Latest research in football - week 38 - 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 Physical responses of professional soccer players during 4 vs. 4 small-sided games with mini-goals according to rule changes
Reference: Biol Sport. 2018 Mar;35(1):75-81. doi: 10.5114/biolsport.2018.70754. Epub 2017 Oct 12.
Authors: Giménez JV, Liu H, Lipińska P, Szwarc A, Rompa P, Gómez MA
Summary: The aim of this study was to investigate the influence of the number of ball touches authorised per game (one touch [T1], two touches [T2], and free touches [FT]) on the players' physical responses throughout the bouts in 4 vs 4 soccer small-sided games (SSGs) with mini-goals (without a goalkeeper). Fourteen professional Polish players (age 23.2±2.7 years, height 177.9±6.1 cm, weight: 73.2±6.9 kg, body fat 12.6±2%, playing experience: 14±5 years) completed nine series of 4 vs 4 SSGs. Each trial included three series of SSGs with a game duration of 4 minutes on an equal sized pitch (30x24 m; 720 m2; individual occupied area per player=90 m2). Differences in physical responses and time-motion characteristics of players were measured with the Global Positioning System (GPS) and assessed using a repeated measures ANOVA to compare the three game conditions and the magnitude-based inference to evaluate the pairwise comparison effects. The results showed that only the variables distance covered at low speed, time walking, time at low speed, and accelerations of >4 m/s² were statistically significantly different among game conditions. The pairwise comparisons only identified significant effects for distance covered at low speed (between FT and T2), for time walking (between FT and T1), for time at moderate and low speed (between FT and T2), and for accelerations of >4 m/s² (between FT and T1). The players' performances are affected by the ball touch constraint during SSGs with mini-goals. The results provide useful information for training and task design that replicate specific physical demands (i.e., accelerations of >4 m/s², time walking or running at a lower speed).

#2 Associations between wellness and internal and external load variables in two intermittent small-sided soccer games
Reference: Physiol Behav. 2018 Sep 17. pii: S0031-9384(18)30619-X. doi: 10.1016/j.physbeh.2018.09.008. [Epub ahead of print]
Authors: Clemente FM
Summary: The purpose of this study was to test the associations between wellness and internal and external load variables during two intermittent small-sided games (SSGs). Ten male amateur soccer players (age: 19.8±1.6 years; experience: 8.3±2.1 years; height: 177.4±3.8 cm; weight: 71.7±4.2 kg) voluntarily participated in this study. The 5 × 5 format was played in 3 × 6 min and 6 × 3 min regimens. Muscle soreness (DOMS), stress, fatigue, and sleep quality were rated before each session. Perceived exertion (RPE); mean heart rate (HRmean); total (TD), jogging (JD), running (RD), and sprinting (SD) distances; player's training load (PTL); and total accelerations (TAc) were monitored during SSGs. In the case of the 3 × 6' regimen, large negative correlations between DOMS and TD (-0.68, [-0.89; -0.20]), JD (-0.66, [-0.89; -0.17]) and SD (-0.63, [-0.88; -0.12]) were found, and very large negative correlations between DOMS and PTL (-0.84, [-0.95; -0.53]) were found. Very large (-0.73, [-0.91; -0.30] and large (-0.61, [-0.87; -0.09]) negative correlations between DOMS and HRmean and PTL, respectively, were observed during the 6 × 3' regimen. Regarding the associations between load variables, during the 6 × 3' regimen, RPE was very largely correlated with TD (0.77, [0.37; 0.93]), JD (0.70, [0.25; 0.90]) and largely correlated with TAc (0.67, [0.19; 0.89]). In the 3 × 6' regimen, large correlations were found between RPE and SD (0.62, [0.10; 0.87]) and TAc (0.61, [0.09; 0.87]). Overall, PTL was nearly perfectly correlated with TD (0.96, [0.86; 0.99]) and JD (0.94, [0.81; 0.98]), very largely correlated with TAc (0.87, [0.61; 0.96]), and largely correlated with RD (0.72, [0.29; 0.91]). The results of this study suggest that wellness status may influence workload in SSGs; in particular, DOMS may be moderately-to-largely detrimental to both internal and external load variables. Moreover, it was confirmed that RPE is moderately-to-largely correlated to objectively measured external load variables.

#3 Influence of contextual variables and the pressure to keep category on physical match performance in soccer players
Reference: PLoS One. 2018 Sep 20;13(9):e0204256. doi: 10.1371/journal.pone.0204256. eCollection 2018.
Authors: García-Unanue J, Pérez-Gómez J, Giménez JV, Felipe JL, Gómez-Pomares S, Gallardo L, Sánchez-Sánchez J
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Summary: Previous studies have analysed the influence of contextual variables on performance and physical demands in soccer. However, the points needed to remain in the category have been an element that has not been analysed previously. The aim of the present study was to investigate the influence of match location, match period, strength of the opponent and the points required to keep category on physical performance in professional soccer players. Fourteen Spanish second B Division League matches played by a professional football team were analysed during the 2016/17 season using GPS devices. The 10 main players of each match used the GPS throughout the match. The variables of Total Distance (m), High Intensity Distance (m), High intensity Accelerations (n), Sprint Time (s) and Sprint Distance (m) were analysed. The most notable differences are found in Total Distance covered. Away games accumulated significantly more distance than those played at home, but only in the second half (+230.65 m, IC95%: 21.94 to 438.19, ES: 0.46, p = 0.031). There are no differences depending on the strength of the opponent. However, players covered greater distances during the first half in those matches that were played furthest from salvation (+235.86 m, 95% CI: 49.03 to 422.70, ES: 0.51, p = 0.014). Total Distance is the main parameter affected by situational variables. In addition, the pressure of being further away from saving the category increases the distance covered by players in a game.

#4 Heading in soccer increases serum neurofilament light protein and SCAT3 symptom metrics
Reference: BMJ Open Sport Exerc Med. 2018 Aug 27;4(1):e000433. doi: 10.1136/bmjsem-2018-000433. eCollection 2018.
Authors: Wallace C, Smirl JD, Zetterberg H, Blennow K, Bryk K, Burma J, Dierijck J, Wright AD, van Donkelaar P
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Summary: The purpose was to determine the effect of heading a soccer ball on serum neurofilament light (NF-L) protein, plasma tau protein and symptom metrics including total number of symptoms reported and symptom severity scores on the Standardized Concussion Assessment Tool- 3rd edition (SCAT3). Eleven male collegiate soccer players were recruited to take part in three experimental conditions including heading, sham and control conditions. Participants were required to perform 40 headers in 20 min in the heading condition, and control 40 soccer balls directed at them with their hands, chest or thigh in the sham condition. No ball contact was made during the control condition. Blood sampling and SCAT3 symptom assessments were completed prior to and 1 hour following conditions. A subset of participants returned 3 weeks following the heading condition for blood sampling. NF-L was elevated at 1 hour (p=0.004) and 1 month (p=0.04) following the heading condition, and at 1 hour (p=0.02) following the control condition. Tau levels remained unchanged following all conditions. The total number of symptoms (TS) and symptom severity (SS) scores from the SCAT3 were both elevated following the heading condition (p=0.01 and p=0.03, respectively). Both TS and SS decreased following sham (p=0.04 and p=0.04) and control conditions (p=0.04 and p=0.04). An acute bout of soccer heading is associated with increased NF-L concentrations at 1 hour and 1 month following the session and can lead to symptoms commonly reported following sport-related concussion.

#5 How sprinters accelerate beyond the velocity plateau of soccer players: waveform analysis of ground reaction forces
Reference: Scand J Med Sci Sports. 2018 Sep 19. doi: 10.1111/sms.13302. [Epub ahead of print]
Authors: Colyer SL, Nagahara R, Takai Y, Salo AIT
Summary: Forces applied to the ground during sprinting are vital to performance. This study aimed to understand how specific aspects of ground reaction force waveforms allow some individuals to continue to accelerate beyond the velocity plateau of others. Twenty-eight male sprint specialists and 24 male soccer players performed maximal-effort 60-m sprints. A 54-force-plate system captured ground reaction forces, which were used to calculate horizontal velocity profiles. Touchdown velocities of steps were matched (8.00, 8.25 and 8.50 m·s-1 ) and the subsequent ground contact forces were analysed. Mean forces were compared across groups and statistical parametric mapping (t-tests) assessed for differences between entire force waveforms. When individuals contacted the ground with matched horizontal velocity, ground contact durations were similar. Despite this, sprinters produced higher average horizontal power (15.7-17.9 W·kg-1 ) than the soccer players (7.9-11.9 W·kg-1 ). Force waveforms did not differ in the initial braking phase (0-~20% of stance). However, sprinters attenuated eccentric force more in the late braking phase and produced a higher anteroposterior component of force across the majority of the propulsive phase, for example from 31-82% and 92-100% of stance at 8.5 m·s-1 . At this velocity, resultant forces were also higher (33-83% and 86-100% of stance) and the force vector was more horizontally orientated (30-60% and 95-98% of stance) in the sprinters. These findings illustrate the mechanisms which allowed the sprinters to continue accelerating beyond the soccer players' velocity plateau. Moreover, these force production demands provide new insight regarding athletes' strength and technique training requirements to improve acceleration at high velocity.

#6 Outcome after Combined Lateral Extra-articular Tenodesis and Anterior Cruciate Ligament Revision in Professional Soccer Players
Reference: J Knee Surg. 2018 Sep 18. doi: 10.1055/s-0038-1672120. [Epub ahead of print]
Authors: Alessio-Mazzola M, Formica M, Russo A, Sanguineti F, Capello AG, Lovisolo S, Felli L
Summary: We report the functional outcome after combined anterior cruciate ligament (ACL) reconstruction and lateral extra-articular tenodesis (LET) for ACL re-rupture and high-grade pivot shift in professional soccer players. For this retrospective review, the medical records of 24 professional soccer players were analyzed. The mean age at surgery was 23.8 ± 4.2 years and the mean follow-up was 42.2 ± 16.9 months. Pre- and postoperative assessment included the KT-1000 Lachman test, pivot shift test, International Knee Documentation Committee (IKDC) subjective knee evaluation, Tegner activity scale (TAS), and Lysholm score. The rate of return to sports and the level of play at final follow-up were recorded. ACL revision was performed with an autologous bone-patellar tendon-bone autograft or a hamstring graft. LET was performed using an extra-articular MacIntosh procedure as modified by Arnold-Coker. Anterior-posterior laxity was significantly reduced at the final clinical assessment (p < 0.0001): 22 patients (91.7%) had a negative pivot shift and 2 (8.3%) had residual glide (+), with significant improvement (p < 0.0001). The mean subjective IKDC and Lysholm score improved from 69.5 ± 11.1 (range: 56-90) to 88.4 ± 8.9 (range: 62.1-100) and from 58.1 ± 11.7 (range: 33-72) to 97.4 ± 3.2 (range: 88-100), respectively, with significant improvement (p  < 0.0001) over preoperative values. The overall failure rate was 8.3%. There were no differences between mean preinjury and final TAS scores (p > 0.05). The rate of return to sports at the same level was 91.7% and the mean time to return to sports was 9.2 ± 2.2 months. Mid-term functional outcome after combined extra-articular reconstruction and ACL revision surgery was satisfactory, with a reduction in residual postoperative rotatory instability and degree of pivot shift.

#7 Efficacy of Injury Prevention Training Is Greater for High-Risk vs Low-Risk Elite Female Youth Soccer Players
Reference: Am J Sports Med. 2018 Sep 18:363546518795677. doi: 10.1177/0363546518795677. [Epub ahead of print]
Authors: De Ste Croix M, Hughes J, Ayala F, Taylor L, Datson N
Summary: The efficacy of robustness training for high- versus low-risk individuals within high-risk groups is currently unknown. The purpose was to explore the efficacy of robustness training on injury risk factors among female youth soccer players and to examine if high-risk athletes are greater responders to such training. A total of 125 elite youth female soccer players on the English FA talent pathway were randomly selected into a training group (n = 71) or a control group (n = 54). Relative leg stiffness, 2-dimensional knee valgus and knee flexion range of motion from a single-legged countermovement jump, and probability of high knee abduction moment (pKAM) risk were all determined before and after a 16-week robustness training program. For further analysis, participants in the training group were split into groups based on risk: high risk (pKAM >0.80, n = 33) and low risk (pKAM <0.55, n = 33). Magnitude-based inferences were used to explore differences between the control and intervention groups and the high- and low-risk groups. Magnitude-based inferences demonstrated significant beneficial effects in the training group for knee valgus, pKAM, and leg stiffness as compared with the control group. The control group demonstrated possible worthwhile differences in knee flexion range of motion as compared with the intervention group. The high-risk group demonstrated likely/very likely worthwhile differences versus the low-risk group for all parameters. Robustness training induces significant beneficial improvements in injury risk factors among female youth soccer players. The beneficial effects of this multidimensional program are greater for those classified as high risk.

#8 Functional Movement Patterns and Body Composition of High-Level Volleyball, Soccer and Rugby Players
Reference: J Sport Rehabil. 2018 Sep 17:1-20. doi: 10.1123/jsr.2018-0087. [Epub ahead of print]
Authors: Campa F, Piras A, Raffi M, Toselli S
Summary: Sports practice leads athletes to develop a specific body composition, coordination patterns and basic motor skills based on the different tactical and physical needs. This study aimed to present and compare a wide range of functional movement patterns and body composition (BC) parameters of high-level male athletes playing different sports, and to determine if there was a relationship between the parameters examined. Thirty volleyball, twenty-five soccer and thirty rugby players (age 25.9±5.0 years, BMI 25.6±4.1 kg/m2) participated in this study. Functional movement patterns and anthropometric measurements were collected by a physician specifically trained. BMI, fat mass, fat free mass, upper arm muscle and fat area, calf muscle and fat area, thigh muscle and fat area, and functional movement screen (FMS) scores. In addition to considering the FMS total score, we separated the screen into 3 parts: FMSmove, FMSflex and FMSstab. The rugby players showed a higher number of asymmetrical and dysfunctional movements than the other athletes (p <0.01), while the highest scores in FMSflex were obtained by the volleyball players (p <0.01). Additionally, most of the asymmetrical and painful movements in the athletes were measured on the shoulder mobility test. Muscle and fat areas differed significantly among the athletes (p <0.05). Significant associations were found between movement patterns and several BC variables. In particular, large negative correlations were measured between percentage of fat mass (r = -0.616; p <0.01), upper arm fat area (r = -0.519; p <0.01) and FMS total score. Functional movement patterns and BC differ in athletes according to the sport practiced. Furthermore, reaching an optimal BC is essential to achieve a satisfactory quality of movement.

#9 The Effect of a 20-Week Corrective Exercise Programme on Functional Movement Patterns in Youth Elite Male Soccer Players
Reference: J Sport Rehabil. 2018 Sep 17:1-18. doi: 10.1123/jsr.2018-0039. [Epub ahead of print]
Authors: Campa F, Spiga F, Toselli S
Summary: Poor functional movement patterns negatively affect the ability to perform fundamental movements with precision and efficiency, increasing injury risk in athletes. The purpose was to examine the effect of a 20-week corrective exercise programme during the competitive season on functional movement patterns in youth elite male soccer players. 65 youth elite male soccer players (age 15.89 ± 0.53 years; weight 67.42 ± 6.78 kg; stature 175.20 ± 6.34 cm) participated in this study. Two of four teams were randomly selected to take part in the corrective programme. Thus, the players were placed into two groups: corrective exercise programme (CEP) and control group (CON). Functional movement screen (FMS) was used to assess the presence of dysfunctional, asymmetrical and painful movements in the players before and after the intervention period. In addition to considering the FMS total score (FMStotal), we separated the screen into 3 parts: FMSmove, FMSflex and FMSstab. A repeated measures ANOVA was conducted to determine the effectiveness of the training programme on FMS scores. The chi-square (χ2) test was performed to determine whether there were significant changes in the frequencies of asymmetric and dysfunctional movements after 20 weeks. No athlete experienced severe injuries during the intervention period. There was a significant group by time interaction (P < 0.01) for FMStotal, FMSmove and FMSstab, in which only the CEP increased their scores after the intervention period (P < 0.05). A χ2 analysis showed a significant (P < 0.05) decrease in asymmetric and dysfunctional movements at the follow-up in CEP, while these changes were not observed in CON. Youth elite soccer players demonstrate a high prevalence of asymmetric movements during FMS testing, but their functional movement patterns can be improved during the competitive season following a specific corrective exercise programme.

#10 Leg strength and power in Polish striker soccer players
Reference: Acta Bioeng Biomech. 2018;20(2):109-116
Authors: Buśko K, Górski M, Nikolaidis PT, Mazur-Różycka J, Łach P, Staniak Z, Gajewski J
Summary: The main goal of the present study was to examine muscle strength and power of dominant and non-dominant leg, knee extensors and flexors, and their correlations with jumping performances in soccer players. A secondary aim was to evaluate muscle sense. 31 male professional strikers (age 20.9 ± 2.3 years, body mass 75.1 ± 6.6 kg, body height 179.5 ± 4.7 cm) participated in the study. The power output of lower extremities and the height of rise of the body mass centre during vertical jumps were measured using a force plate. The maximum muscle torque of the flexors and extensors of the knee were measured under isometric conditions using a special isometric torquemeter. Force sense was measured in isometric conditions in two tests: (a) fifty percent of the maximal voluntary contraction was set as a value of target force and the participants were instructed to reproduce the target force, (b) the participants attempted to develop a torque reproducing a sine course within the range of 10 to 50% of MVC performed. A direct relationship was observed between the peak muscle torque in knee extensors developed during isokinetic contraction at all velocities and power and height of three types of vertical jumps ( p <0.05). No correlation was observed between jumping performance and muscle torque under isometric condition. No differences were found in strength and jumping abilities as well as in force sense between dominant and non-dominant legs. This study offered a comprehensive and complete evaluation of leg muscle strength, sense and power, with the use of using force plate and isokinetic dynamometry.

#11 Nordic Hamstring Strength of Highly Trained Youth Football Players and Its Relation to Sprint Performance
Reference: J Strength Cond Res. 2018 Sep 19. doi: 10.1519/JSC.0000000000002800. [Epub ahead of print]
Authors: Markovic G, Sarabon N, Boban F, Zoric I, Jelcic M, Sos K, Scappaticci M
Summary: We aimed to characterize Nordic hamstring (NH) strength and bilateral NH strength asymmetry in highly trained youth footballers and to investigate the relationship between NH strength and sprint performance. Twenty-two adult and 133 highly trained youth footballers in the age groups U12-U18 participated in this study. Eccentric hamstring strength was assessed using the NH device. Youth footballers (n = 119) also performed 20-m sprint test. Age-related changes in absolute and relative NH strength, and bilateral NH strength asymmetry were analyzed using 1-way analysis of variance. The linear relationship between relative NH strength and sprint performance was established using a Pearson correlation analysis. Significant age-related increases (F = 3.6-18.9; all p < 0.01) in NH strength were reported for all units except N·kg (F = 1.9; p = 0.08). The largest differences in absolute NH strength were seen between U15 and U16 groups. Bilateral NH strength asymmetry varied from 8 to 16% (F = 1.8; p = 0.09) across all age groups. A large correlation between NH strength and sprint performance was observed (r = -0.52; p < 0.01). Our results indicate that NH strength increases nonlinearly with players' age, with the highest values observed in U16 group. Furthermore, bilateral NH strength asymmetry varied nonsignificantly between 8 and 16%. Finally, 27% of variance of sprint performance of youth footballers could be explained by relative NH strength. The reported NH strength data could be used as normative standards during testing and training of youth football players. Present results also suggest that coaches should pay close attention to eccentric hamstring function in youth footballers.

#12 Venous versus capillary sampling for total creatine kinase assay: Effects of a simulated football match
Reference: PLoS One. 2018 Sep 20;13(9):e0204238. doi: 10.1371/journal.pone.0204238. eCollection 2018.
Authors: de Oliveira DCX, Frisselli A, de Souza EG, Stanganelli LCR, Deminice R
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Summary: Capillary rather than venipuncture may be a simpler and less invasive blood collection protocol that would increase the number of potential sampling tests. However, if capillary sampling can be used as an alternative to venipuncture to determine changes in plasma, total creatine kinase (CK) activity in response to a football training session is poorly known. This study aims to determine whether capillary blood sampling would provide representative measures of total CK activity compared to venipuncture in response to a football training session-induced elevated CK plasma levels. Twenty-two players from an under-19 football team performed a simulated football match with 11 players on each team for 90 minutes total duration (two halves of 45 minutes with 15 minutes rest between). Venous and ear lobe capillary blood samples were collected before and after (24h and 48h) the training session. Athletes retested for three consecutive days after exercise during the recovery week. The simulated match significantly increased (P< 0.05) total CK activity as determined in both venous (1.7-fold) and capillary (1.9-fold) blood sampling. Total CK activity determined using capillary samples demonstrated significant correlation (r = 0.85; P < 0.01) and an elevated concordance Lin index (pc = 0.80) when compared to venous sampling total CK. The Bland-Altman plot showed capillary sampling CK overestimated venous CK levels by 130 U/L (61%), with moderated variance and low bias. Our results demonstrated that capillary sampling for total CK activity assay may be considered a reliable alternative to venipuncture to determine changes in plasma total CK activity in response to a football training session.

#13 Motivational Climate in Youth Football Players
Reference: Behav Sci (Basel). 2018 Sep 15;8(9). pii: E83. doi: 10.3390/bs8090083.
Authors: Castro-Sánchez M, Zurita-Ortega F, Ubago-Jiménez JL, Ramírez-Granizo IA, Chacón-Cuberos R
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Summary:  In recent decades, the psychology of sport has gained special relevance in this field, due to the influence of psychological variables on sports performance and the regularity of sports practice. The aim of this research is to analyse the motivational climate of footballers. This study uses a descriptive cross-sectional design on a sample of 156 adolescent football players, using an ad-hoc questionnaire for the recording of socio-demographic variables and the PMCSQ-2 questionnaire on motivational climate in sport. The results of the present investigation indicate that footballers are more oriented towards task than ego, sportsmen who compete in Honor Division being the those who are more oriented towards ego and those of National Division being more oriented towards task. The main conclusion of this research is those who are the motivational climate is related to the division in which the players compete.

#14 Comparative Effects of Tensioning and Sliding Neural Mobilization on Static Postural Control and Lower Limb Hop Testing in Football Players
Reference: J Sport Rehabil. 2018 Sep 17:1-24. doi: 10.1123/jsr.2017-0374. [Epub ahead of print]
Authors: Ferreira J, Bebiano A, Raro D, Martins J, Silva AG
Summary: Context Sliding and tensioning neural mobilization are used to restore normal function of the nervous system, but impose different stresses to it. Particularly, sliding induces greater nerve excursion than tensioning. Conceivably, they might impact nervous system function differently. Objective To compare the effects of tensioning neural mobilization versus sliding neural mobilization of the dominant lower limb on static postural control and hop testing. Design Randomized, parallel and double blinded trial. Setting/Participants Thirty-seven football players. Intervention(s) Participants were randomized into two groups: sliding neural mobilization (n=18) or tensioning neural mobilization (n=19) targeting the tibial nerve. Main Outcome Measures Static postural sway was assessed with a force plate and functional performance with hop tests. Measurements were taken at baseline, after the intervention and at 30 minutes follow up. Results There was a significant effect of time for the center of pressure total displacement and velocity (p<0.05), for the single leg hop test (p<0.05), the 6 meters timed hop test (p<0.05) and the crossover hop test (p<0.05), but no significant effect of the intervention. Conclusion Sliding and tensioning neural mobilization improved postural control and hop testing in football players, and improvements remained 30 minutes after the intervention. Additional research examining the influence of neural mobilization on sensory motor impairments, postural control and functional performance is needed.

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