Latest research in football - week 51 - 2013

Latest research in football

As previous literature updates, we have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Lower extremity dexterity is associated with agility in adolescent soccer athletes
Authors: Lyle MA, Valero-Cuevas FJ, Gregor RJ, Powers CM.
Reference: Scand J Med Sci Sports. 2013 Dec 11. doi: 10.1111/sms.12162. [Epub ahead of print]
Summary: Agility is important for sport performance and potentially injury risk; however, factors affecting this motor skill remain unclear. Here, we evaluated the extent to which lower extremity dexterity (LED) and muscle performance were associated with agility. Fourteen male and 14 female soccer athletes participated. Agility was evaluated using a hopping sequence separately with both limbs and with the dominant limb only. The LED test evaluated the athletes' ability to dynamically regulate foot-ground interactions by compressing a spring prone to buckling with the lower limb. Muscle performance included hip and knee isometric strength and vertical jump height. Correlation analyses were used to assess the associations between muscle performance, LED, and agility. Multiple regression models were used to determine whether linear associations differed between sexes. On average, the female athletes took longer to complete the agility tasks than the male athletes. This difference could not be explained by muscle performance. Conversely, LED was found to be the primary determinant of agility (double limb: R2  = 0.61, P < 0.001; single limb: R2  = 0.63, P < 0.001). Our findings suggest that the sensorimotor ability to dynamically regulate foot-ground interactions as assessed by the LED test is predictive of agility in soccer athletes. We propose that LED may have implications for sport performance, injury risk, and rehabilitation.

#2 Serious shoulder injuries in professional soccer: return to participation after surgery
Authors: Hart D, Funk L.
Reference: Knee Surg Sports Traumatol Arthrosc. 2013 Dec 8. [Epub ahead of print]
Summary: An evidence base for the management and prevention of shoulder injuries in soccer is lacking. The aim of this study was to demonstrate the type, mechanism and recovery time after surgery associated with serious shoulder injuries sustained in professional soccer to build an evidence base foundation. Fifty-two professional soccer players underwent shoulder surgery for injuries sustained during match play. Of these, 25 fulfilled the inclusion criteria. Data were collected for injury mechanism and type; clinical, radiological and surgical findings and procedures; and return to full participation. Subjects were all managed by the same surgeon. Labral injuries represented the most common injury type affecting 21 (84 %) subjects; two rotator cuff (8 %) and two combined labral/rotator cuff (8 %) injuries were less common. Fourteen (56 %) subjects sustained a high-energy trauma injury in a combined abduction and external rotation position. Six (24 %) subjects sustained a low-energy trauma mechanism in variable positions, while five (20 %) had a gradual onset of symptoms. Twenty-two (88 %) subjects reported a dislocation as a feature of their presentation. All of the subjects with high- and low-energy trauma mechanisms reported a dislocation occurring at the time of injury. Eight (32 %) subjects had sustained a previous significant shoulder injury to the ipsilateral side. Goalkeepers did not sustain low-energy trauma injuries. Outfield players returned to full participation in a mean time of 11.6 weeks, while goalkeepers did so in 11.1 weeks post-surgery. Return to participation time ranged from 7 to 24 weeks with a median of 11 weeks. Professional soccer players can expect a return to participation within 12 weeks post-surgery. The majority of serious shoulder injuries in soccer occur at a positional extreme of external rotation and abduction in high-energy situations, while a significant number occur in low-energy situations away from this position. Most serious shoulder injuries in professional soccer are dislocations. Previous shoulder injury is considered a risk factor.

#3 Head Impact Exposure in Youth Football: Elementary School Ages 7-8 Years and the Effect of Returning Players
Authors: Young TJ, Daniel RW, Rowson S, Duma SM.
Reference: Clin J Sport Med. 2013 Dec 9. [Epub ahead of print]
Summary: To provide data describing the head impact exposure of 7- to 8-year-old football players. Head impact data were collected from 19 players over the course of 2 seasons using helmet-mounted accelerometer arrays. Data were collected from 2 youth football teams in Blacksburg, VA, spanning 2 seasons. A total of 19 youth football players aged 7-8 years were investigated. Head impact frequency, acceleration magnitude, and impact location for games, practices, and the season as a whole were measured. The average instrumented player sustained 9 ± 6 impacts per practice, 11 ± 11 impacts per game, and 161 ± 111 impacts per season. The average instrumented player had a median impact of 16 ± 2 g and 686 ± 169 rad/s and a 95th percentile impact of 38 ± 13 g and 2052 ± 664 rad/s throughout a season. Impacts of 40 g or greater tended to occur more frequently in practices than in games, and practices had a significantly higher 95th percentile impact magnitude than games (P = 0.023). Returning players had significantly more impacts than first time players (P = 0.007). These data are a further step toward developing effective strategies to reduce the incidence of concussion in youth football and have applications toward youth-specific football helmet designs.

#4 The development of a soccer-specific training drill for elite-level players
Authors: Kelly DM, Gregson W, Reilly T, Drust B.
Reference: J Strength Cond Res. 2013; 27(4):938-43. doi: 10.1519/JSC.0b013e3182610b7d.
Summary: The use of sports-specific technical practices as a physical training stimulus has increased in recent years in soccer. Such approaches, although effective, can produce different levels of physiological strain in the individual players within the session, thereby limiting the usefulness of the training session for all players. The aim of this study was to develop a high-intensity soccer-specific training (SST) drill that was not only based on the demands of match-play but also would reduce the variability in the physiological response to training compared with other specific drills. To evaluate this approach to training, the SST drill was compared with a "traditional" aerobic interval training (AIT) protocol and a small-sided games (SSG) drill. Each training protocol was carried out across 4 × 4-minute exercise bouts, interspersed by 4 × 3 minutes of active recovery. Mean ± SD heart rates (HRs) for the 4-minute exercise bouts during SST (175 ± 5 b·min) and AIT (174 ± 6 b·min) were significantly higher than that observed during the SSG protocol (170 ± 6 b·min; p < 0.05). Heart rate during the SST drill showed less interparticipant variability (mean ± SD HR ranged from 169 ± 6 to 180 ± 5 b·min) when compared with those during AIT (157 ± 8 to 186 ± 8 b·min) and SSG (143 ± 10 to 179 ± 78 b·min) training conditions. Ratings of perceived exertion (SST, 6 ± 2; AIT, 7 ± 1; SSG, 5 ± 1) across the entire exercise period were similar between the 3 training conditions (p > 0.05). These results indicate that the SST stimulates a more uniform physiological response than other currently adopted specific endurance training protocols used in soccer. This would suggest that it provides a valid alternative to the current approaches used for the aerobic training of players.

#5 Preseason variations in aerobic fitness and performance in elite-standard soccer players: a team study
Authors: Castagna C, Impellizzeri FM, Chaouachi A, Manzi V.
Reference: J Strength Cond Res. 2013 Nov;27(11):2959-65. doi: 10.1519/JSC.0b013e31828d61a8.
Summary: The aim of this study was to examine the effects of individual training loads considered as permanent in selected heart-rate (HR) zones on aerobic fitness and performance in elite professional soccer players. Eighteen professional soccer players were observed during the prechampionship training period (8 weeks). Speeds and HR at 2 and 4 mmol · L blood-lactate concentrations (S2, S4, respectively), VO2max, and Yo-Yo intermittent recovery test level 1 performance (Yo-Yo IR1) were assessed pretraining and posttraining. Training intensities were categorized using 3 HR zones: low intensity (<HR 2 mmol · L), moderate intensity (between HR 2 and 4 mmol · L), and high intensity (>HR 4 mmol · L). Training-session HRs (n = 900) showed a polarized distribution with 73.6 ± 3.7 (2,945 ± 148 minutes), 19.1 ± 3.5 (763 ± 141 minutes), and 7.3 ± 2.9% (292 ± 116 minutes) of the total training time spent at low, moderate, and high intensities, respectively (p < 0.001). The S2 and S4 significantly improved posttraining (+10 and 7%, respectively, p < 0.001). The VO2max and Yo-Yo IR1 values were 6 and 19.5% higher posttraining, respectively (p < 0.01). Training performed at high intensity was significantly related to relative improvement in S2 (r = 0.78, p = 0.002), S4 (r = 0.60, p = 0.03), VO2max (r = 0.65, p = 0.02), and Yo-Yo IR1 (r = 0.66, p = 0.01). The results of this study provided further evidence for HR longitudinal validity and effectiveness of the high-intensity training (i.e., >90% HRmax) in men's professional soccer. In this regard, the time spent at high intensity should be in the range of 7-8% of the total training time during preseason.

#6 Effect of an injury prevention program on muscle injuries in elite professional soccer
Reference: J Strength Cond Res. 2013 Dec;27(12):3275-85. doi: 10.1519/JSC.0b013e318290cb3a.
Authors: Owen AL, Wong del P, Dellal A, Paul DJ, Orhant E, Collie S.
Summary: Due to the continual physical, physiological, and psychological demands of elite level soccer increasing the incidence and risk of injuries, preventative training programs have become a common feature of soccer players training schedule. The aim of the current investigation was to examine the effectiveness of a structured injury prevention program on the number of muscle injuries and the total number of injuries within elite professional soccer. The present study was conducted over 2 consecutive seasons, of which the first (2008-2009) being the intervention season and the second the control season (2009-2010). In total, 26 and 23 elite male professional soccer players competing within the Scottish Premier League and European competition participated. The training program was performed twice weekly for the entirety of the season (58 prevention sessions). The results revealed an increase in the total number of injuries within the intervention season (88 vs. 72); however, this was largely due to the greater number of contusion injuries sustained within the intervention season (n = 44) when compared with control season (n = 23). Significantly less muscle injuries were observed during the intervention season (moderate effect), and this occurred concomitant with a bigger squad size (large effect, p < 0.001). The findings from this study identify that a multicomponent injury prevention-training program may be appropriate for reducing the number of muscle injuries during a season but may not be adequate to reduce all other injuries.


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