Latest research in football - week 49 - 2017

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 Injury and illness epidemiology in soccer - effects of global geographical differences - a call for standardized and consistent research studies
Reference: Biol Sport. 2017 Sep;34(3):249-254. doi: 10.5114/biolsport.2017.66002. Epub 2017 Feb 19.
Authors: Eirale C, Gillogly S, Singh G, Chamari K
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Summary: Soccer is the most popular sport in the world. While injuries and illnesses can affect the players' health and performance, they can also have a major economic impact on teams. Moreover, several studies have shown the favourable association between higher player availability and team success. Therefore, injury prevention could directly impact clubs' financial balance and teams' performance via increased player availability. To be able to develop effective methods of injury prevention, it is vital to first determine the scope and the degree of the problem: the mechanisms and types of injuries, their frequency and severity, etc. According to the most widely known prevention model, systematic injury surveillance is the first and most fundamental step towards injury prevention. Since epidemiological studies have shown that injuries and illnesses in soccer players differ from region to region, it is important to establish a specific injuries and illness database in order to guide specific preventive actions. Since Asia is the largest continent, with the highest number of soccer players, and in the light of the long-term research on injuries performed in UEFA clubs, the authors of the present article present the AFC surveillance. Some methodological issues related to this prospective design study are discussed. The definition of injury and illness and the methods to track players' exposure are described along with the potential challenges related to such a vast scale study. This article is also a call for action to have consistent and standardized epidemiological studies on soccer injuries and illnesses, with the aim to improve their prevention.

#2 Blood pressure, heart rate and perceived enjoyment after small-sided soccer games and repeated sprint in untrained healthy adolescents
Reference: Biol Sport. 2017 Sep;34(3):219-225. doi: 10.5114/biolsport.2017.65997. Epub 2017 Feb 19.
Authors: Hammami A, Kasmi S, Farinatti P, Fgiri T, Chamari K, Bouhlel E
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Summary: The purpose of this study was to examine systolic (SBP) and diastolic blood pressure (DBP), heart rate (HR), rating of perceived exertion (RPE) and perceived enjoyment responses to a repeated-sprint training session (RST) compared to a small-sided soccer game session (SSG) in untrained adolescents. Twelve healthy post-pubertal adolescent males (age 15.8±0.6 years, body mass 59.1±3.7 kg, height 1.7±0.1m) performed RST and SSG sessions in a randomized and counterbalanced order. Blood pressure and HR were measured at rest and at 10, 20 and 30 minutes after interventions, and RPE and enjoyment were assessed. RST and SSG elicited similar exercise HR (74.0% vs. 73.7% of HR peak during RST and SSG respectively, P>0.05). There was no significant change in SBP or DBP after the 2 interventions (all P>0.05, ES<0.5) with a trend to a decrease in SBP after SSG at 30 min after intervention (moderate effect, ES=0.6). Pearson's correlation analysis revealed a significant and large correlation between baseline BP values and magnitude of decline after both RST and SSG. Heart rate during recovery was higher compared with baseline at all times after both sessions (all P<0.05), with HR values significantly lower after SSG versus RST at 30 min after interventions (82.3±3.2 versus 92.4±3.2 beats/min, respectively, P=0.04). RPE was significantly lower (P=0.02, ES=1.1) after SSG than after RST, without significant differences in enjoyment. In conclusion, repeated sprint and small-sided games elicited similar exercise intensity without a significant difference in perceived enjoyment. Post-exercise hypotension after the two forms of training may depend on resting BP of subjects.

#3 Immediate Effects of Ankle Balance Taping with Kinesiology Tape for Amateur Soccer Players with Lateral Ankle Sprain: A Randomized Cross-Over Design
Reference: Med Sci Monit. 2017 Nov 21;23:5534-5541.
Authors: Kim MK, Shin YJ
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Summary: The objective of this study was to investigate the immediate effect on gait function when ankle balance taping is applied to amateur soccer players with lateral ankle sprain. A cross-over randomized design was used. Twenty-two soccer players with an ankle sprain underwent 3 interventions in a random order. Subjects were randomly assigned to ankle balance taping, placebo taping, and no taping groups. The assessment was performed using the GAITRite portable walkway system, which records the location and timing of each footfall during ambulation. Significant differences were found in the velocity, step length, stride length, and H-H base support among the 3 different taping methods (p<0.05). The ankle balance taping group showed significantly greater velocity, step length, and stride length in comparison to the placebo and no taping group. The ankle balance taping group showed a statistically significant decrease (p<0.05) in the H-H base support compared to the placebo and no taping groups, and the placebo group showed significantly greater velocity in comparison to the no taping group (p<0.05). We conclude that ankle balance taping that uses kinesiology tape instantly increased the walking ability of amateur soccer players with lateral ankle sprain. Therefore, ankle balance taping is a useful alternative to prevent and treat ankle sprain of soccer players.

#4 Does Maturity Status Affect The Relationship Between Anaerobic Speed Reserve And Multiple Sprints Sets Performance in Young Soccer Players?
Reference: J Strength Cond Res. 2017 Nov 29. doi: 10.1519/JSC.0000000000002266. [Epub ahead of print]
Authors: Selmi MA, Al-Haddabi B, Yahmed MH, Sassi RH
Summary: The purpose of this study is to examine the relationship between repeated-sprint sets (RSS) performance indices and anaerobic speed reserve (ASR) in young soccer players of different maturity status. One hundred and seventy nine young male soccer players (11.1 to 17.8 years) classified as pre- (n=50), circum- (n=60), or post- (n=69) peak height velocity (PHV) performed multi-stage shuttle run test (MRST) to measure maximal aerobic speed (MAS), 30-m sprint with 10-m splits to estimate maximal anaerobic speed (MAnS), and RSS test. ASR was calculated as the difference between MAS and MAnS. The RSS indices, MAS, MAnS and ASR were significantly different in the three maturity groups (p< 0.001; ES =0.12-0.64). Correlations between RSS performance indices and ASR varied considerably depending on maturity status. Very large correlations between ASR and RSS indices expressed as sum sprint time (SST) and best sprint time (BST) were found for pre- and circum-PHV groups (r=-0.76, -0.79 and r=-0.82, -0.86, respectively). In the post-PHV group, ASR was moderately associated with both SST (r=-0.45) and BST (r=-0.46). To sum up, these results highlighted that the ASR is more related to factors of RSS performance in pre- and circum-PHV male soccer players compared with post-PHV ones. These findings could help coaches and strength and conditioning professionals to better understand how the relationship between ASR and RSS evolve across the maturity and may be considered, therefore, useful in youth soccer selection/training process.

#5 Aerobic Fitness in Top-Class Soccer Referees
Reference: J Strength Cond Res. 2017 Nov 16. doi: 10.1519/JSC.0000000000002264. [Epub ahead of print]
Authors: Castagna C, Bizzini M, Araujo Povoas SC, Schenk K, Busser G, DʼOttavio S
Summary: The aim of this study was to examine the aerobic fitness status of top-class male soccer officials using a cross-sectional design and known population group constructs. Fifty-two field referees (FRs, age 38.4 ± 3.3 years; height 181 ± 5.6 cm; body mass 76.8 ± 6.8 kg; body mass index [BMI] 23.4 ± 1.7 kg·m; body fat 20.4 ± 3.6%; and international refereeing experience 5 ± 3.5 years) and 104 assistant referees (ARs, age 37.8 ± 4.1 years; height 176.9 ± 7.5 cm; body mass 72.1 ± 7.4 kg; BMI 23 ± 1.6 kg·m; body fat 19.2 ± 3.6%; and international refereeing experience 7 ± 3.8 years) from 53 National Football Associations worldwide, and candidates of the preliminary open-list developed by the FIFA Refereeing Department for the 2014 World Cup Final Tournament, were tested for aerobic fitness in laboratory conditions with a progressive speed treadmill test to exhaustion. Large (+8.54%, d = 0.8) and small (+3.1%, d = 0.3) differences in absolute (L·min) and relative (ml·kg·min) V[Combining Dot Above]O2max were found between FR and AR, respectively. Trivial differences (d = 0.07) were shown in running economy (RE) (6 minutes at 8 km·h) between AR and FR. Using the scaling notation (b = 0.64), medium and significant differences were found between match officials for V[Combining Dot Above]O2max and RE (FR > AR; d = 0.6 and 0.67, respectively). Using receiver operating characteristic curve statistics, cutoff values of 3.93 L·min and 50.6 ml·kg·min were detected in absolute and relative V[Combining Dot Above]O2max for the FR and the AR (FR > AR), respectively. The FR showed superior aerobic fitness compared with AR. Training prescription should consider intensities at anaerobic threshold speed (14 km·h, 91% heart rate max) when aerobic fitness development is the aim in elite officials.

#6 Skill not athleticism predicts individual variation in match performance of soccer players
Reference: Proc Biol Sci. 2017 Dec 13;284(1868). pii: 20170953. doi: 10.1098/rspb.2017.0953.
Authors: Wilson RS, David GK, Murphy SC, Angilletta MJ Jr, Niehaus AC, Hunter AH, Smith MD
Summary: Just as evolutionary biologists endeavour to link phenotypes to fitness, sport scientists try to identify traits that determine athlete success. Both disciplines would benefit from collaboration, and to illustrate this, we used an analytical approach common to evolutionary biology to isolate the phenotypes that promote success in soccer, a complex activity of humans played in nearly every modern society. Using path analysis, we quantified the relationships among morphology, balance, skill, athleticism and performance of soccer players. We focused on performance in two complex motor activities: a simple game of soccer tennis (1 on 1), and a standard soccer match (11 on 11). In both contests, players with greater skill and balance were more likely to perform better. However, maximal athletic ability was not associated with success in a game. A social network analysis revealed that skill also predicted movement. The relationships between phenotypes and success during individual and team sports have potential implications for how selection acts on these phenotypes, in humans and other species, and thus should ultimately interest evolutionary biologists. Hence, we propose a field of evolutionary sports science that lies at the nexus of evolutionary biology and sports science. This would allow biologists to take advantage of the staggering quantity of data on performance in sporting events to answer evolutionary questions that are more difficult to answer for other species. In return, sports scientists could benefit from the theoretical framework developed to study natural selection in non-human species.

#7 Effects of lower extremity injuries on aerobic exercise capacity, anaerobic power, and knee isokinetic muscular function in high school soccer players
Reference: J Phys Ther Sci. 2017 Oct;29(10):1715-1719. doi: 10.1589/jpts.29.1715. Epub 2017 Oct 21.
Authors: Ko KJ, Ha GC, Kim DW, Kang SJ
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Summary: The study investigated the effects of lower extremity injuries on aerobic exercise capacity, anaerobic power, and knee isokinetic muscular function in high school soccer players. The study assessed U High School soccer players (n=40) in S area, South Korea, divided into 2 groups: a lower extremity injury group (n=16) comprising those with knee and ankle injuries and a control group (n=24) without injury. Aerobic exercise capacity, anaerobic power, and knee isokinetic muscular function were compared and analyzed. Regarding the aerobic exercise capacity test, significant differences were observed in maximal oxygen uptake and anaerobic threshold between both groups. For the anaerobic power test, no significant difference was observed in peak power and average power between the groups; however, a significant difference in fatigue index was noted. Regarding the knee isokinetic muscular test, no significant difference was noted in knee flexion, extension, and flexion/extension ratio between both groups. Lower extremity injury was associated with reduced aerobic exercise capacity and a higher fatigue index with respect to anaerobic exercise capacity. Therefore, it seems necessary to establish post-injury training programs that improve aerobic and anaerobic exercise capacity for soccer players who experience lower extremity injury.

#8 Seasonal Training Load and Wellness Monitoring in a Professional Soccer Goalkeeper
Reference: Int J Sports Physiol Perform. 2017 Nov 28:1-13. doi: 10.1123/ijspp.2017-0472. [Epub ahead of print]
Authors: Malone JJ, Jaspers A, Helsen WF, Merks B, Frencken WG, Brink MS
Summary: The purpose of this investigation was to: (a) quantify the training load practices of a professional soccer GK, and (b) investigate the relationship between the training load observed and the subsequent self-reported wellness response. One male goalkeeper playing for a team in the top league of the Netherlands participated in this case study. Training load data were collected across a full season using a global positioning system (GPS) device and session rating of perceived exertion (session-RPE). Data was assessed in relation to the number of days to a match (MD- and MD+). In addition, self-reported wellness was assessed using a questionnaire. Duration, total distance, average speed, PlayerLoadTM and load (derived from session-RPE) were highest on MD. The lowest values for duration, total distance and PlayerLoadTM were observed on MD-1 and MD+1. Total wellness scores were highest on MD and MD-3 and were lowest on MD+1 and MD-4. Small to moderate correlations between training load measures (duration, total distance covered, high deceleration efforts and load) and the self-reported wellness scores were found. This exploratory case-study provides novel data about the physical load undertaken by a goalkeeper during one competitive season. The data suggest there are small to moderate relationships between training load indicators and self-reported wellness. This weak relation indicates that the association is not meaningful. This may be due to the lack of position-specific training load parameters we can currently measure in the applied context.

#9 Irisin levels correlate with bone mineral density in soccer players
Reference: J Biol Regul Homeost Agents. 2017 Oct-Dec,;31(4 suppl 1):21-28.
Authors: Colaianni G, Notarnicola A, Sanesi L, Brunetti G, Lippo L, Celi M, Moretti L, Pesce V, Vicenti G, Moretti B, Colucci S, Grano M
Summary: Irisin, a novel myokine produced in response to physical exercise by skeletal muscle, displays anabolic effect on bone and can improve the bone-loss-induced osteoporosis in hind limb suspended mice. It is well known that muscles positively impact the skeleton and in different sports, including soccer, total body bone mineral density (TB-BMD) is elevated. Therefore, we have investigated the correlation between irisin serum levels and total and bone sub-regional BMD in soccer players never studied before. In this study, Caucasian football players of Bari team have been enrolled. Their sera were collected to measure by ELISA kit irisin levels and by dual-energy X-ray absorptiometry (DEXA) analysis measurements of BMD (g • cm−2) in the whole body and different bone sub-regions (head, arms, legs, ribs, dorsal vertebrae, lumbar vertebrae, pelvis) were performed. The BMC (g) was measured in the whole body. By means of Pearson’s (R) and Cohen’s (d) coefficient we investigated the linear association between the irisin serum levels and BMD. In soccer players, we have found a positive correlation between irisin and TB-BMD as demonstrated by the values of Pearson and Cohen’s (d) coefficient. Furthermore, linear association was detected between irisin and BMD of different bone-site such as right arm, lumbar vertebrae and head. A positive trend was also observed analyzing circulating levels of irisin and bone mineral content as well as total Z-score. In conclusion, we have demonstrated the correlation between irisin and total or bone sub-regional BMD in soccer players for the first time, an additional systemic effect of the “sport-hormone” defined myokine.

#10 Prognostic factors for specific lower extremity and spinal musculoskeletal injuries identified through medical screening and training load monitoring in professional football (soccer): a systematic review
Reference: BMJ Open Sport Exerc Med. 2017 Sep 21;3(1):e000263. doi: 10.1136/bmjsem-2017-000263. eCollection 2017.
Authors: Hughes T, Sergeant JC, Parkes MJ, Callaghan MJ
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Summary: Medical screening and load monitoring procedures are commonly used in professional football to assess factors perceived to be associated with injury. The aim was to identify prognostic factors (PFs) and models for lower extremity and spinal musculoskeletal injuries in professional/elite football players from medical screening and training load monitoring processes. The MEDLINE, AMED, EMBASE, CINAHL Plus, SPORTDiscus and PubMed electronic bibliographic databases were searched (from inception to January 2017). Prospective and retrospective cohort studies of lower extremity and spinal musculoskeletal injury incidence in professional/elite football players aged between 16 and 40 years were included. The Quality in Prognostic Studies appraisal tool and the modified Grading of Recommendations Assessment, Development and Evaluation synthesis approach was used to assess the quality of the evidence. Fourteen studies were included. 16 specific lower extremity injury outcomes were identified. No spinal injury outcomes were identified. Meta-analysis was not possible due to heterogeneity and study quality. All evidence related to PFs and specific lower extremity injury outcomes was of very low to low quality. On the few occasions where multiple studies could be used to compare PFs and outcomes, only two factors demonstrated consensus. A history of previous hamstring injuries (HSI) and increasing age may be prognostic for future HSI in male players. The assumed ability of medical screening tests to predict specific musculoskeletal injuries is not supported by the current evidence. Screening procedures should currently be considered as benchmarks of function or performance only. The prognostic value of load monitoring modalities is unknown.

#11 Effects of Plyometric and Directional Training on Speed and Jump Performance in Elite Youth Soccer Players
Reference: J Strength Cond Res. 2017 Nov 22. doi: 10.1519/JSC.0000000000002371. [Epub ahead of print]
Authors: Beato M, Bianchi M, Coratella G, Merlini M, Drust B
Summary: Soccer players perform approximately 1350 activities (every 4-6 s), such as accelerations/decelerations, and changes of direction (COD) during matches. It is well established that COD and plyometric training have a positive impact on fitness parameters in football players. This study analyzed the effect of a complex COD and plyometric protocol (CODJ-G) compared to an isolated COD protocol (COD-G) training on elite football players.A randomized pre-post parallel group trial was used in this study. Twenty-one youth players were enrolled in this study (mean ± SDs; age 17 ± 0.8 years, weight 70.1 ± 6.4 kg, height 177.4 ± 6.2 cm). Players were randomized into two different groups: CODJ-G (n = 11) and COD-G (n = 10), training frequency of 2 times a week over 6 weeks. Sprint 10, 30 and 40 m, long jump, triple hop jump, as well as 505 COD test were considered. Exercise-induced within-group changes in performance for both CODJ-G and COD-G: long jump (effect size (ES) = 0.32 and ES = 0.26, respectively), sprint 10 m (ES = -0.51 and ES = -0.22 respectively), after 6 weeks of training. Moreover, CODJ-G reported substantially better results (between-group changes) in long jump test (ES = 0.32). In conclusion, this study showed that short-term protocols (CODJ-G and COD-G) are important and able to give meaningful improvements on power and speed parameters in a specific soccer population. CODJ-G showed a larger effect in sprint and jump parameters compared to COD-G after the training protocol. This study offers important implications for designing COD and jumps training in elite soccer.

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