Latest research in football - week 26 - 2016

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

Following studies were retrieved for this week:

#1 Differential Effects of 7 and 16 Groups of Muscle Relaxation Training Following Repeated Submaximal Intensity Exercise in Young Football Players
Reference: Percept Mot Skills. 2016 Feb;122(1):227-37. doi: 10.1177/0031512515625383. Epub 2016 Feb 1.
Authors: Sharifah Maimunah SM, Hashim HA
Summary: This study compares two versions of progressive muscle relaxation (PMR) training (7 and 16 muscle groups) on oxygen consumption (VO2), heart rates, rating of perceived exertion and choice reaction time. Football (soccer) players (N = 26; M age = 13.4 yr., SD = 0.5) were randomly assigned to either 7 muscle groups PMR, 16 muscle groups PMR, or a control group. PMR training requires the participants to tense a muscle, hold the muscle contraction, and then relax it. Measurement was conducted prior to and after the completion of 12 sessions of PMR. The dependent variables were measured following four bouts of intermittent exercise consisting of 12 min. of running at 60% VO2max for 10 min. followed by running at 90% VO2max for 2 min. with a 3-min. rest for each bout. Lower VO2, heart rate, perceived exertion, and quicker reaction time were expected in both relaxation groups compared to the control group. The results revealed a significant reduction in heart rates and choice reaction time for both relaxation groups, but the longer version produced significantly quicker choice reaction time.

#2 Improving Children's Coordinative Skills and Executive Functions: The Effects of a Football Exercise Program
Reference: Percept Mot Skills. 2016 Feb;122(1):27-46. doi: 10.1177/0031512515627527. Epub 2016 Feb 1.
Authors: Alesi M, Bianco A, Luppina G, Palma A, Pepi A
Summary: Recent studies have focused on the positive influence of regular physical activity on executive functioning in children. Coordinative skills (agility) and executive functions (updating, attention, inhibition and planning processes) were investigated in children before and after 6 months of a Football Exercise Program compared to a control group of sedentary peers. The participants were 44 children aged 8.8 years: Group 1 comprised 24 children in a football (i.e., soccer) exercise program and Group 2 comprised 20 sedentary children. At pre-test and post-test, coordinative skills and executive functions were measured. After the Football Exercise Program, there were significant differences between sport and sedentary groups in coordinative skills and executive functions. The football group at post-test showed significantly larger gains than the sedentary group on measures of agility, visuo-spatial working memory, attention, planning and inhibition. Findings shed light on the issue to plan structured sport activities as a natural and enjoyable way to improve cognitive skills.

#3 Can subjective comfort be used as a measure of plantar pressure in football boots?
Reference: J Sports Sci. 2016 Jul 11:1-7. [Epub ahead of print]
Authors: Okholm Kryger K, Jarratt V, Mitchell S, Forrester S
Summary: Comfort has been shown to be the most desired football boot feature by players. Previous studies have shown discomfort to be related to increased plantar pressures for running shoes which, in some foot regions, has been suggested to be a causative factor in overuse injuries. This study examined the correlation between subjective comfort data and objective plantar pressure for football boots during football-specific drills. Eight male university football players were tested. Plantar pressure data were collected during four football-specific movements for each of three different football boots. The global and local peak pressures based on a nine-sectioned foot map were compared to subjective comfort measures recorded using a visual analogue scale for global discomfort and a discomfort foot map for local discomfort. A weak (rs = -0.126) yet significant (P < 0.05) correlation was shown between the peak plantar pressure experienced and the visual analogue scale rated comfort. The model only significantly predicted (P > 0.001) the outcome for two (medial and lateral forefoot) of the nine foot regions. Subjective comfort data is therefore not a reliable measure of increased plantar pressures for any foot region. The use of plantar pressure measures is therefore needed to optimise injury prevention when designing studded footwear.

#4 Internal And External Match Loads Of University-Level Soccer Players: A Comparison Between Methods
Reference: J Strength Cond Res. 2016 Jul 7. [Epub ahead of print]
Authors: Sparks M, Coetzee B, Gabbett TJ
Summary: The aim of this study was to use individualized intensity zones to compare the external (velocity and Player Load, PL) and internal loads (heart rate, HR) of a cohort of university-level soccer players. Thirteen soccer players completed a 40 m maximum speed test and the Yo-Yo Intermittent Recovery Test 1 (Yo-Yo IR1) to determine individualized velocity and HR thresholds. HR values and global positioning system (GPS) data of each player were recorded during five league matches. A large (r = 0.46; p ≤0.01) correlation was found between time spent in the low-intensity (LI) velocity zone (LIVZ) and the LI HR zone. Similarly, there were moderate (r = 0.25; p ≤0.01) to large (r = 0.57; p ≤0.01) correlations between the relative and absolute time spent in the moderate-intensity (MI) velocity zone (MIVZ) and the MI HR zone. No significant correlations (p ≤0.01) existed between the high-intensity (HI) velocity zones (HIVZ) and the HI HR zone. On the other hand, PL showed significant correlations with all velocity and HR (absolute and relative) variables, with the exception of an non-significant correlation between the HI HR variables and PL. To conclude, PL showed good correlations with both velocity and HR zones and therefore may have the potential to serve as a good indicator of both external and internal soccer match loads.

#5 The Physical and Athletic Performance Characteristics of Division I Collegiate Female Soccer Players by Position
Reference: J Strength Cond Res. 2016 Jul 7. [Epub ahead of print]
Authors: Lockie RG, Moreno MR, Lazar A, Orjalo AJ, Giuliano DV, Risso FG, Davis DL, Crelling JB, Lockwood JR, Jalilvand F
Summary: Playing positions in soccer can exhibit different movement demands during a match, contributing to variations in physical and performance characteristics. NCAA soccer features different substitution rules when compared to FIFA-sanctioned matches, which could influence each players' characteristics. Therefore, this study determined the athletic performance characteristics of Division I female soccer players. Twenty-six players (3 goalkeepers; 8 defenders; 10 midfielders; 5 forwards) from the same squad completed assessments of: lower-body power (vertical and standing broad jump); linear (0-5, 0-10, 0-30 meter [m] sprint intervals) and change-of-direction (pro-agility shuttle; Arrowhead change-of-direction speed test) speed; and soccer-specific fitness (Yo-Yo Intermittent Recovery Test [YYIRT] levels 1 and 2). Players were split into position groups, and a Kruskal-Wallis H test with post hoc pairwise analyses (p < 0.05) calculated significant between-group differences. There were no differences in age, height, or body mass between the positions. Midfielders had a faster 0-5 m time compared to the defenders (p = 0.017), and the goalkeepers (p = 0.030). The defenders (p = 0.011) and midfielders (p = 0.013) covered a greater YYIRT2 distance compared to the goalkeepers. There were no other significant between-position differences. Overall, Division I collegiate female players from the same squad demonstrated similar characteristics as measured by soccer-specific performance tests, which could allow for flexibility in position assignments. However, a relatively homogenous squad could also indicate commonality in training prescription, particularly regarding acceleration and high-intensity running. Strength and conditioning coaches may have to consider the specific movement demands of individual positions when training these capacities.

#6 Aerial Rotation Effects on Vertical Jump Performance Among Highly Skilled Collegiate Soccer Players
Reference: J Strength Cond Res. 2016 Jul 7. [Epub ahead of print]
Authors: Barker LA, Harry JR, Dufek JS, Mercer JA
Summary: In soccer matches, jumps involving rotations occur when attempting to head the ball for a shot or pass from set pieces such as corner kicks, goal kicks, and lob passes. However, the 3-dimensional ground reaction forces used to perform rotational jumping tasks are currently unknown. Therefore, the purpose of this study was to compare bilateral, 3-dimensional, ground reaction forces of a standard countermovement jump (CMJ0) to a countermovement jump with a 180° rotation (CMJ180) among Division 1 soccer players. Twenty-four participants from the university's soccer team performed 3 trials of the CMJ0 and the CMJ180. Dependent variables included jump height, downward and upward phase times, vertical (Fz) peak force and net impulse relative to mass, and medial-lateral (ML) and anterior-posterior (AP) force couple values. Statistical significance was set a priori at α = 0.05. CMJ180 reduced jump height, increased the AP force couple in the downward and upward phases, and increased upward peak Fz (p<0.05). All other variables were not significantly different between groups (p>0.05). However, we did recognize downward peak Fz trended lower in the CMJ0 condition (p=0.059), and upward net impulse trended higher in the CMJ0 condition (p=0.071). It was concluded jump height was reduced during the rotational jumping task, and rotation occurred primarily via AP ground reaction forces through the entire countermovement jump. Coaches and athletes may consider additional rotational jumping in their training programs to mediate performance decrements during rotational jump tasks.

#7 Aerobic endurance performance do not determine the professional career of elite youth soccer players
Reference: J Sports Med Phys Fitness. 2016 Jul 21. [Epub ahead of print]
Authors: Castillo D, Los Arcos A, Martinez-Santos R
Summary: Physical characteristics have been widely analysed in order to understand why some soccer players are more successful than others. Therefore, the aims of this study were: a) to describe the evolution of aerobic endurance performance across 18 years in a Spanish elite soccer academy, b) to know if the playing position could affect physical testing performance, and c) to look into the alleged impact of this factor on the professional career of soccer players. We considered 162 players belonging to the reserve team of an elite Spanish soccer club from 1994 to 2012. The percentage of players that played in the reserve team for at least five matches in Third Division (2nd B) and later promoted to the Spanish First or Second Division was 32%. The participants were classified in three six-year periods and according to their highest competitive level attained until the 2014/2015 season and their regular tactical position. All the players performed a four-stage submaximal intermittent running test with the running speeds 12 km/h (10 min), 13 km/h (10 min), 14 km/h (10 min), and 15 km/h (5 min) in order to assess the individual velocities associated with a [La]b of 3 mmol l-1 (i.e., V3). No differences (p > 0.05) in aerobic fitness were found between the three six- year periods groups (p>0.05), between the tactical positions nor among the competitive levels attained. These findings indicate that aerobic endurance performance (i.e., V3) is not a pertinent trait when identifying players from different seasons, tactical positions and competitive levels.

#8 Off-season effects on functional performance, body composition and blood parameters in top-level professional soccer players
Reference: J Strength Cond Res. 2016 Jul 18. [Epub ahead of print]
Authors: Requena B, García I, Suárez-Arrones L, Sáez de Villarreal E, Orellana JN, Santalla A
Summary: The purpose of the study was to examine the effects of a standard off-season period (OSP) on aerobic, sprint and jumping performance, body and blood composition in a top-level soccer team. Nineteen soccer players were measured. The OSP included to 2-week of no training (resting phase) and 4 week period of moderate-training load (phase in which each player performed the vacation exercise plan). Player's functional performance (15 and 30 m sprint times (s), vertical jump (m) and incremental field test Vam-Eval (km·h)), percentage of body fat (%) and blood composition (haematological and biochemical data) were measured in mid-, end-season and after the OSP. The percentage of body fat was non-altered during the competitive season (10.8±3.6, 10.5±3.5 %) and increased significantly after the OSP (11.6±3.6 %, p<0.05). Similarly, the maximal aerobic speed (VVam-Eval) velocity (km·h) decreased (p<0.05) from 17.4±1 and 17.3±1.2 during the competitive season to 16.6±0.9 after the OSP. The hematocrit and blood hemoglobin concentration increased (P<.05) during the OSP, showing a blood haemoconcentration adaptation. However, sprint time (s) and jump height (m) showed no significant changes after the OSP. Soccer players maintained their functional performance during high-intensity activities such as jumping or sprinting after the OSP proposed. By contrast, there was a decrease in aerobic performance (VVam-Eval) accompanied by a blood haemoconcentration and an increase of body fat mass associated with a reduction of fat-free mass of the lower-limbs. Our data suggest that an end-season evaluation is needed to design holiday training programs focused on regaining aerobic capacity and body composition.

#9 Influence of oxygen uptake kinetics on physical performance in youth soccer
Reference: Eur J Appl Physiol. 2016 Jul 19. [Epub ahead of print]
Authors: Doncaster G, Marwood S, Iga J, Unnithan V
Summary: The purpose of the study was to examine the relationship between oxygen uptake kinetics (VO2 kinetics) and physical measures associated with soccer match play, within a group of highly trained youth soccer players. Seventeen highly trained youth soccer players (age: 13.3 ± 0.4 year, self-assessed Tanner stage: 3 ± 1) volunteered for the study. Players initially completed an incremental treadmill protocol to exhaustion, to establish gaseous exchange threshold (GET) and VO2max (59.1 ± 5.4 mL kg-1 min-1). On subsequent visits, players completed a step transition protocol from rest-moderate-intensity exercise, followed by an immediate transition, and from moderate- to severe-intensity exercise (moderate: 95 % GET, severe: 60 %∆), during which VO2 kinetics were determined. Physical soccer-based performance was assessed using a maximal Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) and via GPS-derived measures of physical soccer performance during soccer match play, three 2 × 20 min, 11 v 11 matches, to gain measures of physical performance during soccer match play. Partial correlations revealed significant inverse relationships between the unloaded-to-moderate transition time constant (tau) and: Yo-Yo IR1 performance (r = -0.58, P = 0.02) and GPS variables [total distance (TD): r = -0.64, P = 0.007, high-speed running (HSR): r = -0.64, P = 0.008 and high-speed running efforts (HSReff): r = -0.66, P = 0.005]. Measures of VO2 kinetics are related to physical measures associated with soccer match play and could potentially be used to distinguish between those of superior physical performance, within a group of highly trained youth soccer players.

#10 Can a Repeated Sprint Ability Test Help Clear a Previously Injured Soccer Player for Fully Functional Return to Activity? A Pilot Study
Reference: Clin J Sport Med. 2016 Jul 15. [Epub ahead of print]
Authors: Padulo J, Attene G, Ardigò LP, Bragazzi NL, Maffulli N, Zagatto AM, Dello Iacono A
Summary: The purpose of the study was to investigate the effects of fatigue induced by a repeated sprint ability (RSA) test on the neuromuscular responses of soccer players with a recent history of lower limb injuries (CH) and a matched control group in good fitness condition (GH). Nine CH and 9 GH with each player was assessed for blood lactate concentration and jumping performance [squat jump (SJ) and countermovement jump (CMJ)] before/after RSA. Post-RSA rate of perceived exertion (RPE) was obtained. Receiver operating characteristic analysis was performed to calculate RSA sensitivity and specificity in distinguishing between CH and GH. Intraclass correlation coefficient was used to assess reliability. No baseline differences were found for any variable. ΔSJ before/after RSA was -14 ± 2% and -5 ± 2% in CH and GH, respectively (P < 0.05). ΔCMJ before/after RSA was -15 ± 2% and -7 ± 2% in CH and GH, respectively (P < 0.05). ΔSJ-based and ΔCMJ-based (before/after RSA) area under curve (AUC) resulted in 0.90 ± 0.07 and 0.86 ± 0.09, respectively, with both AUCs differentiating between CH and GH with 77.78% sensitivity and 88.89% specificity. Pooled AUC resulted in 0.88 ± 0.06. Intraclass correlation coefficient was high (0.85/0.97). Repeated sprint ability is a simple, low-cost field test potentially able to assist in clinical decision making for return to sport.

The Training Manager -