Latest research in football - week 18 Part II - 2014

#1 Motion Characteristics of Women's College Soccer Matches: Female Athletes in Motion (FAiM) Study
Reference: Int J Sports Physiol Perform. 2014 May;9(3):405-14. doi: 10.1123/IJSPP.2013-0526.
Authors: Vescovi JD1, Favero TG.
Summary: The purpose of this study was quantify the locomotor demands of college female soccer matches and compare the relative proportion of distances in specified velocity bands between players completing an entire half with substitutes. Methods: College female soccer players (n = 113) were assessed during a regular-season match using global positioning system technology. An ANCOVA was used to compare the locomotor characteristics for positions and substitutes, adjusting for duration played. Paired t tests compared the proportion of distances for players substituted out and back into the second half. Results: Defenders covered less total absolute distance than midfielders (first half) and midfielders and forwards (second half) with concomitantly lower work rates. Moderate- and high-intensity running were similar between positions within each half. Midfielders substituted into the match had a lower proportion of moderate-intensity running than those substituted out (15% ± 1.8% vs 19% ± 0.9%), and defenders completing an entire first half had a lower proportion of high-intensity running than defenders substituted in or out (6% ± 1.0% vs 11% ± 1.0% and 16% ± 2.8%). There were no differences in the proportion of distances covered within each velocity band for any position in the second half or for the players substituted out and then back in during the second half. The current findings provide novel insight linking the developmental progression between youth and high-level matches for overall demands and work rates. Moderate- and high-intensity distances cumulatively range from 2100 to 2600 m (26-28% total distance) in female college matches. The high amount of consistency observed for the proportions of distance covered suggest that substitution patterns have little impact on locomotor distribution


#2 Lower Running Performance and Exacerbated Fatigue in Soccer Played at 1600 m
Reference: Int J Sports Physiol Perform. 2014 May;9(3):397-404. doi: 10.1123/IJSPP.2012-0375.
Authors: Garvican LA, Hammond K, Varley MC, Gore CJ, Billaut F, Aughey RJ.
Summary: The purpose of the study was to investigated the decrement in running performance of elite soccer players competing at low altitude and time course for abatement of these decrements. Twenty elite youth soccer players had their activity profile, in a sea-level (SL) and 2 altitude (Alt, 1600 m, d 4, and d 6) matches, measured with a global positioning system. Measures expressed in meters per minute of match time were total distance, low- and high-velocity running (LoVR, 0.01-4.16 m/s; HiVR, 4.17-10.0 m/s), and frequency of maximal accelerations (>2.78 m/s2). The peak and subsequent stanza for each measure were identified and a transient fatigue index calculated. Mean heart rate (HR) during the final minute of a submaximal running task (5 min, 11 km/h) was recorded at SL and for 10 d at Alt. Differences were determined between SL and Alt using percentage change and effect-size (ES) statistic with 90% confidence intervals. Mean HR almost certainly increased on d 1 (5.4%, ES 1.01 ± 0.35) and remained probably elevated on both d 2 (ES 0.42 ± 0.31) and d3 (ES 0.30 ± 0.25), returning to baseline at d 5. Total distance was almost certainly lower than SL (ES -0.76 ± 0.37) at d 4 and remained probably reduced on d 6 (ES -0.42 ± 0.36). HiVR probably decreased at d 4 vs SL (-0.47 ± 0.59), with no clear effect of altitude at d 6 (-0.08 ± 0.41). Transient fatigue in matches was evident at SL and Alt, with a possibly greater decrement at Alt. Despite some physiological adaptation, match running performance of youth soccer players is compromised for at least 6 d at low altitude.


#3 Effects of domestic air travel on technical and tactical performance and recovery in soccer
Reference: Int J Sports Physiol Perform. 2014 May;9(3):378-86. doi: 10.1123/IJSPP.2013-0484.
Authors: Fowler P, Duffield R, Vaile J.
Summary: The current study examined the effects of short-haul air travel on competition performance and subsequent recovery. Six male professional Australian football (soccer) players were recruited to participate in the study. Data were collected from 12 matches, which included 6 home and away matches against the same 4 teams. Together with the outcome of each match, data were obtained for team technical and tactical performance indicators and individual player-movement patterns. Furthermore, sleep quantity and quality, hydration, and perceptual fatigue were measured 2 days before, the day of, and 2 days after each match. More competition points were accumulated (P > .05, d = 1.10) and fewer goals were conceded (P > .05, d = 0.93) in home than in away matches. Furthermore, more shots on goal (P > .05, d = 1.17) and corners (P > .05, d = 1.45) and fewer opposition shots on goal (P > .05, d = 1.18) and corners (P < .05, d = 2.32) occurred, alongside reduced total distance covered (P > .05, d = 1.19) and low-intensity activity (P < .05, d = 2.25) during home than during away matches. However, while oxygen saturation was significantly lower during than before and after outbound and return travel (P < .01), equivocal differences in sleep quantity and quality, hydration, and perceptual fatigue were observed before and after competition away compared with home. These results suggest that, compared with short-haul air travel, factors including situational variables, territoriality, tactics, and athlete psychological state are more important in determining match outcome. Furthermore, despite the potential for disrupted recovery patterns, return travel did not impede player recovery or perceived readiness to train.


#4 Three-dimensional kinematic correlates of ball velocity during maximal instep soccer kicking in males
Reference: Eur J Sport Sci. 2014 Apr 23:1-7. [Epub ahead of print]
Authors: Sinclair J, Fewtrell D, Taylor PJ, Bottoms L, Atkins S, Hobbs SJ.
Summary: Achieving a high ball velocity is important during soccer shooting, as it gives the goalkeeper less time to react, thus improving a player's chance of scoring. This study aimed to identify important technical aspects of kicking linked to the generation of ball velocity using regression analyses. Maximal instep kicks were obtained from 22 academy-level soccer players using a 10-camera motion capture system sampling at 500 Hz. Three-dimensional kinematics of the lower extremity segments were obtained. Regression analysis was used to identify the kinematic parameters associated with the development of ball velocity. A single biomechanical parameter; knee extension velocity of the kicking limb at ball contact Adjusted R2 = 0.39, p ≤ 0.01 was obtained as a significant predictor of ball-velocity. This study suggests that sagittal plane knee extension velocity is the strongest contributor to ball velocity and potentially overall kicking performance. It is conceivable therefore that players may benefit from exposure to coaching and strength techniques geared towards the improvement of knee extension angular velocity as highlighted in this study.


#5 Validity and Reliability of New Agility Test among Elite and Subelite under 14-Soccer Players
Reference: PLoS One. 2014 Apr 21;9(4):e95773. doi: 10.1371/journal.pone.0095773. eCollection 2014.
Authors: Hachana Y, Chaabène H, Ben Rajeb G, Khlifa R, Aouadi R, Chamari K, Gabbett TJ.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3994134/pdf/pone.0095773.pdf
Summary: Agility is a determinant component in soccer performance. This study aimed to evaluate the reliability and sensitivity of a "Modified Illinois change of direction test" (MICODT) in ninety-five U-14 soccer players. A total of 95 U-14 soccer players (mean ± SD: age: 13.61±1.04 years; body mass: 30.52±4.54 kg; height: 1.57±0.1 m) from a professional and semi-professional soccer academy, participated to this study. Sixty of them took part in reliability analysis and thirty-two in sensitivity analysis. The intraclass correlation coefficient (ICC) that aims to assess relative reliability of the MICODT was of 0.99, and its standard error of measurement (SEM) for absolute reliability was <5% (1.24%). The MICODT's capacity to detect change is "good", it's SEM (0.10 s) was ≤ SWC (0.33 s). The MICODT is significantly correlated to the Illinois change of direction speed test (ICODT) (r = 0.77; p<0.0001). The ICODT's MDC95 (0.64 s) was twice about the MICODT's MDC95 (0.28 s), indicating that MICODT presents better ability to detect true changes than ICODT. The MICODT provided good sensitivity since elite U-14 soccer players were better than non-elite one on MICODT (p = 0.005; dz = 1.01 [large]). This was supported by an area under the ROC curve of 0.77 (CI 95%, 0.59 to 0.89, p<0.0008). The difference observed in these two groups in ICODT was not statistically significant (p = 0.14; dz = 0.51 [small]), showing poor discriminant ability. MICODT can be considered as more suitable protocol for assessing agility performance level than ICODT in U-14 soccer players.


#6 Effects of in-season low-volume high-intensity plyometric training on explosive actions and endurance of young soccer players
Reference: J Strength Cond Res. 2014 May;28(5):1335-42. doi: 10.1519/JSC.0000000000000284.
Authors: Ramírez-Campillo R, Meylan C, Alvarez C, Henríquez-Olguín C, Martínez C, Cañas-Jamett R, Andrade DC, Izquierdo M.
Summary: Integrating specific training methods to improve explosive actions and endurance in youth soccer is an essential part of players' development. This study investigated the efficiency of short-term vertical plyometric training program within soccer practice to improve both explosive actions and endurance in young soccer players. Seventy-six players were recruited and assigned either to a training group (TG; n = 38; 13.2 ± 1.8 years) or a control group (CG; n = 38; 13.2 ± 1.8 years) group. All players trained twice per week, but the TG followed a 7-week plyometric program implemented within soccer practice, whereas the CG followed regular practice. Twenty-meter sprint time (20-m), Illinois agility test time, countermovement jump (CMJ) height, 20- (RSI20) and 40- (RSI40) cm drop jump reactive strength index, multiple 5 bounds distance (MB5), maximal kicking test for distance (MKD), and 2.4-km time trial were measured before and after the 7-week period. Plyometric training induced significant (p ≤ 0.05) and small to moderate standardized effect (SE) improvement in the CMJ (4.3%; SE = 0.20), RSI20 (22%; SE = 0.57), RSI40 (16%; SE = 0.37), MB5 (4.1%; SE = 0.28), Illinois agility test time (-3.5%, SE = -0.26), MKD (14%; SE = 0.53), 2.4-km time trial (-1.9%; SE = -0.27) performances but had a trivial and nonsignificant effect on 20-m sprint time (-0.4%; SE = -0.03). No significant improvements were found in the CG. An integrated vertical plyometric program within the regular soccer practice can substitute soccer drills to improve most explosive actions and endurance, but horizontal exercises should also be included to enhance sprinting performance.


#7 Monitoring Accelerations With GPS in Football: Time to Slow Down?
Reference: Int J Sports Physiol Perform. 2014 May;9(3):442-5. doi: 10.1123/IJSPP.2013-0187.
Authors: Buchheit M, Al Haddad H, Simpson BM, Palazzi D, Bourdon PC, Di Salvo V, Mendez-Villanueva A.
Summary: The aims of the current study were to examine the magnitude of between-GPS-models differences in commonly reported running-based measures in football, examine between-units variability, and assess the effect of software updates on these measures. Fifty identical-brand GPS units (15 SPI-proX and 35 SPI-proX2, 15 Hz, GPSports, Canberra, Australia) were attached to a custom-made plastic sled towed by a player performing simulated match running activities. GPS data collected during training sessions over 4 wk from 4 professional football players (N = 53 files) were also analyzed before and after 2 manufacturer-supplied software updates. There were substantial differences between the different models (eg, standardized difference for the number of acceleration >4 m/s2 = 2.1; 90% confidence limits [1.4, 2.7], with 100% chance of a true difference). Between-units variations ranged from 1% (maximal speed) to 56% (number of deceleration >4 m/s2). Some GPS units measured 2-6 times more acceleration/deceleration occurrences than others. Software updates did not substantially affect the distance covered at different speeds or peak speed reached, but 1 of the updates led to large and small decreases in the occurrence of accelerations (-1.24; -1.32, -1.15) and decelerations (-0.45; -0.48, -0.41), respectively. Practitioners are advised to apply care when comparing data collected with different models or units or when updating their software. The metrics of accelerations and decelerations show the most variability in GPS monitoring and must be interpreted cautiously.


#8 Time-motion and physiological profile of football training sessions performed by under-15, under-17, and under-19 elite portuguese players
Reference: Int J Sports Physiol Perform. 2014 May;9(3):463-70. doi: 10.1123/IJSPP.2013-0120.
Authors: Abade EA, Gonçalves BV, Leite NM, Sampaio JE.
Summary: The purpose of the study was to provide the time-motion and physiological profile of regular training sessions (TS) performed during the competitive season by under-15 (U15), under-17 (U17), and under-19 (U19) elite-level Portuguese soccer players. One hundred fifty-one elite players of U15 (age 14.0 ± 0.2 y, n = 56), U17 (age 15.8 ± 0.4 y, n = 66), and U19 (age 17.8 ± 0.6 y, n = 29) participated in the study during a 9-wk period. Time-motion and body-impact data were collected using GPS technology (15 Hz) across 38 randomly selected TS that resulted in a total of 612 samples. In addition, heart rate (HR) was continuously monitored (1 Hz) in the selected TS. The total distances covered (m) were higher in U17 (4648.3 ± 831.9), followed by U19 (4212.5 ± 935.4) and U15 (3964.5 ± 725.4) players (F = 45.84, P < .001). Total body impacts and relative impacts were lower in U15 (total: 490.8 ± 309.5, F = 7.3, P < .01), but no differences were identified between U17 (total: 584.0 ± 363.5) and U19 (total: 613.1 ± 329.4). U19 players had less high- and very-high-intensity activity (above 16 km/h; F = 11.8, P < .001) and moderate-intensity activity (10.0-15.9 km/h; F = 15.07, P < .001). HR values showed significant effects of zone (F = 575.7, P < .001) and interaction with age group (F = 9.7, P < .001), with pairwise differences between all zones (zone 1, <75%; zone 2, 75-84.9%; zone 3, 85-89.9%; zone 4, 90%). All players spent most of their time below 75% HRmax (U15, ~50%; U17, ~42%; U19, ~50%). Results showed high variability between TS, refraining from identifying meaningful trends when measuring performance, although different demands were identified according to age group. The U15 TS were less physiologically demanding, probably because of increased focus on small-sided games to develop basic tactical principles and technical skills. The focus on game-like situations imposed higher external and internal workloads on U17 and U19 players.


#9  Relationships between anthropometric measures and athletic performance, with special reference to repeated-sprint ability, in the Qatar national soccer team
Reference: J Sports Sci. 2014 Apr 17:1-12. [Epub ahead of print]
Authors: Brocherie F, Girard O, Forchino F, Al Haddad H, Dos Santos GA, Millet GP.
Summary: The aim of this study was to determine potential relationships between anthropometric parameters and athletic performance with special consideration to repeated-sprint ability (RSA). Sixteen players of the senior male Qatar national soccer team performed a series of anthropometric and physical tests including countermovement jumps without (CMJ) and with free arms (CMJwA), straight-line 20 m sprint, RSA (6 × 35 m with 10 s recovery) and incremental field test. Significant (P < 0.05) relationships occurred between muscle-to-bone ratio and both CMJs height (r ranging from 0.56 to 0.69) as well as with all RSA-related variables (r < -0.53 for sprinting times and r = 0.54 for maximal sprinting speed) with the exception of the sprint decrement score (Sdec). The sum of six skinfolds and adipose mass index were largely correlated with Sdec (r = 0.68, P < 0.01 and r = 0.55, P < 0.05, respectively) but not with total time (TT, r = 0.44 and 0.33, P > 0.05, respectively) or any standard athletic tests. Multiple regression analyses indicated that muscular cross-sectional area for mid-thigh, adipose index, straight-line 20 m time, maximal sprinting speed and CMJwA are the strongest predictors of Sdec (r2 = 0.89) and TT (r2 = 0.95) during our RSA test. In the Qatar national soccer team, players' power-related qualities and RSA are associated with a high muscular profile and a low adiposity. This supports the relevance of explosive power for the soccer players and the larger importance of neuromuscular qualities determining the RSA.


The following references are from last year. I have no idea why they showed up on this search. However, I thought I will display them as they are free for download as well.

#10 Changes in the anaerobic threshold in an annual cycle of sport training of young soccer players
Reference: Biol Sport. 2013 Jun;30(2):137-43. doi: 10.5604/20831862.1044459. Epub 2013 Apr 11.
Authors: Sliwowski R, Andrzejewski M, Wieczorek A, Barinow-Wojewódzki A, Jadczak L, Adrian S, Pietrzak M, Wieczorek S.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3944579/pdf/JBS-30-1044459.pdf
Summary: The aim of the study was to assess changes in the anaerobic threshold of young soccer players in an annual training cycle. A group of highly trained 15-18 year old players of KKS Lech Poznań were tested. The tests included an annual training macrocycle, and its individual stages resulted from the time structure of the sports training. In order to assess the level of exercise capacities of the players, a field exercise test of increasing intensity was carried out on a soccer pitch. The test made it possible to determine the 4 millimolar lactate threshold (T LA 4 mmol · l(-1)) on the basis of the lactate concentration in blood [LA], to establish the threshold running speed and the threshold heart rate [HR]. The threshold running speed at the level of the 4 millimolar lactate threshold was established using the two-point form of the equation of a straight line. The obtained indicators of the threshold running speed allowed for precise establishment of effort intensity used in individual training in developing aerobic endurance. In order to test the significance of differences in mean values between four dates of tests, a non-parametric Friedman ANOVA test was used. The significance of differences between consecutive dates of tests was determined using a post-hoc Friedman ANOVA test. The tests showed significant differences in values of selected indicators determined at the anaerobic threshold in various stages of an annual training cycle of young soccer players. The most beneficial changes in terms of the threshold running speed were noted on the fourth date of tests, when the participants had the highest values of 4.01 m · s(-1) for older juniors, and 3.80 m · s(-1) for younger juniors. This may be indicative of effective application of an individualized programme of training loads and of good preparation of teams for competition in terms of players' aerobic endurance.


#11 Jump landing characteristics in elite soccer players with cerebral palsy
Reference: Biol Sport. 2013 Jun;30(2):91-5. doi: 10.5604/20831862.1044223. Epub 2013 Apr 11.
Authors: Cámara J, Grande I, Mejuto G, Los Arcos A, Yanci J
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3944576/pdf/JBS-30-1044223.pdf
Summary: The aim of the present study was to analyse the parameters that characterize the vertical ground reaction force during the landing phase of a jump, and to determine the relationship among these parameters in elite soccer players with cerebral palsy (CP). Thirteen male members of the Spanish national soccer team for people with CP (mean age: 27.1 ± 4.7 years) volunteered for the study. Each participant performed three counter movement jumps. The characteristics of the first peak of the vertical ground reaction force during the landing phase of a jump, which corresponds to the forefoot contact with the ground, were similar to the results obtained in previous studies. However, a higher magnitude of rearfoot contact with the ground (F2) was observed in participants with CP than in participants without CP. Furthermore, a significant correlation between F2 magnitude and the elapsed time until its production (T2) was not observed (r = -0.474 for p = 0.102). This result implies that a landing technique based on a delay in the production of F2 might not be effective to reduce its magnitude, contrary to what has been observed in participants without CP. The absence of a significant correlation between these two parameters in the present study, and the high magnitude of F2, suggest that elite soccer players with CP should use footwear with proper cushioning characteristics.


#12 Effects of massage under hypoxic conditions on exercise-induced muscle damage and physical strain indices in professional soccer players
Reference: Biol Sport. 2013 Jun;30(2):81-3. doi: 10.5604/20831862.1044221. Epub 2013 Apr 11
Authors: Gatterer H, Schenk K, Wille M, Murnig P, Burtscher M
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3944577/pdf/JBS-30-1044221.pdf
Summary: Reports based on experiences from masseurs and players, mostly without any scientific background, suggest that the combination of a classical regeneration method (i.e. massage) with exposure to hypoxia may enhance regeneration in soccer. The aim of this study was to evaluate whether this specific combination could affect blood parameters related to muscle damage and physical strain after a soccer game. Approximately 15 hours after two separate championship games, 10 professional male outfield players of the first Austrian division were exposed to normobaric hypoxia (FiO2 13.5% ∼ 4000m) or normoxia for 1 hour (30 minutes rest followed by 30 min massage) (cross-over design). Creatine kinase (CK), urea and uric acid (UA) were measured 4 days before the first game, and 15 and 63 hours after the two games. Match play increased CK values independently of the intervention. No effect of the massage in combination with hypoxia was seen. A trend was found between Δ UA ([UA] 48 hours after exposure minus [UA] before exposure) in response to hypoxia and SaO2 measured in hypoxia (r=0.612, p=0.06). Results show that massage under hypoxic conditions had no additional positive effect on the measured parameters compared to massage alone. Solely the trend of a relationship for Δ UA and SaO2 might indicate that redox alterations are a potential consequence of hypoxic exposure.