Latest research in football - week 38 - 2015

#1 How Effective are F-MARC Injury Prevention Programs for Soccer Players? A Systematic Review and Meta-Analysis
Reference: Sports Med. 2015 Sep 24. [Epub ahead of print]
Authors: Al Attar WS, Soomro N, Pappas E, Sinclair PJ, Sanders RH
Summary: The FIFA Medical and Research Centre (F-MARC) has designed a comprehensive warm-up program targeting muscular strength, body kinaesthetic awareness, and neuromuscular control during static and dynamic movements to decrease injury risk for soccer players. Prior studies have investigated the effectiveness of the F-MARC programs, but have not consistently reported a statistically significant reduction in injury and reduction in time loss due to injury from utilizing the program. The purpose of this study was to conduct a systematic review and meta-analysis of randomized controlled trials and interventional studies that evaluated the efficacy of the F-MARC injury prevention programs in soccer. Two independent researchers searched the relevant article databases. The keyword domains used during the search were 'F-MARC', 'FIFA 11+', 'the 11+', 'injury prevention programs', 'soccer', and variations of these keywords. The initial search resulted in 4299 articles which were filtered to nine articles that met the inclusion criteria. Main inclusion criteria were randomized controlled trials or interventional studies, use of F-MARC injury prevention programs, and the primary outcome measuring overall and lower extremity injuries. Extracted data were entered and analyzed using Comprehensive Meta-Analysis software, version 2 (CMA.V2). The pooled results based on total injuries per 1000 h of exposure showed that F-MARC injury prevention programs had a statistically significant reduction in the overall injury risk ratio of 0.771 (95 % CI 0.647-0.918, p = 0.003) and the lower extremity injury risk ratio of 0.762 (95 % CI 0.621-0.935, p = 0.009). Moreover, FIFA '11+' had a statistically significant reduction in the overall injury risk ratio to 0.654 (95 % CI 0.537-0.798, p < 0.001) and the lower extremity injury risk ratio of 0.612 (95 % CI 0.475-0.788, p < 0.001). However, FIFA '11' did not reach significance for the lower extremity and overall injury reduction. It can be suggested that teams involved in the FIFA '11+' warm-up program will reduce injury rates by between 20 and 50 % in the long term compared with the teams that do not engage in F-MARC programs. This systematic review and meta-analysis indicated that use of F-MARC injury prevention programs, particularly the '11+' program, decreases the risk of injuries among soccer players. These data also support the case for the development and introduction of sport-specific programs.


#2 Heart Rate, Time-Motion, and Body Impacts When Changing the Number of Teammates and Opponents in Soccer Small-Sided Games
Reference: J Strength Cond Res. 2015 Oct;29(10):2723-2730.
Authors: Torres-Ronda L, Gonçalves B, Marcelino R, Torrents C, Vicente E, Sampaio J.
Summary: The purpose of this study was to determine the internal (heart rate) and external load (body load, distance covered, and exertion index) during different types of unbalanced soccer small-sided games (SSGs) in professional (PRO) and amateur (AMA) players. In 2 separated sessions (PRO and AMA), participants played 3 SSG formats (4vs3, 4vs5, and 4v7). Data were analyzed from the fixed team's perspective (4vsX) according to the number of opponents (3, 5 and 7) and from the variable team (3 + Xvs4) according to the teammates (without teammates, 2 and 4 teammates). The time-motion and body impact data were collected using a non-differential global positioning system with integrated heart rate measurement. Differences in internal and external workload between the game formats were compared using Cohen's dunb effect sizes with 95% confidence intervals. Results reveal that the higher the number of players involved in the task, the lower the internal and external workload. The analysis also showed different teammates and opposition-related trends that need to be considered when planning and monitoring training performance. Playing in low-inferiority (4vs3 and 4vs5) had higher physiologic impact to players than the other higher unbalanced situations. This evidence was similar to both PRO and AMA players; however, the PRO presented higher physical and lower physiological responses across games. Our results suggest that coaches should consider the usage of unbalanced SSG formats to simultaneously facilitate the emergence of defensive and offensive proficient scenarios also representing opportunities to increase the practice workload.


#3 Symmetry of proprioceptive sense in female soccer players
Reference: Acta Bioeng Biomech. 2015;17(2):155-63.
Authors: Iwańska D, Karczewska M, Madej A, Urbanik C
Summary: The purpose of the study was to assess the symmetry of proprioceptive sense among female soccer players when trying to reproduce isometric knee extensions (right and left) and to analyze the impact of a given level of muscle force on proprioception. The study involved 12 soccer players aged 19.5 ± 2.65 years. Soccer players performed a control measurement of a maximum 3s (knee at the 90°) position in the joint. Subsequently, 70%, 50%, and 30% of the maximum voluntary contraction (MVC) were all calculated and then reproduced by each subject with feedback. Next, the players reproduced the predefined muscle contraction values in three sequences: A - 50%, 70%, 30%; B - 50%, 30%, 70%; C - 70%, 30%, 50% of MVC without visual control. In every sequence, the participants found obtaining the value of 30% of MVC the most difficult. The value they reproduced most accurately was 70% of MVC. Both trial II and trial III demonstrated that the symmetry index SI significantly differed from values considered acceptable (SIRa). In each successive sequence the largest asymmetry occurred while reproducing the lowest values of MVC (30%) (p < 0.05). High level of prioprioceptive sense is important to soccer players due to the extensive overload associated with dynamics stops or changes in direction while running. Special attention should be paid to develop skills in sensing force of varying levels. It was much harder to reproduce the predefined values if there was no feedback.


#4 The Effect of Two Speed Endurance Training Regimes on Performance of Soccer Players
Reference: PLoS One. 2015 Sep 22;10(9):e0138096. doi: 10.1371/journal.pone.0138096.
Authors: Iaia FM, Fiorenza M, Perri E, Alberti G, Millet GP, Bangsbo J
Download link: http://www.plosone.org/article/fetchObject.action?uri=info:doi/10.1371/journal.pone.0138096&representation=PDFAbstract
Summary: In order to better understand the specificity of training adaptations, we compared the effects of two different anaerobic training regimes on various types of soccer-related exercise performances. During the last 3 weeks of the competitive season, thirteen young male professional soccer players (age 18.5±1 yr, height 179.5±6.5 cm, body mass 74.3±6.5 kg) reduced the training volume by ~20% and replaced their habitual fitness conditioning work with either speed endurance production (SEP; n = 6) or speed endurance maintenance (SEM; n = 7) training, three times per wk. SEP training consisted of 6-8 reps of 20-s all-out running bouts followed by 2 min of passive recovery, whereas SEM training was characterized by 6-8 x 20-s all-out efforts interspersed with 40 s of passive recovery. SEP training reduced (p<0.01) the total time in a repeated sprint ability test (RSAt) by 2.5%. SEM training improved the 200-m sprint performance (from 26.59±0.70 to 26.02±0.62 s, p<0.01) and had a likely beneficial impact on the percentage decrement score of the RSA test (from 4.07±1.28 to 3.55±1.01%) but induced a very likely impairment in RSAt (from 83.81±2.37 to 84.65±2.27 s). The distance covered in the Yo-Yo Intermittent Recovery test level 2 was 10.1% (p<0.001) and 3.8% (p<0.05) higher after SEP and SEM training, respectively, with possibly greater improvements following SEP compared to SEM. No differences were observed in the 20- and 40-m sprint performances. In conclusion, these two training strategies target different determinants of soccer-related physical performance. SEP improved repeated sprint and high-intensity intermittent exercise performance, whereas SEM increased muscles' ability to maximize fatigue tolerance and maintain speed development during both repeated all-out and continuous short-duration maximal exercises. These results provide new insight into the precise nature of a stimulus necessary to improve specific types of athletic performance in trained young soccer players.


#5 Monitoring Locomotor Load in Soccer: Is Metabolic Power, Powerful?
Reference: Int J Sports Med. 2015 Sep 22. [Epub ahead of print]
Authors: Buchheit M, Manouvrier C, Cassirame J, Morin JB
Summary: The aim of the present study was to examine the validity and reliability of metabolic power (P) estimated from locomotor demands during soccer-specific drills. 14 highly-trained soccer players performed a soccer-specific circuit with the ball (3×1-min bouts, interspersed with 30-s passive recovery) on 2 different occasions. Locomotor activity was monitored with 4-Hz GPSs, while oxygen update (VO2) was collected with a portable gas analyzer. P was calculated using either net VO2 responses and traditional calorimetry principles (PVO2, W.kg-1) or locomotor demands (PGPS, W.kg-1). Distance covered into different speed, acceleration and P zones was recorded. While PGPS was 29±10% lower than PVO2 (d<- 3) during the exercise bouts, it was 85±7% lower (d<- 8) during recovery phases. The typical error between PGPS vs. PVO2 was moderate: 19.8%, 90% confidence limits: (18.4;21.6). The correlation between both estimates of P was small: 0.24 (0.14;0.33). Very large day-to-day variations were observed for acceleration, deceleration and > 20 W.kg-1 distances (all CVs > 50%), while average Po2 and PGPS showed CVs < 10%. ICC ranged from very low- (acceleration and > 20 W.kg-1 distances) to-very high (PVO2). PGPS largely underestimates the energy demands of soccer-specific drills, especially during the recovery phases. The poor reliability of PGPS >20 W.kg-1 questions its value for monitoring purposes in soccer.


#6 Assessment of the in-season changes in mechanical and neuromuscular characteristics in professional soccer players
Reference: J Sports Med Phys Fitness. 2015 Sep 22. [Epub ahead of print]
Authors: García-García O, Serrano-Gómez V, Hernández-Mendo A, Tapia-Flores A.
Summary: The aim of this study was to monitor in-season changes in the mechanical and neuromuscular characteristics of knee extensor and flexor muscles in professional soccer players. Twenty-one professional soccer players (soccer group, or SG) and sixteen non soccer playing males (non-soccer group, or NSG) were assessed by tensiomyography on two occasions: just after the start of the competitive season and 10 weeks later. During this time the soccer players' training sessions were built mainly on speed and strength drills. Mixed-design factorial analysis of variance was conducted and effect sizes were calculated. There was a significant interaction between time (assessment points) x group (SG vs NSG) x muscle for contraction time (Tc), maximum radial muscle displacement (Dm), and delay time (Td). In the case of the knee extensors, after 10 weeks, there was a 17.7%-22.7% decrease in Tc, an 8.7%-9.9% decrease in Td, and a 12.2%-14.2% decrease in Dm knee extensor in the SG (p<.01), with a large effect size. In the case of the knee flexors, by contrast, there was an 11.9% increase in Td and a 24.5% increase in Dm (p<.01), with a moderate to large effect size. The findings confirm that mechanical and neuromuscular characteristics change over time and also vary according to the characteristics of the athlete (SG vs. NSG) and the muscle analyzed. In conclusion, soccer coaches could use Tc, Td, and Dm data to individualize work load and intensity and control the effects of neuromuscular training throughout the season using a portable, noninvasive technique that, unlike stress tests, does not cause fatigue and therefore does not interfere with training periodization.


#7 Transference effect of vertical and horizontal plyometrics on sprint performance of high-level U-20 soccer players
Reference: J Sports Sci. 2015 Sep 21:1-10. [Epub ahead of print]
Authors: Loturco I, Pereira LA, Kobal R, Zanetti V, Kitamura K, Abad CC, Nakamura FY
Summary: The aim of this study was to investigate the effects of adding vertical/horizontal plyometrics to the soccer training routine on jumping and sprinting performance in U-20 soccer players. The vertical jumping group (VJG) performed countermovement jumps (CMJ), while the horizontal jumping group (HJG) executed horizontal jumps (HJ). Training interventions comprised 11 sessions, with volume varying between 32 and 60 jumps per session. The analysis of covariance revealed that CMJ height and peak force improved only in the VJG, and that HJ distance and peak force improved in both groups. Velocity in 20 m (VEL 20 m) did not improve in either group; however, velocity in 10 m (VEL 10 m) presented a moderate positive effect size (ES = 0.66) in the HJG, while the ES was large (1.63) for improvement in the 10-20 m acceleration in the VJG, and it was largely negative (-1.09) in the HJG. The transference effect coefficients (calculated by the equation: TEC = result gain (ES) in untrained exercise/result gain (ES) in trained exercise) between CMJ and VEL 20 m and ACC 10-20 m were 1.31 and 2.75, respectively. The TEC between HJ and VEL 10 m, VEL 20 m and ACC 0-10 m were 0.44, 0.17 and 0.44, respectively. The results presented herein indicate that the plyometric training-axis is decisive in determining neuromechanical training responses in high-level soccer players.