Latest research in football - week 31 - 2019

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 Field Methods to Estimate Fat-free Mass in International Soccer Players
Reference: Int J Sports Med. 2019 Jul 31. doi: 10.1055/a-0969-8591. [Epub ahead of print]
Authors: Nuñez FJ, Munguia-Izquierdo D, Petri C, Suarez-Arrones L
Summary: Based on the high financial and logistical costs associated with the assessment of body composition with dual-energy X-ray absorptiometry (DXA), this study determined which field method has the best correlation with DXA data, and developed an equation to estimate fat-free mass (FFM) using the field anthropometric data in international soccer players. A total of 17 international soccer players participated in this study. DXA values provided a criterion measure of FFM. Correlation coefficients, biases, limits of agreement, and differences were used as validity measures, and regression analyses were used to develop the prediction equation. All field methods used to obtain FFM data showed positive correlations (r from 0.90-0.96) with DXA. Only the equation developed by Deurenberg et al. [6] showed no differences from DXA with a low bias. The main strength of this study was providing a valid and accurate equation to estimate FFM specifically in international soccer players.

#2 Prospective Evaluation of Injuries occurred during the Brazilian Soccer Championship in 2016
Reference: Rev Bras Ortop (Sao Paulo). 2019 May;54(3):329-334. doi: 10.1055/s-0039-1692429. Epub 2019 Jun 27.
Authors: Netto DC, Arliani GG, Thiele ES, Cat MNL, Cohen M, Pagura JR
Download link:
Summary: The purpose was to identify the incidence, the prevalence, the characteristics, and the possible risk factors for injuries occurring during the matches of the Brazilian Soccer Championship. A prospective study was carried out to collect data on the injuries that occurred during the 2016 Brazilian Soccer Championship. Lesions were recorded by the physician responsible for each team through an online software. Among the 864 athletes included in the study, 231 (26.7%) of the players presented some injury during the tournament. In total, 312 injuries were recorded during the Brazilian Soccer Championship, with an average of 0.82 injuries per game. The incidence of injuries was 24.9 injuries per 1,000 match hours. Midfielders and forwards presented, respectively, an injury risk 3.6 and 2.4 times higher than goalkeepers. The prevalence and incidence of lesions were, respectively, 26.7% and 24.9 injuries per 1,000 match hours. The most frequently affected body segment was the lower limbs (76.3%), and the athletes acting in midfield and forward positions were the most affected. Moreover, the greater prevalence of injuries occurred in the first part of the championship.

#3 Imaging Assessment of the Pubis in Soccer Players
Reference: Rev Bras Ortop (Sao Paulo). 2019 Apr;54(2):118-127. doi: 10.1016/j.rbo.2017.12.012. Epub 2019 May 10.
Authors: Todeschini K, Daruge P, Bordalo-Rodrigues M, Pedrinelli A, Busetto AM
Download link:
Summary: The purpose was to compare the accuracy of ultrasound (US) with that of magnetic resonance imaging (MRI) in the detection of aponeurosis lesions of the rectus abdominis/adductor longus muscles, to study the characteristics of the athletes and imaging findings associated with pubalgia, and to demonstrate the importance of each method in evaluating this condition. The present study was conducted from 2011 to 2016 with 39 professional soccer players: 15 with pubalgia and 24 without pubalgia. Age, field position, body mass index (BMI), weekly training load, career length, and history of thigh/knee injury and lower back pain were recorded. The following tests were performed: radiographs (anteroposterior view of the pelvis in standing and flamingo positions) to evaluate hip impingement, sacroiliac joint, and pubic symphysis instability; US to analyze the common aponeurosis of the rectus abdominis/adductor longus muscles and inguinal hernias; and MRI for pubic bone degenerative alterations and edema, and lesions in the adductor and rectus abdominis muscles and their aponeurosis. There was an association between pubalgia, high BMI ( p  = 0.032) and muscle alterations ( p  < 0.001). Two patients with pubalgia had inguinal hernias and one patient with pubalgia and two controls had sports hernias. Pubic degenerative changes were frequent in both groups. Aponeurosis lesions were more frequent in patients with pain. The US detection had 44.4% sensitivity and 100% specificity. The evaluation of athletic pubalgia should be performed with radiography, US, and MRI. High BMI, muscle injuries, geodes, and osteophytes are findings associated with pubalgia; US has low sensitivity to detect injuries of the common aponeurosis of the rectus abdominis/adductor longus muscles.

#4 Eighty-two per cent of male professional football (soccer) players return to play at the previous level two seasons after Achilles tendon rupture treated with surgical repair
Reference: Br J Sports Med. 2019 Jul 30. pii: bjsports-2019-100556. doi: 10.1136/bjsports-2019-100556. [Epub ahead of print]
Authors: Grassi A, Rossi G, D'Hooghe P, Aujla R, Mosca M, Samuelsson K, Zaffagnini S
Download link:
Summary: The purpose was to evaluate the time to return to playing following acute Achilles tendon rupture (ATR) and surgical repair in professional male football (soccer) players. Professional male football (soccer) players who sustained an ATR and underwent surgical repair were identified through internet-based injury reports from January 2008 to August 2018. Only League 1 and 2 players with injuries who had at least 1 year of follow-up from the search date were included. Injury history and time to return to play were retrieved from the public platform For athletes who competed for at least two seasons after returning to play, re-ruptures and number of matches played were reported. 118 athletes (mean age 27.2±7.2 years) were included. 113 (96%) returned to unrestricted practice after a mean of 199±53 days, with faster recovery in players involved in national teams. Return to competition was after a mean of 274±114 days. In the 76 athletes with at least two seasons of follow-up, 14 (18%) did not compete at the pre-injury level during the two seasons following the index injury. Six players (8%) sustained a re-rupture within the first two seasons after return to play; four re-ruptures were in footballers who returned to play <180 days after injury. Age >30 years and re-ruptures had higher odds ratios of not returning to the same level of play. 96% of professional male football players who underwent surgery to repair an ATR returned to unrestricted practice and then competition after an average time of 7 and 9 months, respectively. However, 18% did not return to the same level of play within the two seasons following their return, with a higher risk in those experiencing a re-rupture.

#5 Test-Retest Reliability of Skill Tests in the F-MARC Battery for Youth Soccer Players
Reference: Percept Mot Skills. 2019 Jul 30:31512519866038. doi: 10.1177/0031512519866038. [Epub ahead of print]
Authors: Padrón-Cabo A, Rey E, Pérez-Ferreirós A, Kalén A
Summary: This study aimed to evaluate the test-retest reliability of soccer skill tests belonging to the F-MARC test battery. To avoid bias during talent identification and development, coaches and scouts should be using reliable tests for assessing soccer-specific skills in young male players. Fifty-two U-14 outfield male soccer players performed F-MARC soccer skill tests on two occasions, separated by 7 days. After familiarization, we administered two trial sessions of five skill tests: speed dribbling, juggling, shooting, passing, and heading. We assessed absolute reliability by expressing the standard error of measurement as a coefficient of variation with 95% limits of agreement, and we assessed relative reliability with the intraclass correlation coefficient and with Pearson's correlation (r). The results demonstrated satisfactory relative and absolute reliability for speed dribbling, right foot juggling, short passing, shooting a dead ball right, shooting from a pass, heading in front, and heading right. However, reliability values for left foot juggling, chest-head-foot juggling, head-left-foot-right foot-chest-head juggling, long pass, and shooting a dead ball left tests were not strong enough to suggest their usage by coaches in training or sport scientists in research.

#6 Range of Motion and Injury Occurrence in Elite Spanish Soccer Academies. Not Only a Hamstring Shortening-Related Problem
Reference: J Strength Cond Res. 2019 Jul 29. doi: 10.1519/JSC.0000000000003302. [Epub ahead of print]
Authors: Sanz A, Pablos C, Ballester R, Sánchez-Alarcos JV, Huertas F
Summary: Age-related development of range of motion (ROM) during an active hip flexion (active straight leg raise) and its relationship with hamstring injury occurrence were examined in 1657 young male soccer players (9-18 years of age). Age-related differences in ROM showed a significant decrease from U9 to U11 (p = 0.001), from U11 to U13 (p < 0.005), and from U9 to U13 (p < 0.001), whereas ROM increased from U13 to U15 and from U13 to U18 (both p's < 0.001). Interestingly, younger and older players reached similar ROM values (U9-U18, p = 0.87). Higher ROM was found in dominant than nondominant leg in all age groups (all ps < 0.001). No differences related to playing position were found on ROM (all ps > 0.478). During the follow-up period (11 months) 97 hamstring injuries were reported showing higher rates in the older age groups (p < 0.001) and outfield players (p < 0.001). Remarkably, no differences in ROM average were found between injured players and noninjured players (p = 0.152). Our results suggest that ROM during hip flexion does not only depend on the hamstrings shortening but also on the variables related to joint stability, motor control, and hip flexor muscle weakness. Sport scientists in youth sport soccer academies should develop age-specific screening and action plans to develop strength, motor control, and flexibility to optimize ROM and reduce injuries from the grassroots stages.

#7 Comparing the magnitude and direction of asymmetry during the squat, countermovement and drop jump tests in elite youth female soccer players
Reference: J Sports Sci. 2019 Jul 29:1-8. doi: 10.1080/02640414.2019.1649525. [Epub ahead of print]
Authors: Bishop C, Pereira LA, Reis VP, Read P, Turner AN, Loturco I
Summary: The aims of the present study were to provide an in-depth comparison of inter-limb asymmetry and determine how consistently asymmetry favours the same limb during different vertical jump tests. Eighteen elite female under-17 soccer players conducted unilateral squat jumps (SJ), countermovement jumps (CMJ) and drop jumps (DJ) on a portable force platform, with jump height, peak force, concentric impulse and peak power as common metrics across tests. For the magnitude of asymmetry, concentric impulse was significantly greater during the SJ test compared to CMJ (p = 0.019) and DJ (p = 0.003). No other significant differences in magnitude were present. For the direction of asymmetry, Kappa coefficients revealed fair to substantial levels of agreement between the SJ and CMJ (Kappa = 0.35 to 0.61) tests, but only slight to fair levels of agreement between the SJ and DJ (Kappa = -0.26 to 0.18) and CMJ and DJ (Kappa = -0.13 to 0.26) tests. These results highlight that the mean asymmetry value may be a poor indicator of true variability of between-limb differences in healthy athletes. The direction of asymmetry may provide a useful monitoring tool for practitioners in healthy athletes, when no obvious between-limb deficit exists.

#8 Relative age and maturation selection biases in academy football
Reference: J Sports Sci. 2019 Jul 31:1-9. doi: 10.1080/02640414.2019.1649524. [Epub ahead of print]
Authors: Hill M, Scott S, Malina RM, McGee D, Cumming SP
Summary: This study examined the simultaneous effects of relative age and biological maturity status upon player selection in an English professional soccer academy. A total of 202 players from the U9 to U16 age groups, over an eight-year period (total of 566 observations), had their relative age (birth quarter) and biological maturity (categorised as late, on-time or early maturing based upon the Khamis-Roche method of percentage of predicted adult height at time of observation) recorded. Players born in the first birth quarter of the year (54.8%) were over-represented across all age groups. A selection bias towards players advanced in maturity status for chronological age emerged in U12 players and increased with age; 0% of players in the U15 and U16 age group were categorised as late maturing. A clear maturity selection bias for early maturing players was, however, only apparent when the least conservative criterion for estimating maturity status was applied (53.8% early and 1.9% late maturing in the U16 age group). Professional football academies need to recognise relative age and maturation as independent constructs that exist and operate independently. Thus, separate strategies should perhaps be designed to address the respective selection biases, to better identify, retain and develop players.

#9 High return to competition rate following ACL injury - A 10-year media-based epidemiological injury study in men`s professional football
Reference: Eur J Sport Sci. 2019 Jul 29:1-15. doi: 10.1080/17461391.2019.1648557. [Epub ahead of print]
Authors: Werner K, Clemens M, Volker K, Peter A, Tobias T, Karen AF, Tim M
Summary: Ruptures of the anterior cruciate ligament (ACL) typically occur in professional football and epidemiological data about longitudinal injury development is needed. The purpose was to This practice-driven investigation of media-derived ACL data provides information about professional football over 10 years. Injury registration was based on "kicker" sports magazine information that have been recorded over one decade in a standardized manner. Only ACL ruptures in the first German football league were included when they could be verified by a second reliable source. Fifty-seven primary ACL ruptures were verified in the first German football league during the seasons 2007/08 to 2016/17. Among them, 6 re-injuries were found. Mean age at the time of injury was 24.8 years (SD 3.8). 31% (n = 20) of ACL ruptures occurred at the beginning of the season in August or September (p = 0.02). Mean time of RTC after primary ACL ruptures was 226.7 days (SD: 93.5) and 245.6 days (SD: 45.4) after re-injury. Although 62 (98%) players returned to football after injury and only one player immediately finished his career, 54.9% of the affected individuals played 3 years after the ACL rupture in the same league. ACL ruptures lead to longer absence than 7 months from football but does not give reason for immediate career-ending. The decrease in playing level after 3 years illustrate the serious consequences of ACL ruptures in football. Media-based injury reports may provide interesting information.

#10 Gender-dependent evaluation of football as medicine for prediabetes
Reference: Eur J Appl Physiol. 2019 Sep;119(9):2011-2024. doi: 10.1007/s00421-019-04188-5. Epub 2019 Jul 26
Authors: Mohr M, Skoradal MB, Andersen TR, Krustrup P
Summary: Training intensity and health effects of football were investigated gender specifically in individuals with prediabetes. Participants with prediabetes (age 60 ± 6 years) were randomised into a football and dietary advice group (FD-men n = 13 and FD-women n = 14) or a dietary advice only group (D-men n = 12 and D-women n = 11). FD performed football training (twice/week for 16 weeks), while both groups received dietary advice. Body composition, bone variables, blood pressure, blood lipid profile and peak oxygen uptake (VO2peak) were determined pre- and post-intervention. Mean heart rate during football training was 79 ± 2 and 80 ± 3% HRmax for FD-men and FD-women, respectively, with peak heart rate values of 96 ± 1 and 97 ± 2% HRmax, with no gender differences. VO2peak increased more (P < 0.05) in FD-men and FD-women than in D-men and D-women. However, relative delta change in VO2peak was 21 ± 14% in FD-women, which was greater (P < 0.05) than in FD-men (11 ± 12%). Reduction in SBP and DBP, respectively, was similar in FD-men (- 10.8 ± 13.0 and - 7.3 ± 11.8 mmHg) and FD-women (- 11.3 ± 11.0 and - 7.1 ± 6.2 mmHg), with within-gender differences for men. Total plasma cholesterol and LDL cholesterol decreased (P < 0.05) by - 0.7 ± 1.1 and - 0.5 ± 0.9 mmol L-1, respectively, in FD-women and - 0.2 ± 0.4 and - 0.2 ± 0.3 mmol L-1 in FD-men, with no significant gender differences (P = 0.08). Body fat content was lowered (P < 0.05) by 3 and 4%-points in FD-men and FD-women, respectively. Gender-mixed football training combined with dietary advice causes broad-spectrum health effects for men and women with prediabetes, with minor gender-specific differences. Thus, the intensity and training-induced effects of football training are also high for elderly women with prediabetes.

#11 Characteristics of plantar pressure distribution in elite male soccer players with or without history of proximal fifth metatarsal fracture: a case-control study
Reference: J Phys Ther Sci. 2019 Jul;31(7):530-535. doi: 10.1589/jpts.31.530. Epub 2019 Jul 2.
Authors: Kuzuyama M, Perrier J, Kusaki Y, Sato K, Yamaura I, Tsuchiya A
Download link:
Summary: Studies have demonstrated a relationship between plantar pressure distribution and proximal fifth metatarsal fracture. We aimed to investigate the plantar pressure patterns of soccer players with or without a history of proximal fifth metatarsal fracture. Fifty-one male soccer players (31 professional, 20 high-school) participated in this study (mean age, weight, and height ± SD: 21.1 ± 4.7 years, 68.8 ± 5.8 kg, and 175.4 ± 5.9 cm, respectively). Seven of them had a history of proximal fifth metatarsal fracture before this study (the fracture group) and 44 had no history of fracture (the control group). A Win-Pod (Medicapteurs) platform was used to measure foot pressure forces. The center of plantar pressure was measured during double and single-limb stances for 25 seconds. Fifth metatarsal pressure and the center of plantar pressure angle was calculated from the walking footprint. The calculated data were compared between the fracture group and the control group. [Results] Comparisons between the fracture and control groups in terms of morphology and the center of plantar pressure length showed no significant differences. However, the fifth metatarsal pressure and the center of plantar pressure angle were significantly higher in the fracture group. [Conclusion] The results of this study revealed that players with excessive loading in the lateral areas of the foot while walking have a risk of developing proximal fifth metatarsal fracture.

#12 Effects of Bio-Banding upon Physical and Technical Performance during Soccer Competition: A Preliminary Analysis
Reference: Sports (Basel). 2019 Aug 14;7(8). pii: E193. doi: 10.3390/sports7080193.
Authors: Abbott W, Williams S, Brickley G, Smeeton NJ
Download link:
Summary: Bio-banded competition has been introduced to address the variation in physical maturity within soccer. To date, no research has investigated the effect of bio-banded competition relative to chronological competition. The current study investigated the effect of bio-banding upon physical and technical performance in elite youth soccer athletes. Twenty-five male soccer athletes (11-15 years) from an English Premier League soccer academy participated in bio-banded and chronological competition, with physical and technical performance data collected for each athlete. Athletes were between 85-90% of predicted adult stature, and sub-divided into early, on-time and late developers. For early developers, significantly more short passes, significantly less dribbles and a higher rating of perceived exertion (RPE) were evident during bio-banded competition compared to chronological competition (p < 0.05). Significantly more short passes and dribbles, and significantly fewer long passes were seen for on-time developers during bio-banded competition (p < 0.05). For late developers, significantly more tackles, and significantly fewer long passes were evident during bio-banded competition (p < 0.05). No significant differences in physical performance were identified between competition formats. Results demonstrated that bio-banded competition changed the technical demand placed upon athletes compared to chronological competition, without reducing the physical demands. Bio-banded competition can be prescribed to athletes of differing maturation groups dependent upon their specific developmental needs.

The Training Manager -