Latest research in football - week 19 - 2015

#1 Days to Return to Participation After a Hamstrings Strain Among American Collegiate Soccer Players
Reference: J Athl Train. 2015 May 15. [Epub ahead of print]
Authors: Cross KM, Saliba SA, Conaway M, Gurka KK, Hertel J.
Summary: Among US collegiate soccer players, the incidence rate and the event characteristics of hamstrings strains differ between sexes, but comparisons in the return-to-participation (RTP) time have not been reported. The purpose of the study was to compare the RTP time between male and female collegiate soccer players and analyze the influence of event characteristics on the RTP time for each sex. Data were collected from collegiate teams that voluntarily participated in the National Collegiate Athletic Association Injury Surveillance System. Collegiate soccer athletes who sustained 507 hamstrings strains (306 men, 201 women) during the 2004 through 2009 fall seasons were used in this study. Nonparametric statistics were used to evaluate RTP time differences between sexes and among categories of each event characteristic (ie, time of season, practice or competition, player position). Negative binomial regression was used to model the RTP time for each sex. All analyses were performed separately for first-time and recurrent strains. We found no differences in the RTP time between sexes for first-time (median: men = 7.0 days, women = 6.0 days; P = .07) or recurrent (median: men = 11 days, women = 5.5 days; P = .06) hamstrings strains. For male players with first-time strains, RTP time was increased when the strain occurred during competition or the in-season/postseason and varied depending on the division of play. Among female players with first-time strains, we found no differences in RTP time within characteristics. For male players with recurrent hamstrings strains, the RTP time was longer when the injury occurred during the in-season/postseason. Among female players with recurrent strains, RTP time was longer for forwards than for midfielders or defenders. Although we found no differences in the RTP time after hamstrings strains in male and female collegiate soccer players, each sex had unique event characteristics that influenced RTP time.


#2 Using network metrics in soccer: a macro-analysis
Reference: J Hum Kinet. 2015 Apr 7;45:123-34. doi: 10.1515/hukin-2015-0013. eCollection 2015.
Authors: Clemente FM, Couceiro MS, Martins FM, Mendes RS
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4415825/pdf/jhk-45-123.pdf
Summary: The aim of this study was to propose a set of network methods to measure the specific properties of a team. These metrics were organised at macro-analysis levels. The interactions between teammates were collected and then processed following the analysis levels herein announced. Overall, 577 offensive plays were analysed from five matches. The network density showed an ambiguous relationship among the team, mainly during the 2nd half. The mean values of density for all matches were 0.48 in the 1st half, 0.32 in the 2nd half and 0.34 for the whole match. The heterogeneity coefficient for the overall matches rounded to 0.47 and it was also observed that this increased in all matches in the 2nd half. The centralisation values showed that there was no 'star topology'. The results suggest that each node (i.e., each player) had nearly the same connectivity, mainly in the 1st half. Nevertheless, the values increased in the 2nd half, showing a decreasing participation of all players at the same level. Briefly, these metrics showed that it is possible to identify how players connect with each other and the kind and strength of the connections between them. In summary, it may be concluded that network metrics can be a powerful tool to help coaches understand team's specific properties and support decision-making to improve the sports training process based on match analysis.


#3 The relationships between the center of mass position and the trunk, hip, and knee kinematics in the sagittal plane: a pilot study on field-based video analysis for female soccer players
Reference: J Hum Kinet. 2015 Apr 7;45:71-80. doi: 10.1515/hukin-2015-0008. eCollection 2015.
Authors: Sasaki S, Nagano Y, Kaneko S, Imamura S, Koabayshi T, Fukubayashi T
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4415845/pdf/jhk-45-71.pdf
Summary: Athletes with non-contact anterior cruciate ligament tears have common features in the sagittal plane; namely, the body's center of mass (COM) is located posterior to the base of support, the trunk and knee joints are extended, and the hip angle is flexed. However, the relationships among these variables have not been assessed in field-based movements. This study sought to determine relationships between distances from the COM to the base of support and the trunk, hip, and knee positions in women while playing soccer. Sixty events (29 single-leg landing and 31 single-leg stopping events) were analyzed using two-dimensional video analysis. The relationships among the measurement variables were determined using the Pearson's product-moment correlation coefficient, and stepwise multiple linear regression models were used to explore the relationships between the COM position and the kinematic variables. The distance from the COM to the base of support displayed a moderate negative relationship with the trunk angle (r = -0.623, p < .0001, r(2) = 0.388) and a strong positive relationship with the limb angle (r = 0.869, p < .0001, r(2) = 0.755). The limb, knee, and trunk angles were selected in the best regression model (adjusted r(2) = 0.953, p < .0001, f(2) = 20.277). These findings suggest that an increased trunk angle and a decreased limb angle at initial contact are associated with a safer COM position. Neuromuscular training may be useful for controlling the trunk and lower limb positions during dynamic activities.


#4 Validity of the established method of quantifying home advantage in soccer
Reference: J Hum Kinet. 2015 Apr 7;45:7-8. doi: 10.1515/hukin-2015-0001. eCollection 2015.
Authors: Pollard R1, Gómez MÁ2.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4415821/pdf/jhk-45-07.pdf


#5 External Responsiveness of the Yo-Yo IR Test Level 1 in High-level Male Soccer Players
Reference: Int J Sports Med. 2015 May 6. [Epub ahead of print]
Authors: Fanchini M, Schena F, Castagna C, Petruolo A, Combi F, McCall A, Impellizzeri M
Summary: The aim of this study was to assess the external responsiveness, construct validity and internal responsiveness of the Yo-Yo Intermittent Recovery test level 1 and its sub-maximal version in semi-professional players. Tests and friendly matches were performed during the preseason and regular season. The distance covered above 15 km·h-1 was considered as an indicator of the physical match performance. Construct validity and external responsiveness were examined by correlations between test and physical match performance (preseason and regular season) and training-induced changes. Internal responsiveness was determined as Cohen's effect size, standardized response mean and signal-to-noise ratio. The physical match performance increased after training (34.8%). The Yo-Yo Intermittent Recovery test level 1 improved after training (40.2%), showed longitudinal (r=0.69) and construct validity (r=0.73 and 0.59, preseason and regular season) and had higher internal responsiveness compared to its sub-maximal version. The heart rate at the 6th minute in the sub-maximal version did not show longitudinal (r=-0.38) and construct validity (r=0.01 and -0.06, preseason and regular season) and did not significantly change after training (-0.3%). The rate of perceived exertion decreased in the sub-maximal version (- 29.8%). In conclusion, the Yo-Yo Intermittent Recovery test level 1 is valid and responsive, while the validity of its sub-maximal version is questionable.


#6 Longitudinal Development of Explosive Leg Power from Childhood to Adulthood in Soccer Players
Reference: Int J Sports Med. 2015 May 6. [Epub ahead of print]
Authors: Deprez D, Valente-Dos-Santos J, Coelho-E-Silva MJ, Lenoir M, Philippaerts R, Vaeyens R
Summary: The aim of the this study was to investigate the development of explosive leg power by using 2 similar jumping protocols (countermovement jump and standing broad jump) in 555 Belgian, high-level young soccer players, aged between 7 and 20 years. The total sample was divided into 3 longitudinal samples related to growth and maturation (pre-teenchildhood: (6-10 years;), early adolescence: (11-16 years;) and late adolescence: (17-20 years)), and 6 multilevel regression models were obtained. Generally, both jumping protocols emphasized that chronological age, body size dimensions (by means of fat mass in the late childhood and early adolescence groups, fat-free mass in the late adolescence group and stature - (not for CMJ in late childhood group) and fat mass in the late childhood and early adolescence groups, and fat-free mass in the late adolescence group) and motor coordination (one item of a 3-component test battery) are longitudinal predictors of explosive leg power from childhood to young adulthood. The contribution of maturational status was not investigated in this study. The present findings highlight the importance of including non-specific motor coordination in soccer talent development programs.


#7 Effect of Kaempferia parviflora Extract on Physical Fitness of Soccer Players: A Randomized Double-Blind Placebo-Controlled Trial
Reference: Med Sci Monit Basic Res. 2015 May 6;21:100-8. doi: 10.12659/MSMBR.894301.
Authors: Promthep K, Eungpinichpong W, Sripanidkulchai B, Chatchawan U
Summary: Physical fitness is a fundamental prerequisite for soccer players. Kaempferia parviflora is an herbal plant that has been used in some Asian athletes with the belief that it might prevent fatigue and improve physical fitness. This study aimed to determine the effects of Kaempferia parviflora on the physical fitness of soccer players. Sixty soccer players who routinely trained at a sports school participated in a double-blind placebo-controlled trial and were randomly allocated to the treatment group or the placebo group. The participants in both groups were given either 180 mg of Kaempferia parviflora extract in capsules or a placebo once daily for 12 weeks. Baseline data were collected using the following 6 tests of physical performance: a sit-and-reach test, a hand grip strength test, a back-and-leg strength test, a 40-yard technical test, a 50-metre sprint test, and a cardiorespiratory fitness test. All of the tests were performed every 4 weeks throughout the 12-week study period. RESULTS The study showed that after treatment with Kaempferia parviflora, the right-hand grip strength was significantly increased at weeks 4, 8, and 12. The left-hand grip strength was significantly increased at week 8. However, the back-and-leg strength, the 40-yard technical test, the sit-and-reach test, the 50-metre sprint test, and the cardiorespiratory fitness test results of the treatment group were not significantly different from those of the placebo group. CONCLUSIONS Taking Kaempferia parviflora supplements for 12 weeks may significantly enhance some physical fitness components in soccer players.