Latest research in football - week 9 - 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 The evaluation of small-sided games as a talent identification tool in highly trained prepubertal soccer players
Reference: J Sports Sci. 2016 Mar 3:1-8. [Epub ahead of print]
Authors: Fenner JS, Iga J, Unnithan V
Summary: The aim of this study was to evaluate physiological and technical attributes of prepubertal soccer players during multiple small-sided games (SSGs), and determine if SSGs can act as a talent identification tool. Sixteen highly trained U10 soccer players participated and separated into two groups of eight. Each group played six small-sided (4 vs. 4) matches of 5-min duration. Each player was awarded total points for the match result and goals scored. A game technical scoring chart was used to rate each player's performance during each game. Time-motion characteristics were measured using micromechanical devices. Total points had a very large significant relationship with game technical scoring chart (r = 0.758, P < 0.001). High-speed running distance had a significantly large correlation with game technical scoring chart (r = 0.547, P < 0.05). Total distance covered had a significant and moderate correlation with game technical scoring chart (r = 0.545, P < 0.05) and total points (r = 0.438, P < 0.05). The results demonstrated a large agreement between the highest-rated players and success in multiple SSGs, possibly due to higher-rated players covering larger distances in total and at high speed. Consequently, multiple SSG could be used to identify the more talented prepubertal soccer players.

#2 Repeated sprint ability in soccer players: associations with physiological and neuromuscular factors
Reference: J Sports Med Phys Fitness. 2016 Mar 3. [Epub ahead of print]
Authors: Baldi M, DA Silva JF, Buzachera CF, Castagna C, Guglielmo LG
Summary: The purpose was to examine the relationship between repeated sprint ability (RSA, 6 x 40 m (20 m + 20 m) with 20-s recovery) and neuromuscular and aerobic fitness variables in male collegiate soccer players. Twenty-six players (age 22.5 ± 3.6 yr) were tested on separate days for countermovement jump (CMJ), squat jump (SJ), and standing long jump (LJ), and for maximal oxygen consumption ( O2max), velocity at onset of blood lactate accumulation (vOBLA), maximal aerobic speed (v O2max), and peak blood lactate concentration (peak [La]). They were also tested for best and mean times on a repeated shuttle sprint ability test. RSA best time (r = -0.73 and r = -0.54) and RSA mean sprint time (r = - 0.69 and r = -0.62) were significantly (p < 0.01) correlated with LJ and CMJ, respectively. Significant correlations (p < 0.05) were also found between RSA mean sprint time and sprint decrement with vOBLA (r = -0.44) and peak [La] (r = 0.47), respectively. This study showed that RSA performance had a large to very large association with the individual level of jump performance and to a smaller extent to aerobic fitness variables in male collegiate soccer players. Given this finding, lower limbs' explosive-strength performance should be regarded as a relevant factor for male soccer.

#3 The effects of short-term detraining on exercise performance in soccer players
Reference: J Exerc Rehabil. 2016 Feb 1;12(1):54-9. doi: 10.12965/jer.160280. eCollection 2016.
Author: Joo CH
Summary: The aim of the present study was to determine whether 1 week of training cessation can affect exercise performance in well-trained soccer players. Upon the completion of a competitive season, 11 male soccer players went through 1-week training cessation. Performances in the 5-m (1.05±0.04 sec vs 1.02±0.03 sec, P=0.03) and 10-m (1.79±0.06 sec vs 1.74±0.06 sec, P=0.03) sprints were significantly increased after 1 week of detraining with a trend for an increase in the 20-m sprint performance (3.07±0.06 sec vs 3.02±0.07 sec, P=0.06). However, the repeated sprint performance (total sprint time [45.7±2.6 sec vs 48.0±2.6 sec, P=0.01] and fatigue index [5.8%±2.8% vs 7.8%±3.2%; P=0.04]) were reduced. In addition, no significant differences were observed for the 30 m (4.23±0.06 sec vs 4.24±0.09 sec, P=0.63), agility (right: 8.08±0.17 sec vs 8.03±0.37 sec, P=0.54; left: 8.05±0.21 sec vs 8.04±0.30 sec, P=0.84), coordination (13.98±1.21 sec vs 14.06±1.34 sec, P=0.75), Yo-Yo intermittent recovery level 2 (1,040.0±291.8 m vs 1,134.5±232.7 m, P=0.08), and knee extensors and flexors peak torques at all applied angular velocities (P<0.05) after detraining. These results indicate that short-term detraining for well-trained soccer players has a significant effect on the speed endurance performance. It is therefore important for the players and their coaches to plan a suitable training program to maintain exercise performance especially speed endurance during off-season.

#4 Enhanced knee joint function due to accelerated rehabilitation exercise after anterior cruciate ligament reconstruction surgery in Korean male high school soccer players
Reference: J Exerc Rehabil. 2016 Feb 1;12(1):29-36. doi: 10.12965/jer.150266. eCollection 2016.
Authors: Lee M, Sung DJ, Lee J, Oh I, Kim S, Kim S, Kim J
Summary: This study was conducted on Korean male high school soccer players who underwent anterior cruciate ligament reconstruction (ACLR) to identify the effects of an accelerated rehabilitation exercise (ARE) program on knee joint isometric strength, thigh circumference, Lysholm score, and active balance agility. We assigned eight test participants each to a physical therapy group (PTG) and an accelerated rehabilitation exercise group (AREG), and compared differences between the groups. Both the PTG and AREG showed significant increases in 30° away and 60° toward isometric strength after treatment. In addition, significant differences were observed in these strength tests between the two groups. Both groups also showed significant increases in thigh circumference, Lysholm score, and active balance agility after treatment, but no significant differences were observed between the two groups. We conclude that the ARE treatment was more effective for improving isometric strength of the knee joint than that of physical therapy, and that an active rehabilitation exercise program after ACLR had positive effects on recovery performance of patients with an ACL injury and their return to the playing field.

#5 Prevalence of Knee Osteoarthritis in 100 Athletically Active Veteran Soccer Players Compared With a Matched Group of 100 Military Personnel
Reference: Am J Sports Med. 2016 Mar 1. pii: 0363546516629648. [Epub ahead of print]
Authors: Paxinos O, Karavasili A, Delimpasis G, Stathi A
Summary: Although knee injuries in professional soccer (football) have been extensively studied, the prevalence of knee osteoarthritis (OA) in veteran players is not well documented. The purpose was to investigate the prevalence of knee OA in retired professional soccer players in comparison with a group of athletically active military personnel. A group of 100 veteran Greek soccer players aged 35 to 55 years (mean [±SD] age, 46.90 ± 5.9 years) were examined for knee OA and were administered the Knee injury and Osteoarthritis Outcome Score (KOOS) questionnaire. A matched group of 100 athletically active military personnel served as a comparison group. The sonographic prevalence of OA was significantly higher in the veteran soccer group (52%) than in the military group (33%) (n = 200; P = .010). This difference remained significant even after excluding participants with a history of knee surgery (44.1% vs 25.3%, respectively) (n = 151; P = .010). Femoral cartilage thickness was similar between the 2 groups (P = .473), while altered knee alignment had no effect on the prevalence of OA (P = .740). With the exception of perceived pain being more prevalent in the military group, there were no other statistically significant differences between the 2 groups in KOOS values. Veteran soccer players had a higher sonographic prevalence of knee OA but better pain scores than a matched group of athletically active military personnel.

#6 Metabolic Power Requirement of Change of Direction Speed in Young Soccer Players: Not All Is What It Seems
Reference: PLoS One. 2016 Mar 1;11(3):e0149839. doi: 10.1371/journal.pone.0149839. eCollection 2016.
Authors: Hader K, Mendez-Villanueva A, Palazzi D, Ahmaidi S, Buchheit M
Download link:
Summary: The aims of this study were to 1) compare the metabolic power demand of straight-line and change of direction (COD) sprints including 45° or 90°-turns, and 2) examine the relation between estimated metabolic demands and muscular activity throughout the 3 phases of COD-sprints. Twelve highly-trained soccer players performed one 25-m and three 20-m sprints, either in straight-line or with one 45°- or 90°-COD. Sprints were monitored with 2 synchronized 100-Hz laser guns to assess players' velocities before, during and after the COD. Acceleration and deceleration were derived from changes in speed over time. Metabolic power was estimated based on di Prampero's approach (2005). Electromyography amplitude (RMS) of 2 lower limb muscles was measured. The expected energy expenditure during time-adjusted straight-line sprints (matching COD sprints time) was also calculated. Locomotor-dependant metabolic demand was largely lower with COD (90°, 142.1±13.5 compared with time-adjusted (effect size, ES = -3.0; 193.2±18.6 and non-adjusted straight-line sprints (ES = -1.7; 168.4±15.3 Metabolic power requirement was angle-dependent, moderately lower for 90°-COD vs. 45°-COD sprint (ES = -1.0; 149.5±10.4 Conversely, the RMS was slightly- (45°, ES = +0.5; +2.1%, 90% confidence limits (±3.6) for vastus lateralis muscle (VL)) to-largely (90°, ES = +1.6; +6.1 (3.3%) for VL) greater for COD-sprints. Metabolic power/RMS ratio was 2 to 4 times lower during deceleration than acceleration phases. Present results show that COD-sprints are largely less metabolically demanding than linear sprints. This may be related to the very low metabolic demand associated with the deceleration phase during COD-sprints that may not be compensated by the increased requirement of the reacceleration phase. These results also highlight the dissociation between metabolic and muscle activity demands during COD-sprints, which questions the use of metabolic power as a single measure of running load in soccer.

#7 Symptoms of Common Mental Disorders and Adverse Health Behaviours in Male Professional Soccer Players
Reference: J Hum Kinet. 2015 Dec 30;49:277-86. doi: 10.1515/hukin-2015-0130. eCollection 2015.
Authors: Gouttebarge V, Aoki H, Kerkhoffs G
Download link:
Summary: The purpose of the study was to present time, scientific knowledge about symptoms of common mental disorders and adverse health behaviours among professional soccer players is lacking. Consequently, the aim of the study was to determine the prevalence of symptoms of common mental disorders (distress, anxiety/depression, sleep disturbance) and adverse health behaviours (adverse alcohol behaviour, smoking, adverse nutrition behaviour) among professional soccer players, and to explore their associations with potential stressors (severe injury, surgery, life events and career dissatisfaction). Cross-sectional analyses were conducted on baseline questionnaires from an ongoing prospective cohort study among male professional players. Using validated questionnaires to assess symptoms of common mental disorders and adverse health behaviours as well as stressors, an electronic questionnaire was set up and distributed by players' unions in 11 countries from three continents. Prevalence of symptoms of common mental disorders and adverse health behaviours among professional soccer players ranged from 4% for smoking and 9% for adverse alcohol behaviour to 38% for anxiety/depression and 58% for adverse nutrition behaviour. Significant associations were found for a higher number of severe injuries with distress, anxiety/depression, sleeping disturbance and adverse alcohol behaviour, an increased number of life events with distress, sleeping disturbance, adverse alcohol behaviour and smoking, as well as an elevated level of career dissatisfaction with distress, anxiety/depression and adverse nutrition behaviour. Statistically significant correlations (p<0.01) were found for severe injuries and career dissatisfaction with most symptoms of common mental disorders. High prevalence of symptoms of common mental disorders and adverse health behaviours was found among professional players, confirming a previous pilot-study in a similar study population.

#8 Pesticide monitoring on soccer fields via shoe wipes and urine samples
Reference: Environ Res. 2016 Feb 24;147:294-296. doi: 10.1016/j.envres.2016.02.027. [Epub ahead of print]
Authors: Gilden R, Plisko M, Hiteshew K, Friedmann E, Milton D
Summary: We sought to determine the feasibility of measuring pesticide exposure of children using athletic fields to which pesticides were recently applied. This project was a pilot feasibility study designed to measure pre and posttest environmental exposure to Horsepower; a combination herbicide containing (4-Chloro-2-methylphenoxy) acetic acid (MCPA), dicamba and triclopyr. A spot application of Horsepower to a soccer field occurred at 8AM. Six players, ages 5-11 years, provided shoe wipes and urine samples before and after evening soccer practice on the field later the same day. We sent samples to commercial labs where shoe wipes were analyzed for a panel of herbicides and urine samples were analyzed for dicamba, triclopyr, and creatinine. All analytes were below level of detection. We established the feasibility of both the recruitment and sampling procedures. Spot application, in the one instance examined, did not result in measurable exposure to pesticides. A larger study involving both spot and broadcast application and including direct observation of pesticide application is needed to ascertain whether pesticide application on athletic fields results in measurable and potentially hazardous exposure of children.

#9 Effect of Sequencing Strength and Endurance Training in Young Male Soccer Players
Reference: J Strength Cond Res 30(3): 841–850, 2016
Authors: Makhlouf, I, Castagna, C, Manzi, V, Laurencelle, L, Behm, DG, and Chaouachi
Summary: This study examined the effects of strength and endurance training sequence (strength before or after endurance) on relevant fitness variables in youth soccer players. Fifty-seven young elite-level male field soccer players (13.7 ± 0.5 years; 164 ± 8.3 cm; 53.5 ± 8.6 kg; body fat; 15.6 ± 3.9%) were randomly assigned to a control (n = 14, CG) and 3 experimental training groups (twice a week for 12 weeks) strength before (SE, n = 15), after (ES, n = 14) or on alternate days (ASE, n = 14) with endurance training. A significant (p = 0.001) intervention main effect was detected. There were only trivial training sequence differences (ES vs. SE) for all variables (p > 0.05). The CG showed large squat 1 repetition maximum (1RM) and medium sprint, change of direction ability, and jump improvements. ASE demonstrated a trivial difference in endurance performance with ES and SE (p > 0.05). Large to medium greater improvements for SE and ES were reported compared with ASE for sprinting over 10 and 30 m (p < 0.02). The SE squat 1RM was higher than in ASE (moderate, p < 0.02). Postintervention differences between ES and SE with CG fitness variables were small to medium (p ≤ 0.05) except for a large SE advantage with the Yo-Yo intermittent recovery test (p < 0.001, large). This study showed no effect of intrasession training sequence on soccer fitness-relevant variables. However, combining strength and endurance within a single training session provided superior results vs. training on alternate days. Concurrent training may be considered as an effective and safe training method for the development of the prospective soccer player.

The Training Manager -