Latest research in football - week 24 - 2015

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Serum Cartilage Oligomeric Matrix Protein Levels in Collegiate Soccer Athletes over the Duration of an Athletic Season: A Pilot Study
Reference: Cartilage. 2015 Jan;6(1):6-11. doi: 10.1177/1947603514557944.
Authors: Mateer JL, Hoch JM, Mattacola CG, Butterfield TA, Lattermann C
Summary: The primary objective of this study was to measure serum cartilage oligomeric matrix protein (sCOMP) levels weekly in a group of collegiate soccer athletes over the duration of a spring soccer season and 2 weeks following the conclusion of the season while documenting minutes of exercise participation as a measure of exercise intensity. A repeated-measures study design was employed. A volunteer sample of 6 female soccer athletes participated in this study. Serum samples were collected on 10 separate occasions, 1 week prior to the start of the season (baseline), once a week during the 8-week season (PX1-PX8), and once a week for 2 weeks following the conclusion of the season (postseason; PS1 and PS2). Minutes of participation were documented following all spring soccer activities for each week. Once all samples were collected, sCOMP concentrations were determined using a commercially available enzyme-linked immunosorbent assay. The results of Friedman test revealed a significant effect for time (P = 0.003). Post hoc analysis revealed no significant differences between baseline and practice or postseason levels. A qualitative analysis of the sCOMP levels and minutes indicated higher sCOMP levels occurred when the athletes' participation in soccer-related activities was higher. Qualitatively, our findings suggest that as minutes of participation increased, sCOMP levels increased. However, no statistically significant differences were identified. We speculate these increases were an increase in cartilage turnover and an interesting observation related to increases in physical activity. However, the implications are unclear as there was a return to near baseline levels.

#2 Dribbling determinants in sub-elite youth soccer players
Reference: J Sports Sci. 2015 Jun 11:1-9. [Epub ahead of print]
Authors: Zago M, Piovan AG, Annoni I, Ciprandi D, Iaia FM, Sforza C.
Summary: Dribbling speed in soccer is considered critical to the outcome of the game and can assist in the talent identification process. However, little is known about the biomechanics of this skill. By means of a motion capture system, we aimed to quantitatively investigate the determinants of effective dribbling skill in a group of 10 Under-13 sub-elite players, divided by the median-split technique according to their dribbling test time (faster and slower groups). Foot-ball contacts cadence, centre of mass (CoM), ranges of motion (RoM), velocity and acceleration, as well as stride length, cadence and variability were computed. Hip and knee joint RoMs were also considered. Faster players, as compared to slower players, showed a 30% higher foot-ball cadence (3.0 ± 0.1 vs. 2.3 ± 0.2 contacts · s-1, P < 0.01); reduced CoM mediolateral (0.91 ± 0.05 vs. 1.14 ± 0.16 m, P < 0.05) and vertical (0.19 ± 0.01 vs. 0.25 ± 0.03 m, P < 0.05) RoMs; higher right stride cadence (+20%, P < 0.05) with lower variability (P < 0.05); reduced hip and knee flexion RoMs (P < 0.05). In conclusion, faster players are able to run with the ball through a shorter path in a more economical way. To effectively develop dribbling skill, coaches are encouraged to design specific practices where high stride frequency and narrow run trajectories are required.

#3 Acute effects of prolonged intermittent low-intensity isometric warm-up schemes on jump, sprint, and agility performance in collegiate soccer players
Reference: Biol Sport. 2015 Jun;32(2):129-34. doi: 10.5604/20831862.1140427. Epub 2015 Feb 16.
Authors: Pojskić H, Pagaduan JC, Babajić F, Užičanin E, Muratović M, Tomljanović M
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Summary: The aim of the present study was to compare the effects of different warm-up interventions on jump, sprint and agility performance in collegiate soccer players. Twenty-one healthy male college soccer players (age: 20.14 ± 1.65 years; body height: 179.9 ± 8.34 cm; body mass: 74.4 ± 13.0 kg; % body fat: 9.45 ± 4.8) participated in the study. Subjects underwent four different randomized warm-up protocols separated by at least 48 hours. The warm-up schemes were: 1. no conditioning contraction protocol (NCC); 2. dynamic stretching (DS); 3. prolonged intermittent low-intensity isometric exercise (ST); and, 4. ST with an additional external load equal to 30% of body weight (ST + 30% BW). All interventions were preceded by a general warm-up. Results from one-way repeated measures ANOVA demonstrated a significant difference in countermovement jump (CMJ) at F(3,60) = 10.2, ηρ(2) = 0.337, p < 0.01. Post hoc analysis revealed a significant difference in CMJ performance in DS when compared to NCC and ST + 30% BW. No significant difference in CMJ was observed between DS and ST. CMJ scores in NCC, ST, and ST + 30% BW were non-significant. There was a significant difference in speed; F(3, 60) = 6.61, ηρ(2) = 0.248, p < 0.01. Post hoc analysis revealed significantly better time in DS than NCC and ST. However, no difference in speed was observed between DS and ST + 30% BW. Similarly, speed was similar in NCC, ST and ST + 30% BW. A significant difference in agility performance was also observed; F(3, 60) = 24.1, ηρ(2)= 0.546, p < 0.01. Post hoc analysis revealed significantly greater performance gains in DS than NCC. No significant difference in agility was observed in DS, ST and ST + 30% BW. In conclusion, a prolonged intermittent low-intensity isometric protocol using bodyweight only showed similar benefits with dynamic stretching in countermovement jump performance. When the same isometric condition with additional load equal to 30% of bodyweight was applied, effects in speed and agility were similar to dynamic stretching.

#4 Technique determinants of knee joint loads during cutting in female soccer players
Reference: Hum Mov Sci. 2015 Jun 6;42:203-211. doi: 10.1016/j.humov.2015.05.004. [Epub ahead of print]
Authors: Jones PA, Herrington LC, Graham-Smith P
Summary: The aim of this study was to investigate the relationships between technique characteristics and knee abduction moments during 90° cuts. A cross sectional design involving 26 elite and sub-elite female soccer players (mean±SD; age: 21±3.2years, height: 1.68±0.07m, and mass: 59.1±6.8kg) was used to explore relationships between pre-determined technical factors on knee abduction moments during cutting. Three dimensional motion analyses of 90° cuts on the right leg were performed using 'Qualisys Pro Reflex' infrared cameras (240Hz). Ground reaction forces were collected from two AMTI force platforms (1200Hz) embedded into the running track to examine 2nd last and last footfalls. Pearson's correlation coefficients, co-efficients of determination and hierarchical multiple regression were used to explore relationships between a range of technique parameters and peak knee abduction moments. Significance was set at p<.05. Hierarchical multiple regression revealed that initial knee abduction angle, lateral leg plant distance and initial lateral trunk lean could explain 67% (62% adjusted) of the variation in peak knee abduction moments (F(1,22)=8.869, p=.007). These findings reveal potential modifiable technical factors to lower peak knee abduction moments during cutting.

#5 Player load, acceleration and deceleration during 45 competitive matches of elite soccer
Reference: J Strength Cond Res. 2015 Jun 5. [Epub ahead of print]
Authors: Terje D, Jørgen I, Gertjan E, Geir Håvard H, Ulrik W.
Summary: The use of time motion analysis has advanced our understanding of position-specific, work rate profiles and the physical requirements of soccer players. Still, many of the typical soccer activities can be neglected, as these systems only examine activities measured by distance and speed variables. This study used tri-axial accelerometer and time-motion analysis to obtain new knowledge about elite soccer players' match load. Furthermore, we determined acceleration/deceleration profiles of elite soccer players and their contribution to the players' match load. The dataset includes every domestic home game (n = 45) covering three full seasons (2009, 2010, 2011) for the participating team (Rosenborg FC), and includes eight central defenders (CD, n = 68), nine full-backs (FB, n = 83), nine central midfielders (CM, n = 70), seven wide midfielders (WM, n = 39), and five attackers (A, n = 50). A novel finding was that accelerations contributed to 7-10% of the total player load for all player positions, while decelerations contributed to 5-7%. Furthermore, the results indicate that other activities besides the high-intensity movements contribute significantly to the players' total match workload. Therefore, motion analysis alone may underestimate player load because many high-intensity actions is without a change in location at the pitch or they are classified as low speed activity according to current standards. This new knowledge may help coaches to better understand the different ways players achieve match load and could be used in developing individualised programs that better meet the "positional physical demands" in elite soccer.

#6 Lower limb kinematics of male and female soccer players during a self-selected cutting maneuver: Effects of prolonged activity
Reference: Knee. 2015 Jun 3. pii: S0968-0160(15)00109-X. doi: 10.1016/j.knee.2015.05.005. [Epub ahead of print]
Authors: McGovern A, Dude C, Munkley D, Martin T, Wallace D, Feinn R, Dione D, Garbalosa JC
Summary: Despite the recent emphasis on injury prevention, anterior cruciate ligament (ACL) injury rates remain high. This study aimed to ascertain the effects of prolonged activity on lower limb kinematics during a self-selected cutting maneuver. Angular kinematics were recorded during an agility test performed until the completion time was greater than the mean plus one SD of baseline trials. Cut type was identified and the hip and knee angles at 33 ms post heel strike were determined. A linear mixed effects model assessed the effects of cut type, gender, and activity status on the hip and knee angles. Males performed sidestep cuts more frequently than females. Females increased the incidence of sidestep cuts after prolonged activity. At the hip, a gender-cut type interaction existed for the transverse (p=0.001) and sagittal (p=0.11) planes. Females showed more internal rotation during sidestep and more external rotation and less flexion during crossover cuts. For the frontal plane, a gender-activity status interaction (p = 0.032) was due to no change within females but greater hip adduction during prolonged activity within males. With prolonged activity, both genders displayed less hip (p=0.29) and knee (p=0.009) flexion and more knee (p=0.001) adduction. Females displayed less hip and knee flexion than men (p=0.001). Sidestep may be more risky than crossover cuts. Both genders place themselves in at-risk postures with prolonged activity due to less hip and knee flexion.

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