Latest research in football - week 16 - 2016

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 Manipulation of exercise to rest ratio within set duration on physical and technical outcomes during small-sided games in elite youth soccer players
Reference: Hum Mov Sci. 2016 Apr 12;48:1-6. doi: 10.1016/j.humov.2016.03.013. [Epub ahead of print]
Authors: Christopher J, Beato M, Hulton AT
Summary: Training practices for elite soccer players should take into account specific technical, tactical and physical components. As a consequence of these demands small-sided games (SSGs) have become a popular conditioning tool that replicate the demands encountered during match play. The aim of this investigation was to examine how the manipulation of exercise to rest ratio, within the same overall duration, affected both physical and technical outcomes during SSGs in elite youth soccer. Twelve elite youth soccer players participated in three variations of eight minute 6v6 SSGs. The three variations included eight minutes continuous, 2×4min and 4×2min. Players perceived the continuous 8min block as the hardest (4.5±1.5AU), followed by the 2×4min (3.9±1.4AU) and the 4×2min (3.3±1.4AU), although no difference in mean HR or physical measures via GPS analysis between SSGs was evident. From the technical perspective, only goals scored reached significance, with post hoc analysis identifying the number of goals scored were significantly higher during the 4×2min and 2×4min SSGs compared to 8min continuous block. These results show that subjective ratings of exertion differed between conditions, but only minor technical manipulations were observed by adjusting work to rest ratios, with no significant effect on physical performance.


#2 Soccer and bone development.
Reference: Osteoporos Int. 2016 Apr 14. [Epub ahead of print]
Authors: Mautalen CA

#3 Social Hostility in Soccer and Beyond.
Reference: PLoS One. 2016 Apr 14;11(4):e0153577. doi: 10.1371/journal.pone.0153577. eCollection 2016.
Authors: Van Doesum NJ, Van Prooijen JW, Verburgh L, Van Lange PA
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Summary: Social hostility is seldom expressed overtly. More often than not, individuals try to get their hostile message across without risking violent altercations. However, subtle and relatively covert hostility is not easy to research. We suggest a novel way with the SoMi paradigm, a social decision making task that offers participants the opportunity to be socially mindful or socially hostile by leaving or limiting choice to others. Sampling a general population we find that, relative to friends and strangers, foes are indeed met with greater social hostility (Study 1). Focusing on the highly competitive environment of youth soccer, we find that rival team members elicit social hostility, whereas teammates elicit social mindfulness (Study 2). We conclude that social mindfulness and social hostility play a subtle role in the dynamics of interpersonal and/or intergroup relationships, in which leaving or limiting choice is one of the subtle ways to express benevolent versus hostile intentions; the SoMi paradigm may thus be helpful in identifying which way the ball rolls.

#4 Consistency Of Field-Based Measures Of Neuromuscular Control Using Force Plate Diagnostics In Elite Male Youth Soccer Players
Reference: J Strength Cond Res. 2016 Apr 6. [Epub ahead of print]
Authors: Read P, Oliver JL, De Ste Croix MB, Myer GD, Lloyd RS.
Summary: Deficits in neuromuscular control during movement patterns such as landing are suggested pathomechanics that underlie sport-related injury. A common mode of assessment is measurement of landing forces during jumping tasks; however, these measures have been used less frequently in male youth soccer players and reliability data is sparse. The aim of this study was to examine the reliability of a field-based neuromuscular control screening battery using force plate diagnostics in this cohort. Twenty six pre-peak height velocity (PHV) and twenty five post-PHV elite male youth soccer players completed a drop vertical jump (DVJ), single leg 75% horizontal hop and stick (75%HOP) and single leg countermovement jump (SLCMJ). Measures of peak landing vertical ground reaction force (pVGRF), time to stabilisation (TTS), time to pVGRF, and pVGRF asymmetry were recorded. A test, re-test design was used and reliability statistics included: change in mean, intraclass correlation coefficient (ICC) and coefficient of variation (CV). No significant differences in mean score were reported for any of the assessed variables between test sessions. In both groups, pVGRF and asymmetry during the 75%HOP and SLCMJ demonstrated largely acceptable reliability (CV ≤ 10%). Greater variability was evident in DVJ pVGRF and all other assessed variables, across the three protocols (CV range = 13.8 - 49.7%). ICC values ranged from small to large and were generally higher in the post-PHV players. The results of this study suggest that pVGRF and asymmetry can be reliably assessed using a 75%HOP and SLCMJ in this cohort. These measures could be utilized to support a screening battery for elite male youth soccer players and for test re-test comparison.

#5 Thoracolumbar Chance fracture during a professional female soccer game: case report.
Reference: Einstein (Sao Paulo). 2016 Mar;14(1):67-70. doi: 10.1590/S1679-45082016RC3432.  [Article in English, Portuguese]
Authors: Gotfryd AO, Franzin FJ, Hartl R
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Summary: We report a rare case of an unstable flexion-distraction spine fracture with ligament involvement that occurred during a professional female soccer game. There were no neurological déficit. The patient had a painful midline gap which suggested ligamentar injury that was not immediately recognized. Despite that, proper immobilization and referral to hospital for further evaluation avoided additional spinal cord damage. The patient underwent a monosegmental posterior instrumentation spine fusion and after 6 months returned to professional soccer activities. This paper alerts to the possibility of occurrence of severe and unstable spine injuries during soccer practice and the importance of an adequate initial care at the game field in order to avoid iatrogenic neurological injuries.

#6 Evaluation of energy expenditure in forward and backward movements performed by soccer referees.
Reference: Braz J Med Biol Res. 2016;49(5):e5061. doi: 10.1590/1414-431X20155061. Epub 2016 Apr 12.
Authors: Paes MR, Fernandez R
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Summary: The aim of this study was to measure the energy expenditure for locomotor activities usually performed by soccer referees during a match (walking, jogging, and running) under laboratory conditions, and to compare forward with backward movements. The sample was composed by 10 male soccer referees, age 29±7.8 years, body mass 77.5±6.2 kg, stature 1.78±0.07 m and professional experience of 7.33±4.92 years. Referees were evaluated on two separate occasions. On the first day, maximal oxygen uptake (VO2max) was determined by a maximal treadmill test, and on the second day, the oxygen consumption was determined in different speeds of forward and backward movements. The mean VO2max was 41.20±3.60 mL·kg-1·min-1 and the mean heart rate achieved in the last stage of the test was 190.5±7.9 bpm. When results of forward and backward movements were compared at 1.62 m/s (walking speed), we found significant differences in VO2, in metabolic equivalents, and in kcal. However, the same parameters in forward and backward movements at jogging velocities (2.46 m/s) were not significantly different, showing that these motor activities have similar intensity. Backward movements at velocities equivalent to walking and jogging are moderate-intensity activities, with energy expenditure less than 9 kcal. Energy expenditure was overestimated by at least 35% when calculated by mathematical equations. In summary, we observed that backward movements are not high-intensity activities as has been commonly reported, and when calculated using equations available in the literature, energy expenditure was overestimated compared to the values obtained by indirect calorimetry.

#7 Effects of tapering on physical match activities in professional soccer players.
Reference: J Sports Sci. 2016 Apr 11:1-6. [Epub ahead of print]
Authors: Fessi MS, Zarrouk N, Di Salvo V, Filetti C, Barker AR, Moalla W
Summary: This study aimed to examine: (i) the effect of decreasing training load (TL) during taper weeks on physical match activities in professional soccer players, and (ii) to disclose the relationship between weekly TL and physical match activities. Rating of perceived exertion was collected after each training session and match to quantify the TL in 19 professional players over 17 standard and 7 taper weeks during the season. Physical match activities were quantified by a computerised match analysis system and compared between standard training and taper weeks. Compared to standard weeks, the duration and frequency of training sessions during the taper weeks decreased (-21.7% and -18.8%, respectively; P < 0.01) with no change in intensity (-4.8%; P = 0.09). Consequently, the weekly TL decreased during the taper weeks (-25.5%; P < 0.01). Increases in distance covered by intense running (+15.1%; P < 0.05), high-intensity running (HIR) (+15.7%; P < 0.01), number of sprints (+17.8%; P < 0.05) and number of high-speed runs (+15.7%; P < 0.05) were observed during the seven matches played after the taper weeks. High relationships were observed between TL and HIR distance covered, number of HIR and number of sprints (r = -0.53; r = -0.55; r = -0.65, respectively; P < 0.01). Decreasing TL during taper weeks by reducing training duration and frequency but maintaining intensity was associated with an increase in physical activities during matches. However, it needs to be determined whether tapering or other match factors led to the changes in match activity.

#8 Coordination analysis of players' distribution in football using cross-correlation and vector coding techniques.
Reference: J Sports Sci. 2016 Apr 15:1-9. [Epub ahead of print]
Authors: Moura FA, van Emmerik RE, Santana JE, Martins LE, Barros RM, Cunha SA
Summary: The purpose of this study was to investigate the coordination between teams spread during football matches using cross-correlation and vector coding techniques. Using a video-based tracking system, we obtained the trajectories of 257 players during 10 matches. Team spread was calculated as functions of time. For a general coordination description, we calculated the cross-correlation between the signals. Vector coding was used to identify the coordination patterns between teams during offensive sequences that ended in shots on goal or defensive tackles. Cross-correlation showed that opponent teams have a tendency to present in-phase coordination, with a short time lag. During offensive sequences, vector coding results showed that, although in-phase coordination dominated, other patterns were observed. We verified that during the early stages, offensive sequences ending in shots on goal present greater anti-phase and attacking team phase periods, compared to sequences ending in tackles. Results suggest that the attacking team may seek to present a contrary behaviour of its opponent (or may lead the adversary behaviour) in the beginning of the attacking play, regarding to the distribution strategy, to increase the chances of a shot on goal. The techniques allowed detecting the coordination patterns between teams, providing additional information about football dynamics and players' interaction.

#9 Rehabilitation after a grade III latissimus dorsi tear of a soccer player: A case report.
Reference: J Back Musculoskelet Rehabil. 2016 Apr 15. [Epub ahead of print]
Authors: Fysentzou C.
Summary: Latissimus dorsi, grade III tendon tears are an uncommon injury. There are very few cases reported in the literature, but most importantly, no cases could be found that relate to soccer. The purpose of the study was to present a successful, non-operative rehabilitation program for a professional athlete, after a grade III latissimus dorsi tear. A 37 year old healthy, elite professional soccer goalkeeper was injured during a championship game. The athlete fell on his left side with an outstretched and externally rotated upper extremity in order to catch a ball that was going very close to the left pole of his goal-post. After on-field and off-field clinical examinations, the diagnosis was a left latissimus dorsi tendon tear which was later confirmed by MRI as a grade III tear. During the first two weeks, intervention consisted of anti-inflammatory treatment and light therapeutic exercises. As the pain was subsiding and the strength was returning, the treatment shifted to purely strengthening and functional training. Four weeks after the injury, the athlete presented with pain 0/10 in all functional activities and full ROM in both active and passive movements. Before discharge, the athlete underwent a sport specific training program, without any complains, that cleared him to participate in normal training with the rest of the team. Three months after the injury the strength of the player's left shoulder was 5/5 in all movements. The protocol used yielded an accelerated return to sport (soccer) and function compared with other published research after a grade III latissimus dorsi tendon tear. One year later, the goalkeeper was still playing in the same competitive level without any re-injuries or complains, which means that this treatment protocol withstood the test of time.

#10 Improving Sprint Performance in Soccer: Effectiveness of Jump Squat and Olympic Push Press Exercises.
Reference: PLoS One. 2016 Apr 21;11(4):e0153958. doi: 10.1371/journal.pone.0153958. eCollection 2016.
Authors: Loturco I, Pereira LA, Kobal R, Maldonado T, Piazzi AF, Bottino A, Kitamura K, Cal Abad CC, de Arruda M, Nakamura FY
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Summary: Training at the optimum power load (OPL) is an effective way to improve neuromuscular abilities of highly trained athletes. The purpose of this study was to test the effects of training using the jump squat (JS) or Olympic push-press (OPP) exercises at the OPL during a short-term preseason on speed-power related abilities in high-level under-20 soccer players. The players were divided into two training groups: JS group (JSG) and OPP group (OPPG). Both groups undertook 12 power-oriented sessions, using solely JS or OPP exercises. Pre- and post-6 weeks of training, athletes performed squat jump (SJ), countermovement jump (CMJ), sprinting speed (5, 10, 20 and 30 m), change of direction (COD) and speed tests. To calculate the transfer effect coefficient (TEC) between JS and MPP OPP and the speed in 5, 10, 20, and 30 m, the ratio between the result gain (effect size [ES]) in the untrained exercise and result gain in the trained exercise was calculated. Magnitude based inference and ES were used to test the meaningful effects. The TEC between JS and VEL 5, 10, 20, and 30 m ranged from 0.77 to 1.29, while the only TEC which could be calculated between OPP and VEL 5 was rather low (0.2). In addition, the training effects of JS on jumping and speed related abilities were superior (ES ranging from small to large) to those caused by OPP (trivial ES). To conclude, the JS exercise is superior to the OPP for improving speed-power abilities in elite young soccer players.

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