Latest research in football - week 30 - 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 Assessment of isokinetic peak torque reliability of the hip flexor, extensor, adductors and, abductors muscles in female soccer players from 16 to 25 years old
Reference: J Sports Med Phys Fitness. 2015 Jul 15. [Epub ahead of print]
Authors: Dos Santos Andrade M1, Mascarin NC, Benedito-Silva AA, Carderelli Minozzo F, Vancini RL, Barbosa de Lira CA.
Summary: The purpose was to evaluate test-retest reliability of concentric flexor, extensor, abductor and adductor muscular isokinetic hip torques in female soccer players. Sixteen highly-trained female soccer players were evaluated. Isokinetic dynamometer assessment was performed at 30°/s and 150°/s concentrically. The muscles tested were hip flexor (Fl), extensor (Ext), adductor (Add) and abductor (Abd). The reproducibility of the measured peak torque (PT) was analyzed by using the intraclass correlation coefficient (ICC). The difference in PT between the first and second tests was tested using Student's t test. The ICC for the observed PT values revealed moderate to high reproducibility (ranging from 0.55 to 0.76) for the hip Fl and Ext measurements at 150º/s and for Add and Abd measurements at 30 and 150º/s. For the hip Fl and Ext measurements at 30º/s the ICC was poor. The isokinetic assessment of the concentric PT values generated by the hip Fl and Ext and Add and Abd is moderate to highly reproducible, when assessed at the highest test velocity (150º/s). The test-retest reliability of hip isokinetic strength measures seems to be affected by the type muscle and test velocity.

#2 Effects of Combined Resistance Training and Plyometrics on Physical Performance in Young Soccer Players
Reference: Int J Sports Med. 2015 Jul 16. [Epub ahead of print]
Authors: Franco-Márquez F, Rodríguez-Rosell D, González-Suárez JM, Pareja-Blanco F, Mora-Custodio R, Yañez-García JM, González-Badillo JJ.
Summary: This study aimed to determine the effects of combined resistance training and plyometrics on physical performance in under-15 soccer players. One team (n=20) followed a 6-week resistance training program combined with plyometrics plus a soccer training program (STG), whereas another team (n=18) followed only the soccer training (CG). Strength training consisted of full squats with low load (45-60% 1RM) and low-volume (2-3 sets and 4-8 repetitions per set) combined with jumps and sprints twice a week. Sprint time in 10 and 20 m (T10, T20, T10-20), CMJ height, estimated one-repetition maximum (1RMest), average velocity attained against all loads common to pre- and post-tests (AV) and velocity developed against different absolute loads (MPV20, 30, 40 and 50) in full squat were selected as testing variables to evaluate the effects of the training program. STG experienced greater gains (P<0.05) in T20, CMJ, 1RMest, AV and MPV20, 30, 40 and 50 than CG. In addition, STG showed likely greater effects in T10 and T10-20 compared to CG. These results indicate that only 6 weeks of resistance training combined with plyometrics in addition to soccer training produce greater gains in physical performance than typical soccer training alone in young soccer players.

#3 Reliability of the 30-15 Intermittent Fitness Test in Semi-Professional Soccer Players
Reference: Int J Sports Physiol Perform. 2015 Jul 13. [Epub ahead of print]
Authors: Thomas C, Dos'Santos T, Jones PA, Comfort P
Summary: The purpose of this investigation was to determine the reliability of the 30-15 Intermittent Fitness Test (30-15IFT) in semi-professional soccer players. Fourteen male semi-professional soccer players performed the 30-15IFT on two occasions, separated by 7 days. Reliability was assessed by intraclass correlation coefficient (ICC), typical error of measurement (TE) expressed as a coefficient of variation (CV), and smallest worthwhile change (SWC), to determine any significant difference between testing sessions. Maximal intermittent running velocity (VIFT) demonstrated good reliability (ICC = .80) for between session reliability. The CV was 2.5% for between session reliability of the 30-15IFT. As the SWC (0.70 km/h) falls within the range in which the individual's true score is likely to lie (1.0 km/h), the usefulness of the VIFT was rated as 'Marginal'. Despite the usefulness of the 30-15IFT being deemed 'Marginal', a change in performance as small as 1.0 km/h (2 stages) in VIFT could be considered substantial or 'real'. This study demonstrates that VIFT in the 30-15IFT is reliable, resulting in a reliable assessment of team-sport specific cardiorespiratory fitness, with changes as small as 1.0 km/h (2 stages) in VIFT considered meaningful.

#4 Psychometric and Physiological Responses to a Pre-season Competitive Camp in the Heat With a 6-hr Time Difference in Elite Soccer Players
Reference: Int J Sports Physiol Perform. 2015 Jul 13. [Epub ahead of print]
Authors: Buchheit M, Cholley Y, Lambert P.
Summary: The aim of the present study was to examine in elite soccer players some psychometric and physiological responses to a competitive camp in the heat, after travelling across 6 time-zones. Data from 12 elite professional players (24.6±5.3 yr) were analyzed. They participated in an 8-day pre-season summer training camp in Asia (heat index 34.9±2.4 °C). Players' activity was collected during all training sessions and the friendly game using 15-Hz GPS. Perceived training/playing load was estimated using session rate of perceived exertion (RPE) and training/match duration. Psychometric measures of wellness were collected upon awakening before, during and after the camp using simple questionnaires. HR response to a submaximal 4-min run (12 km/h) and the ratio between velocity and force load (accelerometer-derived measure, a marker of neuromuscular efficiency) response to 4 ~60-m runs (22-24 km/h) were collected before, at the end and after the camp. After a large increase, the RPE/m.min-1 ratio decreased substantially throughout the camp. There were possible small increases in perceived fatigue and small decreases in subjective sleep quality on the 6th day. There were also likely moderate (~3%) decreases in HR response to the submaximal run, both at the end and after the camp, which were contemporary to possible small (~8%) and most-likely moderate (~19%) improvements in neuromuscular efficiency, respectively. Despite transient increases in fatigue and reduced subjective sleep quality by the end of the camp, these elite players showed clear signs of heat acclimatization, which were associated with improved cardiovascular fitness and neuromuscular running efficiency.

#5 Soccer and sexual health education: a promising approach for reducing adolescent births in Haiti
Reference: Rev Panam Salud Publica. 2015 May;37(4-5):316-23.
Authors: Kaplan KC, Lewis J, Gebrian B, Theall K
Summary: The purpose of the study was to explore the effect of an innovative, integrative program in female sexual reproductive health (SRH) and soccer (or fútbol, in Haitian Creole) in rural Haiti by measuring the rate of births among program participants 15-19 years old and their nonparticipant peers. A retrospective cohort study using 2006-2009 data from the computerized data-tracking system of the Haitian Health Foundation (HHF), a U.S.-based nongovernmental organization serving urban and rural populations in Haiti, was used to assess births among girls 15-19 years old who participated in HHF's GenNext program, a combination education-soccer program for youth, based on SRH classes HHF nurses and community workers had been conducting in Haiti for mothers, fathers, and youth; girl-centered health screenings; and an all-female summer soccer league, during 2006-2009 (n = 4 251). Bivariate and multiple logistic regression analyses were carried out to assess differences in the rate of births among program participants according to their level of participation (SRH component only ("EDU") versus both the SRH and soccer components ("SO") compared to their village peers who did not participate. Hazard ratios (HRs) of birth rates were estimated using Cox regression analysis of childbearing data for the three different groups. In the multiple logistic regression analysis, only the girls in the "EDU" group had significantly fewer births than the nonparticipants after adjusting for confounders (odds ratio = 0.535; 95% confidence interval (CI) = 0.304, 0.940). The Cox regression analysis demonstrated that those in the EDU group (HR = 0.893; 95% CI = 0.802, 0.994) and to a greater degree those in the SO group (HR = 0.631; 95% CI = 0.558, 0.714) were significantly protected against childbearing between the ages of 15 and 19 years. HHF's GenNext program demonstrates the effectiveness of utilizing nurse educators, community mobilization, and youth participation in sports, education, and structured youth groups to promote and sustain health for adolescent girls and young women.

#6 Patient-Reported Outcomes in Male and Female Collegiate Soccer Players During an Athletic Season
Reference: J Athl Train. 2015 Jul 24. [Epub ahead of print]
Authors: Hoch JM, Druvenga B, Ferguson BA, Houston MN, Hoch MC
Summary: Clinicians are urged to document patient-based outcomes during rehabilitation to measure health-related quality of life (HRQOL) from the patient's perspective. It is unclear how scores on patient-reported outcome instruments (PROs) vary over the course of an athletic season because of normal athletic participation. Our primary purpose was to evaluate the effect of administration time point on HRQOL during an athletic season. Secondary purposes were to determine test-retest reliability and minimal detectable change scores of 3 PROs commonly used in clinical practice and if a relationship exists between generic and region-specific outcome instruments. Twenty-three collegiate soccer athletes (11 men, 12 women) participated in the study and were measured at 5 time points over a spring season. We administered the Disablement in the Physically Active Scale (DPA), Foot and Ankle Ability Measure-Sport, and Knee Injury and Osteoarthritis Outcome Score (KOOS). Time effects were observed for the DPA (P = .011) and KOOS Quality of Life subscale (P = .027). However, the differences between individual time points did not surpass the minimal detectable change for the DPA, and no post hoc analyses were significant for the KOOS-Quality of Life subscale. Test-retest reliability was moderate for the KOOS-Pain subscale (intraclass correlation coefficient = 0.71) and good for the remaining KOOS subscales, DPA, and Foot and Ankle Ability Measure-Sport (intraclass correlation coefficients > 0.79). The DPA and KOOS-Sport subscale demonstrated a significant moderate relationship (P = .018). Athletic participation during a nontraditional, spring soccer season did not affect HRQOL. All 3 PROs were reliable and could be used clinically to monitor changes in health status throughout an athletic season. Our results demonstrate that significant deviations in scores were related to factors other than participation, such as injury. Finally, both generic and region-specific instruments should be used in clinical practice.

#7 Stress, Sleep and Recovery in Elite Soccer: A Critical Review of the Literature
Reference: Sports Med. 2015 Jul 24. [Epub ahead of print]
Authors: Nédélec M, Halson S, Abaidia AE, Ahmaidi S, Dupont G.
Summary: In elite soccer, players are frequently exposed to various situations and conditions that can interfere with sleep, potentially leading to sleep deprivation. This article provides a comprehensive and critical review of the current available literature regarding the potential acute and chronic stressors (i.e. psychological, sociological and physiological stressors) placed on elite soccer players that may result in compromised sleep quantity and/or quality. Sleep is an essential part of the recovery process as it provides a number of important psychological and physiological functions. The effects of sleep disturbance on post-soccer match fatigue mechanisms and recovery time course are also described. Physiological and cognitive changes that occur when competing at night are often not conducive to sleep induction. Although the influence of high-intensity exercise performed during the night on subsequent sleep is still debated, environmental conditions (e.g. bright light in the stadium, light emanated from the screens) and behaviours related to evening soccer matches (e.g. napping, caffeine consumption, alcohol consumption) as well as engagement and arousal induced by the match may all potentially affect subsequent sleep. Apart from night soccer matches, soccer players are subjected to inconsistency in match schedules, unique team schedules and travel fatigue that may also contribute to the sleep debt. Sleep deprivation may be detrimental to the outcome of the recovery process after a match, resulting in impaired muscle glycogen repletion, impaired muscle damage repair, alterations in cognitive function and an increase in mental fatigue. The role of sleep in recovery is a complex issue, reinforcing the need for future research to estimate the quantitative and qualitative importance of sleep and to identify influencing factors. Efficient and individualised solutions are likely needed.

#8 Hip Strength Testing of Soccer Players With Long-Standing Hip and Groin Pain: What are the Clinical Implications of Pain During Testing?
Reference: Clin J Sport Med. 2015 Jul 22. [Epub ahead of print]
Authors: Rafn BS, Tang L, Nielsen MP, Branci S, Hölmich P, Thorborg K.
Summary: The purpose was to investigate whether self-reported pain during hip strength testing correlates to a large degree with hip muscle strength in soccer players with long-standing unilateral hip and groin pain. Twenty-four male soccer players with unilateral long-standing hip and groin pain were assessed at the Sports Orthopaedic Research Center-Copenhagen (SORC-C), Arthroscopic Centre Amager, Copenhagen University Hospital, Denmark. The soccer players performed 5 reliable hip muscle strength tests (isometric hip flexion, adduction, abduction, isometric hip flexion-modified Thomas test, and eccentric hip adduction). Muscle strength was measured with a hand-held dynamometer, and the players rated the pain during testing on a numerical rating scale (0-10). In 4 tests (isometric hip adduction, abduction, flexion, and eccentric adduction), no significant correlations were found between pain during testing and hip muscle strength (Spearman rho = -0.28 to 0.06, P = 0.09-0.39). Isometric hip flexion (modified Thomas test position) showed a moderate negative correlation between pain and hip muscle strength (Spearman rho = -0.44, P = 0.016). Self-reported pain during testing does not seem to correlate with the majority of hip muscle strength tests used in soccer players with long-standing hip and groin pain.

#9 Evaluating individual training adaptation with Smartphone-derived heart rate variability in a collegiate female soccer team
Reference: J Strength Cond Res. 2015 Jul 11. [Epub ahead of print]
Authors: Flatt AA, Esco MR
Summary: Monitoring individual responses throughout training may provide insight to coaches regarding how athletes are coping to the current program. It is unclear if the evolution of heart rate variability (HRV) throughout training in team sport athletes can be useful in providing early indications of individual adaptation. The current study evaluated relationships between changes in resting cardiac-autonomic markers derived from a novel smartphone device within the first 3 weeks of a 5-week conditioning program and the eventual change in intermittent running performance at week 5 among 12 collegiate female soccer players. Change variables from week 1 to week 3 of the weekly mean and weekly coefficient of variation (CV) for resting heart rate ([INCREMENT]RHRmean and [INCREMENT]RHRcv, respectively) and log transformed root mean square of successive R-R intervals multiplied by 20 ([INCREMENT]Ln rMSSDmean and [INCREMENT]Ln rMSSDcv, respectively) were compared to changes in Yo-Yo Intermittent Recovery Test Level 1 performance ([INCREMENT]Yo-Yo). A very large and significant correlation was found between [INCREMENT]Yo-Yo and [INCREMENT]Ln rMSSDcv (r = -0.74; p = <0.01) and a large, non-significant correlation was found with [INCREMENT]Ln rMSSDmean (r = 0.50; p = 0.096). This study suggests that a decrease in Ln rMSSDcv within the first 3 weeks of training is a favorable response, indicative of positive adaptation. Collecting daily HRV data with a smartphone application utilizing ultra-short HRV measures appears useful for athlete monitoring.

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