Latest research in football - week 32 - 2015

#1 GPS and Injury Prevention in Professional Soccer
Reference: J Strength Cond Res. 2015 Jul 11. [Epub ahead of print]
Authors: Ehrmann FE, Duncan CS, Sindhusake D, Franzsen WN, Greene DA.
Summary: This study investigated the relationship between GPS variables measured in training and gameplay and injury occurrences in professional soccer. Nineteen professional soccer players competing in the Australian Hyundai A-League were monitored for one entire season using 5Hz Global Positioning System (GPS) units (SPI-Pro GPSports, Canberra, Australia) in training sessions and pre-season games. The measurements obtained were Total Distance, High Intensity Running Distance, Very High Intensity Running Distance, New Body Load and Metres per Minute. Non-contact soft tissue injuries were documented throughout the season. Players' seasons were averaged over one and four week blocks according to when injuries occurred. These blocks were compared to each other and to players' seasonal averages. Players performed significantly higher Metres per Minute in the weeks preceding an injury compared to their seasonal averages (+9.6 % and +7.4 % for one and four week blocks respectively) (p<0.01), indicating an increase in training and gameplay intensity leading up to injuries. Furthermore, injury blocks showed significantly lower average New Body Load compared to seasonal averages (-15.4 % and -9.0 % for one and four week blocks respectively) (p<0.01 and p=0.01). Periods of relative under-preparedness could potentially leave players unable to cope with intense bouts of high intensity efforts during competitive matches. Although limited by FIFA regulations, the results of this study isolated two variables predicting soft tissue injuries for coaches and sports scientist to consider when planning and monitoring training.


#2 Boot-insole effects on comfort and plantar loading at the heel and fifth metatarsal during running and turning in soccer
Reference: J Sports Sci. 2015 Jul 22:1-8. [Epub ahead of print]
Authors: Nunns MP, Dixon SJ, Clarke J, Carré M.
Summary: Plantar loading may influence comfort, performance and injury risk in soccer boots. This study investigated the effect of cleat configuration and insole cushioning levels on perception of comfort and in-shoe plantar pressures at the heel and fifth metatarsal head region. Nine soccer academy players (age 15.7 ± 1.6 years; height 1.80 ± 0.40 m; body mass 71.9 ± 6.1 kg) took part in the study. Two boot models (8 and 6 cleats) and two insoles (Poron and Poron/gel) provided four footwear combinations assessed using pressure insoles during running and 180° turning. Mechanical and comfort perception tests differentiated boot and insole conditions. During biomechanical testing, the Poron insole generally provided lower peak pressures than the Poron/gel insole, particularly during the braking step of the turn. The boot model did not independently influence peak pressures at the fifth metatarsal, and had minimal influence on heel loads. Specific boot-insole combinations performed differently (P < 0.05). The 8-cleat boot and the Poron insole performed best biomechanically and perceptually, but the combined condition did not. Inclusion of kinematic data and improved control of the turning technique are recommended to strengthen future research. The mechanical, perception and biomechanical results highlight the need for a multi-faceted approach in the assessment of footwear.


#3 Effects of plyometric training on maximal-intensity exercise and endurance in male and female soccer players
Reference: J Sports Sci. 2015 Jul 22:1-7. [Epub ahead of print]
Authors: Ramírez-Campillo R, Vergara-Pedreros M, Henríquez-Olguín C, Martínez-Salazar C, Alvarez C, Nakamura FY, De La Fuente CI, Caniuqueo A, Alonso-Martinez AM, Izquierdo M.
Summary: In a randomised controlled trial design, effects of 6 weeks of plyometric training on maximal-intensity exercise and endurance performance were compared in male and female soccer players. Young (age 21.1 ± 2.7 years) players with similar training load and competitive background were assigned to training (women, n = 19; men, n = 21) and control (women, n = 19; men, n = 21) groups. Players were evaluated for lower- and upper-body maximal-intensity exercise, 30 m sprint, change of direction speed and endurance performance before and after 6 weeks of training. After intervention, the control groups did not change, whereas both training groups improved jumps (effect size (ES) = 0.35-1.76), throwing (ES = 0.62-0.78), sprint (ES = 0.86-1.44), change of direction speed (ES = 0.46-0.85) and endurance performance (ES = 0.42-0.62). There were no differences in performance improvements between the plyometric training groups. Both plyometric groups improved more in all performance tests than the controls. The results suggest that adaptations to plyometric training do not differ between men and women.


#4 Use of the RSA/RCOD index to identify training priority in soccer players
Reference: J Strength Cond Res. 2015 Jul 15. [Epub ahead of print]
Authors: Wong DP, Hjelde GH, Cheng CF, Ngo JK.
Summary: The use of RSA/RCOD index indicates the repeated change-of-direction (RCOD) performance relative to the repeated sprint ability (RSA), and provides a standardized approach to prioritize training needs for RSA and RCOD. To compare the RSA/RCOD index among different age groups, RSA and RCOD were measured from 20 under-16 players (U16), 20 under-19 players (U19), and 17 first team professional players (PRO) from a football (soccer) club that has regular participation in the UEFA Champions League. Each player performed the RSA and RCOD tests, during which the fastest time (FT), average time (AT), total time (TT), and percentage decrement score (%Dec) were recorded. No significant differences were found in RSA/RCOD index-FT, AT, TT, and %Dec among the three groups (p > 0.05), and between U19 and PRO in all RSA and RCOD measures (p > 0.05). Most values of RSA/RCOD index were 0.51 among the U16, U19 and PRO groups. Moreover, we concluded that the RSA/RCOD index might not be further changed after 16 years of age unless specific training programs for RSA and RCOD are prescribed. Therefore, this study provides an empirical case and coaches can establish the RSA/RCOD index value relevant to their training system and monitor players' training needs of RSA and RCOD in a longer term.


#5 Agreement between Two Methods of Dietary Data Collection in Male Adolescent Academy-Level Soccer Players
Reference: Nutrients. 2015 Jul 17;7(7):5948-5960.
Authors: Briggs MA, Rumbold PL, Cockburn E, Russell M, Stevenson EJ
Download link: www.mdpi.com/2072-6643/7/7/5262/pdf
Summary: Collecting accurate and reliable nutritional data from adolescent populations is challenging, with current methods providing significant under-reporting. Therefore, the aim of the study was to determine the accuracy of a combined dietary data collection method (self-reported weighed food diary, supplemented with a 24-h recall) when compared to researcher observed energy intake in male adolescent soccer players. Twelve Academy players from an English Football League club participated in the study. Players attended a 12 h period in the laboratory (08:00 h-20:00 h), during which food and drink items were available and were consumed ad libitum. Food was also provided to consume at home between 20:00 h and 08:00 h the following morning under free-living conditions. To calculate the participant reported energy intake, food and drink items were weighed and recorded in a food diary by each participant, which was supplemented with information provided through a 24-h recall interview the following morning. Linear regression, limits of agreement (LOA) and typical error (coefficient of variation; CV) were used to quantify agreement between observer and participant reported 24-h energy intake. Difference between methods was assessed using a paired samples t-test. Participants systematically under-reported energy intake in comparison to that observed (p < 0.01) but the magnitude of this bias was small and consistent (mean bias = -88 kcal·day-1, 95% CI for bias = -146 to -29 kcal·day-1). For random error, the 95% LOA between methods ranged between -1.11 to 0.37 MJ·day-1 (-256 to 88 kcal·day-1). The standard error of the estimate was low, with a typical error between measurements of 3.1%. These data suggest that the combined dietary data collection method could be used interchangeably with the gold standard observed food intake technique in the population studied providing that appropriate adjustment is made for the systematic under-reporting common to such methods.


#6 The effect of concurrent training organisation in youth elite soccer players
Reference: Eur J Appl Physiol. 2015 Jul 19. [Epub ahead of print]
Authors: Enright K, Morton J, Iga J, Drust B.
Summary: This study compared the adaptive responses to two concurrent training programmes frequently used in professional soccer. Fifteen youth soccer players (17.3 ± 1.6 years, 1.82 ± 0.06 m, 77.0 ± 7.3 kg; VO2 peak, 62.0 ± 4.7 ml-1 kg-1 min-1) who compete in the English Premier League volunteered for this study. In addition to completing their habitual training practices, the participants were asked to alter the organisation concurrent training by performing strength (S) training either prior to (S + E, n = 8) or after (E + S, n = 7) soccer-specific endurance training (E) 2d wk-1 for 5 wk-1. With the exception of 30 m sprint, IMVC PF, quadriceps strength (60°/sCON, 180°/sCON, 120°/sECC) pooled data revealed training effects across all other performances measures (P < 0.05). Whilst ANCOVA indicated no significant interaction effects for training condition, the difference between the means divided by the pooled standard deviation demonstrated large effect sizes in the E + S condition for in HBS 1-RM [S + E vs E + S; -0.54 (9.6 %) vs -1.79 (19.6 %)], AoP-M [-0.72 (7.9 %) vs -1.76 (14.4 %)], SJ [-0.56, (4.4 %), vs -1.08, (8.1 %)], IMVC-LR; [-0.50, (20.3 %) vs -1.05 (27.3 %)], isokinetic hamstring strength 60°/s CON [-0.64, (12.2 %) vs -0.95 (19.2 %)], 120°/sECC [-0.78 (27.9 %) vs -1.55 (23.3 %)] and isokinetic quadriceps strength 180°/s CON [-0.23 (2.5 %) vs -1.52 (13.2 %)]. Results suggest the organisation of concurrent training, recovery time allocated between training bouts and the availability nutrition may be able to modulate small but clinically significant changes in physical performance parameters associated with match-play. This may have practical implications for practitioners who prescribe same day concurrent training protocols.


#7 Modelling relationships between match events and match outcome in elite football
Reference: Eur J Sport Sci. 2015 Jul 20:1-10. [Epub ahead of print]
Authors: Liu H, Hopkins WG, Gómez MA
Summary: Identifying match events that are related to match outcome is an important task in football match analysis. Here we have used generalised mixed linear modelling to determine relationships of 16 football match events and 1 contextual variable (game location: home/away) with the match outcome. Statistics of 320 close matches (goal difference ≤ 2) of season 2012-2013 in the Spanish First Division Professional Football League were analysed. Relationships were evaluated with magnitude-based inferences and were expressed as extra matches won or lost per 10 close matches for an increase of two within-team or between-team standard deviations (SD) of the match event (representing effects of changes in team values from match to match and of differences between average team values, respectively). There was a moderate positive within-team effect from shots on target (3.4 extra wins per 10 matches; 99% confidence limits ±1.0), and a small positive within-team effect from total shots (1.7 extra wins; ±1.0). Effects of most other match events were related to ball possession, which had a small negative within-team effect (1.2 extra losses; ±1.0) but a small positive between-team effect (1.7 extra wins; ±1.4). Game location showed a small positive within-team effect (1.9 extra wins; ±0.9). In analyses of nine combinations of team and opposition end-of-season rank (classified as high, medium, low), almost all between-team effects were unclear, while within-team effects varied depending on the strength of team and opposition. Some of these findings will be useful to coaches and performance analysts when planning training sessions and match tactics.


#8 Quantification of the perceived training load and its relationship with changes in physical fitness performance in junior soccer players
Reference: J Sports Sci. 2015 Jul 29:1-8. [Epub ahead of print]
Authors: Gil-Rey E, Lezaun A, Los Arcos A.
Summary: The aim of this study was to determine the relationship between perceived respiratory and muscular training load (TL) and changes in physical fitness in elite and non-elite junior soccer players. Twenty-eight elite (n = 14, 17.6 ± 0.6 years, 70.3 ± 4.4 kg, 179.7 ± 5.6 cm) and non-elite (n = 14, 17.5 ± 0.5 years, 71.1 ± 6.5 kg, 178.1 ± 5.6 cm) soccer players belonging to a Spanish first and third division football academies and competing in junior Spanish first division (2012-2013) participated in the study. Countermovement jump (CMJ), CMJ arm swing, 5 and 15 m sprints and the Université de Montreal endurance test were performed in January and 9 weeks later in March. In order to quantify TLs, after each training session and match, players reported their session rating of perceived exertion (sRPE) separately for respiratory (sRPEres) and leg musculature (sRPEmus). Elite players accumulated greater weekly training volume (361 ± 14 vs. 280 ± 48 min; effect sizes (ES) = 5.23 ± 1.74; most likely), and perceived respiratory (1460 ± 184 vs. 1223 ± 260 AU; ES = 1.12 ± 0.79; very likely) and muscular (1548 ± 216 vs. 1318 ± 308 AU; ES = 0.99 ± 0.84; likely) TL than did non-elite players. Training volume, sRPEres-TL and sRPEmus-TL were positively and largely correlated (r = 0.67-0.71) with the changes in aerobic fitness. The present results suggest that a low training volume and TL can impair improvement in aerobic fitness in junior soccer players during the in-season period.


#9 Effects of 6-Weeks Resistance Training Combined With Plyometric and Speed Exercises on Physical Performance of Pre-Peak Height Velocity Soccer Players
Reference: Int J Sports Physiol Perform. 2015 Jul 27. [Epub ahead of print]
Authors: Rodriguez-Rosell D1, Franco-Márquez F, Pareja-Blanco F, Mora-Custodio R, Yáñez-García JM, González-Suárez JM, González-Badillo JJ.
Summary: The purpose of this study was to analyze the effects of a low-load, high-velocity resistance training (RT) combined with plyometrics on physical performance in pre-peak height velocity (PHV) soccer players. Thirty young soccer players from the same academy were randomly assigned to either a strength training (STG, n = 15) or a control group (CG, n = 15). Strength training consisted of full squat exercise with low-load (45-58% 1RM) and low-volume (4-8 repetitions per set) combined with jumps and sprints twice a week over 6 weeks of preseason. The effect of the training protocol was assessed using sprint performance over 10 and 20 m (T10, T20, T10-20), countermovement jump (CMJ), estimated one-repetition maximum (1RMest) and average velocity attained against all loads common to pre- and post-tests (AV) in full squat. STG showed significant improvements (P = .004 - .001) and moderate to very large standardized effects (ES = 0.71 - 2.10) in all variables measured, whereas no significant gains were found in CG (ES = -0.29 to 0.06). Moreover, significant test × group interactions (P < .003 - .001) and greater between-groups ES (0.90 - 1.97) were found for all variables in favour of STG compared to CG. Only 6 weeks of preseason low-volume and low-loads RT combined with plyometrics can lead to relevant improvements in strength, jump and sprint performance. Thus, the combination of field soccer training and lightweight strength training could be used for a greater development of the tasks critical to soccer performance in pre-PHV soccer players.


#10 Moderate Altitude Affects High Intensity Running Performance in a Collegiate Women's Soccer Game
Reference: J Hum Kinet, 2015, 
Authors: Bohner JD, Hoffman JR, McCormack WP, Scanlon TC, Townsend JR, Stout JR, Fragala MS, Fukudua DH
Summary: The effect of altitude on soccer game activity profiles was retrospectively examined in six NCAA Division I female soccer players. Comparisons were made between two matches played at sea level (SL) and one match played at a moderate altitude (1839 m). A 10-Hz global positioning system device was used to measure distance and velocity. The rate of total distance capacity (TDC) and high intensity running (HIR) as well as percent of time at HIR were evaluated. Significant differences were seen in the distance rate (120.55 ± 8.26 m?min-1 versus 105.77 ± 10.19 m?min-1) and the HIR rate (27.65 ± 9.25 m?min-1 versus 25.07 ± 7.66 m?min-1) between SL and altitude, respectively. The percent of time at HIR was not significantly different (p = 0.064), yet tended to be greater at SL (10.4 ± 3.3%) than at altitude (9.1 ± 2.2%). Results indicate that teams residing at SL and competing at a moderate altitude may have a reduced ability in distance covered and a high intensity run rate.