Latest research in football - week 14 - 2013

#1 Effects of a 10-week resistance exercise program on soccer kick biomechanics and muscle strength
Authors: Evaggelos M, Athanasios K, Konstantinos M, Vasileios K, Eleftherios K.
Reference: J Strength Cond Res. 2013 Mar 27. [Epub ahead of print]
Summary: The purpose of the study was to examine the effects of a resistance exercise program on soccer kick biomechanics. Twenty male amateur soccer players were divided in the Experimental (EG) and the Control (CG) group, each consisting of ten players. The EG followed a 10-week resistance exercise program mainly for the lower limb muscles. Maximal instep kick kinematics, electromyography and ground reaction forces (GRFs) as well as maximum isometric leg strength were recorded before and after training. A two-way analysis of variance showed significantly higher ball speed values only for the EG, while no significant differences were observed for the CG. The EG showed a decline in joint angular velocities and an increase in biceps femoris EMG of the swinging leg during the backswing phase followed by a significant increase in segmental and joint velocities and muscle activation of the same leg during the forward swing phase. The EG also showed significantly higher vertical GRFs and rectus femoris and gastrocnemius activation of the support leg. Similarly, maximum and explosive isometric force significantly increased after training only for the EG. These results suggest that increases in soccer kicking performance after a 10-week resistance training program were accompanied by increases in maximum strength as well as an altered soccer kick movement pattern, characterized by a more explosive backward - forward swinging movement and higher muscle activation during the final kicking phase.


#2 Effect of gene actn3 on strength and endurance in soccer players
Authors: Pimenta EM, Coelho DB, Barros Coelho EJ, Cruz IR, Morandi RF, De Azambuja Pussieldi G, Santos Carvalho MR, Silami-Garcia E, De Paz Fernández JA.
Reference: J Strength Cond Res. 2013 Mar 27. [Epub ahead of print]
Summary: The purpose of the present study is to compare the performance capacity of soccer players with different genotype groups of ACTN3 (XX, RX and RR) in strength, speed and endurance tests. Two hundred professional players of Brazilian soccer first division teams participated in this study. Speed, jump and endurance tests results were compared to the polymorphisms of the ACTN3 gene. It was noticed that RR individuals spent less time to run a 10m path, compared to XX individuals (p<0.05). The RR individuals also presented significant lower time rates at the 20 and 30m path, compared to RX and XX individuals. In jump tests, RR individuals presented significant higher rates, compared to RX and XX individuals. As for aerobic tests, the XX individuals presented significant higher rates of VO2 maximum, compared to the RR group and did not differ from the RX group. The main conclusion of this study is that soccer players of genotype ACTN3/RR are the fastest in short distances and present higher jump potential. ACTN3/XX individuals presented the highest aerobic capacity. These findings can be used in training load adjustment and can influence the development of tactical schemes in soccer matches.

#3 Perceptual-cognitive skills and their interaction as a function of task constraints in soccer
Authors: Roca A, Ford PR, McRobert AP, Williams AM
Reference: J Sport Exerc Psychol. 2013 Apr;35(2):144-55.
Summary: The purpose of the study to examined the role of and interaction between the different perceptual-cognitive skills underlying anticipation and decision making. Skilled and less skilled players interacted as defenders with life-size film sequences of 11 versus 11 soccer situations. Participants were presented with task conditions in which the ball was located in the offensive or defensive half of the pitch (far vs. near conditions). Participants' eye movements and verbal reports of thinking were recorded across two experiments. Skilled players reported more accurate anticipation and decision making than less skilled players, with their superior performance being underpinned by differences in task-specific search behaviors and thought processes. The perceptual-cognitive skills underpinning superior anticipation and decision making were shown to differ in importance across the two task constraints. Findings have significant implications for those interested in capturing and enhancing perceptual-cognitive skill in sport and other domains.


#4 Alteration of IGFBP-1 in Soccer Players Due to Intensive Training
Authors: Lagundzin D, Vucic V, Glibetic M, Nedic O.
Reference: Int J Sport Nutr Exerc Metab. 2013 Mar 26. [Epub ahead of print]
Summary: Physical activity is accompanied by the changes in insulin-like growth factor I (IGF-I)/IGF-binding protein 1 (IGFBP-1) axis. Inconsistent results concerning IGF-I and IGFBP-1 levels were reported. In this study we have raised some questions on the events that occur at molecular level of the exercise-related IGFBP-1 changes. We have examined the fragmentation pattern of IGFBP-1, IGFBP-1 protease activity, interaction between IGFBP-1 and alpha2-macroglobulin (α2M) and possible existence of minor structural changes of IGFBP-1 in professional soccer players. Athletes had significantly greater amount of fragmented IGFBP-1, whereas no difference was found in the amount of intact IGFBP-1 compared to controls. An increased activity of matrix metalloprotease-9 (MMP-9) was detected in athletes, causing IGFBP-1 degradation down to the fragment of 9 kDa as the major one. The amount of α2M, which protects IGFBP-1 from proteolysis, or the amount of IGFBP-1/α2M complexes was unaltered. Finally, we have examined whether IGFBP-1 isolated from soccer players exhibited altered reactivity with several chemical surfaces used in surface-enhanced laser desorption/ionization-time of flight mass spectrometry (SELDI-TOF MS). Different reactivity was detected with anion and cation exchangers, suggesting existence of at least one sequence within IGFBP-1, whose ionization pattern was not equal in athletes and controls. Differences in spectra obtained with ion exchanges may reflect differences in IGFBP-1 phosphorylation. Physiological implications of the events described in this study on the IGF-I availability are, at this time, unknown. It can be hypothesized that IGFBP-1 proteolysis leads to altered distribution of IGF-I among IGFBPs, which may affect the final IGF-associated response.


#5 Effect of an Injury Prevention Program on Muscle Injuries in Elite Professional Soccer
Authors: Owen AL, Wong DP, Dellal A, Paul DJ, Orhant E, Collie S.
Reference: J Strength Cond Res. 2013 Mar 21. [Epub ahead of print]
Summary: The purpose of the current investigation was to examine the effectiveness of a structured injury prevention program on the number of muscle injuries as well as the total number of injuries within elite professional soccer. The present study was conducted over two 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 programme 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, however this was largely due to the greater number of 44 contusion injuries sustained within the intervention season when compared to control season, in which 23 contusion appeared. Significantly less muscle injuries were observed during the intervention season (moderate effect) and this occurred concomitant with a bigger squad size (large effect). The findings from this study identify a multi component 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.


#6 Acute hamstring injuries in Swedish elite football: a prospective randomised controlled clinical trial comparing two rehabilitation protocols
Authors: Askling CM, Tengvar M, Thorstensson A.
Reference: Br J Sports Med. 2013 Mar 27. [Epub ahead of print]
Summary: The purpose of the study was to compare the effectiveness of two rehabilitation protocols after acute hamstring injury in Swedish elite football players by evaluating time needed to return to full participation in football team-training and availability for match selection. Seventy-five football players with an acute hamstring injury, verified by MRI, were randomly assigned to one of two rehabilitation protocols. Thirty-seven players were assigned to a protocol emphasising lengthening exercises, L-protocol and 38 players to a protocol consisting of conventional exercises, C-protocol. The outcome measure was the number of days to return to full-team training and availability for match selection. Reinjuries were registered during a period of 12 months after return. The results show a significant shorter for the players in the L-protocol (28 days), compared with the C-protocol (51 days). Irrespective of protocol, stretching-type of hamstring injury took significantly longer time to return than sprinting-type, L-protocol: mean 43 vs 23 days and C-protocol: mean 74 vs 41 days, respectively. The L-protocol was significantly more effective than the C-protocol in both injury types. One reinjury was registered, in the C-protocol. The authors concluded that a rehabilitation protocol emphasising lengthening type of exercises is more effective than a protocol containing conventional exercises in promoting time to return in Swedish elite football.


#7 Does Ramadan Affect the Risk of Injury in Professional Football?
Authors: Eirale C, Tol JL, Smiley F, Farooq A, Chalabi H
Reference: Clin J Sport Med. 2013 Mar 22. [Epub ahead of print]
Summary: The purpose was to investigate whether fasting during Ramadan influences injury incidence in professional Muslim and non-Muslim footballers. Professional First Division Footballers of Qatar participated in this study. 527 male football players (462 Muslim and 65 non-Muslim) from 7-8 league clubs. Daily collection of training and match exposure was performed from August 2008 until April 2011 by club medical staff. Injuries during training and match play were recorded on standardized injury cards. Injury incidence was calculated as number of injuries per hour exposed to risk, and expressed as rate per 1000 hours. The probability of injury for different Arabic months between Muslims and non-Muslims was calculated using Generalized Estimating Equations (GEEs). The results showed no significant difference in total, match, and training injury incidence between the Ramadan and non-Ramadan periods. Non-Muslim footballers had a significantly higher injury incidence rate than Muslim footballers both during Ramadan (8.5 vs 4.0 injuries/1000 hours) and non Ramadan (6.6 vs 4.9 injuries/1000 hours) periods. The GEE analysis revealed that after adjusting for age and random factors (month and club), the probability of match injury among non-Muslims was the highest in Ramadan and the 2 consecutive following months. Finally, there was no change in injury patterns over the months of the Islamic calendar. The authors concluded that Ramadan does not impact injury incidence for Muslim footballers in Qatar, suggesting the current adjustments and scheduling of football activities during Ramadan are sufficient. The increased match injury among non-Muslims during and 2 months post-Ramadan may suggest less effective coping strategies.