Latest research in football - week 20 - 2014

#1 Seasonal Changes in Multiple Indices of Body Composition in Professional Football Players
Reference: Int J Sports Med. 2014 May 9. [Epub ahead of print]
Authors: Iga J, Scott M, George K2, Drust B
Summary: We examined the seasonal variability of indicators of adiposity and generic and population-specific equations of estimating body fat in professional football players. Anthropometric data of 35 outfield players (age, 20±4 years; stature, 1.82±0.06 m; body mass 77.1±7.3 kg) were collected over a playing season. There were a significant main effects for time for all indicators (p<0.001). Post hoc analysis revealed significant changes in body composition between July and mid-August (∑4SF-DW: 1.6 mm, p<0.001; ∑4SF-R: 2.4 mm, p=0.002; ∑5SF: 2.0 mm, p<0.002; ∑8SF: 3.8 mm, p=0.001; Reilly et al.: 0.4%, p=0.001; Durnin and Wormsley: 0.7%, p<0.001). Although all indicators were sensitive to detect small changes in body composition between training mesocycles, we advocate the use of the sum of 4 skinfolds by Reilly et al. to monitor changes in body composition in professional football players; if an estimate of percent body fat is required, the population-specific equation by Reilly et al. may be utilised.


#2 Risk and consequences of osteoarthritis after a professional football career: a systematic review of the recent literature
Reference: J Sports Med Phys Fitness. 2014 May 14. [Epub ahead of print]
Authors: Gouttebarge V, Inklaar H, Frings-Dresen MH.
Summary: The aim of the present study was to assess whether previous injury is a risk determinant for knee and ankle osteoarthritis (OA) in former professional football players and to explore OA-related activity and work limitations. To retrieve the relevant recent literature, the Medline, Embase and Sportdiscus databases were systematically searched for studies published from January 2000 to May 2012. Included studies must be primary studies that are written in English, Dutch, French or German and involve former professional football players; injury had to be studied as an independent variable; and knee/ankle OA, work participation or limited activities had to be described as an outcome. The data from included studies were extracted using a standardised extraction form, and the methodological quality was assessed. No studies were retrieved about injury as a risk determinant for knee/ankle OA in former professional football players. Four studies about OA-related activity and work limitations were included (three of high and one of moderate methodological quality). Up to 17% of former professional football players with knee/ankle OA reported suffering from joint pain and discomfort during activities such as squatting, walking and climbing stairs. Former professional football players with knee/ankle OA reported that their conditions were very painful, chronically painful and affected their daily lives, while 28% reported work-related limitations. Knee and ankle OA in former professional football players causes joint pain and discomfort that has negative consequences for daily life and work activities. An OA health examination programs should be developed to empower the sustainable health and functioning of professional football players.


#3 Competing with Lower Level Opponents Decreases Intra-Team Movement Synchronization and Time-Motion Demands during Pre-Season Soccer Matches
Reference: PLoS One. 2014 May 9;9(5):e97145. doi: 10.1371/journal.pone.0097145. eCollection 2014.
Folgado H, Duarte R, Fernandes O, Sampaio J.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4016249/pdf/pone.0097145.pdf
Summary: This study aimed to quantify the time-motion demands and intra-team movement synchronization during the pre-season matches of a professional soccer team according to the opposition level. Positional data from 20 players were captured during the first half of six pre-season matches of a Portuguese first league team. Time-motion demands were measured by the total distance covered and distance covered at different speed categories. Intra-team coordination was measured by calculating the relative phase of all pairs of outfield players. Afterwards, the percentage of time spent in the -30° to 30° bin (near-in-phase mode of coordination) was calculated for each dyad as a measure of space-time movement synchronization. Movement synchronization data were analyzed for the whole team, according to each dyad average speed and by groups of similar dyadic synchronization tendencies. Then, these data were compared according to the opponent team level (first league; second league; amateurs). Time-motion demands showed no differences in total distance covered per opposition levels, while matches opposing teams of superior level revealed more distance covered at very high intensity. Competing against superior level teams implied more time in synchronized behavior for the overall displacements and displacements at higher intensities. These findings suggest that playing against higher-level opponents (1st league teams) increased time-motion demands at high intensities in tandem with intra-team movement synchronization tendencies.


#4 The Yo-Yo IE2 Test: Physiological Response for Untrained Men vs Trained Soccer Players
Reference: Med Sci Sports Exerc. 2014 May 12. [Epub ahead of print]
Authors: Krustrup P, Bradley PS, Christensen JF, Castagna C, Jackman S, Connolly L, Randers MB, Mohr M, Bangsbo J.
Summary: To examine the physical capacity and physiological response to the Yo-Yo Intermittent Endurance level 2 test (IE2) for untrained individuals and trained male soccer players, and to investigate the determinants of intense intermittent exercise performance. Thirty-four healthy untrained males (UTR) and fifteen age-matched trained soccer players (TR) performed a maximal incremental treadmill test (ITT) and a Yo-Yo IE2 test. Muscle biopsies and blood samples were obtained and HR were measured before, during and after tests. UTR had a 67% lower (P<0.01) Yo-Yo IE2 performance (665±271 vs. 2027±298 m; ES:4.8), 34% lower (P<0.01) VO2max and 19% lower (P<0.05) resting muscle glycogen than TR. Blood lactate and heart rates during the first 560 m of the Yo-Yo IE2 test were higher (P<0.01) in UTR than TR (560 m: 7.4±2.8 vs. 2.4±0.8 mmol·L; ES:1.7-2.8; 188±11 vs. 173±8 bpm, ES:0.9-1.5) with no differences at exhaustion. Time >95%HRmax was lower (P<0.01) in UTR than TR (1.0±1.1 vs. 6.3±2.9 min, ES:3.1). Mean rate of muscle creatine phosphate utilization (16.5±9.5 vs. 4.3±2.7 mmol·kgd.w·min), muscle lactate accumulation (16.8±9.1 vs. 4.2±2.9 mmol·kgd.w·min), and glycogen breakdown (29.6±14.2 vs. 7.7±5.4 mmol·kgd.w·min) were 4-fold higher (P<0.01,ES:1.4-1.7) in UTR than TR. For UTR, correlations (P<0.01) were observed between Yo-Yo IE2 performance and VO2max (r=0.77), ITT performance (r=0.79) and muscle citrate synthase activity (r=0.57), but not for TR (r=-0.12-0.50; P>0.05). The Yo-Yo IE2 test was shown to possess high construct validity by showing large differences in performance, heart rates and anaerobic metabolism between untrained individuals and trained soccer players. Additionally, VO2max appeared to be important for intermittent exercise performance in untrained individuals, but not for trained soccer players.


#5 Importance of Muscle Power Variables in Repeated and Single Sprint Performance in Soccer Players
Reference: Journal of Human Kinetics. Volume 40, Issue 1, Pages 201–211, ISSN (Online) 1899-7562, ISSN (Print) 1640-5544, DOI: 10.2478/hukin-2014-0022, April 2014

Authors: López-Segovia M, Dellal A, Chamari K, González-Badillo JJ
Download link: http://www.degruyter.com/view/j/hukin.2014.40.issue-1/hukin-2014-0022/hukin-2014-0022.xml?format=INT
Summary: This study examined the relationship between lower body power and repeated as well as single sprint performance in soccer players. The performance of nineteen male soccer players was examined. The first testing session included the countermovement jump (CMJL) and the progressive full squat (FSL), both with external loads. Power in the CMJL and FSL was measured with each load that was lifted. The second session included a protocol of 40-m repeated sprints with a long recovery period (2 min). The number of sprints executed until there was a 3% decrease in performance for the best 40-m sprint time was recorded as a repeated sprint index (RSI). The RSI was moderately associated with power output relative to body mass in the CMJL and FSL (r = 0.53/0.54, p ≤ 0.05). The most and least powerful players (determined by FSL) showed significant differences in the RSI (9.1 ± 4.2 vs. 6.5 ± 1.6) and 10 m sprint time (p = 0.01). Repeated and single sprints are associated with relatively lower body power in soccer players.


#6 The effect of 8-week plyometric training on leg power, jump and sprint performance in female soccer player
Reference: J Strength Cond Res. 2014 May 21. [Epub ahead of print]
Authors: Ozbar N, Ates S, Agopyan A.
Summary: The aim of this study was to determine the effect of 8-week plyometric training on the leg power, jump and sprint performance in female soccer players. Eighteen of female soccer players from Women 2 League (age = 18.2 ± 2.3 years, height = 161.3 ± 5.4 cm, body mass = 56.6 ± 7.2 kg,) were randomly assigned to a control (n=9) and a plyometric (n=9) groups. Both groups continued together with regular technical and tactical soccer training for 4 days a week. Additionally, the plyometric groups followed by plyometric training, during 8-week in one day per week, 60 minutes session duration. During the 8-week period, the control group was hindered from any additional conditioning training. All players' jumps (triple hop, countermovement and standing broad jump), running speed (20-m) and peak power were evaluated before and after 8-week. No significant difference was found between groups at pre-test variables (p > 0.05). Significant improvements were found to all of the post-test of the both groups (p < 0.05) except 20-m sprint test of the control group (p > 0.05). Triple hop distance, countermovement jump, standing broad jump, peak power and 20-m sprint test values were all significantly improved for the plyometric group, compared with the control group (p<0.05). We concluded that short duration plyometric training an improved important component of athletic performance in female soccer players. The results indicate that safe, effective and alternative plyometric training can be useful to strength and conditioning coaches, especially in competition season where less time is available for training.


#7 The examination of the heart rate recovery after anaerobic running in soccer players
Reference: Coll Antropol. 2014 Mar;38(1):207-11.
Authors: Taskin H, Erkmen N, Cicioglu I.
Summary: The purpose of this study was to examine the heart rate recovery depending on anaerobic running. A total of 23 professional soccer players who were player of Turkish Super Leagues, were examined. Anaerobic Run test was applied to the soccer players and their heart rates were recorded before running, just after running, in 3rd and 6th minutes of recovery period. Any statistical differences were not found between the heart rates before run and in 6th minute after run (p > 0.05). On the other hand, there was a statistical difference between the heart rates before run, after run and in 3rd minute after run; the heart rates after run and before run; the heart rates in 3rd and 6th minutes of recovery (p < 0.05). A relationship was determined between the heart rates after run, before run (r = 0.457) and in 3rd minute of recovery (r = 0.537) and the heart rates in 3rd and 6th minutes of recovery (r = 0.629). On the other hand, no relation was found between the heart rates before run, in 3rd minute recovery (r = 0.247) and in 6th minute of recovery (r = -0.004) and the heart rates just after run and in 6th minute of recovery (r = 0.280) (p > 0.05). In conclusion, even if the increase of heart rate occurring after anaerobic run doesn't completely return to normal in 3rd minute of recovery, it will supply the athlete with a suitable condition for the second loading with regard to efficient rest. It is thought that a rest over 3 minutes should be given for athletes to make the heart rate after anaerobic run return to normal.