Latest research in football - week 8 - 2015

#1 The association of environmental heat stress with performance: Analysis of the 2014 FIFA World Cup Brazil
Reference: Br J Sports Med, online first
Authors: Nassis GP, Brito J, Dvorak J, Chalabi, H, Racinais S
Summary: The 2014 FIFA World Cup Brazil included 64 matches in temperate to tropical environmental conditions. We analysed performance data in relation to the environmental conditions to identify potential association. Wet-bulb globe temperature (WBGT) parameters were obtained at the centre of the field 1 h before the start of play. Environmental stress was estimated (low, moderate and high) for each match using WBGT and relative humidity. Various physical and technical performance indices were recorded during each match (average of both teams).
 Over the 64 matches, 28 were played under low, 20 under moderate and 16 under high environmental stress. There was no difference in actual playing time ( p=0.517), total distance covered
( p=0.491), number of goals scored ( p=0.485) and number of cards (p=0.618) between the matches played under different environmental stress categories. The number of sprints was lower in high than in moderate or low environmental stress (−10%, p<0.05) but peak speed was unaffected. The distance covered at high intensity was also lower under high (24.8±2.8 m/min/ player) than low environmental stress (26.9±2.3 m/min/ player, p=0.02). Number of passes was not different but the rate of successful passes was higher under high (76.8±4.4%) than low (73.6±10.8%) environmental stress (p=0.031).
 Top-level players seem to modulate their activity pattern during matches in a hot and humid environment (ie, less high-intensity but more low- intensity running and successful passes) to preserve the global match characteristics (ie, similar actual playing time, total distance covered, peak running speed and goals scored).


#2 Match Running Performance During Fixture Congestion in Elite Soccer: Research Issues and Future Directions
Reference: Sports Med. 2015 Feb 19. [Epub ahead of print]
Authors: Carling C, Gregson W, McCall A, Moreira A, Wong DP, Bradley PS.
Summary: It has been proposed that match congestion in elite soccer results in residual fatigue and under performance in ensuing competition due to insufficient recovery time. In this article, matters relating to match congestion and running performance in elite soccer competition are discussed. We suggest a need to determine the extent to which elite players are, in reality, exposed to periods of match congestion and hence to potential declines in performance. Despite evidence of exercise-induced muscle damage combined with a decline in physical performance up to 72 h post-match, research using time-motion analyses suggests that running performance represented by distances covered is unaffected over periods of match congestion. We recommend analysis of alternative movement variables including accelerations, decelerations and turns that are taxing metabolically and contribute greatly to muscle damage. Moreover, a holistic approach combining subjective ratings with biochemical, hormonal and immunological responses to exercise would be pertinent, especially in players frequently exposed to match congestion. Contemporary practitioners typically implement various post-match recovery treatments during dense schedules in an attempt to accelerate recovery and ensure that subsequent running performance is not unduly affected. However, empirical evidence to support their efficacy in maintaining running performance is lacking and we recommend controlled intervention studies using match simulations in an attempt to verify their effectiveness. These points are critically addressed using findings from the current scientific literature, while gaps in the current body of knowledge and future directions for research are highlighted.


#3 Body composition assessment of English Premier League soccer players: a comparative DXA analysis of first team, U21 and U18 squads
Reference: J Sports Sci. 2015 Feb 16:1-8. [Epub ahead of print]
Authors: Milsom J, Naughton R, O'Boyle A, Iqbal Z, Morgans R, Drust B, Morton JP.
Summary: Professional soccer players from the first team (1st team, n = 27), under twenty-one (U21, n = 21) and under eighteen (U18, n = 35) squads of an English Premier League soccer team were assessed for whole body and regional estimates of body composition using dual-energy X-ray absorptiometry (DXA). Per cent body fat was lower in 1st team (10.0 ± 1.6) compared with both U21 (11.6 ± 2.5, P = 0.02) and U18 (11.4 ± 2.6, P = 0.01) players. However, this difference was not due to variations (P = 0.23) in fat mass between squads (7.8 ± 1.6 v 8.8 ± 2.1 v 8.2 ± 2.4 kg, respectively) but rather the presence of more lean mass in 1st team (66.9 ± 7.1 kg, P < 0.01) and U21 (64.6 ± 6.5 kg, P = 0.02) compared with U18 (60.6 ± 6.3 kg) players. Accordingly, fat mass index was not different (P = 0.138) between squads, whereas lean mass index was greater (P < 0.01) in 1st team players (20.0 ± 1.1 kg · m-2) compared with U18 players (18.8 ± 1.4 kg · m-2). Differences in lean mass were also reflective of higher lean tissue mass in all regions, for example, upper limbs/lower limbs and trunk. Data suggest that training and nutritional interventions for younger players should therefore be targeted to lean mass growth as opposed to body fat loss.


#4 Assessment of P wave duration and P wave dispersion in high level football referees
Reference: J Sports Med Phys Fitness. 2015 Feb 18. [Epub ahead of print]
Authors: Yucesir I, Sahin Yildiz B, Coskun O, Yakal S, Bayraktar B, Metin G, Altan M, Yildiz M.
Summary: P wave dispersion and P wave maximal duration reflect the activation of atrial muscle and is influenced by the mass of the excited tissue. It may reflect atrial remodelling, most likely atrial fibrosis. The purpose of this study is to measure P wave duration and P wave dispersion in the high level football referees. We recruited 104 elite and national referees with a training history of many years. The control group was made of 32 healthy sedentary subjects. The difference between P maximum and P minimum durations was defined as P wave dispersion. Echocardiographic parameters such as left atrial diameter were assessed with a Vivid 3 cardiovascular ultrasound system [3S sector probe (1.5--3.6 MHz), GE]. P wave maximum duration, P wave dispersion, left ventricle posterior wall thickness, inter--ventricular septum thickness and left atrial diameter were increased in the football referees as compared with healthy sedentary subjects. There were significant correlations of P wave dispersion with left atrial diameter and left ventricle posterior wall thickness. P wave maximum duration, P wave dispersion and left atrial diameter were increased in the football referees. Also, there was a significant correlation between P wave dispersion and left atrial diameter.


#5 On winning the "lottery": psychological preparation for football penalty shoot-outs
Reference: J Sports Sci. 2015 Feb 17:1-8. [Epub ahead of print]
Authors: Wood G, Jordet G, Wilson MR.
Summary: The outcome of penalty shoot-outs is often referred to as a "lottery", suggesting that luck, rather than the skill level of the player, predetermines outcome success. Throughout this article, we hope to show why such attitudes towards physical and psychological preparation can increase anxiety, diminish perceptions of control and negatively affect the behaviour and subsequent performance of penalty takers. From the synthesis of this evidence, we provide task-specific recommendations that are structured around the dynamic nature of emotions that players are likely to experience during each phase of the shoot-out and which can be implemented or adapted to suit the individual needs of the player. These recommendations are designed to provide a framework to help applied professionals to optimise the psychological preparation for this scenario with the overall aim of helping players to (re)gain control of this situation.


#6 Perception of spin and the interception of curved football trajectories
Reference: J Sports Sci. 2015 Feb 16:1-9. [Epub ahead of print]
Authors: Casanova R, Borg O, Bootsma RJ.
Summary: Using plain white and chequered footballs, we evaluated observers' sensitivity to rotation direction and the effects of ball texture on interceptive behaviour. Experiment 1 demonstrated that the maximal distance at which observers (n = 8) could perceive the direction of ball rotation decreased when rotation frequency increased from 5 to 11 Hz. Detection threshold distances were nevertheless always larger for the chequered (decreasing from 47 to 28 m) than for the white (decreasing from 15 to 11 m) ball. In Experiment 2, participants (n = 7) moved laterally along a goal line to intercept the two balls launched with or without ±4.3 Hz sidespin from a 30-m distance. The chequered ball gave rise to shorter movement initiation times when trajectories curved outward (±6 m arrival positions) or did not curve (±2 m arrival positions). Inward curving trajectories, arriving at the same ±2 m distances from the participants as the non-curving trajectories, evoked initial movements in the wrong direction for both ball types, but the amplitude and duration of these reversal movements were attenuated for the chequered ball. We conclude that the early detection of rotation permitted by the chequered ball allowed modulation of interception behaviour without changing its qualitative characteristics.


#7 Influence of non-preferred foot technical training in reducing lower limbs functional asymmetry among young football players
Reference: J Sports Sci. 2015 Feb 16:1-9. [Epub ahead of print]
Authors: Guilherme J, Garganta J, Graça A, Seabra A.
Summary: The functional asymmetry of the lower limbs has been regarded as a relevant factor of the performance of football players. We purposed to ascertain whether a specific technical training programme for the non-preferred foot has implications in the increasing utilisation rate of the respective member during the game. Young football players (n = 71) were randomly divided into experimental group (N = 35; 14.37 ± 1.94 years) and control group (N = 36; 14.50 ± 1.81 years). The study was developed into three stages: first, assessment of the index utilisation of both limbs during the game; second, application of a technical training programme that includes the drilling of specific motor skills exclusively directed to the non-preferred foot; and third, assessment of the new rate of both limbs' utilisation after the predefined six months. The main findings were: (1) the use of the non-preferred foot increased significantly with the technical training programme in the experimental group and remained constant in the control group; (2) the use of the preferred foot decreased significantly in the experimental group and remained similar in control group. We concluded that a systematic and specific technical training for the non-preferred foot increases its use and reduces functional asymmetry in game situation, consequently improving the player's performance.


#8 Reliability of externally fixed dynamometry hamstring strength testing in elite youth football players
Reference: J Sci Med Sport. 2015 Feb 4. pii: S1440-2440(15)00038-9. doi: 10.1016/j.jsams.2015.01.012. [Epub ahead of print]
Authors: Wollin M, Purdam C, Drew MK
Summary: The purpose was to investigate inter and intra-tester reliability of an externally fixed dynamometry unilateral hamstring strength test, in the elite sports setting. Sixteen, injury-free, elite male youth football players (age=16.81±0.54 years, height=180.22±5.29cm, weight 73.88±6.54kg, BMI=22.57±1.42) gave written informed consent. Unilateral maximum isometric peak hamstring force was evaluated by externally fixed dynamometry for inter-tester, intra-day and intra-tester, inter-week reliability. The test position was standardised to correlate with the terminal swing phase of the gait running cycle. Inter and intra-tester values demonstrated good to high levels of reliability. The intra-class coefficient (ICC) for inter-tester, intra-day reliability was 0.87 (95% CI=0.75-0.93) with standard error of measure percentage (SEM%) 4.7 and minimal detectable change percentage (MDC%) 12.9. Intra-tester, inter-week reliability results were ICC 0.86 (95% CI, 0.74-0.93), SEM% 5.0 and MDC% 14.0. This study demonstrates good to high inter and intra-tester reliability of isometric externally fixed dynamometry unilateral hamstring strength testing in the regular elite sport setting involving elite male youth football players. The intra-class coefficient in association with the low standard error of measure and minimal detectable change percentages suggest that this procedure is appropriate for clinical and academic use as well as monitoring hamstring strength in the elite sport setting.