Latest research in football - week 42 - 2015

#1 What is the extent of exposure to periods of match congestion in professional soccer players?
Reference: J Sports Sci. 2015 Oct 13:1-9. [Epub ahead of print]
Authors: Carling C, McCall A, Le Gall F, Dupont G
Summary: This study investigated exposure to periods of match congestion in regular starter players in a professional soccer team across 4 competitive seasons (2009-2013). Players were divided into 2 groups: club players (club match exposure only, n = 41) and national team players (club and national team exposure, n = 22). The frequency of congested periods that players were potentially exposed to per season was initially determined: 2-match cycles - potential exposure to 2 successive matches separated by a ≤ 3-day interval calculated immediately from the end of play in match 1 to the start of play in match 2 occurred on 12.5 ± 5.1 and 16.0 ± 4.7 occasions for club and national team players, respectively. Multiple-match cycles: potential exposure to 3-, 4-, 5- or 6-matches played successively within a ≤ 4-day period commencing from the day after each match occurred on 8.5 ± 2.1, 4.3 ± 1.7, 3.0 ± 0.8 and 1.8 ± 0.5 occasions for club and 11.5 ± 2.4, 6.5 ± 0.6, 4.5 ± 1.9 and 3.0 ± 1.4 occasions for national team players, respectively. With regard to actual exposure in club and national team players, respectively, participation in both matches in 2-match cycles attained 61.2% and 59.3% while 90-min play in both matches was only completed on 38.2% and 40.5% of occasions and ≥75-min play on 47.6% and 50.0% of occasions, despite availability to play in both groups being >86%. While availability to play in all players was frequently >70% for multiple-match cycles, a trend was observed for a sharp decline in participation as the number of matches in the cycles increased. Therefore, the present players were not extensively exposed to periods of fixture congestion.


#2 Changes in Passive Tension of the Hamstring Muscles During a Simulated Soccer Match
Reference: Int J Sports Physiol Perform. 2015 Oct 9. [Epub ahead of print]
Authors: Marshall PW, Lovell R, Siegler JC
Summary: Passive muscle tension is increased following damaging eccentric exercise. Hamstring strain injury is associated with damaging eccentric muscle actions, but no research has examined changes in hamstring passive muscle tension throughout a simulated sport activity. We measured hamstring passive tension throughout a 90-minute simulated soccer match, including the warm-up period, and every 15-minutes throughout the 90-minute simulation. Passive hamstring tension of fifteen amateur male soccer players was measured using the instrumented straight leg raise test. Absolute torque (Nm) and slope (Nm.°-1) of the recorded torque-angular position curve were used for data analysis, in addition to total leg range of motion. Players performed a 15-minute pre-match warm-up, then performed the 90-minute soccer simulation (SAFT90) including a 15-minute half-time rest period. Reductions in passive stiffness from 20 to 50° of passive hip flexion between 22.1 to 29.2% (p<0.05) were observed after the warm-up period. During the SAFT90 passive tension increased in the latter 20% of the range of motion between 10.1 to 10.9% (p<0.05) concomitant to a 4.5% increase in total hamstring range of motion (p=0.0009). The findings of this study imply that hamstring passive tension is reduced following an active warm-up that includes dynamic stretching, but does not increase in a pattern suggestive of eccentric induced muscle damage during soccer-specific intermittent exercise. Hamstring range of motion and passive tension increases are best explained by improved stretch tolerance.


#3 Player acceleration and deceleration profiles in professional Australian football
Reference: J Sports Med Phys Fitness. 2015 Sep;55(9):931-9.
Authors: Johnston RJ, Watsford ML, Austin D, Pine MJ, Spurrs RW
Summary: This study aimed to determine the validity and reliability of global positioning system (GPS) units for measuring a standardized set of acceleration and deceleration zones and whether these standardized zones were capable of identifying differences between playing positions in professional Australian football. Eight well trained male participants were recruited to wear two 5 Hz or 10 Hz GPS units whilst completing a team sport simulation circuit to measure acceleration and deceleration movements. For the second part of this article 30 professional players were monitored between 1-29 times using 5 Hz and 10 Hz GPS units for the collection of acceleration and deceleration movements during the 2011 and 2012 Australian Football League seasons. Players were separated into four distinct positional groups - nomadic players, fixed defenders, fixed forwards and ruckman. The GPS units analysed had good to poor levels of error for measuring the distance covered (<19.7%), time spent (<17.2%) and number of efforts performed (<48.0%) at low, moderate and high acceleration and deceleration zones. The results demonstrated that nomadic players and fixed defenders perform more acceleration and deceleration efforts during a match than fixed forwards and ruckman. These studies established that these GPS units can be used for analysing the distance covered and time spent at the acceleration and deceleration zones used. Further, these standardized zones were proven to be capable of distinguishing between player positions, with nomadic players and fixed defenders required to complete more high acceleration and deceleration efforts during a match.


#4 Influence of Yo-Yo IR2 Scores on Internal and External Workloads and Fatigue Responses of Tag Football Players during Tournament Competition
Reference: PLoS One. 2015 Oct 14;10(10):e0140547. doi: 10.1371/journal.pone.0140547. eCollection 2015.
Authors: Hogarth LW, Burkett BJ, McKean MR
Download link: http://www.plosone.org/article/fetchObject.action?uri=info:doi/10.1371/journal.pone.0140547&representation=PDF
Summary: The purpose of this study was to: a) identify changes in jump height and perceived well-being as indirect markers of fatigue, b) determine the internal and external workloads performed by players, and c) examine the influence of Yo-Yo IR2 on changes in jump height, perceived well-being and internal and external workloads during a tag football tournament. Microtechnology devices combined with heart rate (HR) chest straps provided external and internal measures of match work-rate and workload for twelve male tag football players during the 2014 Australian National Championships. Jump height and perceived well-being were assessed prior to and during the tournament as indirect measures of fatigue. Changes in work-rate, workload and fatigue measures between high- and low-fitness groups were examined based on players' Yo-Yo IR2 score using a median split technique. The low- and high-fitness groups reported similar mean HR, PlayerloadTM/min, and distance/min for matches, however the low-fitness group reported higher perceived match-intensities (ES = 0.90-1.35) for several matches. Further, the high-fitness group reported higher measures of tournament workload, including distance (ES = 0.71), PlayerloadTM (ES = 0.85) and Edwards' training impulse (TRIMP) (ES = 1.23) than the low-fitness group. High- and low-fitness groups both showed large decreases (ES = 1.46-1.49) in perceived well-being during the tournament, although jump height did not decrease below pre-tournament values. Increased Yo-Yo IR2 appears to offer a protective effect against player fatigue despite increased workloads during a tag football tournament. It is vital that training programs adequately prepare tag football players for tournament competition to maximise performance and minimise player fatigue.


#5 Knee Extension Strength and Hamstrings-to-Quadriceps Imbalances in Elite Soccer Players
Reference: Int J Sports Med. 2015 Oct 28. [Epub ahead of print]
Authors: Bogdanis GC, Kalapotharakos VI
Summary: This study examined the relationship between hamstrings-to-quadriceps strength ratio (H:Q) and relative strength of the knee extensors in elite soccer players. Peak torque was measured during isokinetic knee extension/flexion at angular velocities of 60°·s-1, 180°·s-1 and 300°·s-1. 18 professional players were divided into 2 groups, depending on their H:Q at 60°·s-1. Players in the lower H:Q group (n=7) had significantly smaller H:Q ratios compared with the higher H:Q group (n=11) at all angular velocities (60°·s-1: 49.2%; 95% CI: 61.3-57.8% vs. 59.5%; 95% CI: 52.2-46.2%, p=0.001). Players in the lower H:Q group had greater knee-extension peak torque compared with the higher H:Q group (60°·s-1: 313; 95% CI: 335-291 vs. 269; 95% CI: 289-250 N·m, p=0.01). No differences were found in hamstrings' strength between the 2 groups (60°·s-1: 156; 95% CI: 170-143 vs. 160; 95% CI: 173-148 N·m, p=0.96). Negative correlations between knee extension peak torque and H:Q ratio were observed at all angular velocities (r=-0.65 to -0.67, p<0.01). In conclusion, a low H:Q strength ratio measured during isokinetic strength testing in professional soccer players, is observed mainly in those with strong quadriceps muscles, while players with lower quadriceps strength have H:Q ratios around the recommended values.


#6 A Tool to Quickly Detect Short Hamstring Syndrome in Boys who Play Soccer
Reference: Int J Sports Med. 2015 Oct 28. [Epub ahead of print]
Authors: Piqueras-Rodríguez F, Palazón-Bru A, Martínez-St John DR, Folgado-de la Rosa DM, Gil-Guillén VF
Summary: There is a lack of studies of alternative techniques differing from the straight leg raise test (SLR) and the passive knee extension test (PKE) to diagnose short hamstring syndrome (SHS). We built a predictive model with simple parameters to diagnose SHS and implemented it in a mobile app. This cross-sectional study analyzed 85 Spanish boys aged 10-16 years who played soccer in 2012. SHS (SLR<70° and/or PKE>15°), and grade II SHS (SLR<60° and/or PKE≥35°). Secondary variables: toe-touch test (TT), body mass index (BMI), age, laterality and number of years registered as part of a federation. A risk table implemented in a mobile app was built to estimate the probability of SHS and grade II SHS according to secondary variables. The area under the ROC curve (AUC) was calculated and we constructed risk groups. Scoring factors for SHS: low TT, younger age and lower BMI. AUC: 0.89 (95% CI: 0.82-0.96, p<0.001). Scoring factors for grade II SHS: younger age, higher BMI, left footed and lower TT. AUC: 0.78 (95% CI: 0.68-0.88, p<0.001). We provide a tool with minimum material but with a high discriminatory power to quickly calculate whether a boy who plays soccer has SHS. The models need validation studies.


#7 Influence of the MCT1 rs1049434 on Indirect Muscle Disorders/Injuries in Elite Football Players
Reference: Sports Med Open. 2015;1(1):33. Epub 2015 Oct 11.
Authors: Massidda M, Eynon N, Bachis V, Corrias L, Culigioni C, Piras F, Cugia P, Scorcu M, Calò CM
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4600723/pdf/40798_2015_Article_33.pdf
Summary: The aim of this study was to investigate the association between MCT1 rs1049434 polymorphism and indirect muscle injuries in elite football players. One hundred and seventy-three male elite Italian football players (age = 19.2 ± 5.3 years) were recruited from a first-league football club participating at the Official National Italian Football Championship (Serie A, Primavera, Allievi, Giovanissimi). The cohort was genotyped for the MCT1 rs1049434 polymorphism, and muscle injuries data were collected during the period of 2009-2014 (five football seasons). Genomic DNA was extracted using a buccal swab, and genotyping was performed using PCR method. Structural-mechanical injuries and functional muscle disorder were included in the acute indirect muscle injury group. Participants with the MCT1 AA (AA = 1.57 ± 3.07, n = 69) genotype exhibit significantly higher injury incidents compared to participants with the TT genotype (TT = 0.09 ± 0.25, n = 22, P = 0.04). The MCT1 rs1049434 polymorphism is associated with the incidence of muscle injuries in elite football players. We anticipate that the knowledge of athletes' genetic predisposition to sports-related injuries might aid in individualizing training programs.


#8 Effects of strength training on squat and sprint performance in soccer players
Reference: Journal of Strength & Conditioning Research, 10/2015, doi: 10.1519/JSC.0000000000001243
Authors: Styles WJ, Matthews MJ, Comfort P
Summary: Researchers have demonstrated that increases in strength result in increases in athletic performance, although the development of strength is still neglected in some sports. Our aim was to determine whether a simple in-season strength training program would result in increases in maximal squat strength and short sprint performance, in professional soccer players. Professional soccer players (n=17, age = 18.3 +/- 1.2 years, height = 1.79 +/- 0.06 m, body mass (BM) = 75.5 +/- 6.1 kg) completed one repetition maximum (1RM) back squat and sprint tests (5-, 10-, 20 m) before and after a six-week (2 x week) in-season strength training (85-90% 1RM) intervention. Strength training resulted in significant improvements in absolute and relative strength (pre: 125.4 +/- 13.8 kg, post 149.3 +/- 16.2 kg, p < 0.001, Cohen's d = 0.62; 1RM/BM pre: 1.66 +/- 0.24 kg.kg-1, post 1.96 +/- 0.29 kg.kg-1, p < 0.001, Cohen's d = 0.45; respectively). Similarly, there were small yet significant improvements in sprint performance over 5 m (pre 1.11 +/- 0.04 s, post 1.05 +/- 0.05 s, p < 0.001, Cohen's d = 0.55) 10 m (pre 1.83 +/- 0.05 s, post 1.78 +/- 0.05 s, p < 0.001, Cohen's d = 0.45) and 20 m (pre 3.09 +/- 0.07 s, post 3.05 +/- 0.05 s, p < 0.001, Cohen's d = 0.31). Changes in maximal squat strength appear to be reflected in improvements in short sprint performance highlighting the importance of developing maximal strength to improve short sprint performance. Moreover this demonstrates that these improvements can be achieved during the competitive season in professional soccer players.