Latest research in football - week 18 - 2015

#1 Change of Direction Speed in Soccer Players is Enhanced by Functional Inertial Eccentric Overload and Vibration Training
Reference: Int J Sports Physiol Perform. 2015 May 1. [Epub ahead of print]
Authors: Tous-Fajardo J, Gonzalo-Skok O, Arjol-Serrano JL, Tesch P
Summary: This study examined the effects of a novel iso-inertial eccentric overload and vibration training (EVT) paradigm on change of direction speed and multiple performance tests applicable to soccer. Twenty-four young, male players were assigned to EVT (n=12) or conventional combined (CONV, n=12) group, once weekly for 11 weeks. EVT consisted of 2 sets of 6-10 repetitions in 5 specific and 3 complementary exercises. CONV used comparable volume (2 sets of 6-10 reps in 3 sequences of 3 exercises) of conventional combined weight, plyometric and linear speed exercises. Pre- and post intervention tests included 25-m sprint with 4 x 45° change of direction (COD) every 5th m (V-cut test), 10- and 30-m sprints, repeat sprint ability (RSA), countermovement jump (CMJ) and hopping (RJ5). Group comparison showed very likely to likely better performance for EVT in the COD (effect size; ES=1.42), 30-m (ES=0.98), 10-m (ES=1.17), and average power (ES=0.69) and jumping height (ES=0.69) during RJ5. There was a large (r=-0.55) relationship between the increase in average hopping power and the reduced V-cut time. As EVT, not CONV, improved COD ability but also linear speed and reactive jumping, this "proof-of-principle" study suggests this novel exercise paradigm performed once weekly, could serve as a viable adjunct to improve performance tasks specific to soccer.
 
 
#2 A coach's political use of video-based feedback: a case study in elite-level academy soccer
Reference: J Sports Sci. 2015 May 5:1-9. [Epub ahead of print]
Authors: Booroff M, Nelson L, Potrac P
Summary: This paper examines the video-based pedagogical practices of Terry (pseudonym), a head coach of a professional junior academy squad. Data were collected through 6 in-depth, semi-structured interviews and 10 field observations of Terry's video-based coaching in situ. Three embracing categories were generated from the data. These demonstrated that Terry's video-based coaching was far from apolitical. Rather, Terry strategically used performance analysis technologies to help fulfil various objectives and outcomes that he understood to be expected of him within the club environment. Kelchtermans' micropolitical perspective, Callero's work addressing role and Groom et al.'s grounded theory were primarily utilised to make sense of Terry's perceptions and actions. The findings point to the value of developing contextually grounded understandings of coaches' uses of video-based performance analysis technology. Doing so could better prepare coaches for this aspect of their coaching practice.
 
 
#3 Effects of Two Football Stud Types on Knee and Ankle Kinetics of Single-leg Land-Cut and 180° Cut Movements on Infilled Synthetic Turf
Reference: J Appl Biomech. 2015 May 7. [Epub ahead of print]
Authors: Bennett HJ, Brock E, Brosnan JT, Sorochan JC, Zhang S
Summary: Higher ACL injury rates have been recorded in cleats with higher torsional resistance in American football, which warrants better understanding of shoe/stud dependent joint kinetics. The purpose of this study was to determine differences in knee and ankle kinetics during single-leg land-cuts and 180° cuts on synthetic infilled turf while wearing three shoes. Fourteen recreational football players performed single-leg land-cut and 180° cuts in non-studded running shoe, and football shoe with natural (NTS) and synthetic turf studs (STS). Knee and ankle kinetic variables were analyzed with a 3×2 (shoe×movement) repeated measures ANOVA (p<0.05). A significant shoe by movement interaction was found in loading-response peak knee adduction moments, with NTS producing smaller moments compared to both STS and RS only in 180° cuts. Reduced peak negative plantarflexor powers were also found in NTS compared to STS. The single-leg land-cut produced greater loading-response and pushoff peak knee extensor moments as well as peak negative and positive extensor and plantarflexor powers, but smaller loading peak knee adduction moments and pushoff peak ankle eversion moments than 180° cuts. Overall, the STS and 180° cuts resulted in greater frontal plane knee loading and should be monitored for possible increased ACL injury risks.
 
 
#4 Plantar flexor neuromuscular adjustments following match-play football in hot and cool conditions
Reference: Scand J Med Sci Sports. 2015 Jun;25 Suppl 1:154-63. doi: 10.1111/sms.12371.
Authors: Girard O, Nybo L, Mohr M, Racinais S.
Summary: We assessed neuromuscular fatigue and recovery of the plantar flexors after playing football with or without severe heat stress. Neuromuscular characteristics of the plantar flexors were assessed in 17 male players at baseline and ∼30 min, 24, and 48 h after two 90-min football matches in temperate (∼20 °C and 55% rH) and hot (∼43 °C and 20% rH) environments. Measurements included maximal voluntary strength, muscle activation, twitch contractile properties, and rate of torque development and soleus EMG (i.e., root mean square activity) rise from 0 to 30, -50, -100, and -200 ms during maximal isometric contractions for plantar flexors. Voluntary activation and peak twitch torque were equally reduced (-1.5% and -16.5%, respectively; P < 0.05) post-matches relative to baseline in both conditions, the latter persisting for at least 48 h, whereas strength losses (∼5%) were not significant. Absolute explosive force production declined (P < 0.05) 30 ms after contraction onset independently of condition, with no change at any other epochs. Globally, normalized rate of force development and soleus EMG activity rise values remained unchanged. In football, match-induced alterations in maximal and rapid torque production capacities of the plantar flexors are moderate and do not differ after competing in temperate and hot environments.