Last 30 days

Friday, March 29, 2013

Recent studies with practical applications to elite football





 

Testing visual elements at Panathinaikos FC Performance Lab (March 2008)

 
Soichi (2013). Peripheral visual perception during exercise: why we cannot see. Exercise & Sport Sciences Reviews 41(2): 87-92

Faculty of Sports and Health Science, Fukuoka University,  Japan

Peripheral visual perception may be relevant to performance in sports. Peripheral visual perception seems to be impaired during strenuous exercise. The hypothesis proposed is that a decrease in cerebral oxygenation is associated with impairment in peripheral visual perception during strenuous exercise. Recent behavioral and physiological data are presented to support the hypothesis.

Free access
http://journals.lww.com/acsm-essr/Fulltext/2013/04000/Peripheral_Visual_Perception_During_Exercise___Why.4.aspx


Lehr et al (2013). Field-expedient screening and injury risk algorithm categories as predictors of noncontact lower extremity injury. Scand J Med Sci Sports March 20, [Epub ahead of print]

Department of Physical Therapy, Lebanon Valley College, Pennsylvania, USA.

In athletics, efficient screening tools are sought to curb the rising number of noncontact injuries and associated health care costs. The authors hypothesized that an injury prediction algorithm that incorporates movement screening performance, demographic information, and injury history can accurately categorize risk of noncontact lower extremity (LE) injury. One hundred eighty-three collegiate athletes were screened during the preseason. The test scores and demographic information were entered into an injury prediction algorithm that weighted the evidence-based risk factors. Athletes were then prospectively followed for noncontact LE injury. Subsequent analysis collapsed the groupings into two risk categories: Low (normal and slight) and High (moderate and substantial). Using these groups and noncontact LE injuries, relative risk (RR), sensitivity, specificity, and likelihood ratios were calculated. Forty-two subjects sustained a noncontact LE injury over the course of the study. Athletes identified as High Risk (n = 63) were at a greater risk of noncontact LE injury (27/63) during the season [RR: 3.4 95% confidence interval 2.0 to 6.0].

Conclusion
These results suggest that an injury prediction algorithm composed of performance on efficient, low-cost, field-ready tests can help identify individuals at elevated risk of noncontact LE injury.



Meister et al. (2013). Indicators for high physical strain and overload in elite football players. Scand J Med Sci Sports March 20, [Epub ahead of print]

Institute of Sports and Preventive Medicine (FIFA, Medical Centre of Excellence), Saarland University, Saarbrücken, Germany Institute of Sports Medicine, University Paderborn, Paderborn, GermanyUniversity of Basel, Institute of Exercise and Health Sciences, Basel, Switzerland.


Laboratory, psychological and performance parameters as possible indicators of physical strain and overload during highly demanding competition phases were evaluated in elite male football players. In two studies with the same objective, periods of high (HE: >270 min during 3 weeks before testing) and low (LE: <270 min) match exposure were compared over the course of an entire season. In study 1 (n=88 players of the first and second German leagues; age: 25.6±4.3 years; body mass index (BMI): 23.2±1.0 kg/m(2) ), blood count, CK, urea, uric acid, CRP and ferritin were determined. In study 2, 19 players of the third German league and the highest under-19 league (age: 19.7±2.8 years; BMI: 22.8±1.7 kg/m(2) ) were screened for individual vertical jump height, maximal velocity and by the Recovery-Stress-Questionnaire for Athletes (REST-Q Sport). The mean differences in exposure times were 180 min (study 1: quartiles: 105, 270 min) and 247 min (study 2: 180, 347 min), respectively. Significant differences were found neither in blood parameters (study 1; P>0.36) nor in physiological testing results or in REST-Q scores (study 2; P>0.20).

Conclusion
A 3-week period of high match exposure in elite football players does not affect laboratory, psychometric and performance parameters.


Casals and Martinez (2013). Modelling player performance in basketball through mixed models. Int J Perfom Anal Sport, 13(1): 64-82

University of Wales, Cardiff

The aims of this study were to identify variables which may potentially influence player performance, and to implement a statistical model to study their relative contribution in order to explain two outcomes: points and win score. We used all the possible variables affecting player performance creating a comprehensive database from two sources of statistical information about the NBA 2007 regular season: www.basketball-reference.com and www.nbastuffer.com. The data employed for the analysis were composed of 2187 cases (27 players * 81 games), having followed a filtering process. We dealt with a balanced study design with repeated measurements given that each player was observed the same number of games, and therefore the player was considered as a random effect. We carried out mixed models to quantify the variability in points and win score among players. Minutes played, the usage percentage and the difference of quality between teams were the main factors for variations in points made and win score. The interaction between player position and age was important in win score.

Conclusions
We encourage managers and coaches of sports teams to choose appropriate methods according to their aims. Future research should take into consideration the use of models with random effects on players' characteristics.


Fradua et al (2013). Designing small-sided games for training tactical aspects in soccer: extrapolating pitch sizes from full-size professional matches. J Sport Sci 31(6): 573-581.

University of Granada, Physical Education and Sport , Granada , Spain.

The aims of this study were to examine the 1) individual playing area, 2) length and width of the rectangle encompassing the individual playing area and 3) distance between the goalkeepers and their nearest team-mates during professional soccer matches and compare these to previously reported pitch sizes for small-sided games (SSGs). Data were collected from four Spanish La Liga matches of the 2002-03 season, and notated post-event using the Amisco® system. The pitch sizes obtained from real matches were smaller and different from those used previously for SSGs. In addition, the current pitch sizes show significant (P < 0.001) effect of ball location in all variables examined. For example, overall individual playing area (F [5, 2562] = 19.99, P < 0.001, η(2 )= 0.04) varied significantly across six different zones of the pitch. Based on these empirical results, pitch sizes with individual playing areas ranging from 65 m(2) to 110 m(2) and length to width ratio of 1:1 and 1:1.3 are generally recommended for training tactical aspects according to different phases of play.

Conclusion
It is possible to design SSGs with a more valid representation of the tactical conditions experienced in full-size matches and their use may improve the training effect of tactical aspects of match performance in soccer.



Eynon et al. (2013). ACTN3 R577X polymorphism and team-sport performance: a study involving three European cohorts. J Sci Med Sport March 20 [Epub ahead of print]

School of Sport and Exercise Sciences, Victoria University, Australia; Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, Australia.


We compared the genotype and allele frequencies of the ACTN3 R577X (rs1815739) polymorphisms between team-sport athletes (n=205), endurance athletes (n=305), sprint/power athletes (n=378), and non-athletic controls (n=568) from Poland, Russia and Spain; all participants were unrelated European men. Genomic DNA was extracted from either buccal epithelium or peripheral blood using a standard protocol. Genotyping was performed using several methods, and the results were replicated following recent recommendations for genotype-phenotype association studies. Genotype distributions of all control and athletic groups met Hardy-Weinberg equilibrium (all p>0.05). Team-sport athletes were less likely to have the 577RR genotype compared to the 577XX genotype than sprint/power athletes [odds ratio: 0.58, 95% confidence interval: 0.34-0.39, p=0.045]. However, the ACTN3 R577X polymorphism was not associated with team-sports athletic status, compared to endurance athletes and non-athletic controls. Furthermore, no association was observed for any of the genotypes with respect to the level of competition (elite vs. national level).

Conclusion
The ACTN3 R577X polymorphism was not associated with team-sport athletic status, compared to endurance athletes and non-athletic controls, and the observation that the 577RR genotype is overrepresented in power/sprint athletes compared with team-sport athletes needs to be confirmed in future studies.


Sparks and Close (2013). Validity of a portable urine refractometer: the effects of sample freezing. J Sports Sci 31(7): 745-749.

Department of Sport and Physical Activity , Edge Hill University, UK.

The use of portable urine osmometers is widespread, but no studies have assessed the validity of this measurement technique. Furthermore, it is unclear what effect freezing has on osmolality. One-hundred participants of mean (±SD) age 25.1 ± 7.6 years, height 1.77 ± 0.1 m and weight 77.1 ± 10.8 kg provided single urine samples that were analysed using freeze point depression (FPD) and refractometry (RI). Samples were then frozen at -80°C (n = 81) and thawed prior to re-analysis. Differences between methods and freezing were determined using Wilcoxon's signed rank test. Relationships between measurements were assessed using intraclass correlation coefficients (ICC) and typical error of estimate (TE). Osmolality was lower (P = 0.001) using RI (634.2 ± 339.8 mOsm · kgH2O(-1)) compared with FPD (656.7 ± 334.1 mOsm · kgH2O(-1)) but the TE was trivial (0.17). Freezing significantly reduced mean osmolality using FPD (656.7 ± 341.1 to 606.5 ± 333.4 mOsm · kgH2O(-1); P < 0.001), but samples were still highly related following freezing (ICC, r = 0.979, P < 0.001, CI = 0.993-0.997; TE = 0.15; and r=0.995, P < 0.001, CI = 0.967-0.986; TE = 0.07 for RI and FPD respectively). Despite mean differences between methods and as a result of freezing, such differences are physiologically trivial.

Conclusion
The use of RI appears to be a valid measurement tool to determine urine osmolality.


Source: Pubmed

Friday, March 8, 2013

Applied Physiology: what's new?


uefa.com

 
Girard et al (2013). Hot conditions improve power output during repeated cycling sprints without modifying neuromuscular fatigue characteristics. Eur J Appl Physiol 113(2): 359-369
 
ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
 
This study investigated the effect of hot conditions on repeated sprint cycling performance and post-exercise alterations in isometric knee extension function. Twelve physically active participants performed 10 × 6-s "all-out" sprints on a cycle ergometer (recovery = 30 s), followed 6 min later by 5 × 6-s sprints (recovery = 30 s) in either a neutral (24 °C/30 %rH) or a hot (35 °C/40 %rH) environment. Neuromuscular tests including voluntary and electrically evoked isometric contractions of the knee extensors were performed before and after exercise. Average core temperature during exercise was higher (38.0 ± 0.1 vs. 37.7 ± 0.1 °C, respectively; P < 0.05) in hot versus neutral environments. Peak power output decreased (-17.9 % from sprint 1 to sprint 10 and -17.0 % from sprint 11 to sprint 15; P < 0.001) across repetitions. Average peak power output during the first ten sprints was higher (+3.1 %; P < 0.01) in the hot ambient temperature condition. Maximal strength (-12 %) and rate of force development (-15 to -26 %, 30-200 ms from the onset of contraction) decreased (P < 0.001) during brief contractions after exercise, irrespectively of the ambient temperature. During brief maximal contractions, changes in voluntary activation (~80 %) were not affected by exercise or temperature. Voluntary activation declined (P < 0.01) during the sustained contraction, with these reductions being more pronounced (P < 0.05) after exercise but not affected by the ambient temperature. Resting twitch amplitude declined (P < 0.001) by ~42 %, independently of the ambient temperature.

Conclusion
Heat exposure has no effect on the pattern and the extent of isometric knee extensor fatigue following repeated cycling sprints in the absence of hyperthermia.
 
 
Nybo et al (2012). Markers of muscle damage and performance recovery following exercise in the heat. Med Sci Sports Exerc Dec 14 [Epub ahead of print]

Department of Exercise and Sport Sciences,  University of Copenhagen, Denmark.
ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Qatar
Aspire Academy for Sports Excellence, Qatar.

Plasma creatine kinase, serum myoglobin, muscle glycogen and performance parameters (sprint, endurance and neuromuscular testing) were evaluated in 17 semiprofessional soccer players before, immediately after and during 48 h of recovery from a match played in 43°C (HOT) and compared to a control match (21°C with similar turf and set-up). Muscle temperature was ~ 1°C higher (P<0.001) following the game in HOT compared to control, and reached individual values between 39.9 and 41.1°C. Serum myoglobin levels increased by more than 3 fold following the matches (P<0.01), but values were not different in HOT compared to control and they were similar to baseline values following 24 h of recovery. Creatine kinase was significantly elevated both immediately and 24 h after the matches, but the response following HOT was reduced compared to control. Muscle glycogen responses were similar across trials and remained depressed for more than 48 h following both matches. Sprint performance and voluntary muscle activation were impaired to a similar extend following the matches (sprint by ~ 2% and voluntary activation by ~ 1.5%; P<0.05). Both of these performance parameters as well as intermittent endurance capacity (estimated by a Yo-Yo IR1 test) were fully recovered 48 h after both matches.

Conclusion
Environmental heat stress does not aggravate the recovery response from competitive intermittent exercise associated with elevated muscle temperatures and markers of muscle damage, delayed resynthesis of muscle glycogen and impaired post-match performance.
 
 
Areta et al. (2013). Timing and distribution of protein ingestion during prolonged recovery from resistamce exercise alters myofibrillar protein synthesis. J Physiol March 4 [Epub ahead of print]
 
RMIT University, Australian Institute of Sport, McMaster University & Nestle Research Center

Quantity and timing of protein ingestion are major factors regulating myofibrillar protein synthesis (MPS). However, the effect of specific ingestion patterns on MPS throughout a 12 h period is unknown. We determined how different distribution of protein feeding during 12 h recovery after resistance exercise affects anabolic responses in skeletal muscle. 24 healthy trained males were assigned to three groups (n=8/group) and undertook a bout of resistance exercise followed by ingestion of 80 g of whey protein throughout 12 h recovery as either: 8x10 g every 1.5 h (PULSE); 4x20 g every 3 h (intermediate: INT); or 2x40 g every 6 h (BOLUS). Muscle biopsies were obtained at rest and after 1, 4, 6, 7 and 12 h post-exercise. Resting and post-exercise MPS (L-[ring-13C6] phenylalanine), and muscle mRNA abundance and cell signalling were assessed. All ingestion protocols increased MPS above rest throughout 1-12 h recovery (88-148%, P<0.02), but INT elicited greater MPS than PULSE and BOLUS (31-48%, P<0.02). In general signalling showed a BOLUS>INT>PULSE hierarchy in magnitude of phosphorylation. MuRF-1 and SLC38A2 mRNA were differentially expressed with BOLUS.  

Conclusion
20 g of whey protein consumed every 3 h was superior to either PULSE or BOLUS feeding patterns for stimulating myofibrillar protein synthesis throughout the day.  
  

Pruscino et al (2013). Effects of compression garments on recovery following intermittent exercise. Eur J Appl Physiol Jan 12 [Epub ahead of print]
 
Department of Physiology, University of Melbourne, Melbourne, Australia,
The objective of the study was to examine the effects of wearing compression garments for 24 h post-exercise on the biochemical, physical and perceived recovery of highly trained athletes. Eight field hockey players completed a match simulation exercise protocol on two occasions separated by 4 weeks after which lower-limb compression garments (CG) or loose pants (CON) were worn for 24 h. Blood was collected pre-exercise and 1, 24 and 48 h post-exercise for IL-6, IL-1β, TNF-α, CRP and CK. Blood lactate was monitored throughout exercise and for 30 min after. A 5 counter-movement jump (5CMJ) and squat jump were performed and perceived soreness rated at pre-exercise and 1, 24 and 48 h post-exercise. Perceived recovery was assessed post-exercise using a questionnaire related to exercise readiness. Repeated measures ANOVA was used to assess changes in blood, perceptual and physical responses to recovery. CK and CRP were significantly elevated 24 h post-exercise in both conditions (p < 0.05). No significant differences were observed for TNF-α, IL1-β, IL-6 between treatments (p > 0.05). Power and force production in the 5CMJ was reduced and perceived soreness was highest at 1 h post-exercise (p < 0.05). Perceived recovery was lowest at 1 h post-exercise in both conditions (p < 0.01), whilst overall, perceived recovery was greater when CG were worn (p < 0.005).

Conclusion
None of the blood or physical markers of recovery indicates any benefit of wearing compression garments post-exercise. However, muscle soreness and perceived recovery indicators suggest a psychological benefit may exist.


Beaven et al (2012). Intermittent lower-limb occlusion enhances recovery after strenuous exercise. Appl Physiol Nutr Metab, 37(6): 1132-9
 
United Kingdom Sports Council, London, UK.

Repeated cycles of vascular occlusion followed by reperfusion initiate a protective mechanism that acts to mitigate future cell injury. Such ischemic episodes are known to improve vasodilation, oxygen utilization, muscle function, and have been demonstrated to enhance exercise performance. Thus, the use of occlusion cuffs represents a novel intervention that may improve subsequent exercise performance. Fourteen participants performed an exercise protocol that involved lower-body strength and power tests followed by repeated sprints. Occlusion cuffs were then applied unilaterally (2 × 3-min per leg) with a pressure of either 220 (intervention) or 15 mm Hg (control). Participants immediately repeated the exercise protocol, and then again 24 h later. The intervention elicited delayed beneficial effects (24 h post-intervention) in the countermovement jump test with concentric (effect size (ES) = 0.36) and eccentric (ES = 0.26) velocity recovering more rapidly compared with the control. There were also small beneficial effects on 10- and 40-m sprint times. In the squat jump test there were delayed beneficial effects of occlusion on eccentric power (ES = 1.38), acceleration (ES = 1.24), and an immediate positive effect on jump height (ES = 0.61).

Conclusion
Specific beneficial effects on recovery of power production and sprint performance were observed both immediately and 24 h after intermittent unilateral occlusion was applied to each leg.


Samuels (2012) Jet lag and travel fatigue: a comprehensive management plan for sport medicine physicians and high-performance support teams. Clin J Sport Med 22(3): 268-273

Centre for Sleep and Human Performance, Calgary, Canada.

The impact of transcontinental travel and high-volume travel on athletes can result in physiologic disturbances and a complicated set of physical symptoms. Jet lag and travel fatigue have been identified by athletes, athletic trainers, coaches, and physicians as important but challenging problems that could benefit from practical solutions. Currently, there is a culture of disregard and lack of knowledge regarding the negative effects of jet lag and travel fatigue on the athlete's well-being and performance. In addition, the key physiologic metric (determination of the human circadian phase) that guides jet lag treatment interventions is elusive and thus limits evidence-based therapeutic advice. A better understanding of preflight, in-flight, and postflight management options, such as use of melatonin or the judicious application of sedatives, is important for the sports clinician to help athletes limit fatigue symptoms and maintain optimal performance. The purpose of this article was to provide a practical applied method of implementing a travel management program for athletic teams.

Sources:
American Journal of Physiology
Applied Physiology Nutrition and Metabolism
Clinical Sports Medicine
European Journal of Applied Physiology
Journal of Physiology
Medicine & Science in Sport & Exercise