Latest research in football - week 29 - 2014

#1 Altered neuromuscular control of leg stiffness following soccer-specific exercise
Reference: Eur J Appl Physiol. 2014 Jul 18. [Epub ahead of print]
Authors: Oliver JL, De Ste Croix MB, Lloyd RS, Williams CA.
Summary: The purpose was to examine changes to neuromuscular control of leg stiffness following 42 min of soccer-specific exercise. Ten youth soccer players, aged 15.8 ± 0.4 years, stature 1.73 ± 0.06 m and mass 59.8 ± 9.7 kg, hopped on a force plate at a self-selected frequency before and after simulated soccer exercise performed on a non-motorised treadmill. During hopping, muscle activity was measured using surface electromyography from four lower limb muscles and analysed to determine feedforward- and feedback-mediated activity, as well as co-contraction. There was a small, non-significant change in stiffness following exercise (26.6 ± 10.6 vs. 24.0 ± 7.0 kN m-1, p > 0.05, ES = 0.25), with half the group increasing and half decreasing their stiffness. Changes in stiffness were significantly related to changes in centre of mass (CoM) displacement (r = 0.90, p < 0.01, extremely large correlation) but not changes in peak ground reaction force (r = 0.58, p > 0.05, large correlation). A number of significant relationships were observed between changes in stiffness and CoM displacement with changes in feedforward, feedback and eccentric muscle activity of the soleus and vastus lateralis muscles following exercise (r = 0.64-0.98, p < 0.05, large-extremely large correlations), but not with changes in co-contraction (r = 0.11-0.55, p > 0.05, small-large correlations). Following soccer-specific exercise individual changes in feedforward- and reflex-mediated activity of the soleus and vastus lateralis, and not co-contraction around the knee and ankle, modulate changes in CoM displacement and leg stiffness.


#2 Epidemiologic study of young soccer player's injuries in U12 to U20
Reference: J Sports Med Phys Fitness. 2014 Aug;54(4):526-35.
Authors: Tourny C, Sangnier S, Cotte T, Langlois R, Coquart J.
Summary: The aim of this study was an epidemiological report of the injuries to young soccer players from pretraining centres (12 to 15 years: U12-U15) and training centres (16 to 20 years: U16-U20). Over 3 years, 618 injuries were analysed, concerning an average of 137 players per season (66 and 71 players in U12-U15 and U16-U20, respectively). The injuries were diagnosed by a physician. Numerous injury-related information were documented: player, player's age category, date of the injury, site of the injury, injured side, type of injury, circumstances: training vs. match and contact vs non-contact, number of days of play missed, severity, and player's position.The injury rate was higher in matches than in training sessions. Non-contact injuries accounted for 77.0% of the injuries for U12-U15 and 65.6% for U16-U20. The injuries were mainly to the thigh and hip in pretraining players (23.3% and 19.0%, respectively), and to the thigh and ankle in training players (32.1% and 20.3%, respectively). Contact injuries occurred more frequently during matches, presumably because of the higher intensity of play. The analysis of match injuries by position indicated that for U12-U15, during the matches, lateral defenders were injured most often: 30.4%. For U16-U20, axial midfielders and axial defenders were most subject to injuries during the matches (26.6% and 23.1%, respectively). These results may help to improve the programming of training. Between the first and third seasons of this study, a decrease in injuries during both matches and training sessions: from 174 to 107 (decrease of 38.5%).

#3 Groin pain and soccer players: male versus female occurrence
Reference: J Sports Med Phys Fitness. 2014 Aug;54(4):487-93.
Authors: Karlsson MK, Dahan R, Magnusson H, Nyquist F, Rosengren BE.
Summary: Groin pain is common in soccer players. Comparison of results from different studies, especially between genders, is difficult as studies use different definitions and data collection procedures. Therefore we conducted a study of both male and female soccer players enabling direct gender comparison. The study enrolled 479 male soccer players aged 25 years (17-43) (mean with range) and 144 female soccer players aged 23 years (16-47), who answered a mailed questionnaire that included specific questions on groin pain and sports history. Data are presented as proportions (%) or as mean with 95% confidence intervals (95% CI). Groin pain was experienced by 55% of male soccer players and 28% of female soccer players, resulting in an odds ratio (OR) of 2.9 (95% CI 1.9, 4.5). Groin pain occurred more often in the preseason, than during the rest of the season in both male and female players (both P<0.001). Playing position in the team or playing league did not seem to influence the risk of suffering groin pain. In soccer players, male gender and preseasonal training appear to be risk factors for developing groin pain.


#4 Effects of a very short-term preseason training procedure on the fitness of soccer players
Reference: J Sports Med Phys Fitness. 2014 Aug;54(4):432-40.
Authors: Meckel Y, Harel U, Michaely Y, Eliakim A.
Summary: The aim of the study was to examine the effect of a very short-term training program on the immediate and late changes in the fitness level of young soccer players during the pre-season period. Twenty-four young (17-18 years) soccer players were randomly assigned to either an interval (9 to 5 X 1000 m) or continuous (9000 to 5000 m) training group, matched for total running distance. While the number of intervals or total distance was reduced every day, speed was increased in each session throughout the five days of both training programs. Each group performed 20 m shuttle run, 10 m sprint, 5 X 10 m run, 250 m run and vertical jump test, before (pre), immediately after (post) and 10 days after (late) completion of five successive training days during the preseason period for the upcoming soccer season. There was a significant increase in aerobic capacity both immediately post-training and in the late test, in both training groups. We found a significantly greater reduced performance in the 250 m run immediately following training in the interval compared to the continuous training group. In addition, there was a decrease in vertical jump that was significantly greater in the interval compared to the continuous training group, both immediately post-training and in the late test. Very short interval or continuous preseason training programs induce significant improvement in aerobic fitness but lead to stagnation or deterioration in anaerobic performance. Considering the opposing effects of both training modes (positive on the aerobic power but negative on the anaerobic performance), coaches should make their choices based on the relevant conditions at hand.


#5 The elements of executive attention in top soccer referees and assistant referees
Reference: J Hum Kinet. 2014 Apr 9;40:235-43. doi: 10.2478/hukin-2014-0025. eCollection 2014.
Authors: Pietraszewski P, Roczniok R, Maszczyk A, Grycmann P, Roleder T, Stanula A, Fidos-Czuba O, Ponczek M.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4096105/pdf/jhk-40-235.pdf
Summary: The aim of the present study was to compare executive attention of top soccer referees and assistant referees at different levels of professional attainment. The sample consisted of 53 subjects (FIFA and national level) - 30 referees and 23 assistant referees. Executive attention of assistant referees was significantly better than the referees' (p<0.01). Furthermore, extraclass and international referees demonstrated better executive attention than the first-league referees (p<0.01). The research results have proved that referees' executive attention differs depending on their function and professional level, as well as indicated that the quality of abilities may influence the number and correctness of decisions made during a game. This elementary cognitive process may be strongly shaped by individual's experience and age. This finding may be instrumental in screening referees and developing criteria for recruiting future referees.


#6 Return to Play After Lateral Meniscectomy Compared With Medial Meniscectomy in Elite Professional Soccer Players
Reference: Am J Sports Med. 2014 Jul 17. pii: 0363546514540271. [Epub ahead of print]
Authors: Nawabi DH, Cro S, Hamid IP, Williams A.
Summary: Meniscectomy is frequently performed in elite soccer athletes to allow return to a high level of performance as early as possible. Although lateral meniscectomy is known to have more serious long-term sequelae than medial meniscectomy, little is known about the effect of lateral meniscectomy on the time to return to play during the early recovery phase in professional soccer players. The hypothesis was that lateral meniscectomy results in longer times to return to preinjury level of competition and a higher incidence of adverse outcomes compared with medial meniscectomy in elite professional soccer players. A single-surgeon database containing the injury history and operative details of elite soccer athletes from 2005 to 2009 was used to identify players who had undergone an isolated partial lateral or medial meniscectomy. The time to return to preinjury level of competition, the incidence of adverse events during early recovery, and the need for further arthroscopy were recorded. Time to return to play was analyzed by using the Kaplan-Meier method. A multivariate analysis was used to control for age, location of meniscectomy, percentage of meniscus excised, and type of tear. Ninety soccer players were identified, of which 42 had a lateral meniscectomy and 48 had a medial meniscectomy. The median time to return to play, to the nearest week, was longer in the lateral group than the medial group (7 vs 5; P < .001). At all time points after surgery, the cumulative probability of returning to play was 5.99 times greater (95% confidence interval, 3.34-10.74; P < .001) after medial meniscectomy. More lateral meniscectomy cases experienced adverse events related to pain/swelling-29 (69%) vs 4 (8%) (P < .001)-and required a second arthroscopy: 3 (7%) vs 0 (P = .098). The time to return to preinjury level of competition is significantly longer after lateral than medial meniscectomy in elite professional soccer athletes. Lateral meniscectomy has a higher incidence of adverse events in the early recovery period, including pain/swelling and the need for further arthroscopy. It is also associated with a significantly lower rate of return to play. These findings form the basis of an important discussion that must be had with player and club before a lateral meniscectomy is performed in elite soccer athletes.


#7 Inter-individual Variability in Soccer Players of Different Age Groups Playing Different Positions
Reference: J Hum Kinet. 2014 Apr 9;40:213-25. doi: 10.2478/hukin-2014-0023. eCollection 2014.
Authors: Nikolaidis P, Ziv G, Lidor R, Arnon M.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4096101/pdf/jhk-40-213.pdf
Summary: The purpose was to profile physical characteristics and motor abilities of three age groups of soccer players - under 14 years, 14-17, and over 17, playing different positions - goalkeepers, defenders, midfielders, and forwards; and (b) to examine the inter-individual variability among the players in each age group in all physical and physiological measurements performed in the study. In addition, anthropometric, power, strength, and flexibility tests were administered. Findings showed large inter-individual variability in all three age groups and in all playing positions. Differences between playing positions were found only in the 14-17 group (body mass) and in the over-17 group (body height, body mass, fat-free mass, and mean power in the Wingate Anaerobic Test). Due to the observed large inter-individual variability, it was concluded that the findings obtained in the physical and physiological tests should be interpreted with caution when attempting to differentiate between successful and unsuccessful soccer players, as well as when trying to predict future success in soccer.


#8 Importance of muscle power variables in repeated and single sprint performance in soccer players
Reference: J Hum Kinet. 2014 Apr 9;40:201-11. doi: 10.2478/hukin-2014-0022. eCollection 2014.
Authors: López-Segovia M, Dellal A, Chamari K, González-Badillo JJ.
Download link: http://www.ffrm.es/documents/10391/60480/Importance+of+Muscle+Power+variables+in+Repeated+and+Single+Sprint+Performa
Summary: This study examined the relationship between lower body power and repeated as well as single sprint performance in soccer players. The performance of nineteen male soccer players was examined. The first testing session included the countermovement jump (CMJL) and the progressive full squat (FSL), both with external loads. Power in the CMJL and FSL was measured with each load that was lifted. The second session included a protocol of 40-m repeated sprints with a long recovery period (2 min). The number of sprints executed until there was a 3% decrease in performance for the best 40-m sprint time was recorded as a repeated sprint index (RSI). The RSI was moderately associated with power output relative to body mass in the CMJL and FSL (r = 0.53/0.54, p ≤ 0.05). The most and least powerful players (determined by FSL) showed significant differences in the RSI (9.1 ± 4.2 vs. 6.5 ± 1.6) and 10 m sprint time (p ± 0.01). Repeated and single sprints are associated with relatively lower body power in soccer players.


#9 Relationship between performance characteristics and the selection process in youth soccer players
Reference: J Hum Kinet. 2014 Apr 9;40:189-99. doi: 10.2478/hukin-2014-0021. eCollection 2014.
Authors: Lago-Peñas C, Rey E, Casáis L, Gómez-López M
Download link: http://www.degruyter.com/view/j/hukin.2014.40.issue-1/hukin-2014-0021/hukin-2014-0021.xml
Summary: The purpose of this study was to establish the anthropometric and physical profiles of elite young soccer players according to their playing position, and to determine their relevance for the selection process. One hundred and fifty-six young male soccer players participated in the study. Players were classified into the following groups: Goalkeepers (n=16), Central Defenders (n=26), External Defenders (n=29), Central Midfielders (n=34), External Midfielders (n=28), and Forwards (n=23). Anthropometric variables of participants (body height, body mass, body mass index, 6 skinfolds, 4 diameters, and 3 perimeters) were measured. Participants performed the Yo-Yo test, sprint tests (30 m flat sprint and Balsom agility test) and 2 jump tests (countermovement jump and the Abalakov test). At the end of the season, the technical staff of the club selected some of the players to continue playing on the same team and the rest were not selected. The results show that heavier and taller outfield players performed better in vertical jumps and sprint tests, whereas leaner outfield players performed better in the Yo-Yo test. Fat percentage of selected players was lower than that of the non-selected ones. The rest of the body components were similar in the selected and non-selected players within each playing position. Moreover, the selected players performed slightly better than the non-selected players in the physical test, but these differences were not statistically significant.


#10 Pressure Pain Sensitivity Changes After Usage of Shock-Absorbing Insoles Among Young Soccer Players Training on Artificial Turf: A Randomized Controlled Trial
Reference: J Orthop Sports Phys Ther. 2014 Jul 16:1-28. [Epub ahead of print]
Authors: Madeleine P, Hoej BP, Fernández-de-Las-Peñas C, Rathleff MS, Kaalund S.
Summary: Study Design Prospective, randomized, controlled single-blind intervention trial. Objectives The use of shock-absorbing insoles (SAI) was hypothesized to result in significant larger increases in pressure pain threshold (PPT) after 3 weeks of use compared with usual insoles. Background SAI can decrease self-reported pain among young players training soccer on artificial turf. However, nothing is known about the underlying changes in pain sensitivity assessed by PPT. Methods 75 players were included from the youth teams of Under-15, Under-17, and Under-19 years of Aalborg BK. A randomization stratified by team level and age was made; 1 group received SAI while the control group (CON) continued using their usual insoles. Assessments were made after 3 weeks of training on artificial turf (baseline) and 3 weeks later (follow-up) with SAI/CON. The primary outcome was changes in PPTs from baseline to follow-up. The PPTs were measured over 13 locations on the plantar surface of the foot, leg, and lower back on the non-preferred kicking leg. Results A significantly larger increase was found in PPTs from baseline to follow-up for the SAI group compared with the CON group (62, 95%CI 40;85 kPa). The PPTs increased significantly more among the SAI group compared with the CON group (P<0.05) for the abductor digiti minimi (82, 95%CI 6;157 kPa), tibialis anterior (125, 95%CI 20;230 kPa), medial gastrocnemius (83, 95%CI -6;171 kPa) and, erector spinae (86, 95%CI -17;188 kPa). Conclusion The use of SAI resulted in increased PPTs after 3 weeks of training on artificial turf compared with CON underlining that shock absorbing insoles may play a protective role on pressure sensitivity and pain perception.