Latest research in football - week 13 - 2016

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Interpreting daily heart rate variability changes in collegiate female soccer players.
Reference: J Sports Med Phys Fitness. 2016 Mar 11. [Epub ahead of print]
Authors: Flatt AA, Esco MR, Nakamura FY, Plews DJ.
Summary: Heart rate variability (HRV) is an objective physiological marker that may be useful for monitoring training status in athletes. However, research aiming to interpret daily HRV changes in female athletes is limited. The objectives of this study were (1) to assess daily HRV (i.e., log-transformed root mean square of successive R-R interval differences, lnRMSSD) trends both as a team and intra-individually in response to varying training load (TL) and (2) to determine relationships between lnRMSSD fluctuation (coefficient of variation, lnRMSSDcv) and psychometric and fitness parameters in collegiate female soccer players (n=10). Ultra-short, Smartphone-derived lnRMSSD and psychometrics were evaluated daily throughout 2 consecutive weeks of high and low TL. After the training period, fitness parameters were assessed. When compared to baseline, reductions in lnRMSSD ranged from unclear to very likely moderate during the high TL week (effect size ± 90% confidence limits [ES ± 90% CL] = -0.21 ± 0.74 to -0.64 ± 0.78, respectively) while lnRMSSD reductions were unclear during the low TL week (ES ± 90% CL = -0.03 ± 0.73 to -0.35 ± 0.75, respectively). A large difference in TL between weeks was observed (ES ± 90% CL = 1.37 ± 0.80). Higher lnRMSSDcv was associated with greater perceived fatigue and lower fitness (r [upper and lower 90% CL] = -0.55 [-0.84, -0.003] large, -0.65 [-0.89, -0.15] large). Athletes with lower fitness or higher perceived fatigue demonstrated greater reductions in lnRMSSD throughout training. This information can be useful when interpreting individual lnRMSSD responses throughout training for managing player fatigue.

#2 Soccer players' fitting perception of different upper boot materials.
Reference: Appl Ergon. 2016 Jul;55:27-32. doi: 10.1016/j.apergo.2016.01.005. Epub 2016 Jan 26.
Authors: Olaso Melis JC, Priego Quesada JI, Lucas-Cuevas AG, González García JC, Puigcerver Palau S.
Summary: The present study assessed the influence of upper boot materials on fitting perception. Twenty players tested three soccer boots only differing in the upper boot material (natural calf leather, natural kangaroo leather and synthetic leather). Players reported fitting perception and preference on specific foot areas using a perceived fitting scale. Ratings were averaged for every foot area. Repeated measures ANOVA was used to analyze the differences between boots. The kangaroo leather boots were perceived tighter and closer to the preferred fitting in general fitting, metatarsals area and instep area. The synthetic leather boots were perceived as the loosest and as the most distant boot from the preferred fitting in medial front area and instep area. In conclusion, the type of upper boot material influences the fitting perception of soccer players. The kangaroo leather was the material whose fitting was perceived closest to the players fitting preference.

#3 Prevalence and Risk Factors for Voice Problems Among Soccer Coaches.
Reference: J Voice. 2016 Mar 15. pii: S0892-1997(16)00032-1. doi: 10.1016/j.jvoice.2016.02.003. [Epub ahead of print]
Authors: Fellman D, Simberg S
Summary: The prevalence of voice problems has been investigated in various occupations, but research investigating sports coaches' voice problems seems to be limited even if coaches are an occupational group whose work requires heavy voice use. The aim of this study was to determine the prevalence of voice problems among soccer coaches and identify risk factors that can contribute to the problems. The data were collected with a web questionnaire that was sent to 500 soccer coaches. Overall, 109 male coaches, who practiced soccer coaching to various extents, responded to the questionnaire. The presence of six vocal symptoms was investigated, as well as environmental factors and health-related factors that may have an influence on the voice. The results showed that the prevalence of voice problems among soccer coaches was high. In total, 28.4% of the participants reported two or more frequently occurring vocal symptoms. The most common symptom was throat clearing or coughing followed by voice becomes low or hoarse. The coaches who had vocally demanding main occupations alongside their coaching tasks had an increased risk for voice problems. Moreover, a significant association was found between chronic rhinitis and frequently occurring vocal symptoms, as well as between stress and frequently occurring vocal symptoms. Given the extent of voice problems and the fact that soccer coaches have a vocally demanding occupation, it would be important to increase the awareness of voice use among this group. Soccer coaches are in immense need of more information about voice ergonomics during their coaching education.

#4 Effect of motor control training on hip muscles in elite football players with and without low back pain.
Reference: J Sci Med Sport. 2016 Mar 3. pii: S1440-2440(16)00053-0. doi: 10.1016/j.jsams.2016.02.008. [Epub ahead of print]
Authors: Mendis MD, Hides JA.
Summary: Previous research has shown that motor control training improved size and function of trunk muscles in elite football players with and without low back pain (LBP). Imbalances in hip muscles have been found in athletes with LBP and it is not known if motor control training can change these muscles. This study investigated if a motor control intervention program affected hip muscle size in elite football players with and without LBP. Forty-six players from one club in the Australian Football League (AFL) participated in a motor control training program delivered across the season as a stepped-wedge intervention design with 3 treatment arms: 15 weeks intervention, 8 weeks intervention and a wait-list control who received 7 weeks intervention toward the end of the playing season. Presence of LBP was assessed by interview and physical examination. Cross-sectional areas of iliacus, psoas, iliopsoas, sartorius, gluteus minimus, and gluteus medius muscles were measured from magnetic resonance images taken at 3 time points during the season. Iliopsoas, sartorius and gluteus medius muscle size increased for players who received intervention (p<0.05). For players with current LBP, sartorius and gluteus medius muscle size increased for those who received motor control training (p<0.05). Motor control training programs aimed at the lumbo-pelvic region also benefit the hip muscles. For players with current LBP, the intervention mitigated sartorius muscle atrophy and increased gluteus medius muscle size. These findings may help guide the management of LBP in elite football players.

#5 Health conditions detected in a comprehensive periodic health evaluation of 558 professional football players.
Reference: Br J Sports Med. 2016 Mar 24. pii: bjsports-2015-095829. doi: 10.1136/bjsports-2015-095829. [Epub ahead of print]
Authors: Bakken A, Targett S, Bere T, Adamuz MC, Tol JL, Whiteley R, Wilson MG, Witvrouw E, Khan KM, Bahr R.
Summary: Despite the widespread use of periodic health evaluation (PHE) to detect and prevent injury and illness in athletes, its effectiveness in detecting health conditions and relevant risk factors is still debated. The purpose was to assess health conditions detected by a comprehensive PHE in professional male football players and evaluate their consequences for participation clearance. A total of 558 professional football players in Qatar completed a PHE prior to the 2013 or 2014 seasons: history, general medical (including blood test), cardiovascular (12-lead ECG and echocardiography) and a musculoskeletal examination, including a specific test battery targeting lower extremity strength and flexibility. On the basis of the PHE, players were either cleared or not cleared for participation. In 533 players (95.5%), at least one health condition was detected requiring treatment or follow-up. Vitamin D deficiency or insufficiency (≤30 ng/mL) was the most common medical condition (n=499, 89.4%), followed by hepatitis B non-immunity or infection (n=164, 29.4%). Cardiac screening identified 48 players (8.6%) with one or more abnormal findings (ECG (n=19, 3.4%) and echocardiography (n=14, 2.5%)). Musculoskeletal conditions were observed in 180 players (32.3%); injuries to or strength deficits of the hip/groin and thigh accounted for the largest proportion. Medical clearance was temporarily not given in 69 players (12.4%), while further examinations were being conducted. One player was disqualified from competitive football. PHE revealed a high prevalence of health conditions requiring treatment or follow-up in professional footballers; however, only 12.4% of conditions impacted on final clearance for participation.

#6 The challenge and impact of engaging hard-to-reach populations in regular physical activity and health behaviours: an examination of an English Premier League 'Football in the Community' men's health programme.
Reference: Public Health. 2016 Mar 18. pii: S0033-3506(16)00065-2. doi: 10.1016/j.puhe.2016.02.008. [Epub ahead of print]
Authors: Curran K, Drust B, Murphy R, Pringle A, Richardson D.
Summary: The purpose was to investigate the challenges that men from hard-to-reach (HTR) populations encounter when attempting to commit to regular participation in physical activity and health behaviours, and to explore the psychological and social effects of participation in a twelve week football-led health improvement intervention. A twelve week football specific physical activity intervention targeting men from HTR populations was delivered by Everton Football Clubs' Football in the Community (FitC) scheme as part of a national programme of men's health delivered in/by English Premier League (EPL) football clubs. Men living in homeless shelters and/or recovering from substance misuse were recruited over a period of three months. The programme consisted of a two hour football session, twice weekly, alongside the dissemination of healthy living messages. Football sessions were conducted by a qualified FitC coach. This research was conducted during a twelve week period of immersed practitioner-research. Ethnographic and observational methodologies were adopted. Psychosocial issues were discussed with participants through informal client-researcher interactions and data were logged via field notes. Records of attendance were logged. Participants who failed to attend a session were contacted and their reason(s) for non-attendance were recorded. Data were analysed using deductive and inductive reasoning. Despite the apparent ambition of the participants to regularly participate in the FitC programme, adherence to the programme was poor. Economic, environmental and social barriers to engagement in the programme were apparent. Engagement in the programme resulted in positive psychosocial developments; the development of structure, social interaction and social capital. Community based football-led health improvement programmes endorsed by professional football clubs appear well positioned to connect with, and attract, men from HTR populations. The evidence suggests that such programmes can improve psychosocial health amongst these populations. However, a bottom-up programme design and management strategy is required in order to reduce the challenges facing HTR participants when attempting to regularly engage in physical activity and health behaviours.

#7 Longitudinal Changes and Seasonal Variation in Body Composition in Professional Australian Football Players.
Reference: Int J Sports Physiol Perform. 2016 Mar 22. [Epub ahead of print]
Authors: Bilsborough JC, Kempton T, Greenway K, Cordy J, Coutts AJ.
Summary: The purpose was to compare development and variations in body composition of early, mid and late career professional Australian Football (AF) players over three successive seasons. Regional and total body composition body (body mass (BM), fat mass (FM), fat-free soft tissue mass (FFSTM), and bone mineral content (BMC)) was assessed four times, at the same time of each season: 1) start pre-season (SP); 2) end pre-season (EP); mid-season (MS); and end-season (ES) from 22 professional AF players using pencil beam dual energy x-ray absorptiometry. Nutritional intake for each player was evaluated concomitantly using 3-day food diaries. Players were classified according to their age at the beginning of the observational period as either early (<21 y; N = 8), mid (21-25 y; N = 9) or late (>25 y; N = 5) career athletes. Early career players had lower FFSTM, BMC and BM compared to mid and late throughout. FM and %FM had greatest variability, particularly in the early career players. FM reduced and FFSTM increased from SP to EP, whilst FM and FFSTM decreased from EP to MS. FM increased and FFSTM decreased from MS to ES, whilst FM and FFSTM increased during the off-season. Early career players may benefit from greater emphasis upon specific nutrition and resistance training strategies aimed at increasing FFSTM, whilst all players should balance training and diet towards the end of season to minimise increases in FM.

#8 Range of motion of body segments is larger during the maximal instep kick than during the submaximal instep kick in experienced football players.
Reference: J Sports Med Phys Fitness. 2016 Mar 30. [Epub ahead of print]
Authors: Langhout R, Tak I, van der Westen R, Lenssen T.
Summary: Football players with groin injury refrain from maximal kicking. Previous groin injury is related to decreased hip range of motion (ROM). Information on ROM differences between maximal and submaximal kicking within players is lacking. The first aim of this study is to quantify ROM of body segments during the maximal (MaxK) and submaximal (SubK) instep kick at four keypoints. The second aim is to study ROM differences of tension arc and movement trajectories between MaxK and SubK. Maximal (100% ball speed) and submaximal (70% ball speed) instep kicks from 15 experienced football players were registered with motion capture. ROM of hip, spine, pelvis and knee segments were determined at four keypoints. Differences in segmental ROM for the tension arc and movement trajectories between MaxK and SubK were studied. Effect sizes (ES) were calculated. Ball speed was 98.8(±9.0) km/h for Maxk and 69.5(±7.1) km/h for SubK. Three keypoints timed similarly (p<0.05) for MaxK and SubK. MaxK shows increased ROM for all segments (p<0.05) but not for hip flexion. MaxK results in enlargement of tension arc and movement trajectories. Spine flexion (ES 3.2 ) and pelvis posterior tilt (ES 2.2) show the greatest relative increase. Maximal kicking shows larger segmental ROM than submaximal kicking. Enlargement of tension arc and movement trajectories relate to increased segmental velocity, according to biomechanical concepts. Central body actions play an important role in kicking. This information can be used to further identify kicking strategies in athletes with injury.

#9 Sports teams as complex adaptive systems: manipulating player numbers shapes behaviours during football small-sided games.
Reference: Springerplus. 2016 Feb 27;5:191. doi: 10.1186/s40064-016-1813-5. eCollection 2016.
Authors: Silva P, Vilar L, Davids K, Araújo D, Garganta J
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Summary: Small-sided and conditioned games (SSCGs) in sport have been modelled as complex adaptive systems. Research has shown that the relative space per player (RSP) formulated in SSCGs can impact on emergent tactical behaviours. In this study we adopted a systems orientation to analyse how different RSP values, obtained through manipulations of player numbers, influenced four measures of interpersonal coordination observed during performance in SSCGs. For this purpose we calculated positional data (GPS 15 Hz) from ten U-15 football players performing in three SSCGs varying in player numbers (3v3, 4v4 and 5v5). Key measures of SSCG system behaviours included values of (1) players' dispersion, (2) teams' separateness, (3) coupling strength and time delays between participants' emerging movements, respectively. Results showed that values of participants' dispersion increased, but the teams' separateness remained identical across treatments. Coupling strength and time delay also showed consistent values across SSCGs. These results exemplified how complex adaptive systems, like football teams, can harness inherent degeneracy to maintain similar team spatial-temporal relations with opponents through changes in inter-individual coordination modes (i.e., players' dispersion). The results imply that different team behaviours might emerge at different ratios of field dimension/player numbers. Therefore, sport pedagogists should carefully evaluate the effects of changing RSP in SSCGs as a way of promoting increased or decreased pressure on players.

#10 Quantification of energy expenditure of recreational football.
Reference: J Sports Sci. 2016 Mar 28:1-4. [Epub ahead of print]
Authors: Beato M, Impellizzeri FM, Coratella G, Schena F
Summary: There is a strong relationship between low physical activity level and cardiovascular diseases (CVD). The popularity of football may be used to promote physical activity and previous evidence has shown it is effective to decrease the risk of CVD. However, the energy expenditure (EE) of recreational football is not well known but it is crucial to develop preventive health programmes. Fifteen sedentary middle-aged male participants were involved (mean ± SDs; age 43.9 ± 3.1 years, weight 83.0 ± 13.6 kg, height 174.9 ± 6.8 cm). EE was estimated from the heart rate (HR)-VO2 relation during 1-h 5-a-side matches (futsal). Participants covered 3412 ± 381 m in 52 ± 2 min, at an average HR of 85 ± 2% of maximum HR. Estimated EE during a recreational futsal match was 634 ± 92 kcal. One futsal recreational match corresponds to about 50% of American College of Sport Medicine recommended physical activity quantity per week. Based on this estimation: once, twice and 3 sessions per week are equivalent to 50% (634 kcal), 100% (1268 kcal) and 150% (1902 kcal), respectively, of EE suggested in international guidelines. This EE estimation may have important implications for designing recreational football training protocols in health programmes and dose response studies.

#11 Injury recurrence is lower at the highest professional football level than at national and amateur levels: does sports medicine and sports physiotherapy deliver?
Reference: Br J Sports Med. 2016 Mar 25. pii: bjsports-2015-095951. doi: 10.1136/bjsports-2015-095951. [Epub ahead of print]
Authors: Hägglund M, Waldén M, Ekstrand J.
Summary: Previous injury is a well-documented risk factor for football injury. The time trends and patterns of recurrent injuries at different playing levels are not clear. The aim was to compare recurrent injury proportions, incidences and patterns between different football playing levels, and to study time trends in recurrent injury incidence. Time-loss injuries were collected from injury surveillance of 43 top-level European professional teams (240 team-seasons), 19 Swedish premier division teams (82 team-seasons) and 10 Swedish amateur teams (10 team-seasons). Recurrent injury was defined as an injury of the same type and at the same site as an index injury within the preceding year, with injury <2 months defined as an early recurrence, and >2 months as a delayed recurrence. Seasonal trend for recurrent injury incidence, expressed as the average annual percentage of change, was analysed using linear regression. 13  050 injuries were included, 2449 (18.8%) being recurrent injuries, with 1944 early (14.9%) and 505 delayed recurrences (3.9%). Recurrence proportions were highest in the second half of the competitive season for all cohorts. Recurrence proportions differed between playing levels, with 35.1% in the amateur cohort, 25.0% in the Swedish elite cohort and 16.6% in the European cohort (χ2 overall effect, p<0.001). A decreasing trend was observed in recurrent injury incidence in the European cohort, a -2.9% average annual change over the 14-year study period (95% CI -5.4% to -0.4%, p=0.026). Similarly, a decreasing tendency was also seen in the Swedish premier division. Recurrence proportions showed an inverse relationship with playing level, and recurrent injury incidence has decreased over the past decade.

#12 Fracture epidemiology in male elite football players from 2001 to 2013: 'How long will this fracture keep me out?'
Reference: Br J Sports Med. 2016 Mar 25. pii: bjsports-2015-095838. doi: 10.1136/bjsports-2015-095838. [Epub ahead of print]
Authors: Larsson D, Ekstrand J, Karlsson MK
Summary: Determining fracture risk and rehabilitation periods after specific fractures in professional football is essential for team planning. The aim was to identify fracture epidemiology and absences after different types of fractures in male professional football players. 2439 players from 41 professional male teams in 10 countries were followed prospectively from 2001 to 2013. Team medical staff registered fractures, absences after fractures and player exposure. 364 fractures were recorded, with an incidence of 0.27/1000 h of exposure (95% CI 0.25 to 0.30). The incidence of traumatic fractures was 0.25 (0.22 to 0.27) and that of stress fractures was 0.03 (0.02 to 0.04). 45% of traumatic fractures and 86% of stress fractures affected the lower extremities. Absence after a fracture was 32 days (1-278) (median (range)), compared to that after a traumatic fracture of 30 days (1-278) and a stress fracture of 65 days (6-168) (p<0.001). Annual fracture incidence was stable during the study period (R2=0.051, b=-0.011 (95% CI -0.043 to 0.021)). Young players had a relative risk of 10.9 (3.3 to 35.6) of sustaining stress fractures compared to old players (p<0.01). The fracture incidence did not differ between individuals in different playing positions (p=0.10). A male professional football team can expect 1 to 2 fractures per season. There are more traumatic fractures than stress fractures; while most fractures affect the lower extremities, stress fractures yield longer absences than traumatic fractures and young players have more stress fractures than old players. There is no difference in risk among players at different playing positions.
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