Latest research in football - week 15 - 2015

As previous literature 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 Hamstring fatigue and muscle activation changes during six sets of Nordic hamstring exercise in amateur soccer players
Reference: J Strength Cond Res. 2015 Apr 15. [Epub ahead of print]
Authors: Marshall PW, Lovell R, Knox MF, Brennan SL, Siegler JC
Summary: The Nordic hamstring exercise (NHE) is a bodyweight movement commonly prescribed to increase eccentric hamstring strength and reduce the incidence of strain injury in sport. This study examined hamstring fatigue and muscle activation responses throughout six sets of five repetitions of the NHE. Ten amateur level soccer players performed a single session of six-sets of five-repetitions of NHE. Maximal eccentric and concentric torque output (Nm) was measured after every set. Hamstrings electromyograms (EMG) were measured during all maximal contractions and exercise repetitions. Hamstring maximal eccentric torque was reduced throughout the range of motion after only a single set of NHE between 7.9 to 17.1% (p<0.05), with further reductions in subsequent sets. Similarly, maximal concentric torque reductions between 7.8 to 17.2% were observed throughout the range of motion after one set of NHE (p<0.05). During the descent phase of the NHE repetitions, hamstring muscle activity progressively increased as the number of sets performed increased. These increases were observed in the first-half of the range of motion. During the ascent phase biceps femoris muscle activity but not medial hamstrings was reduced from the start of exercise during latter sets of repetitions. These data provide unique insight into the extent of fatigue induced from a bodyweight only exercise after a single set of five repetitions. Strength and conditioning coaches need to be aware of the speed and extent of fatigue induced from NHE, particularly in practical settings where this exercise is now prescribed prior to sport-specific training sessions (i.e. the FIFA-11 before soccer training).

#2 Effects of isolated or combined carbohydrate and caffeine supplementation between 2 daily training sessions on soccer performance
Reference: Appl Physiol Nutr Metab. 2015 Jan 12:1-7. [Epub ahead of print]
Authors: Andrade-Souza VA, Bertuzzi R, de Araujo GG, Bishop D, Lima-Silva AE
Summary: This study aimed to investigate whether isolated or combined carbohydrate (CHO) and caffeine (CAF) supplementation have beneficial effects on performance during soccer-related tests performed after a previous training session. Eleven male, amateur soccer players completed 4 trials in a randomized, double-blind, and crossover design. In the morning, participants performed the Loughborough Intermittent Shuttle Test (LIST). Then, participants ingested (i) 1.2 g·kg-1 body mass·h-1 CHO in a 20% CHO solution immediately after and 1, 2, and 3 h after the LIST; (ii) CAF (6 mg·kg-1 body mass) 3 h after the LIST; (iii) CHO combined with CAF (CHO+CAF); and (iv) placebo. All drinks were taste-matched and flavourless. After this 4-h recovery, participants performed a countermovement jump (CMJ) test, a Loughborough Soccer Passing Test (LSPT), and a repeated-sprint test. There were no main effects of supplementation for CMJ, LSPT total time, or best sprint and total sprint time from the repeated-sprint test (p > 0.05). There were also no main effects of supplementation for heart rate, plasma lactate concentration, rating of perceived exertion (RPE), pleasure-displeasure, and perceived activation (p > 0.05). However, there were significant time effects (p < 0.05), with heart rate, plasma lactate concentration, RPE, and perceived activation increasing with time, and pleasure-displeasure decreasing with time. In conclusion, isolated and/or combined CHO and CAF supplementation is not able to improve soccer-related performance tests when performed after a previous training session.

#3 Goal or Gold: Overlapping Reward Processes in Soccer Players upon Scoring and Winning Money
Reference: PLoS One. 2015 Apr 15;10(4):e0122798. doi: 10.1371/journal.pone.0122798.
Authors: Häusler AN, Becker B, Bartling M, Weber B
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Summary: Social rewards are important incentives for human behavior. This is especially true in team sports such as the most popular one worldwide: soccer. We investigated reward processing upon scoring a soccer goal in a standard two-versus-one situation and in comparison to winning in a monetary incentive task. The results show a strong overlap in brain activity between the two conditions in established reward regions of the mesolimbic dopaminergic system, including the ventral striatum and ventromedial pre-frontal cortex. The three main components of reward-associated learning i.e. reward probability (RP), reward reception (RR) and reward prediction errors (RPE) showed highly similar activation in both con-texts, with only the RR and RPE components displaying overlapping reward activity. Passing and shooting behavior did not correlate with individual egoism scores, but we observe a positive correlation be-tween egoism and activity in the left middle frontal gyrus upon scoring after a pass versus a direct shot. Our findings suggest that rewards in the context of soccer and monetary incentives are based on similar neural processes.

#4 Biomechanical and physiological response to a contemporary soccer match-play simulation
Reference: J Strength Cond Res. 2015 Apr 14. [Epub ahead of print]
Authors: Page R, Marrin K, Brogden C, Greig M
Summary: The intermittent activity profile of soccer match-play increases the complexity of the physical demands. Laboratory models of soccer match-play have value in controlled intervention studies, developed around manipulations of the activity profile to elicit a desired physiological or biomechanical response. Contemporary notational analyses suggest a profile comprising clusters of repeat sprint efforts, with implications for both biomechanical and physiological load. Eighteen male soccer players completed a 90min treadmill protocol based on clusters of repeat sprint efforts. Each 15min bout of exercise was quantified for uni-axial (medial-lateral [PLML], anterior-posterior [PLAP] and vertical [PLV]) and tri-axial PlayerLoad (PLTotal). The relative contributions of the uni-axial PlayerLoad vectors (PLML%, PLAP%, and PLV%) were also examined. In addition to rating of perceived exertion, the physiological response comprised heart rate, blood lactate concentration, and both peak and average oxygen consumption. Tri-axial PlayerLoad increased (p = 0.02) with exercise duration (T0-15= 206.26 ± 14.37 a.u; T45-60 = 214.51 ± 14.97 a.u) and remained elevated throughout the 2 half. This fatigue effect was evident in both the PLML and PLAP movement planes. The mean relative contributions of PLV%:PLAP%:PLML% were consistent at ∼ 48:28:23. The physiological response was comparable with match-play, and a similar magnitude of increase at ∼5% was observed in physiological parameters. Changes in PlayerLoad might reflect a change in movement quality with fatigue, with implications for both performance and injury risk, reflecting observations of match-play. The high frequency of speed change elicits a 23% contribution from medio-lateral load, negating the criticism of treadmill protocols as 'linear'.

#5 Relationship between static and dynamic balance abilities in Italian professional and youth league soccer players
Reference: Phys Ther Sport. 2014 Dec 17. pii: S1466-853X(14)00108-4. doi: 10.1016/j.ptsp.2014.12.003. [Epub ahead of print]
Authors: Pau M, Arippa F, Leban B, Corona F, Ibba G, Todde F, Scorcu M
Summary: The purpose of the study was to assess the existence of correlations between static and dynamic balance abilities in young and professional elite soccer players. Fifty-one elite players who regularly compete at national level divided into two groups: Professional (age 18-34, n = 20) and Under 15-17 (age 14-16, n = 31) participate in the investigation. Dynamic balance was assessed for the case of a single-leg landing task by means of vertical time to stabilization (TTS) and postural sway calculated on the basis of center-of-pressure (COP) trajectories (sway area, COP displacements in antero-posterior and medio-lateral direction, COP path length). The same parameters were also measured for a 20 s one-legged stance to assess static balance abilities. No significant correlations were found between static and dynamic balance parameters except for TTS and COP displacements in the antero-posterior direction (r = 0.29, p = 0.003). Professional players are characterized by lower TTS in comparison with youth leagues players (0.767 vs. 1.188 s for the dominant limb, p < 0.001) and exhibit reduced sway area (of 34-40%, p < 0.05) for both conditions tested. The assessment of balance in soccer players should be performed with both dynamic and static tests, considering that the postural control performances in the two cases are not related.

#6 Impact of the FIFA 11+ on the structure of select muscles in adolescent female soccer players
Reference: Phys Ther Sport. 2014 Nov 6. pii: S1466-853X(14)00102-3. doi: 10.1016/j.ptsp.2014.10.007. [Epub ahead of print]
Authors: Whittaker JL, Emery CA
Summary: The purpose was to determine the impact of an injury prevention program (FIFA11+) on the structure of select trunk and leg muscles in adolescent female soccer players. 23 female soccer players (aged 14-16) recruited from a FIFA11 + implementation trial grouped by high and low 11 + exposure participated in this study. Pre and post-season sonographic measures of the rectus abdominis, external and internal oblique, transversus abdominis, inter-recti distance (IRD), lumbar multifidus, gluteus medius and minimus, and vastus medialis. Mean (95% confidence intervals; CI) were calculated for pre, post and pre-post season change of all parameters and univariate analyses used to compare groups (α = 0.001). Both low (mean = 149 ± 9 exercises/year) and high (mean = 314 ± 15 exercises/year) 11 + exposure groups demonstrated significant post-season decreases in IRD at rest (p < 0.001) and during a leg lift (p < 0.001). No other between or within group differences existed. Levels of FIFA11 + exposure were not associated with differential changes in the morphology of investigated muscles. As the IRD of participants in both exposure groups decreased it is possible that the protective mechanism of the FIFA11 + may be associated with alterations in neuromuscular control that result in abdominal wall adaptations.

#7 Reaching older people with PA delivered in football clubs: the reach, adoption and implementation characteristics of the Extra Time Programme
Reference: BMC Public Health. 2015 Mar 5;15(1):220.
Authors: Parnell D, Pringle A, McKenna J, Zwolinsky S, Rutherford Z, Hargreaves J Authors: Trotter L, Rigby M, Richardson D
Summary: Older adults (OA) represent a core priority group for physical activity and Public Health policy. As a result, significant interest is placed on how to optimise adherence to interventions promoting these approaches. Extra Time (ET) is an example of a national programme of physical activity interventions delivered in professional football clubs for OA aged 55+ years. This paper aims to examine the outcomes from ET, and unpick the processes by which these outcomes were achieved. This paper represents a secondary analysis of data collected during the evaluation of ET. From the 985 OA reached by ET, n=486 adopted the programme and completed post-intervention surveys (typically 12 weeks). We also draw on interview data with 18 ET participants, and 7 staff who delivered the programme. Data were subject to thematic analysis to generate overarching and sub themes. Of the 486 participants, the majority 95%, (n= 462) were White British and 59.7% (n=290) were female. Most adopters (65.4%/n=318) had not participated in previous interventions in the host clubs. Social interaction was the most frequently reported benefit of participation (77.2%, n=375). While the reach of the club badge was important in letting people know about the programme, further work enhanced adoption and satisfaction. These factors included (i) listening to participants, (ii) delivering a flexible age-appropriate programme of diverse physical and social activities, (iii) offering activities which satisfy energy drives and needs for learning and (iv) extensive opportunities for social engagement. Findings emerging from this study indicate that physical activity and health interventions delivered through professional football clubs can be effective for engaging OA.

#8 MRI of the wrist is not recommended for age determination in female football players of U-16/U-17 competitions
Reference: Scand J Med Sci Sports. 2015 Apr 16. doi: 10.1111/sms.12461. [Epub ahead of print]
Authors: Tscholl PM, Junge A, Dvorak J, Zubler V.
Summary: Age determination on magnetic resonance imaging (MRI) of the wrist is a reliable method in male football players to evaluate their eligibility to participate in Under 17 tournaments. MRI of the wrist was performed in 487 female volunteers aged 13-19 years from Brazil, Germany, Malaysia, and Tanzania, and in 139 female football players participating in Under-16 and Under-17 football tournaments. A previously validated method for grading fusion of the distal radial epiphysis in male adolescent was used. Moderate correlation of chronological age and epiphyseal fusion was found in the normative control group (r = .59) and weak correlation in female football players (r = .27). Complete fusion of the distal radial epiphysis was observed in two 15-year-old volunteers of the control group (1.7%) and in 17.6% (3 of 17) of 14-year-old football players. Up to 10.8% (47 of 437) in the control group and 14.4% (20 of 139) of the football players 17 years or younger had complete fused epiphysis. Because of earlier osseous maturity in female adolescents, the grade of fusion of the distal radial epiphysis on MRI is not recommended for pretournament age determination for the age of 17 and younger in female.

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