Latest research in football - week 40 - 2013

#1 Incidence of decreased hip range of motion in youth soccer players and response to a stretching program: a randomized clinical trial
Authors:  de Castro, J.V., Machado, K.C., Scaramussa, K., and Gomes, J.L.
Reference: J. Sport Rehab. 22: 100-107, 2013.
Summary: After years of focusing on the management of anterior cruciate ligament (ACL) injuries, the most common soccer-related injuries, the orthopedic community has concluded that soccer players have a wide range of variation in joint biomechanics and has thus started to focus research efforts on the morphological factors that might contribute to ACL trauma. One such factor is decreased hip-rotation range of motion (ROM), which may be due to compensatory musculoskeletal changes occurring in response to longstanding soccer practice since childhood. This study sought to assess decreased hip rotation and the influence of stretching exercises on the behavior of the hip joint in players of the youth soccer categories of a Brazilian soccer team. A randomized clinical trial was used consisting of 262 male soccer players. Subjects were randomly allocated into 2 groups-control or a stretching program and measured for hip-rotation ROM after 12 wk. The findings suggest that hip-rotation ROM decreases over the years in soccer players. In the study sample, adherence to a stretching program improved only external hip-rotation ROM in the nondominant limb. Playing soccer can restrict rotation ROM of the hip, and adherence to stretching exercises may decrease the harmful effects on the hip joints.


#2 Isolated inferior peroneal retinculum tear in professional soccer players
Authors: Staresinic M, Bakota B, Japjec M, Culjak V, Zgaljardic I, Sebecic B.
Reference: Injury. 2013 Sep;44 Suppl 3:S67-70. doi: 10.1016/S0020-1383(13)70202-X.
Summary: Peroneal tendon dislocations are rare injuries that can easily be misdiagnosed. Up to date literature mostly describes proximal peroneal tendon dislocations due to superior peroneal retinaculum (SPR) tear. In this article, we present the assessment, diagnostic algorithm and a new therapeutic option for the distal dislocation of the long peroneal tendon due to isolated inferior peroneal retinaculum (IPR) tear. Between 2001 and 2011 three patients with distal peroneal tendon dislocation were operated. All of them were competitive athletes in the national soccer league. They presented with an ankle sprain and prolonged problems on the lateral side of the foot with no improvement after conservative therapy measures. Coleman block test was performed; ultrasound and MRI showed a tendon dislocation under the IPR. The patients underwent surgical repair that consisted of peroneal tubercle excision, a new lateral calcanear groove formation for both peroneal tendons and IPR plasty. At the two year follow up the American Orthopedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Score showed a significant increase. The decrease of painful stimuli assessed by a Visual Analogue Scale (VAS) was significant as well. At an average of 12 weeks after the surgery, the patients returned to their level of sport activity before injury and didn't report similar problems later. Description of distal peroneal tendon dislocations is limited in the literature. This topic should be considered in differential diagnostics of an acute and chronic ankle sprain which leads to chronic ankle pain and instability. The authors recommend surgical treatment as a method of choice especially in professional athletes.


#3 Competing together: Assessing the dynamics of team-team and player-team synchrony in professional association football
Authors: Duarte R, Araújo D, Correia V, Davids K, Marques P, Richardson MJ.
Reference: Hum Mov Sci. 2013 Aug;32(4):555-66. doi: 10.1016/j.humov.2013.01.011. Epub 2013 Jul 3.
Summary: This study investigated movement synchronization of players within and between teams during competitive association football performance. Cluster phase analysis was introduced as a method to assess synchronies between whole teams and between individual players with their team as a function of time, ball possession and field direction. Measures of dispersion (SD) and regularity (sample entropy - SampEn - and cross sample entropy - Cross-SampEn) were used to quantify the magnitude and structure of synchrony. Large synergistic relations within each professional team sport collective were observed, particularly in the longitudinal direction of the field (0.89±0.12) compared to the lateral direction (0.73±0.16, p<.01). The coupling between the group measures of the two teams also revealed that changes in the synchrony of each team were intimately related (Cross-SampEn values of 0.02±0.01). Interestingly, ball possession did not influence team synchronization levels. In player-team synchronization, individuals tended to be coordinated under near in-phase modes with team behavior (mean ranges between -7 and 5° of relative phase). The magnitudes of variations were low, but more irregular in time, for the longitudinal (SD: 18±3°; SampEn: 0.07±0.01), compared to the lateral direction (SD: 28±5°; SampEn: 0.06±0.01, p<.05) on-field. Increases in regularity were also observed between the first (SampEn: 0.07±0.01) and second half (SampEn: 0.06±0.01, p<.05) of the observed competitive game. Findings suggest that the method of analysis introduced in the current study may offer a suitable tool for examining team's synchronization behaviors and the mutual influence of each team's cohesiveness in competing social collectives.

#4 Changes in jump, sprint and coordinative performances following a senior soccer match
Authors: Cortis, C., Tessitore, A., Lupo, C., Perroni, F., Pesce, C., and Capranica, L.
Reference: J. Strength. Cond. Res., 2013. [epub ahead of print]
Summary: This study aimed 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 (52.3+/-10.2years) male soccer players were administered jump (countermovement jump [CMJ]; repeated jump [RJ]), sprint (10m and 10m while dribbling the ball [10mDB]), 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 HR>85% of individual HRmax occurred for 50% of playing time. Subjective ratings at the end of the match were 12.9+/-2.2pt and 2.7+/-2.2pt for RPE and RMP, respectively. Post-match CMJ, 10m, 10mDB, AP, IP 80bpm, and IP 120bpm performances did not show any difference with respect to pre-match values, whereas improvements (P<0.05) in RJ (pre-match: 17.4+/-3.9cm; post-match 19.3+/-4.8cm) and IP 180bpm (pre-match: 30.4+/-15.1s; post-match: 50.3+/-18.9s) emerged. These findings indicate 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 considering that players consider soccer as highly motivating, with advancing years this sport could help players in preserving high mental and physical functions, as well as maintaining active engagement in life through social interactions.


#5 Pre-Season Variations in Aerobic Fitness and Performance in Elite Standard Soccer Players: a Team-Study

Authors: Castagna, C., Impellizzeri, F.M., Chauachi, A., and Manzi, V..
Reference: J. Strength. Cond. Res., 2013. [epub ahead of print]
Summary:  The aim of this study was to examine the effects of individual training load considered as permanence in selected heart-rate zones (HR) on aerobic fitness and performance in professional elite-soccer players. Eighteen professional soccer players were observed during the pre-championship training period (8 weeks). Speeds and HR at 2 and 4 mmoll blood lactate concentrations (S2, S4 respectively), 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 mmoll), moderate-intensity (between HR 2 and 4 mmoll) and high-intensity (>HR 4 mmoll). Training-session HRs (n=900) showed a polarized distribution with 73.6+/-3.7 (2945+/-148 min), 19.1+/-3.5 (763+/-141 min) and 7.3+/-2.9% (292+/-116 min) of the total training time spent at low, moderate and high intensity, respectively (p<0.001). The S2 and S4 significantly improved post-training (+10 and 7%, respectively p<0.001). The VO2max and Yo-Yo IR1 values were 6 and 19.5% higher post training, respectively (p<0.01). Training spent 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). These study results provided further evidence to HR longitudinal validity and effectiveness of the high-intensity training (i.e. >90% HRmax) in male professional soccer. In this regard time spent at high-intensity should be in the range of 7-8% of total training time during pre-season.


#6 Supramaximal intermittent running performance in relation to age and locomotor profile in highly-trained young soccer players
Authors: Buchheit, M. and Mendez-Villanueva, A.
Reference: J. Sports. Sci., 2013. [epub ahead of print]
Summary: The aim of the study was to examine supramaximal intermittent running performance in highly-trained young soccer players, with regard to age and locomotor profile. Twenty-seven Under 14, 19 U16 and 16 U18 highly-trained soccer players performed an incremental intermittent running test (30-15 Intermittent Fitness Test) to assess supramaximal intermittent running performance (VIFT), an incremental running test to estimate maximal aerobic speed (VVam-Eval) and a 40-m sprint to estimate maximal sprinting speed (MSS). U16 and U18 presented very likely greater VIFT (19.2 +/- 0.9, 19.7 +/- 1.0 vs. 17.4 +/- 0.9 km . h-1) and VVam-Eval (16.2 +/- 0.9, 16.7 +/- 1.0 vs. 14.6 +/- 0.9 km . h-1) than U14, while there was no clear difference between U16 and U18. MSS (25.1 +/- 1.6, 29.3 +/- 1.6 and 31.0 +/- 1.1 km . h-1 for U14, U16 and U18) was very likely different between all groups. When data were pooled together, VIFT was very largely correlated with VVam-Eval and MSS (overall r =0.89, partial r = 0.74 and 0.29, respectively). Within-age group correlations showed that the older the players, the greater the magnitude of the correlations between VIFT and VVam-Eval (r = 0.67, 0.73 and 0.87). In conclusion, the major predictors of VIFT were, in order of importance, VVam-Eval and MSS; however, the older the players, the greater the correlations with VVam-Eval.


#7 Cardiovascular health profile of elite female football players compared to untrained controls before and after short-term football training
Authors: Randers, M.B., Andersen, L.J., Orntoft, C., Bendiksen, M., Johansen, L., Horton, J., Hansen, P.R., and Krustrup, P.
Reference: J. Sports. Sci. 31: 1421-1431, 2013.
Summary:  This study examined the intermittent exercise performance and cardiovascular health profile in elite female football players in comparison to untrained young women, as well as a subgroup subjected to football training 2x1 h . week(-1) for 16 weeks. Twenty-seven Danish national team players (elite trained, ET) and 28 untrained women (UT) underwent dual-energy X-ray absorptiometry-scanning (DXA), comprehensive transthoracic echocardiography, treadmill and Yo-Yo Intermittent Endurance level 2 (IE2) testing. Eight women in UT were also tested after the football training period. Maximal oxygen uptake rate (VO2max), peak ventilation and peak lactate were 40, 18 and 51% higher (P< 0.01) in ET than UT, respectively. Cardiac dimensions and function were greater in ET than UT, with left ventricular diastolic diameter, right ventricular diastolic diameter, tricuspid annular plane systolic excursion (TAPSE) and peak transmitral flow in early diastole divided by peak transmitral flow velocity in late diastole during atrial contraction (E/A-ratio) being 13, 19, 27 and 41%, respectively, greater in ET than UT (P< 0.001 to< 0.05). Yo-Yo IE2 performance was 7-fold higher in ET than UT (1772 +/- 508 vs. 234 +/- 66 m, P< 0.001), fat mass was 51% lower (P< 0.001) and high density lipoprotein (HDL) cholesterol levels were 20% higher (P< 0.01). Sixteen weeks of football elevated VO2max and Yo-Yo IE2 performance by 16 and 40%, respectively, and lowered fat mass by 6%. Cardiac function was markedly improved by 16 weeks of football training with 26 and 46% increases in TAPSE and E/A ratio, respectively, reaching levels comparable to ET. In summary, elite female football players have a superior cardiovascular health profile and intermittent exercise performance compared to untrained controls, but short-term football training can markedly improve the cardiovascular health status.

#8 Resting ECG in elite football players
Authors: Bohm, P., Ditzel, R., Ditzel, H., Urhausen, A., and Meyer, T.
Reference: J. Sports. Sci., 2013. [epub ahead of print]
Summary: The purpose of the study was to evaluate ECG abnormalities in a large sample of elite football players. Data from 566 elite male football players (57 of them of African origin) above 16 years of age were screened retrospectively (age: 20.9 ± 5.3 years; BMI: 22.9 ± 1.7 kg · m–2, training history: 13.8 ± 4.7 years). The resting ECGs were analysed and classified according to the most current ECG categorisation of the European Society of Cardiology (ESC) (2010) and a classification of Pelliccia et al. (2000) in order to assess the impact of the new ESC-approach. According to the classification of Pelliccia, 52.5% showed mildly abnormal ECG patterns and 12% were classified as distinctly abnormal ECG patterns. According to the classification of the ESC, 33.7% showed ‘uncommon ECG patterns’. Short-QT interval was the most frequent ECG pattern in this group (41.9%), followed by a shortened PR-interval (19.9%). When assessed with a QTc cut-off-point of 340 ms (instead of 360 ms), only 22.2% would have had ‘uncommon ECG patterns’. Resting ECG changes amongst elite football players are common. Adjustment of the ESC criteria by adapting proposed time limits for the ECG (e.g. QTc, PR) should further reduce the rate of false-positive results.


#9 Physiological and performance responses to the "FIFA 11+" (part 1): is it an appropriate warm-up?

Authors: Bizzini, M., Impellizzeri, F.M., Dvorak, J., Bortolan, L., Schena, F., Modena, R., and Junge, A.
Reference: J. Sports. Sci. 31: 1481-1490, 2013. [epub ahead of print]
Summary:  The aim of the study was to examine the post-exercise effects of the "FIFA 11+" on various physical performance and physiological variables, to understand whether this programme is an appropriate warm-up for football players. Results were compared with the literature using a meta-analytical approach. Twenty amateur male football players [mean age 25.5 (s +/- 5.1) years, body mass 75(8) kg, height 181(6) cm] participated in the study. They were tested twice before (control period) and once after the "FIFA 11+" for: 20-m sprints, agility, vertical jump, stiffness, isometric maximal voluntary contraction (MVC), rate of force development (RFD), and star excursion balance test. Oxygen uptake, lactate and core temperature were also measured. Pre-post warm-up differences were found for all the performance variables (from 1.0 to 6.2%; 0.015 < P < 0.001) with the exclusion of MVC (-13%; P = 0.426) and RFD (-10%; P = 0.205). After the warm-up there was an increase (0.004 <P < 0.001) in resting oxygen uptake from 325(87) to 379(142) mL . min(-1), in core temperature from 37.3(0.3) to 37.7(0.3) degrees C, and in lactate from 1.0(0.2) to 2.6(1.1) mmol . L(-1). In conclusion, the "FIFA 11+" prevention programme can be considered an appropriate warm-up, inducing improvements in football players comparable with those obtained with other warm-up routines reported in the literature.

#10 The presence of bilateral imbalance of the lower limbs in elite youth soccer players of different ages
Authors: Atkins, S., Hesketh, C., and Sinclair, J.
Reference: J. Strength. Cond. Res., 2013. [epub ahead of print]
Summary: The aim of this study was to examine bilateral differences in ground reaction forces, measured during a deep squat exercise, in a population of elite youth soccer players. Bilateral muscle balance is a key component in promoting musculoskeletal health of performers, yet there is a limited evidence base investigating such imbalances in youth. Seventy-four subjects were assigned to performance groups according to chronological age (Under 13, 14, 15, 16, 17 yr). Analysis of physical maturity status revealed that very few players were classified as 'early' or 'late' maturers. Players completed an overhead deep squat exercise, as part of pre-season functional movement screening. Peak ground reaction forces were assessed using a twin force plate system. Significant differences (p </= 0.05) were identified between right and left side PGRF for all groups except the youngest (U13) and oldest (U17). Non-dominant 'sides' showed the highest levels of PGRF across all groups. The magnitude of PGRF was not significantly different both within and between groups, except for the left side in the U13 to U15 groups (p = 0.04). Results from this study show that performance asymmetry is marked in adolescence. There appears a 'trigger point' during the early stage of adolescence, when bilateral imbalances become marked. These differences do seem to reduce during the later stages of adolescence. Correct attention to focussed training, designed to remediate any imbalance, is warranted in adolescent groups. This is important with respect of the key associations between bilateral asymmetry and risk of injury.


#11 Variability of objective and subjective intensities during ball drills in youth soccer players
Authors: Los Arcos, A., Martinez-Santos, R., Yanci, J., Martin, J., and Castagna, C.
Reference: J. Strength. Cond. Res., 2013 [epub ahead of print].
Summary: The aim of this study was to examine the intra (intraclass coefficient correlation, ICC) and inter-subject variability (coefficient of variation, CV) of soccer ball drills (BD) involving or not opposition in male youth soccer. For this purpose a collective ball dribbling (DB) exercise and a 7-a-side ball game without coach encouragements were considered. Exercise intensity was assessed as heart rate (HR), training load (TL) and perceived exertion scales (PES). Fourteen U-14 male soccer players (age 14.79+/-0.43 and experience 6.5 years) of a Spanish First Division club academy participated in the study. BD were examined for variability over 5 successive training sessions in similar field conditions. Results showed that 7-a-side was significantly (p=0.000) more demanding than DB. Indeed the TL, HRmax, HRmean, overall perceived exertion (OPE) and leg muscular perceived exertion (MPE) resulted 141, 8.7, 11, 56 and 72 %, higher in 7-a-side than in DB, respectively. In the 7-a-side condition good inter (CV<10%) and low intra-subject (ICC<0.7) variability were observed. In the DB condition CVs were below 10% CV only for HR variables and the ICC value were higher than 0.7 only for MPE. Despite the moderate reproducibility of BD not considering opponents this condition did not reveal to induce homogeneous physiological responses in young soccer players. Therefore the use of this kind of drills may be questionable when considered as alternative of moderate intensity generic aerobic training. Inter-players variability may be lower during team opposition drills despite the occurrence of frequent duel this suggesting their use as conditioning exercise when specific training (i.e. ball use during drills) is to be prescribed.