Latest research in football - week 42 - 2014

#1 Early osteoarthritis and reduced quality of life after retirement in former professional soccer players
Reference: Clinics (Sao Paulo). 2014 Sep;69(9):589-94.
Authors: Arliani GG, Astur DC, Yamada RK, Yamada AF, Miyashita GK, Mandelbaum B, Cohen M.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4192424/pdf/cln-69-09-589.pdf
Summary: This study aims to compare the prevalence of osteoarthritis in two groups: one comprising former professional soccer players and the other comprising non-professional-athlete participants. Twenty-seven male former professional soccer players and 30 male volunteers from different non-sports professional areas participated in the study. All participants underwent bilateral knee radiography and magnetic resonance imaging. In addition, the quality of life, knee pain and joint function were evaluated and compared using questionnaires given to all participants in both groups. Specific knee evaluations, with regard to osteoarthritis and quality of life, were performed in both groups using the Knee Injury and Osteoarthritis Outcome Score subjective questionnaires and the Short-form 36. The chi-squared test, Fisher's exact test, the Mann-Whitney U test and Student's t-test were used for group comparisons. The between-groups comparison revealed significant differences in the following: pain, symptoms and quality of life related to the knee in the Knee Injury and Osteoarthritis Outcome Score subscales; the physical aspects subscale of the SF-36; total whole-organ magnetic resonance imaging scores with regard to the dominant and non-dominant knees. Former soccer players had worse scores than the controls in all comparisons. Both the clinical and magnetic resonance evaluations and the group comparisons performed in this study revealed that former soccer players have a worse quality of life than that of a control group with regard to physical aspects related to the knee; these aspects include greater pain, increased symptoms and substantial changes in radiographic and magnetic resonance images of the knee.
 
 
#2 Multilevel Development Models of Explosive Leg Power in High-Level Soccer Players
Reference: Med Sci Sports Exerc. 2014 Oct 9. [Epub ahead of print]
Authors: Deprez D, Valente-Dos-Santos J, Silva MJ, Lenoir M, Philippaerts R, Vaeyens R.
Summary: The aim of the present study was to model developmental changes in explosive power based on the contribution of chronological age, anthropometrical characteristics, motor coordination parameters and flexibility. Two different longitudinal, multilevel models were obtained to predict countermovement jump (CMJ) and standing broad jump (SBJ) performance in 356 high-level, youth soccer players, aged 11 to 14 years at baseline. Biological maturity status was estimated (age at peak height velocity, APHV) and variation in the development of explosive power was examined based on three maturity groups (APHV; earliest<P33, P33<average<P66, latest>P66). The best fitting model for the CMJ performance of the latest maturing players could be expressed as: 8.65 + 1.04 x age + 0.17 x age + 0.15 x leg length + 0.12 x fat-free mass + 0.07 x sit-and-reach + 0.01 x moving sideways. The best models for average and earliest maturing players were the same as for the latest maturing players, minus 0.73 and 1.74 cm, respectively. The best fitting model on the SBJ performance could be expressed as follows: 102.97 + 2.24 x age + 0.55 x leg length + 0.66 x fat-free mass + 0.16 x sit-and-reach + 0.13 jumping sideways. Maturity groups had a negligible effect on SBJ performance. These findings suggest that different jumping protocols (vertical vs. long jump) highlight the need for special attention in the evaluation of jump performance. Both protocols emphasized growth, muscularity, flexibility and motor coordination as longitudinal predictors. The use of the SBJ is recommended in youth soccer identification and selection programs, as biological maturity status has no impact on its development through puberty.
 
 
#3 The effect of 8-week plyometric training on leg power, jump and sprint performance in female soccer players
Reference: J Strength Cond Res. 2014 Oct;28(10):2888-94. doi: 10.1519/JSC.0000000000000541.
Authors: Ozbar N, Ates S, Agopyan A.
Summary: The aim of this study was to determine the effect of 8-week plyometric training (PT) on the leg power and jump and sprint performance in female soccer players. Eighteen female soccer players from Women Second League (age = 18.2 ± 2.3 years, height = 161.3 ± 5.4 cm, body mass = 56.6 ± 7.2 kg) were randomly assigned to control (n = 9) and plyometric (n = 9) groups. Both groups continued together with regular technical and tactical soccer training for 4 days a week. Additionally, the plyometric group underwent PT for 8 weeks, 1 day per week, 60-minute session duration. During the 8-week period, the control group was hindered from any additional conditioning training. All players' jumps (triple hop, countermovement jump, and standing broad jump), running speed (20 m), and peak power were evaluated before and after 8 weeks. No significant difference was found between the groups at pretest variables (p > 0.05). Significant improvements were found in the posttest of both the groups (p ≤ 0.05), except for 20-m sprint test in 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 in the plyometric group, compared with the control group (p ≤ 0.05). We concluded that short duration PT is an improved important component of athletic performance in female soccer players. The results indicate that safe, effective, and alternative PT can be useful to strength and conditioning coaches, especially during competition season where less time is available for training.
 
 
#4 The Reliability and Validity of a Soccer-Specific Nonmotorised Treadmill Simulation (Intermittent Soccer Performance Test)
Reference: Journal of Strength & Conditioning Research: July 2014 - Volume 28 - Issue 7 - p 1971–1980 doi: 10.1519/JSC.0000000000000310
Authors: Aldous JWF, Akubat I, Chrismas BCR, Watkins SL, Mauger AR, Midgley AW, Abt G, Taylor L
Summary: This study investigated the reliability and validity of a novel nonmotorised treadmill (NMT)-based soccer simulation using a novel activity category called a “variable run” to quantify fatigue during high-speed running. Twelve male University soccer players completed 3 familiarization sessions and 1 peak speed assessment before completing the intermittent soccer performance test (iSPT) twice. The 2 iSPTs were separated by 6–10 days. The total distance, sprint distance, and high-speed running distance (HSD) were 8,968 ± 430 m, 980 ± 75 m and 2,122 ± 140 m, respectively. No significant difference (p > 0.05) was found between repeated trials of the iSPT for all physiological and performance variables. Reliability measures between iSPT1 and iSPT2 showed good agreement (coefficient of variation: <4.6%; intraclass correlation coefficient: >0.80). Furthermore, the variable run phase showed HSD significantly decreased (p ≤ 0.05) in the last 15 minutes (89 ± 6 m) compared with the first 15 minutes (85 ± 7 m), quantifying decrements in high-speed exercise compared with the previous literature. This study validates the iSPT as a NMT-based soccer simulation compared with the previous match-play data and is a reliable tool for assessing and monitoring physiological and performance variables in soccer players. The iSPT could be used in a number of ways including player rehabilitation, understanding the efficacy of nutritional interventions, and also the quantification of environmentally mediated decrements on soccer-specific performance.
 
 
#5 Periodization Based on Small-Sided Soccer Games: Theoretical Considerations
Reference: Strength & Conditioning Journal: October 2014 - Volume 36 - Issue 5 - p 34–43 doi: 10.1519/SSC.0000000000000067
Authors: Clemente FM, Martins FM, Mendes RS
Summary: Small-sided games are usually used in soccer training to develop elements of physiological, physical, technical, and tactical performance. Nevertheless, few studies have attempted to analyze the physiological effects or provide methodological considerations for training periodization using such games. Thus, the aim of this paper is to review the general effects of small-sided games in terms of physiological responses. As a result, a small review was developed to consider some methodological considerations to implement in soccer training. Finally, an example was proposed of a week spent carrying out soccer microcycles and orientations in order to adopt small-sided games for each session.
 
 
#6 Changes in hydration, body-cell mass and endurance performance of professional soccer players through a competitive season
Reference: J Sports Med Phys Fitness. 2014 Oct 10. [Epub ahead of print]
Authors: Mascherini G, Gatterer H, Lukaski H, Burtscher M, Galanti G.
Summary: The purpose was to determine changes of the bioelectrical impedance vector (BIVA) throughout a soccer season and to ascertain whether vector changes are associated with endurance performance changes. Eighteen professional male soccer players (age = 21.8±3.0 yr, height = 1.8±0.07 m, mass =7.2±6.5 kg) participated in the study. BIVA was conducted serially on 8 occasions throughout one soccer season. Endurance performance (Yo--Yo test) was assessed before the first training session of the pre--season training, after the pre--season training and at the end of the season. Vector length shortened (p<0.05) during pre--season training and was associated with improvements in endurance performance (r=0.569, p=0.034). Vector length and phase--angle increased at mid--season compared to post pre--season training (p<0.05). Vector length at end--season was lower compared to mid--season (p<0.05). No further changes in endurance performance occurred. Bioimpedance vector variations from baseline indicate that fluid--gains occur during the pre--season training, possibly due to plasma volume expansion and enhanced glycogen storage, accompanied by improvements in endurance performance. The vector migration and the increase in phase angle during the competitive season indicate fluid--loss and an increase in body cell mass without effects on performance. At the very end of the season, when training volume and intensity are reduced, body fluid increases again.
 
 
#7 Hamstring Strain Prevention in Elite Soccer Players
Reference: Strength & Conditioning Journal: October 2014 - Volume 36 - Issue 5 - p 10–20 doi: 10.1519/SSC.0000000000000076
Authors: Turner AN, Cree J, Comfort P, Jones L, Chavda S, Bishop C, Reynolds, A
Summary: Hamstring strains are a common soft tissue injury in elite soccer.
The injury and reinjury rates for this are high and efficacious prevention strategies are yet to be standardized. After the research herein, training modalities emphasizing hamstring eccentric strength training progressing from low –velocity to high-velocity activities and the prevention of fatigue are recommended.
 
 
#8 The Influence of Athletic Status on the Passive Properties of the Muscle-Tendon Unit and Traditional Performance Measures in Division I Female Soccer Players and Nonathlete Controls
Reference: J Strength Cond Res 28(7): 2026–2034, 2014
Authors: Palmer, TB, Thompson, BJ, Hawkey, MJ, Conchola, EC, Adams, BM, Akehi, K, Thiele, RM, and Smith, DB.
Summary: The purpose of this study was to determine if passive muscle-tendon properties of the posterior muscles of the hip and thigh and lower-body muscle power could discriminate between athletic status in division I female soccer athletes and nonathlete controls. Ten athletes (mean ± SE, age = 18.70 ± 0.34 years; mass = 64.61 ± 2.16 kg; height = 165.99 ± 1.46 cm; thigh muscle cross-sectional area = 94.08 ± 2.58 cm2) and 11 nonathletes (mean ± SE, age = 19.64 ± 0.51 years; mass = 62.81 ± 2.60 kg; height = 162.44 ± 2.20 cm; thigh muscle cross-sectional area = 86.33 ± 2.81 cm2) performed 2 instrumented straight-leg raise (iSLR) assessments using an isokinetic dynamometer programmed in passive mode to move the foot toward the head at 5°·s−1. During each iSLR, passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curve, and maximum range of motion (ROM) was determined as the point of discomfort but not pain, as indicated by the participant. Lower-body power characteristics were assessed through a countermovement vertical jump (CMJ) test. The results indicated that phase 1 and 2 slopes, CMJ height, and peak power (Pmax) were significantly higher (p = 0.004–0.036) for the athletes compared with the nonathletes; however, maximum ROM was not different (p = 0.601) between groups. Significant relationships were also observed between phase 1 and 2 slopes, and CMJ height and Pmax (r = 0.483–0.827; p ≤ 0.001–0.027). These findings suggest that in addition to traditional power characteristics, passive stiffness may also be a sensitive and effective measure for discriminating athletes from nonathletes. Coaches and practitioners may use these findings when designing training programs aimed at increasing musculotendinous stiffness of the posterior hip and thigh muscles and to help identify athletes with high overall athletic potential.
 
 
#9 The Effect of 8-Week Plyometric Training on Leg Power, Jump and Sprint Performance in Female Soccer Players
Reference: J Strength Cond Res 28(10): 2888–2894, 2014
Authors: Ozbar, N, Ates, S, and Agopyan, A.
Summary: The aim of this study was to determine the effect of 8-week plyometric training (PT) on the leg power and jump and sprint performance in female soccer players. Eighteen female soccer players from Women Second League (age = 18.2 ± 2.3 years, height = 161.3 ± 5.4 cm, body mass = 56.6 ± 7.2 kg) were randomly assigned to control (n = 9) and plyometric (n = 9) groups. Both groups continued together with regular technical and tactical soccer training for 4 days a week. Additionally, the plyometric group underwent PT for 8 weeks, 1 day per week, 60-minute session duration. During the 8-week period, the control group was hindered from any additional conditioning training. All players' jumps (triple hop, countermovement jump, and standing broad jump), running speed (20 m), and peak power were evaluated before and after 8 weeks. No significant difference was found between the groups at pretest variables (p > 0.05). Significant improvements were found in the posttest of both the groups (p ≤ 0.05), except for 20-m sprint test in 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 in the plyometric group, compared with the control group (p ≤ 0.05). We concluded that short duration PT is an improved important component of athletic performance in female soccer players. The results indicate that safe, effective, and alternative PT can be useful to strength and conditioning coaches, especially during competition season where less time is available for training.
 
 
#10 High-Intensity Interval Training Every Second Week Maintains VO2max in Soccer Players During Off-Season
Reference: J Strength Cond Res 28(7): 1946–1951, 2014
Authors: Slettaløkken, G and Rønnestad, BR
Summary: Reduced endurance training among semiprofessional soccer players during off-season may have negative effect on game performance during the competition season. This negative effect can be prevented by adding high-intensity interval training (HIT) to normal activity. In this study, we want to compare 2 different frequencies of HIT (5 bouts of 4 minutes on 87–97% peak heart rate) session on maintenance of aerobic fitness among semiprofessional soccer players during a 6-week off-season period. Seventeen male players at second and third highest soccer division in Norway participated. The subjects were randomized into 1 HIT session every second week (HIT 0.5) or 1 HIT session per week (HIT 1). All participants performed a 20-m shuttle run test and a maximal oxygen uptake (VO2max) test on treadmill before and after the training intervention. VO2max (HIT 0.5, 63.4 ± 5.9 ml·kg−1·min−1; HIT 1, 65.6 ± 2.1 ml·kg−1·min−1) and 20-m shuttle run performance (HIT 0.5, 2335 ± 390 m, HIT 1, 2531 ± 106 m) were not different between the groups before the training intervention. VO2max was maintained after the training intervention in both HIT 0.5 and HIT 1 (64.0 ± 5.9 ml·kg−1·min−1and 64.3 ± 1.3 ml·kg−1·min−1, respectively). There was a reduction in distance covered during the 20-m shuttle run test in HIT 1 and when groups were pooled (−7.9 ± 5.7% and −6.4 ± 7.9%, respectively, p ≤ 0.05). In conclusion, HIT 1 did not maintain VO2max better than HIT 0.5 when added to normal off-season activity. However, performance in 20-m shuttle run, which is a more soccer-specific fitness test than VO2max test, was slightly reduced when both groups was pooled.
 
 
#11 Allometric modelling of peak oxygen uptake in male soccer players of 8-18 years of age
Reference: Ann Hum Biol. 2014 Oct 8:1-9. [Epub ahead of print]
Authors: Valente-Dos-Santos J, Coelho-E-Silva MJ, Tavares OM, Brito J, Seabra A, Rebelo A, Sherar LB, Elferink-Gemser MT, Malina RM.
Summary: Peak oxygen uptake (VO2peak) is routinely scaled as mL O2 per kilogram body mass despite theoretical and statistical limitations of using ratios. The purpose was to examine the contribution of maturity status and body size descriptors to age-associated inter-individual variability in VO2peak and to present static allometric models to normalize VO2peak in male youth soccer players. Total body and estimates of total and regional lean mass were measured with dual energy X-ray absorptiometry in a cross-sectional sample of Portuguese male soccer players. The sample was divided into three age groups for analysis: 8-12 years, 13-15 years and 16-18 years. VO2peak was estimated using an incremental maximal exercise test on a motorized treadmill. Static allometric models were used to normalize VO2peak. The independent variables with the best statistical fit explained 72% in the younger group (lean body mass: k = 1.07), 52% in mid-adolescent players (lean body mass: k = 0.93) and 31% in the older group (body mass: k = 0.51) of variance in VO2peak. The inclusion of the exponential term pubertal status marginally increased the explained variance in VO2peak (adjusted R2 =  36-75%) and provided statistical adjustments to the size descriptors coefficients. The allometric coefficients and exponents evidenced the varying inter-relationship among size descriptors and maturity status with aerobic fitness from early to late-adolescence. Lean body mass, lean lower limbs mass and body mass combined with pubertal status explain most of the inter-individual variability in VO2peak among youth soccer players.
 
 
#12 The efficacy of acute nutritional interventions on soccer skill performance
Reference: Sports Med, 2014. 44(7): 957-70.
Authors: Russell M, Kingsley M
Summary: The use of nutritional ergogenic aids in team sports such as soccer is now commonplace. Aligned with the primary aim of soccer, which is to score more goals than the opposition within the allotted time, the quality of performance of technical actions (i.e., skills) executed during soccer-specific exercise is likely to determine success. However, when seeking to maintain soccer skill performance, information about the efficacy of nutritional interventions is lacking and factors which might modulate the efficacy of such strategies are unclear. This review aimed (i) to systematically evaluate the current research that examines the efficacy of nutritional interventions on soccer skills, and (ii) to provide a qualitative commentary on factors that have the potential to modulate the efficacy of such strategies. Relevant databases (PubMed and SPORTDiscus) were searched up to and including 1 July, 2013 for studies that investigated the efficacy of acute nutritional interventions on soccer skill performances. Overall, 279 records were retrieved. Articles were sequentially excluded from the review based on specific criteria, being: (A) articles that did not report outcomes directly relating to skilled performances in soccer, (B) articles that examined the influence of interventions that were not nutritional in origin and/or were nutritional in origin but provided >3 hours before skill testing commenced, (C) articles that were review papers, and (D) post-acceptance withdrawal of articles methods from database. Articles were independently assessed for the quality of the methods employed based upon the Physiotherapy Evidence Database (PEDro) scale. Records achieving a minimum PEDro score of 5 out of 10 were included in this review. Qualitative appraisal of 13 articles was performed after the application of exclusion criteria and quality assurance processes. The majority (n = 8) of articles examined the influence of carbohydrates on technical performance whereas fewer studies investigated the influence of caffeine ingestion (n = 2) and fluid provision (n = 3). RESULTS: Findings were reported for a total of 171 participants and all but one of the included articles used cross-over study designs. Most participants (94 %) were male, highly trained (reported maximal aerobic capacity range 50-59 ml.kg(-1).min(-1)) and exercised in temperate environments (reported temperature range 13-25 degrees C). Six of the eight studies reported that carbohydrates, consumed in the form of a 6-8 % solution of glucose, sucrose or maltodextrin at rates of 30-60 g.h(-1), enhanced at least one aspect of skilled performance over the duration of exercise (75-90 min). Although some evidence exists to support the consumption of caffeine (6 mg.kg(-1) body mass [BM]) and prescribed fluid to preserve skills performed during soccer-specific exercise, findings from the small number of included studies were inconsistent. The outcome measures and methods used to quantify skilled performance were not consistent across studies; consequently, it was not possible to perform meta-analyses to produce pooled effect sizes in this review. The findings from this systematic review suggest that nutritional interventions, which provide carbohydrate, caffeine and fluid, have potential to preserve skills performed under conditions that induce soccer-specific fatigue. The weight of current evidence supports the consumption of carbohydrate, but is less conclusive with respect to caffeine and fluid provision. It is likely that the efficacy of a nutritional intervention will be modulated by factors including the dose consumed, the mode of administration, individual responsiveness to the intervention and interactions with other physiological changes occurring during soccer-specific exercise. Consequently, these factors should be considered when using carbohydrates, caffeine and fluid provision to maintain skilled performances in soccer. Future research should seek to optimise the nutritional strategies employed to maintain technical performance throughout match-play.