Latest research in football - week 11 - 2013

Latest research in football

As previous 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 Injuries in Male and Female Adolescent Soccer Players

Authors: Schneider AS, Mayer HM, Geißler U, Rumpf MC, Schneider C.
Reference: Sportverletz Sportschaden. 2013 Feb 27.
Summary: This study presented data of injuries in adolescent male and female soccer players in different leagues in Germany. 1110 soccer players (male = 841; female = 269) aged 12 - 19 years from 60 clubs in Southern Germany were investigated. A total of 664 (79 %) of the 841 boys and 67 (25 %) of the 269 girls reported being injured due to soccer. The girls showed a higher rate of injuries compared to the boys, 2.85 vs. 7.10. The lower extremities were affected in 70 % of all reported cases. Strains were the most common injuries in the lower and upper extremities (35 %). 51.5% of all injuries in boys were reported as non-contact, while 52.1 % of the injuries in girls were reported as contact injuries. Similar amounts of injuries were observed in training versus games for both genders. Prevention procedures, such as a thorough warm-up, should be implemented before every game and training to reduce the risk of injury.

#2 High-Intensity Re-Warm-Ups Enhance Soccer Performance
Authors: Zois J, Bishop D, Fairweather I, Ball K, Aughey RJ.
Reference: Int J Sports Med. 2013 Feb 26. [Epub ahead of print]
Summary: The purpose of this study was to investigate the effects of high-intensity, short-duration, re-warm-ups on team-sport-related performance. A randomized, cross-over study was used in which the participants performed 2×26-min periods of an intermittent activity protocol (IAP) on a non-motorized treadmill, interspersed by 15-min of passive recovery (CON); 3-min small-sided game (SSG); or a 5RM leg-press. Measures included counter-movement jump (CMJ), repeated-sprint, the Loughborough soccer passing test (LSPT), blood lactate concentration, heart-rate (HR), and perceptual measures. The results show a 5RM re-warm-up improved flight-time to contraction-time ratio when compared to SSG and CON re-warm-ups, remaining higher following the second IAP. Relative-maximum rate-of-force development was greater in the 5RM condition following the second IAP compared to SSG and CON. Repeated-sprint ability during the second IAP improved in the 5RM re-warm-up; peak velocity, mean velocity, and acceleration were 4, 3, and 18% greater, respectively. Within groups, the SSG re-warm-up improved LSPT performance post-intervention; 6.4% and following the second IAP 6.2%, compared to pre-intervention. A 5RM leg-press re-warm-up improved physical performance, while a SSG re-warm-up enhanced skill execution following standardized intermittent exercise.

#3 Heat stress impairs repeated jump ability after competitive elite soccer games
Authors: Mohr M, Krustrup P.
Reference: J Strength Cond Res. 2013 Mar;27(3)
Summary: This purpose of the study was to examine the effect of environmental heat stress on repeated jump performance after elite competitive soccer games. Nineteen male elite soccer players from 2 Scandinavian teams, which took part in the Champions League Qualification, where 6 games (3 home and 3 away) were played, participated in this study. While the home games took place at an average ambient temperature of ~12° C (used as control games; CON) and the away games in hot conditions (~30.0° C; HOT). Baseline measurement consisted of a repeated countermovement jump (CMJ) test consisting of 5 jumps separated by 5 seconds of recovery. Mean CMJ performance after HOT was ~38 cm, which was 6.0% lower than Baseline (~40. cm) and tended to be lower than in the CON (39.6 cm). The mean CMJ performance after CON was not different from Baseline. Peak CMJ performance after HOT was ~41.1 cm, which was not different from the other two measurements (Baseline or CON (~42.0 vs. 41.7 cm). The relative decline in repeated CMJ performance from Baseline to after HOT correlated to relative net loss in body mass during HOT. This study demonstrates that repeated CMJ performance deteriorates after a soccer game played in warm environmental settings, which is partly associated with severe dehydration.

#4 The Effect of Combined Resisted Agility and Repeated Sprint Training Vs. Strength Training on Female Elite Soccer Players'
Authors: Shalfawi SA, Haugen T, Jakobsen TA, Enoksen E, Tønnessen E.
Reference: J Strength Cond Res. 2013 Feb 25. [Epub ahead of print]
Summary: The purpose of the study was to compare the effects of in-season combined resisted agility and repeated sprint training vs. strength training on soccer players` agility, linear single sprint speed, vertical jump, repeated sprint ability, and aerobic capacity. Twenty well-trained elite female soccer players were randomly assigned to either agility & repeated sprint training group (ARS) or strength training group (STR) for a 10-week period. Pre- and post-testing consisted of squat jump (SJ), counter movement jump (CMJ) and repeated sprint ability (RSA), 40-m maximal straight sprint, agility test and a Beep-test. The ARS training implemented did not have a significant effect on agility, although there was a tendency for improvements. There was a significant effect on Beep-test performance from level and a trivial - small effect on all other physical variables measured in this study. The STR training group had a significant effect on Beep-test and SJ performance. Additionally, the strength training implemented in this study had a trivial negative effect on agility performance. However, there were no differences between groups. The authors concluded that the results indicate the importance of a well planned program of conditioning that do not result in a decreased performance of the players with special reference to the time of implementation of such conditioning training programs. As there was no decline in performance observed, in-season training can be used to maintain the soccer players' physical performance during the competition period.

#5 Effects of stabilization training on trunk muscularity and physical performances in youth soccer players
Authors: Hoshikawa Y, Iida T, Muramatsu M, Ii N, Nakajima Y, Chumank K, Kanehisa H.
Reference: J Strength Cond Res. 2013 Feb 25. [Epub ahead of print]
Summary: The aim of the present study was to examine the effects of stabilization training on trunk muscularity and physical performances in youth male soccer players aged 12 - 13 yrs. Twenty eight subjects participated in this study and 16 were allocated to a training (TG) group and 12 players were into a control (CON) group. The training consisted of a 5 stabilization exercise (elbow-toe, elbow-heel, side-bridge, modified one-legged squat, and bent-knee push-up) executed 4-6 times per week for 6 months. Pre- and post-exercise variables were, muscle cross-sectional areas (MCSAs) of five muscles (rectus abdominus, oblique, psoas major, quadratus lumborum, and erector spinae) - determined using MRI,  peak torques during hip extension and flexion at 1.05 rad/s, heights of squat (SJ) and countermovement jumps (CMJ) and 15 m sprint time. Both groups significantly increased the CSAs of the five muscle groups and improved sprint time, however the TG significantly increased the SJ and CMJ heights. Furthermore, a greater increase in hip extension torque was found in TG compared to CON. The authors concluded that a 6 month stabilization strength training did not increase trunk muscularity, however improve hip extensor strength and jumping performance of early adolescent soccer players.

#6 Pre-Season Variations in Aerobic Fitness and Performance in Elite Standard Soccer Players: a Team-Study
Authors: Castagna C, Impellizzeri FM, Chauachi A, Manzi V.
Reference: J Strength Cond Res. 2013 Feb 25. [Epub ahead of print]
Summary: The purpose of this study was to examine the effects of individual training load considered as stability in selected heart-rate zones (HR) on aerobic fitness and performance in professional elite-soccer players. Eighteen professional soccer players were observed during an 8-week pre-championship training period. Running velocity and heart rate (HR) at 2 and 4 mmol/l blood lactate concentrations (S2, S4), VO2max and Yo-Yo intermittent recovery test level 1 performance (Yo-Yo IR1) were assessed pre and post training. Training intensities were categorized using three HR zones: low-intensity (<HR 2 mmol/l), moderate-intensity (between HR 2 and 4 mmol/l) and high-intensity (>HR 4 mmol/l). Nine-hundred training-session HRs showed significant different amount and times spend in different zones. The S2 and S4 significantly improved post-training. The VO2max and Yo-Yo IR1 values were 6 and 19.5% higher post training. The authors showed that training spent at high-intensity was significantly related to relative improvement in S2, S4, VO2max and Yo-Yo IR1. The results of this study shows the HRs longitudinal validity and effectiveness of the high-intensity training (i.e. >90% HRmax) in male professional soccer. Interestingly, high-intensity training time should be in the range of 7-8% of total training time during pre-season.

#7 Changes in jump, sprint and coordinative performances following a senior soccer match
Authors: Cortis C, Tessitore A, Lupo C, Perroni F, Pesce C, Capranica L.
Reference: J Strength Cond Res. 2013 Feb 22. [Epub ahead of print]
Summary: The purpose of the study was to verify the short-term after-effects of a soccer match on senior players' all-out and inter-limb coordination performances. Right before (pre-match) and after (post-match) a match, 10 senior male soccer players were administered countermovement jump (CMJ), repeated jump (RJ), 10-m sprint with (10-mDB) and without the ball, in-phase (IP) and anti-phase (AP) inter-limb coordination (synchronized hand and foot flexions and extensions at 80, 120, 180bpm). Heart rate (HR) responses, and subjective ratings of perceived exertion (RPE) and muscle pain (RMP) were used to evaluate the intensity of the friendly match. During the match heart rates HR>85% of individual HRmax occurred for 50% of playing time. Player’s ratings at the end of the match were ~13 for RPE. Post-match CMJ, 10m, 10mDB, AP, IP 80bpm, and IP 120bpm performances were not different with respect to pre-match values, whereas significant improvements in RJ and IP 180bpm were observed. The authors concluded that senior soccer players are able to cope with the high demands of match-play and suggest that an acute bout of intense exercise has an arousing effect that counteracts fatigue effects and facilitates the performance of old trained individuals on complex motor behaviors relying on central executive control. In this context, football can be used in preserving high mental and physical functions, as well as maintaining active engagement in life through social interactions.

#8 Effect of short-term maximal exercise on biochemical markers of muscle damage, total antioxidant status, and homocysteine levels in football players
Authors: Hammouda O, Chtourou H, Chaouachi A, Chahed H, Ferchichi S, Kallel C, Chamari K, Souissi N.
Reference: Asian J Sports Med. 2012 Dec;3(4):239-46.
Summary: Prolonged physical exercise results in transient elevations of biochemical markers of muscular damage. The purpose of the study was to examined the effect of short-term maximal exercise on these markers (homocysteine (Hcy) and total antioxidant status (TAS)) in 18 trained male football players. Blood samples were collected 5-min before and 3-min after a 30-s Wingate test. The results indicated that plasma biochemical markers of muscle injury increased significantly after the Wingate test. Moreover, significant increase of white blood Cells and their main subpopulations (i.e. monocytes, neutrophiles, and lymphocytes) has been observed. Likewise, uric acid, total bilirubin, and TAS increased significantly after exercise. However, Hcy levels were unaffected by the Wingate test (for 3-min post-exercise measurement). The authors concluded that short-term maximal exercise (e.g. 30-s Wingate test) is of sufficient intensity and duration to increase markers of muscle damage, and TAS. Increases in the selected enzymes probably come primarily from muscle damage.

#9 Diminutions of acceleration and deceleration output during professional football match play
Authors: Akenhead R, Hayes PR, Thompson KG, French D.
Reference: J Sci Med Sport. 2013 Jan 15.
Summary: The purpose of the study was to examined distances covered at low (1-2ms(-2)), moderate (2-3ms(-2)) and high (>3ms(-2)) acceleration (L(ACC), M(ACC) and H(ACC) respectively) and deceleration (L(DEC), M(DEC), and H(DEC) respectively) during competitive football games in addition to temporal and transient patterns of acceleration and deceleration in 36 professional male professional footballers. A 10Hz non-differential global positioning system (NdGPS) was used to assess match data, organized in six 15min periods (P1: 1-15min, P2: 16-30min, P3: 31-45min, P4: 46-60min, P5: 61-75min, and P6: 76-90min) for analysis of temporal patterns, and into eighteen 5min periods for analysis of transient patterns. Results showed that distance covered at L(ACC), M(ACC), H(ACC), L(DEC), M(DEC), and H(DEC) was 424±75m, 242±25m, 178±38m, 365±54m, 210±23m and 162±29m respectively. Between period decrements ranged from 8.0% to 13.2% from P1 to P3, 9.2% to 16.3% from P4 to P6, and from 14.9% to 21.0% from P1 to P6. Following PEAK H(ACC) (148% of mean 5min H(ACC)), H(ACC) at 5(POST) was 10.4% lower than mean (p<0.01). The authors concluded that time-dependent reductions in distances covered suggest that acceleration and deceleration capability are acutely compromised during match play. Further, the occurrence of transient fatigue may be supported by the findings that H(ACC) and H(DEC) performance following PEAK was approximately 10% lower than mean values.

#10 Recurrent hamstring muscle injury: applying the limited evidence in the professional football setting with a seven-point programme
Authors: Brukner P, Nealon A, Morgan C, Burgess D, Dunn A.
Reference: Br J Sports Med. 2013 Feb 15. [Epub ahead of print]
Summary: The purpose of the study was to use a clinical example to describe a treatment strategy for the management of recurrent hamstring injuries and examine the evidence for each intervention. On average a professional footballer sustained five hamstring injuries in a relatively short period of time and the injuries were managed successfully with a seven-point programme consisting of 1) biomechanical assessment and correction, 2) neurodynamics, 3) core stability, 4) eccentric strengthening, 5) overload running programme, 6) injection therapies and 7) stretching/relaxation. The paper reviewed evidence for each of these treatment options. As there were only limited evidence available in most cases it was impossible to define which aspects of the programme contributed to a successful outcome. Treatment choices should be made by using a combination of clinical experience and research evidence.

#11 Effects of playing surface on physiological responses and performance variables in a controlled football simulation
Authors: Hughes MG, Birdsey L, Meyers R, Newcombe D, Oliver JL, Smith PM, Stembridge M, Stone K, Kerwin DG.
Reference: J Sports Sci. 2013 Jan 15. [Epub ahead of print]
Summary: Despite the increasing acceptance of artificial turf in football, only a few studies have investigated whether matches are altered by the type of surface. To the knowledge of the authors no research has compared physiological responses to football activity on artificial vs. natural surfaces. A football match-simulation was used to compared the surface on physiological parameters. Neither mean heart rate nor blood lactate nor fatigue index. differed between the two pitch surfaces. Measures of sprint, jumping and agility performance declined through the match simulation, however, there was again no differences between the two types of pitches. The ability to turn after sprinting was affected by surface type but this difference was dependent on the type of turn. Although there were small differences in the ability to perform certain movements between artificial and natural surfaces, the results suggest that fatigue and physiological responses to football activity do not differ markedly between surface-type using the high-quality pitches of the present study.

#12 Lower incidence of arm-to-head contact incidents with stricter interpretation of the Laws of the Game in Norwegian male professional football
Authors: Bjørneboe J, Bahr R, Dvorak J, Andersen TE.
Reference: Br J Sports Med. 2013 Jan 11. [Epub ahead of print]
Summary: The purpose of the study was to assess whether a stricter interpretation of the Laws of the Game (red cards for high elbows in heading duels and for late/two foot tackles) could reduce the potential for injuries in Norwegian male professional football. The rate of incidents and injuries from the 2010 season (pre-intervention) was compared to the 2011 season (post-intervention). An incident was recorded if the match was interrupted by the referee, and the player lay down for more than 15 s, and appeared to be in pain or received medical treatment. Time-loss injuries were recorded by the medical staff of each club. There was no significant difference in the incidents, tackling characteristics or contact injury rate. However, significant reduction in incidence of total head incidents, and head-incidents caused by arm-to-head contact was observed post-intervention. The authors concluded that stricter rule enforcement did not alter rate of injury.

#13 Time-of-day effects on biochemical responses to soccer-specific endurance in elite Tunisian football players
Authors: Hammouda O, Chtourou H, Chaouachi A, Chahed H, Bellimem H, Chamari K, Souissi N.
Reference: J Sports Sci. 2013 Jan 14. [Epub ahead of print]
Summary: The purpose was to investigate footballers' diurnal variation of performance during the Yo-Yo intermittent recovery test and the associated biochemical responses. Fifteen youth male footballers performed two randomised Yo-Yo tests, one at 07:00 h and the second one at 17:00 h. Blood samples were collected before and 3 min after each test for the assessment of metabolic responses. Resting oral temperature and rating of perceived exertion (RPE) after and peak heart rate during the Yo-Yo test were recorded at both times-of-day. Core temperature and performances during the Yo-Yo test increased significantly from the morning to the evening without significant time-of-day effects on peak heart rate and RPE. Moreover, pre- and post-Yo-Yo test biochemical parameters (high-density lipoprotein, triglycerides, glucose, creatine-kinase) were higher at 17:00 h than 07:00 h. Only post-exercise lactate levels were significant higher in the evening with all biochemical variables being increased after the exercise. These findings suggest a possible link between the diurnal fluctuation of metabolic responses and the related pattern of specific-endurance performances in footballers. Therefore, the higher biochemical responses observed in the evening could explain, partially, the greater performance and metabolic solicitation at this time-of-day.

#14 The time-frame of acute resistance exercise effects on football skill performance: The impact of exercise intensity
Authors: Draganidis D, Chatzinikolaou A, Jamurtas AZ, Carlos Barbero J, Tsoukas D, Theodorou AS, Margonis K, Michailidis Y, Avloniti A, Theodorou A, Kambas A, Fatouros I.
Reference: J Sports Sci. 2013 Jan 9. [Epub ahead of print]
Summary: The aim of this study was to determine the recovery rate of football skill performance following resistance exercise of moderate or high intensity. Ten elite football players participated in three different trials: control, low-intensity resistance exercise (4 sets, 8-10 repetitions/set, 65-70% 1 repetition maximum (1RM)) and high-intensity resistance exercise (4 sets, 4-6 repetitions/set, 85-90% 1RM) in a counterbalanced manner. In each experimental condition, participants were evaluated pre, post, and at 24, 48, 72 h post exercise time points. Football skill performance was assessed through the Loughborough Soccer Passing Test, long passing, dribbling, shooting and heading. Delayed onset muscle soreness, knee joint range of motion, and muscle strength (1RM) in squat were considered as muscle damage markers. Blood samples analyzed for creatine kinase activity, C-reactive protein, and leukocyte count. Passing and shooting performance declined significantly post-exercise following resistance exercise. Strength declined post-exercise following high-intensity resistance exercise. Both trials induced only a mild muscle damage and inflammatory response in an intensity-dependent manner. The authors concluded that the results indicate that football skill performance is minimally affected by acute resistance exercise independent of intensity suggesting that elite players may be able to participate in a football practice or match after only 24 h following a strength training session.

#15 Injury risk in professional football players with special reference to the playing position and training periodization
Authors: Mallo J, Dellal A.
Reference: J Sports Med Phys Fitness. 2012 Dec;52(6):631-8.
Summary: The aim of this study was to examine injury incidence in professional football players according to the playing positions and with a special reference to training periodization. A Spanish professional team was followed prospectively for the 2007-08 and 2008-09 seasons and exposure times and time-loss injuries were individually recorded during all training sessions and matches. Heart rate was monitored in all training sessions. The results were a total of 114 injuries were registered during the study period (mean injury incidence: 6.6 injuries per 1000 hours). There was a significant differences between playing positions with regards to the frequency of injuries and forwards and central defenders sustained the greatest number of injury episodes and the highest match absence. Most common injury was ligament sprains and muscle strains and accounted for 50% of all injuries and 62% of all match absences. The highest incidence of sprains was achieved during pre-season and the beginning of the competition period. The risk to sustain a muscular strain peaked at the beginning and in the final weeks of the competition period and was related to mean heart rate during the training stage. The authors concluded that there exists a difference of injury risk according to the period of the season and therefore, injury prevention strategies should be introduced from pre-season. Moreover, training workloads should be controlled to avoid increasing the risk of muscle strains.

#16 The possession game? A comparative analysis of ball retention and team success in European and international football, 2007-2010.
Author: Collet C.
Reference: J Sports Sci. 2013 Jan;31(2)
Summary: As possession is thought of as central to success in modern football, the question remains if ball possession impacts team outcomes. Most studies focused on English or Spanish domestic play. The authors used data from five European leagues, UEFA and FIFA tournaments and the study found that while possession time and passing predicted aggregated team success in domestic league play, both variables were poor predictors at the individual match level once team quality and home advantage were accounted for. In league play, the effect of greater possession was consistently negative; in the Champions League, it had virtually no impact. In national team tournaments, possession failed to reach significance when offensive factors were accounted for. Much of the success behind the 'possession game' was thus a function of elite teams confined in geographic and competitive space. That ball hegemony was not consistently tied to success suggests that a nuanced approach to possession is needed to account for variant strategic environments (and compels match analysts to re-examine the metric's overall value.

#17 Hamstring injuries in professional football players: magnetic resonance imaging correlation with return to play
Authors: Cohen SB, Towers JD, Zoga A, Irrgang JJ, Makda J, Deluca PF, Bradley JP.
Reference: Sports Health. 2011 Sep;3(5):423-30.
Summary: The purpose of the study was to correlate time for return to play in professional football players with magnet resonance imagery (MRI) findings after acute hamstring strains and to create an MRI scoring scale predictive of return to sports. Professional football players (N = 83) were used in this study. Forty-three cases of acute hamstring strains with MRI evaluation were evaluated. Records were retrospectively reviewed, and MRIs were evaluated by 2 musculoskeletal radiologists, graded with a traditional radiologic grade, and scored with a new MRI score. Results were correlated with games missed. Results show that players missed on average 2.6 games. Based on MRI, the hamstring injury involved the biceps femoris long head in 34 cases and the proximal and distal hamstrings in 25 and 22 cases, respectively. When < 50% of the muscle was involved, the average number of games missed was 1.8; if > 75%, then 3.2. Ten players had retraction, missing 5.5 games. By MRI, grade I injuries yielded an average of 1.1 missed games; grade II, 1.7; and grade III, 6.4. Players who missed 0 or 1 game had an MRI score of 8.2; 2 or 3 games, 11.1; and 4 or more games, 13.9. The authors concluded that rapid return to play (< 1 week) occurred with isolated long head of biceps femoris injures with < 50% of involvement and minimal perimuscular edema, correlating to grade I radiologic strain (MRI score < 10). Prolonged recovery (missing > 2 or 3 games) occurs with multiple muscle injury, injuries distal to musculotendinous junction, short head of biceps injury, > 75% involvement, retraction, circumferential edema, and grade III radiologic strain (MRI score > 15).

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