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Saturday, February 2, 2013

Sports Science in Elite Football: what's new?

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Hagglund et al(2013). Risk factors for lower extremity muscle injury in professional soccer: the UEFA injury study. American Journal of Sports Medicine 41(2): 327-335.


Between 2001 and 2010, 26 soccer clubs (1401 players) from 10 European countries participated in the study. Individual player exposure and time loss muscle injuries in the lower extremity were registered prospectively by the club medical staffs during 9 consecutive seasons. Hazard ratios (HRs) were calculated for player-related factors from simple and multiple Cox regression, and odds ratios (ORs) were calculated for match-related variables from simple and multiple logistic regression, presented with 95% confidence intervals (CIs).

RESULTS:

There were 2123 muscle injuries documented in the major lower extremity muscle groups: adductors (n = 523), hamstrings (n = 900), quadriceps (n = 394), and calf (n = 306). Injuries to the adductors (56%; P = .015) and quadriceps (63%; P< .001) were more frequent in the kicking leg. Multiple analysis indicated that having a previous identical injury in the preceding season increased injury rates significantly for adductor (HR, 1.40; 95% CI, 1.00-1.96), hamstring (HR, 1.40; 95% CI, 1.12-1.75), quadriceps (HR, 3.10; 95% CI, 2.21-4.36), and calf injuries (HR, 2.33; 95% CI, 1.52-3.57). Older players (above mean age) had an almost 2-fold increased rate of calf injury (HR, 1.93; 95% CI, 1.38-2.71), but no association was found in other muscle groups. Goalkeepers had reduced injury rates in all 4 muscle groups. Match play on away ground was associated with reduced rates of adductor (OR, 0.56; 95% CI, 0.43-0.73) and hamstring injuries (OR, 0.76; 95% CI, 0.63-0.92). Quadriceps injuries were more frequent during preseason, whereas adductor, hamstring, and calf injury rates increased during the competitive season.

CONCLUSION:

Intrinsic factors found to increase muscle injury rates in professional soccer were previous injury, older age, and kicking leg. Injury rates varied during different parts of the season and also depending on match location.


Lovell et al (2013). Effects of different half-time strategies on second half soccer-specific speed, power and dynamic strength. Scandinavian Journal of Medicine & Science in Sports 23(1): 105-113.

This study compared the effects of whole body vibration (WBV) and a field-based re-warm-up during half-time (HT) on subsequent physical performance measures during a simulated soccer game. Ten semi-professional male soccer players performed 90-min fixed-intensity soccer simulations (SAFT90), using a multi-directional course. During the HT period players either remained seated (CON), or performed intermittent agility exercise (IAE), or WBV. At regular intervals during SAFT90, vastus lateralis temperature (Tm) was recorded, and players also performed maximal counter-movement jumps (CMJ), 10-m sprints, and knee flexion and extension contractions. At the start of the second half, sprint and CMJ performance and eccentric hamstring peak torque were significantly reduced compared with the end of the first half in CON (P≤0.05). There was no significant change in these parameters over the HT period in the WBV and IAE interventions (P>0.05). The decrease in Tm over the HT period was significantly greater for CON and WBV compared with IAE (P≤0.01). A passive HT interval reduced sprint, jump and dynamic strength performance. Alternatively, IAE and WBV at HT attenuated these performance decrements, with limited performance differences between interventions.


Bosquet et al (2013). Effect of training cessation on muscular performance: A meta-analysis. Scandinavian Journal of Medicine & Science in Sports Epub ahead of print 24 January 2013

The purpose of this study was to assess the effect of resistance training cessation on strength performance through a meta-analysis. Seven databases were searched from which 103 of 284 potential studies met inclusion criteria. Training status, sex, age, and the duration of training cessation were used as moderators. Standardized mean difference (SMD) in muscular performance was calculated and weighted by the inverse of variance to calculate an overall effect and its 95% confidence interval (CI). Results indicated a detrimental effect of resistance training cessation on all components of muscular performance: [submaximal strength; SMD (95% CI) = −0.62 (−0.80 to −0.45), P < 0.01], [maximal force; SMD (95% CI) = −0.46 (−0.54 to −0.37), P < 0.01], [maximal power; SMD (95% CI) = −0.20 (−0.28 to −0.13), P < 0.01]. A dose–response relationship between the amplitude of SMD and the duration of training cessation was identified. The effect of resistance training cessation was found to be larger in older people (> 65 years old). The effect was also larger in inactive people for maximal force and maximal power when compared with recreational athletes. Resistance training cessation decreases all components of muscular strength. The magnitude of the effect differs according to training status, age or the duration of training cessation.


Sander et al. (2012). Effect of functional exercises in th ewarm up on sprint performance. Journal of Strength & Conditioning Research Epub ahead of print June 12

The process of warming up prepares athletes for subsequent stress and increases their level of performance. Functional exercises are often included in warm-up programs for power sports, although a positive effect of functional exercises has not been confirmed. The aim of this study was to measure a possible effect on sprint performance of functional exercises included in a warm-up program. A total of 121 elite youth soccer players between 13 and 18 years old participated in this study and performed two different warm-up programs. The first program (NWP) consisted of five minutes of nonspecific running, coordination exercises, stretching and acceleration runs. The second program (WPS) was the same with additional functional exercises. The subjects were tested in linear sprints of approximately 30 meters and in change-of-direction sprints of approximately 10 meters. The t-test for dependent samples shows significant differences between the groups for each segment of the linear sprint (p< 0.01 for 5 m; p< 0.001 for 10 m, 15 m, 20 m, 25 m, 30 m); however, the effect sizes are small. In the change of direction sprint, the t-test also shows significant differences between the groups (p< 0.01 for 10 m left, 10 m right; p< 0.001 for 5 m right). These effect sizes are also small. In the change-of-direction sprint time for 5 m left, the data show no significant differences between the groups. The results show no effects on sprint performance of functional exercises that are implemented in addition to a general warm-up. It appears that a general warm-up program, such as the NWP, generates sufficient activation of the performance-limiting muscles for sprint performance. Functional exercises did not lead to a supplemental activation with a positive effect on sprint performance. Therefore, a warm-up for sprint performance should contain nonspecific running, coordination exercises, stretching exercises and acceleration runs. These components lead to sufficient activation of the muscles involved in sprint performance. Coaches should use the limited time available for warm-up to work efficiently. The recommendation for warm-up is to pass on functional exercises, that have no additional effect in enhancing performance.


Valente-dos-Santos et al. (2012). Modeling developmental changes in functional capacities and soccer-specific skills in male players aged 11-17 years. Pediatric Exercise Science, 24 (4), 603-621.

This study evaluates the contributions of age, growth, skeletal maturation, playing position and training to longitudinal changes in functional and skill performance in male youth soccer. Players were annually followed over 5 years (n = 83, 4.4 measurements per player). Composite scores for functional and skill domains were calculated to provide an overall estimate of performance. Players were also classified by maturity status and playing position at baseline. After testing for multicollinearity, two-level multilevel (longitudinal) regression models were obtained for functional and skill composite scores. The scores improved with age and training. Body mass was an additional predictor in both models [functional (late maturing): 13.48 + 1.05 × centered on chronological age (CA)—0.01 × centered CA2—0.19 × fat mass (FM) + 0.004 × annual volume training—1.04 × dribbling speed; skills (defenders): 7.62 + 0.62 × centered CA—0.06 × centered CA2 + 0.04 × fat-free mass—0.03 x FM + 0.005 × annual volume training—0.19 × repeated-sprint ability + 0.02 × aerobic endurance]. Skeletal maturity status was a significant predictor of functional capacities and playing position of skill performance.


Lundkvist et al. (2012). An interpretative phenomenological analysis of burnout and recovery in elite soccer coaches Qual. Res. Sport, Exerc. & Health, 4 (3), 400-419.

Knowledge about the personal experience of burnout in elite coaches is sparse. We therefore studied subjective experiences associated with burnout in a group of elite soccer coaches; specifically how they describe perceived causes of burnout, symptoms and the subsequent recovery process. A qualitative approach was used, because our aim was to study the coaches' personal experiences of burnout. We conducted semi-structured interviews and used interpretative phenomenological analysis to analyse the data. We interviewed eight Swedish elite soccer coaches who had previously reported high levels of burnout. We found two burnout profiles that matched the coaches' perceived causes of burnout. The first was associated with problems in handling the performance culture itself and the second had to do with the overall situation, including workload, family and health. Our findings describe coach burnout as stemming from a combination of issues, related to both home and work. When combined with work overload, coaches who have problems handling the performance culture in elite sports, and who lack the tools to enhance recovery, are particularly vulnerable to burnout

Source: PubMed

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