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Friday, February 22, 2013

Sports Science in Elite Football: what's new? PART 2

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Dellal et al (2013). The effects of a congested fixture period on physical performance, technical activity and injury rate during matches in a professional soccer team. Br J Sports Med Febr 19 [Epub ahead of print] 

In modern professional soccer, the ability to recover from official match-play and intense training is often considered a determining factor in subsequent performance. To investigate the influence of playing multiple games with a short recovery time between matches on physical activity, technical performance and injury rates. The variation of physical (overall distance, light-intensity, low-intensity, moderate-intensity and high-intensity running) and technical performance (successful passes, balls lost, number of touches per possession and duels won) of 16 international players was examined during three different congested periods of matches (six games in 18 days) from the French League and Cup (n=12), and the UEFA Champions' League (n=6) during the 2011-2012 season and compared with that reported in matches outside these periods. Data were collected using a computerised match analysis system (Amisco). Injury rate, time loss injuries, as well as the mechanism, circumstances and severity of the injury were also analysed. No differences were found across the six successive games in the congested period, and between no congested and the three congested periods for all the physical and technical activities. The total incidence of injury (matches and training) across the prolonged congested periods did not differ significantly to that reported in the non-congested periods. However, the injury rate during match-play was significantly higher during the congested period compared with the non-congested period (p<0.001). The injury rate during training time was significantly lower during the congested period compared with the non-congested periods (p<0.001). The mean lay-off duration for injuries was shorter during the congested periods compared with the non-congested periods (9.5±8.8 days vs 17.5±29.6 days, respectively p=0.012, effect sizes=0.5).

Conclusions:
Although physical activity, technical performance and injury incidence were unaffected during a prolonged period of fixture congestion, injury rates during training and match-play and the lay-off duration were different to that reported in matches outside this period.

Ivarsson et al (2013). Psychological predictors of injury occurence: a prospective investigation of professional Swedish soccer players. J Sport Rehabil 22(1): 19-26

Athletes participating in sport are exposed to a high injury risk. Previous research has found a great number of risk factors (both physiological and psychological) that could increase injury risk. One limitation in previous studies is that few have considered the complex interaction between psychological factors in their research design. The aim of the study was to examine whether personality, stress, and coping predicted injury occurrence in an elite soccer population based on a hypothesized model. 56 (n = 38 male, n = 18 female) Swedish Premiere League soccer players were selected based on convenience sampling. Participants completed 4 questionnaires including the Swedish Universities Scales of Personality, Life Events Survey for Collegiate Athletes, and Brief COPE during the initial questionnaire administration. Subsequent to the first meeting, participants also completed the Hassle and Uplift Scale5 once per wk for a 13-wk period throughout the competitive season. A path analysis was conducted examining the influence of personality traits (ie, trait anxiety), state-level stressors (ie, negative-life-event stress and daily hassles), and coping on injury frequency. Results of the path analysis indicated that trait anxiety, negative-life-event stress, and daily hassle were significant predictors of injury among professional soccer players, accounting for 24% of the variance.

Conclusions:
The findings highlight the need for athletes, coaches, and medical practitioners to attempt to reduce state-level stressors, especially daily hassles, in minimizing injury risk. Educating and training athletes and coaches in proactive stress-management techniques appears warranted.


Nedelec et al (2013). Recovery in soccer: part II-recovery strategies. Sports Med 43(1): 9-22

In the formerly published part I of this two-part review, we examined fatigue after soccer matchplay and recovery kinetics of physical performance, and cognitive, subjective and biological markers. To reduce the magnitude of fatigue and to accelerate the time to fully recover after completion, several recovery strategies are now used in professional soccer teams. During congested fixture schedules, recovery strategies are highly required to alleviate post-match fatigue, and then to regain performance faster and reduce the risk of injury. Fatigue following competition is multifactorial and mainly related to dehydration, glycogen depletion, muscle damage and mental fatigue. Recovery strategies should consequently be targeted against the major causes of fatigue. Strategies reviewed in part II of this article were nutritional intake, cold water immersion, sleeping, active recovery, stretching, compression garments, massage and electrical stimulation. Some strategies such as hydration, diet and sleep are effective in their ability to counteract the fatigue mechanisms. Providing milk drinks to players at the end of competition and a meal containing high-glycaemic index carbohydrate and protein within the hour following the match are effective in replenishing substrate stores and optimizing muscle-damage repair. Sleep is an essential part of recovery management. Sleep disturbance after a match is common and can negatively impact on the recovery process. Cold water immersion is effective during acute periods of match congestion in order to regain performance levels faster and repress the acute inflammatory process. Scientific evidence for other strategies reviewed in their ability to accelerate the return to the initial level of performance is still lacking. These include active recovery, stretching, compression garments, massage and electrical stimulation. While this does not mean that these strategies do not aid the recovery process, the protocols implemented up until now do not significantly accelerate the return to initial levels of performance in comparison with a control condition.

Conclusions:
In conclusion, scientific evidence to support the use of strategies commonly used during recovery is lacking. Additional research is required in this area in order to help practitioners establish an efficient recovery protocol immediately after matchplay, but also for the following days. Future studies could focus on the chronic effects of recovery strategies, on combinations of recovery protocols and on the effects of recovery strategies inducing an anti-inflammatory or a pro-inflammatory response.


Elias et al (2012). Effectiveness of water immersion on post-match recovery in elite professional footballers. Int J Sports Physiol Perform Sept 4 [Epub ahead of print]

The efficacy of a single exposure to 14-min of contrast water therapy (CWT) or cold water immersion (COLD) on recovery post-match in elite professional footballers was investigated. Twenty four elite footballers participated in a match followed by one of 3 recovery interventions. Recovery was monitored for 48-hrs post-match. Repeat-sprint ability (6 x 20-m), static and countermovement jump performance, perceived soreness and fatigue were measured pre, immediately following, 24 and 48 h after the match. Soreness and fatigue were also measured 1 h post-match. Post-match, players were randomly assigned to complete passive recovery (PAS) (n=8), COLD (n=8) or CWT (n=8). Immediately post-match, all groups exhibited similar psychometric and performance decrements, which persisted for 48 h only in the PAS group. Repeat-sprinting performance remained slower at 24 and 48 h for PAS (3.9% and 2.0%) and CWT (1.6% and 0.9%) but was restored by COLD (0.2% and 0.0%). Soreness after 48 h was most effectively attenuated by COLD (ES 0.59±0.10) but remained elevated for CWT (ES 2.39±0.29) and PAS (ES 4.01±0.97). Similarly, COLD more successfully reduced fatigue after 48 h (ES 1.02±0.72) compared to CWT (ES 1.22±0.38) and PAS (ES 1.91±0.67). Declines in static and countermovement jump were ameliorated best by COLD.

Conclusions:
An elite professional football match results in prolonged physical and psychometric deficits for 48 h. Cold water immersion was more successful at restoring physical performance and psychometric measures than CWT, with PAS being the poorest.


Nassis G (2012). Effect of altitude on football performance: analysis of the 2010 FIFA World Cup data. J Strength Cond Res May 29 [Epub ahead of print]

Laboratory studies show that altitude ascent impairs endurance performance. Limited data exist on football, and information from official matches are very scarce even for other team sports. The aim of this study was to examine the effect of altitude on football performance during the 2010 World Cup. It was hypothesized that: a) total distance covered, an index of endurance, would be reduced above the altitude of 580 m, and b) technical skills would be affected since altitude alters ball flight characteristics. Physical performance, goals scored and goal keepers' errors that resulted in goals conceded were recorded from the official game statistics of FIFA during the South Africa 2010 World Cup. Matches were played at: sea level (altitude: 0 m), 660 m, 1200-1400 m and 1401-1753 m. After testing for data normality, mean differences were checked with a one-way ANOVA. Results show a 3.1% lower total distance was covered by the teams during the matches played at 1200-1400 m and 1401-1753 m (p< 0.05) compared to sea level. Indices of technical skills including number of goals scored per game and errors made by the goal keepers that resulted in goals conceded, did not differ with altitude.

Conclusion:
Playing football above 1200 m had negative effects on endurance but not technical skills during World Cup 2010 matches. It seems that teams should follow several days of acclimatization before playing at altitude as low as 1200 m, to ameliorate the negative effects of altitude on physical performance.

Source: PubMed

Tuesday, February 12, 2013

Saturday, February 2, 2013

Sports Science in Elite Football: what's new?

dailymail.co.uk

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