Latest research in football - week 24 - 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 Gender-related cardiac dimension differences between female and male professional soccer players
Reference: J Sports Med Phys Fitness. 2017 Jun 8. doi: 10.23736/S0022-4707.17.07422-9. [Epub ahead of print]
Authors: Sansonio de Morais A, Assuncao Ferreira G, Lima-Silva AE, Gomes Filho A
Summary: The aim of this study was to determine if cardiac hypertrophy differs between professional female and male soccer players. Twenty-two female and 20 male professional soccer players, and their respective non-athlete controls (22 females and 19 males) were submitted to an echocardiogram. Females had a shorter left ventricular intracavitary diameter and wall thicknesses than males in both groups. However, these differences disappeared when cardiac dimensions were expressed relative to body mass area (p > 0.05). Compared to their respective controls, female and male soccer players had a longer (p < 0.05) left ventricular end-systolic diameter (female: 1.87 ± 0.16 vs. 1.77 ± 0.15 cm/m2 and male: 1.83 ± 0.21 vs. 1.73 ± 0.16 cm/m2), left ventricular end-diastolic diameter (female: 2.86 ± 0.25 vs. 2.74 ± 0.22 cm/m2 and male: 2.81 ± 0.26 vs. 2.55 ± 0.66 cm/m2), left ventricular posterior wall thickness (female: 0.44 ± 0.06 vs. 0.39 ± 0.04 cm/m2 and male: 0.43 ± 0.04 vs. 0.39 ± 0.10 cm/m2), left ventricular septal wall thickness (female: 0.47 ± 0.06 vs. 0.41 ± 0.04 cm/m2 and male: 0.45 ± 0.04 vs. 0.40 ± 0.11 cm/m2), and left ventricular mass index (female: 91.8 ± 22.1 vs. 72.3 ± 10.5 g/m2 and male: 121.7 ± 20.3 vs. 99.8 ± 13.8 g/m2 ). Part of the gender differences in cardiac dimensions might be attributed to differences in body dimension. Soccer training increases cardiac dimensions even with BSA correction and females seem to have similar left ventricle remodeling compared to males.

#2 Comparison of the movement patterns between small- and large-side games training and competition in professional soccer players
Reference: J Sports Med Phys Fitness. 2017 Jun 8. doi: 10.23736/S0022-4707.17.07343-1. [Epub ahead of print]
Authors: Gimenez JV, Del-Coso J, Leicht AS, Gomez MA
Summary: The purpose of this investigation was to compare the movement patterns of professional soccer players during a small-sided game (SSG), a large-sided game (LSG) and a competitive friendly match (FM). Fourteen professional players participated in three training routines with a similar relative pitch area per player. The SSG and LSG consisted of 8 repetitions of 4-min game play, interspersed by 2-min of active recovery, and their data were compared to the first 32 minutes of a FM. All movement patterns from walking to sprint running were recorded using 10Hz GPS devices while player perception of exertion was recorded via visual analogue scale, post-trial. Total running distance (3852±405 vs. 3359±429 and 3088 ± 414 m), running distance at 5-6.9 m/s (222±98 vs. 75±53 and 49±35 m) and maximal running speed (7.0±0.7 vs. 6.1±0.4 and 6.0±0.7 m/s) were significantly greater during FM than for SSG and LSG. However, the number of accelerations (462±16 vs. 458±12 vs. 422±15) and decelerations (733±31 vs. 692 ±24 vs. 609±27), and the rating of perceived exertion (8±1 vs. 7±1 vs. 5±1) were significantly greater during SSG compared to LSG and FM. Although smaller game-based training routines do not replicate exactly the movement patterns of a competitive match, they can increase the execution of short-term and high-intensity movements for specialised training in professional soccer players.

#3 High-speed running and sprinting as an injury risk factor in soccer: Can well-developed physical qualities reduce the risk?
Reference: J Sci Med Sport. 2017 May 25. pii: S1440-2440(17)30442-5. doi: 10.1016/j.jsams.2017.05.016. [Epub ahead of print]
Authors: Malone S, Owen A, Mendes B2, Hughes B, Collins K, Gabbett TJ
Summary: This study investigated the association between high-speed running (HSR) and sprint running (SR) and injuries within elite soccer players. The impact of intermittent aerobic fitness as measured by the end speed of the 30-15 intermittent fitness test (30-15VIFT) and high chronic workloads (average 21-day) as potential mediators of injury risk were also investigated. 37 elite soccer players from one elite squad were involved in a one-season study. Training and game workloads (session-RPE×duration) were recorded in conjunction with external training loads (using global positioning system technology) to measure the HSR (>14.4kmh-1) and SR (>19.8kmh-1) distance covered across weekly periods during the season. Lower limb injuries were also recorded. Training load and GPS data were modelled against injury data using logistic regression. Odds ratios (OR) were calculated with 90% confidence intervals based on 21-day chronic training load status (sRPE), aerobic fitness, HSR and SR distance with these reported against a reference group. Players who completed moderate HSR (701-750-m: OR: 0.12, 90%CI: 0.08-0.94) and SR distances (201-350-m: OR: 0.54, 90%CI: 0.41-0.85) were at reduced injury risk compared to low HSR (≤674-m) and SR (≤165-m) reference groups. Injury risk was higher for players who experienced large weekly changes in HSR (351-455-m; OR: 3.02; 90%CI: 2.03-5.18) and SR distances (between 75-105-m; OR: 6.12, 90%CI: 4.66-8.29). Players who exerted higher chronic training loads (≥2584 AU) were at significantly reduced risk of injury when they covered 1-weekly HSR distances of 701-750m compared to the reference group of <674m (OR=0.65, 90% CI 0.27-0.89). When intermittent aerobic fitness was considered based on 30-15VIFT performance, players with poor aerobic fitness had a greater risk of injury than players with better-developed aerobic fitness. Exposing players to large and rapid increases in HSR and SR distances increased the odds of injury. However, higher chronic training loads (≥2584 AU) and better intermittent aerobic fitness off-set lower limb injury risk associated with these running distances in elite soccer players.

#4 The match-to-match variation of match-running in elite female soccer
Reference: J Sci Med Sport. 2017 May 25. pii: S1440-2440(17)30435-8. doi: 10.1016/j.jsams.2017.05.009. [Epub ahead of print]
Authors: Trewin J, Meylan C, Varley MC, Cronin J
Summary: The purpose of this study was to examine the match-to-match variation of match-running in elite female soccer players utilising GPS, using full-match and rolling period analyses. Elite female soccer players (n=45) from the same national team were observed during 55 international fixtures across 5 years (2012-2016). Data was analysed using a custom built MS Excel spreadsheet as full-matches and using a rolling 5-min analysis period, for all players who played 90-min matches (files=172). Variation was examined using co-efficient of variation and 90% confidence limits, calculated following log transformation. Total distance per minute exhibited the smallest variation when both the full-match and peak 5-min running periods were examined (CV=6.8-7.2%). Sprint-efforts were the most variable during a full-match (CV=53%), whilst high-speed running per minute exhibited the greatest variation in the post-peak 5-min period (CV=143%). Peak running periods were observed as slightly more variable than full-match analyses, with the post-peak period very-highly variable. Variability of accelerations (CV=17%) and Player Load (CV=14%) was lower than that of high-speed actions. Positional differences were also present, with centre backs exhibiting the greatest variation in high-speed movements (CV=41-65%). Practitioners and researchers should account for within player variability when examining match performances. Identification of peak running periods should be used to assist worst case scenarios. Whilst micro-sensor technology should be further examined as to its viable use within match-analyses.

#5 Changes in sprint-related outcomes during a period of systematic training in a girls' soccer academy
Reference: J Strength Cond Res. 2017 Jun 8. doi: 10.1519/JSC.0000000000002055. [Epub ahead of print]
Authors: Wright MD, Atkinson G
Summary: Longitudinal data tracking performance indicators collected during structured training are lacking in young female soccer players. Therefore, changes in 5-m acceleration, 20-m speed, change-of-direction speed and repeated-sprint ability were quantified during a three-year period in an FA Centre of Excellence. Fourteen players (mean age = 12.1 years, SD = ±0.9) were recruited and their best performance scores from pre-season and in-season testing were averaged. Players were typically exposed to soccer (2 x 90 min per week) and strength and conditioning training (1 x 70 min per week) and played 20 soccer matches (50-80 min) during 35-week seasons. Mean (±90%CL) overall improvements over the three years were 5.9% (1.3) (most likely large) for speed, 4.0% (1.0) (most likely large) for repeated-sprint ability, 8.8% (1.1) for acceleration and 8.3% (1.4) for change-of-direction speed (both most likely very large). Improvements between years one and two ranged from most likely moderate to very large. Further small improvements in change-of-direction speed and 20-m speed (both likely) were observed between years two and three. Individual differences in response were apparent only for change-of-direction speed, which were moderate and small between years two and three. Most likely very large to near perfect within-player correlations were observed between maturation and sprint measures. These data from a single-arm longitudinal study indicate that systematic exposure to training, which includes one dedicated strength and conditioning session each week, is associated with improvements in sprint related physical qualities in girls.

#6 Distinguishing Playing Status Through a Functionally Relevant Performance Measure in Female Division I Collegiate Soccer Athletes
Reference: J Strength Cond Res. 2017 Jun 8. doi: 10.1519/JSC.0000000000002053. [Epub ahead of print]
Authors: Magrini MA, Colquhoun RJ, Sellers JH, Conchola EC, Hester GM, Thiele RM, Pope ZK, Smith DB
Summary: Although soccer is predominately an endurance sport, high velocity movements may be an important indicator of athletic success. The purpose of this investigation was to establish whether squat jumps (SJ) can differentiate starters from non-starters with a female collegiate division I soccer team. Eighteen female division I soccer athletes were separated into two groups: 9 starters (age: 19.5 ± 1.0; mass = 64.8 ± 11.5 kg; height = 167.5 ± 7.7 cm; games started = 18.2 ± 4.7; minutes played = 1633.8 ± 478.2 min) and 9 non-starters (age: 19.4 ± 1.4 years; mass = 63.3 ± 4.2 kg; height = 164.7 ± 6.8 cm; games started 0.7 ± 1.3; minutes played 158.2 ± 269.3). Each athlete performed 3 maximal SJs at a starting knee angle of 110° without arm swing. Each participant's SJ height, mean power (MP), peak power (PP), mean velocity (MV), and peak velocity (PV) were measured during each attempt by a linear position transducer (LPT). No statistically significant differences (p ≥ 0.05) in MP and PP between the starters and non-starters were observed. However, starters performed significantly better than non-starters in SJ height (p = 0.002), MV (p = 0.025), and PV (p = 0.015). Additionally, SJ height was strongly correlated with MV (r = 0.628) and PV (r = 0.647). These findings suggest that SJ height, MV and PV, may be important variables for discriminating differences between starters and non-starters in division I female soccer athletes and a strong indicator of explosive performance.

#7 Cameroonian professional soccer players and risk of atherosclerosis
Reference: BMC Res Notes. 2017 Jun 2;10(1):186. doi: 10.1186/s13104-017-2508-x.
Authors: Nansseu JR, Ama Moor VJ, Takam RDM, Zing-Awona B, Azabji-Kenfack M, Tankeu F, Tchoula CM, Moukette BM, Ngogang JY
Summary: Elevated titers of antibodies against oxidized low-density lipoproteins-cholesterol (ox-LDL-Ab) have been reported among professional athletes, paradoxically reflecting an increased risk of developing atherogenic and/or cardiovascular events. This study aimed to determine titers of ox-LDL-Ab in a group of Cameroonian professional soccer players, and evaluate their evolution during part of a competition season as well as the plasmatic antioxidant status to find out if this latter correlates with ox-LDL-Ab . We conducted a descriptive cohort study in 2012 including 18 healthy male soccer players. Three samplings were performed in March (T1), May (T2), and July 2012 (T3) to assess the lipid profile, titers of ox-LDL-Ab, and plasmatic concentrations of four antioxidants: the ferric reducing antioxidant power (FRAP), reduced glutathione (GSH), superoxide dismutase (SOD), and uric acid. Ages ranged from 16 to 28 years with a median (interquartile range) of 19.5 (19-23) years. Total cholesterol, high-density lipoproteins-cholesterol (HDL-C), low-density lipoproteins-cholesterol (LDL-C) and triglycerides varied within normal ranges throughout the three samplings. While total cholesterol and LDL-C titers increased significantly (p = 0.003 and p = 0.006, respectively), triglycerides and HDL-C values varied non-significantly throughout the measurements (p = 0.061 and p = 0.192, respectively). The median ox-LDL-Ab titers were respectively: 653.3 (468.2-838.8) mIU/ml at T1, 777.7 (553.7-1150.7) mIU/ml at T2, and 1037.7 (901.7-1481.5) mIU/ml at T3. Overall, ox-LDL-Ab titers increased significantly from T1 to T3 (p = 0.006). Concomitantly, uric acid and FRAP concentrations decreased significantly (p = 0.001 and p = 0.003, respectively); on the contrary, GSH and SOD values increased, but insignificantly (p = 0.115 and p = 0.110, respectively). There was a positive and significant correlation between ox-LDL-Ab and HDL-C (ρ = 0.519, p = 0.027), and between ox-LDL-Ab and SOD (ρ = 0.504, p = 0.033) at T2. Ox-LDL-Ab values were expected to increase with each new visit (β = 201.1; p = 0.041) and each IU/ml of SOD titers (β = 23.6; p = 0.019). These Cameroonian professional soccer players exhibited high levels of ox-LDL-Ab reflecting elevated levels of oxidatively-modified LDL-C particles with an increment over time, this being insufficiently counterbalanced by the antioxidant defense mechanisms. As a consequence, they may be at increased atherogenic and cardiovascular risks.

#8 How Do Soccer Players Adjust Their Activity in Team Coordination? An Enactive Phenomenological Analysis
Reference: Front Psychol. 2017 May 26;8:854. doi: 10.3389/fpsyg.2017.00854. eCollection 2017.
Authors: Gesbert V, Durny A, Hauw D
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Summary: This study examined how individual team members adjust their activity to the needs for collective behavior. To do so, we used an enactive phenomenological approach and explored how soccer players' lived experiences were linked to the active regulation of team coordination during eight offensive transition situations. These situations were defined by the shift from defensive to offensive play following a change in ball possession. We collected phenomenological data, which were processed in four steps. First, we reconstructed the diachronic and synchronic dynamics of the players' lived experiences across these situations in order to identify the units of their activity. Second, we connected each player's units of activity side-by-side in chronological order in order to identify the collective units. Each connection was viewed as a collective regulation mode corresponding to which and how individual units were linked at a given moment. Third, we clustered each collective unit using the related objectives within three modes of regulation-local (L), global (G), and mixed (M). Fourth, we compared the occurrences of these modes in relation to the observable key moments in the situations in order to identify typical patterns. The results indicated four patterns of collective regulation modes. Two distinct patterns were identified without ball possession: reorganize the play formation (G and M) and adapt to the actions of putting pressure on the ball carrier (M). Once the ball was recovered, two additional patterns emerged: be available to get the ball out of the recovery zone (L) and shoot for the goal (L and M). These results suggest that team coordination is a fluctuating phenomenon that can be described through the more or less predictable chaining between these patterns. They also highlight that team coordination is supported by several modes of regulation, including our proposal of a new mode of interpersonal regulation. We conclude that future research should investigate the effect of training on the enaction of this mode in competition.

#9 Emergency response facilities including primary and secondary prevention strategies across 79 professional football clubs in England
Reference: Br J Sports Med. 2017 Jun 14. pii: bjsports-2016-097440. doi: 10.1136/bjsports-2016-097440. [Epub ahead of print]
Authors: Malhotra A, Dhutia H, Gati S, Yeo TJ, Finnochiaro G, Keteepe-Arachi T, Richards T, Walker M, Birt R, Stuckey D, Robinson L, Tome M, Beasley I, Papadakis M, Sharma S
Summary: The aim was to assess the emergency response planning and prevention strategies for sudden cardiac arrest (SCA) across a wide range of professional football clubs in England. A written survey was sent to all professional clubs in the English football league, namely the Premiership, Championship, League 1 and League 2. Outcomes included: (1) number of clubs performing cardiac screening and frequency of screening; (2) emergency planning and documentation; (3) automated external defibrillator (AED) training and availability; and (4) provision of emergency services at sporting venues. 79 clubs (86%) responded to the survey. 100% clubs participated in cardiac screening. All clubs had AEDs available on match days and during training sessions. 100% Premiership clubs provided AED training to designated staff. In contrast, 30% of lower division clubs with AEDs available did not provide formal training. Most clubs (n=66; 83%) reported the existence of an emergency action plan for SCA but formal documentation was variable. All clubs in the Premiership and League 1 provided an ambulance equipped for medical emergencies on match days compared with 75% of clubs in the Championship and 66% in League 2. The majority of football clubs in England have satisfactory prevention strategies and emergency response planning in line with European recommendations. Additional improvements such as increasing awareness of European guidelines for emergency planning, AED training and mentorship with financial support to lower division clubs are necessary to further enhance cardiovascular safety of athletes and spectators and close the gap between the highest and lower divisions.

#10 Validity of heart rate-based indices to measure training load and intensity in elite football players
Reference: J Strength Cond Res. 2017 Jun 12. doi: 10.1519/JSC.0000000000002057. [Epub ahead of print]
Authors: Silva P, Santos ED, Grishin M, Rocha JM
Summary: This study aimed to identify the most sensible heart rate-based indices to physical measures of training load and intensity. Twenty professional football players competing in the Russian league and in the UEFA Champions League were monitored during 15 training sessions (270 individual records) using GPS devices (10 Hz) and heart rate telemetry. Expert knowledge and a collinearity r < .5 were used initially to select the external physical markers for the final analysis. A multivariate-adjusted within-subjects model was employed to quantify the correlations between heart rate indices with various measures of training intensity and load. The number of accelerations > 2.5 m/s and the number of high intensity bursts remained in the final multivariate model for training load. The adjusted correlations with Banister's TRIMP were r = .49 and r = .3, respectively. For training intensity, the same previous variables expressed as per minute plus the volume of high speed running per minute remained in the final model. The adjusted correlations with the percentage of time spent above 80% of individual maximum heart rate (tHR80%) were, in the same order, r = .3, r = .22 and r = .18. The results of this study demonstrate the validity of TRIMP and tHR80% as measures of training load and intensity, respectively, and identified accelerations and high intensity repeated efforts (high intensity bursts) as being moderately predictive of heart rate responses.

#11 Federation Internationale de Football Association (FIFA) 2014 World Cup Impact on Hospital-Treated Suicide Attempt (Overdose) in Tehran
Reference: Suicide Life Threat Behav. 2017 Jun 13. doi: 10.1111/sltb.12359. [Epub ahead of print]
Authors: Hassanian-Moghaddam H, Ghorbani F, Rahimi A, Farahani TF, Sani PSV, Lewin TJ, Carter GL
Summary: Social influences on suicidal behaviors may be important but are less frequently studied than the influences of mental illness, physical illness, and demographic variables. Major international sporting events may have an impact on suicidal behaviors at the national and local level, an effect possibly mediated by gender and age. We examined the association of hospital-treated deliberate self-poisoning episodes (by gender and by age) in Tehran: before, during, and after the 2014 FIFA World Cup held in Brazil, in which the Iranian national team participated and was eliminated after the pool games. We used a time series analysis within an autoregressive integrated moving average model and found a significant increase in hospital-treated deliberate self-poisoning during the 4-week period of the 2014 FIFA World Cup in Brazil in females but a nonsignificant increase in males. A significant increase was also seen in the youngest age group (12-20 years), but not in the two older age groups. If the effects of nonsuccess at major international sporting events could be shown to have a potential harmful effect on aggregate local or national rates of suicidal behaviors, the possibility of preventative interventions and preemptive additional service provision could be planned in advance of these events.

American Football
#1 A Season of American Football is not Associated with Changes in Plasma Tau
Reference: J Neurotrauma. 2017 Jun 14. doi: 10.1089/neu.2017.5064. [Epub ahead of print]
Authors: Oliver J, Jones M, Anzalone A, Kirk M, Gable D, Repshas J, Johnson T, Hogland K, Blennow K, Zetterberg H
Summary: American football athletes are routinely exposed to sub-concussive impacts over the course of the season. This study sought to examine the effect of a season of American football on plasma tau, a potential marker of axonal damage. Nineteen (n =19) National Collegiate Association (NCAA) American football athletes underwent serial blood sampling over the course of the 2014-2015 season at those times in which the number and magnitude of head impacts likely changed. Non-contact, sport-control, NCAA men's swim athletes (n=19) provided a single plasma sample for comparison. No significant differences were observed between control swim athletes and American football athletes following a period of non-contact (p = 0.569) or a period of contact (p = 0.076). Those American football athletes categorized as starters (n=11) had higher tau concentrations than non-starters (n=8) following a period of non-contact (p = 0.039) and contact (p = 0.036), but not higher than swimmers (p = 1.000 and p = 1.000, respectively). No difference was noted over the course of the season in American football athletes irrespective of starter status. Despite routine head impacts, common to the sport of American football, no changes were observed over the course of the season in American football athletes, irrespective of starter status. Further, no difference was observed between American football athletes and non-contact control swim athletes following a period of non-contact or contact. These data suggest that plasma tau is not sensitive enough to detect damage associated with repetitive sub-concussive impacts sustained by collegiate level American football athletes.

Australian Football
#1 Identifying high risk loading conditions for in-season injury in elite Australian football players
Reference: J Sci Med Sport. 2017 May 25. pii: S1440-2440(17)30438-3. doi: 10.1016/j.jsams.2017.05.012. [Epub ahead of print]
Authors: Stares J, Dawson B, Peeling P, Heasman J, Rogalski B, Drew M, Colby M, Dupont G, Lester L
Summary: The purpose was to examine different timeframes for calculating acute to chronic workload ratio (ACWR) and whether this variable is associated with intrinsic injury risk in elite Australian football players. Internal (session rating of perceived exertion: sRPE) and external (GPS distance and sprint distance) workload and injury data were collected from 70 players from one AFL club over 4 seasons. Various acute (1-2 weeks) and chronic (3-8 weeks) timeframes were used to calculate ACWRs: these and chronic load categories were then analysed to determine the injury risk in the subsequent month. Poisson regression with robust errors within a generalised estimating equation were utilised to determine incidence rate ratios (IRR). Altering acute and/or chronic timeframes did not improve the ability to detect high injury risk conditions above the commonly used 1:4 week ACWR. Twenty-seven ACWR/chronic load combinations were found to be "high risk conditions" (IRR>1, p<0.05) for injury within 7 days. Most (93%) of these conditions occurred when chronic load was low or very low and ACWR was either low (<0.6) or high (>1.5). Once a high injury risk condition was entered, the elevated risk persisted for up to 28 days. Injury risk was greatest when chronic load was low and ACWR was either low or high. This heightened risk remained for up to 4 weeks. There was no improvement in the ability to identify high injury risk situations by altering acute or chronic time periods from 1:4 weeks.

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