relating to a match. The scale is an easy and efficient tool that can be used to monitor an aspect of recovery.

#10 Accurate Prediction Equation to Assess Body Fat in Male and Female Adolescent Football Players
Reference: Int J Sport Nutr Exerc Metab. 2018 Aug 30:1-23. doi: 10.1123/ijsnem.2018-0099. [Epub ahead of print]
Authors: Lozano-Berges G, Matute-Llorente Á, Gómez-Bruton A, González-Agüero A, Vicente-Rodríguez G, Casajús JA
Summary: The aims of this study were (a) to determine which of the most used anthropometric equations was the most accurate to estimate percentage of body fat (%BF), (b) to develop a new specific anthropometric equation, and (c) to validate this football-specific equation. A total of 126 (13.3±0.6 y) football players (86 males) participated in the present study. Participants were divided into two groups: 98 players were included in the assessment of existing equations and in the development of the new prediction equation; and 28 were used to validate it. %BF was measured with dual-energy X-ray absorptiometry (DXA) and also estimated with six different %BF anthropometric equations: Johnston, Slaughter, Carter, Faulkner, Deurenberg and Santi-Maria. Paired t-tests were used to analyze differences between methods. A football-specific equation was developed by a stepwise linear-regression. The existing anthropometric equations showed significant bias for %BF when compared to DXA (p<.001; constant error [CE] ranged from -4.57 to 9.24%; standard error of estimate [SEE] ranged from 2.46 to 4.20). On the other hand, the developed football-specific equation was %BF = 11.115 + 0.775(triceps skinfold) + 0.193(iliac-crest skinfold) - 1.606(sex). The developed equation demonstrated neither %BF differences (p=.121; CE=0.57%; SEE=0.36) when compared to DXA, presenting a high cross-validation prediction power (R2=0.85). Published anthropometric equations were not accurate to estimate %BF in adolescent football players. Due to the fact that the developed football-specific equation showed neither differences nor heteroscedasticity when compared to DXA, this equation is recommended to assess %BF in adolescent football players.

#11 Comparative effects of single vs. double weekly plyometric training sessions on jump, sprint and COD abilities of elite youth football players
Reference: J Sports Med Phys Fitness. 2018 Aug 28. doi: 10.23736/S0022-4707.18.08804-7. [Epub ahead of print]
Authors: Bianchi M, Coratella G, Dello Iacono A, Beato M
Summary: Plyometrics are widely implemented as training methodology for enhancing functional sports performance. Although several studies have analysed the plyometrics effects due to training plans with a frequency of 2-3 times a week, few of them provided evidence supporting an equal efficiency of similar training programs implementing lower training frequency such as one training session a week. Twenty-one players (elite academy, Switzerland) were included in the current study (mean ± SD; age 17 ± 0.8 years, weight 70.1 ± 6.4 kg, height 177.4 ± 6.2 cm). This study used a randomised pre-post parallel group trial design. The participants were assigned to either a low-volume plyometric training group (LPG = 10 participants) or a high-volume plyometric training group (HPG = 11 participants). A long jump test, a single-leg triple hop test, sprint (10, 30 and 40 m) and 505 change of directions (COD) test were performed. Exercise-induced meaningful changes in performance for both LPG and HPG occurred after the training. LPG and HPG reported improvements in long jump (ES=1.0 and 0.77), triple hop right (ES=0.32 and 0.28), triple hop left (ES=0.46 and 0.32), 10 m sprint (ES=0.62 and 1.0). Both LPG and HPG are effective training modalities inducing benefits in jump and sprint tests for elite young football players. Fitness coaches and sports scientists could integrate their training plans with the protocols described in this study.

#12 Prediction of Attendance Demand in European Football Games: Comparison of ANFIS, Fuzzy Logic, and ANN
Reference: Comput Intell Neurosci. 2018 Aug 7;2018:5714872. doi: 10.1155/2018/5714872. eCollection 2018.
Authors: Şahin M, Erol R
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Summary: An artificial neural network (ANN), adaptive neurofuzzy inference system (ANFIS) models, and fuzzy rule-based system (FRBS) models are developed to predict the attendance demand in European football games, in this paper. To determine the most successful method, each of the methods is analyzed under different situations. The Elman backpropagation, feed-forward backpropagation, and cascade-forward backpropagation network types are developed to determine the outperforming ANN model. The backpropagation and hybrid optimization methods are used for training fuzzy inference system (FIS) to determine the outperforming ANFIS model. The fuzzy logic model is developed after experimenting different forms of membership functions. To this end, the data of 236 soccer games are used to train the ANN and ANFIS models, and 2017/2018 season's data of these clubs are used to test all of the models. The results of all models are compared with each other and real past data. To assess the performance of each model, two error measures that are Mean Absolute Percent Error (MAPE) and Mean Absolute Deviation (MAD) are implemented. These measures reveal that the ANN model that has Elman network type outperforms the other models. Finally, the results emphasize that the proposed ANN model can be effectively used for prediction purposes.

#13 Exercise loading for cardiopulmonary assessment and evaluation of endurance in amputee football players
Reference: J Phys Ther Sci. 2018 Aug;30(8):960-965. doi: 10.1589/jpts.30.960. Epub 2018 Jul 24.
Authors: Mikami Y, Fukuhara K, Kawae T, Sakamitsu T, Kamijo Y, Tajima H, Kimura H, Adachi N
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Summary: It is difficult for amputees to perform conventional cardiopulmonary exercise testing. Values were determined for two-legged, one-legged, and two-armed exercise testing in healthy adult males (Study 1), for comparison with preliminary measurements of endurance in amputee football players (Study 2). In Study 1, cardiopulmonary exercise testing was performed in healthy adult males. Correlations between oxygen uptake in two-legged and one-legged/two-armed exercise were calculated and a comparison was made between one-legged exercise and two-armed exercise for each measured value. In Study 2, cardiopulmonary exercise testing was performed on male amputee football players using a two-arm-driven ergometer. The measured values obtained for healthy adult males and amputee football players were compared. In Study 1, peak work rate and peak heart rate values of healthy participants were significantly higher in two-armed exercise than in one-legged exercise. The correlation between peak oxygen uptake values for two-legged and one-legged exercise was decreased. In Study 2, peak work rate of two-armed exercise was significantly higher in amputee football players than in healthy participants.  Study 1 suggested that musculoskeletal factors might have greater significance for one-legged exercise than for two-armed exercise. Study 2 suggested that para-sports, including amputee football, may contribute to physical strength and health maintenance in lower leg amputees.

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