Latest research in football - week 13 - 2014

#1 Biochemical impact of soccer: an analysis of hormonal, muscle damage, and redox markers during the season
Authors: Silva JR, Rebelo A, Marques F, Pereira L, Seabra A, Ascensão A, Magalhães J.
Reference: Appl Physiol Nutr Metab. 2014 Apr;39(4):432-8. doi: 10.1139/apnm-2013-0180. Epub 2013 Oct 28.
Summary: This study aimed to analyze changes in performance, muscle function, and stress-related biochemical markers in professional soccer players (n = 14) at 4 timepoints (3 for performance and 4 for stress-related biochemical markers) during the soccer season preseason (E1), midseason (E2), end of the season (E3) and after the end of the recovery period (E4). Performance in 5- and 30-m sprints, countermovement jump, and agility, and maximal isokinetic knee extension and knee flexion strength were measured (E1 to E3). We observed increased in-season levels of myoglobin (E2 > E1 and E4; p < 0.05), a higher testosterone/cortisol ratio (T/C), and increased levels of creatine kinase (CK), C-reactive protein, superoxide dismutase (SOD), protein sulfhydryls (-SH), and malondialdehyde (E2 and E3 > E1 and E4; p < 0.05). Lower cortisol concentrations (E3 < E1 and E4; p < 0.05) and glutathione reductase activity (E3 < E2 and E4; p < 0.05) were observed at the end of the season. T/C, CK, SOD, -SH, and malondialdehyde decreased during the off-season, and cortisol and glutathione reductase increased (E3 < E4; p < 0.05). Agility increased in E2 and E3 (p < 0.01). Significant correlations were found during the season between hormonal and muscle function parameters (r = 0.56-0.86; p < 0.05). In addition, in E2, significant associations were observed between match-accumulated time (MATE2; minutes played by each player during the competition period), performance, and hormonal and redox parameters (r = 0.456-0.615; p < 0.05). In conclusion, this study shows that soccer players face significant changes in biomarkers of physiologic strain (muscle damage and oxidative stress-related markers) during the season, but values return to normal during the off-season. Additionally, MAT influences physical, hormonal, and oxidative stress-related parameters in professional soccer players.


#2 Acute and sub-acute effects of repetitive kicking on hip adduction torque in injury-free elite youth soccer players
Authors: Jensen J, Bandholm T, Hölmich P, Thorborg K.
Reference: J Sports Sci. 2014 Mar 26. [Epub ahead of print]
Summary: Hip adduction strength is important for kicking and acceleration in soccer players. Changes in hip adduction strength may therefore have an effect on soccer players' athletic performance. The purpose of this study was to investigate the acute and sub-acute effects of a kicking drill session on hip strength, concerning isometric hip adduction, abduction and flexion torque of the kicking leg and the supporting leg. Ten injury-free male elite soccer players, mean ± s age of 15.8 ± 0.4 years participated. All players underwent a specific 20 min kicking drill session, comprising 45 kicks. The players were tested the day before, 15 min after and 24 h after the kicking drill session by a blinded tester using a reliable test procedure. The isometric hip-action and leg-order were randomized. For the kicking leg, hip adduction torque increased from 2.45 (2.19-2.65) Nm ∙ kg-1, median (25th-75th percentiles), at pre-kicking to 2.65 (2.55-2.81) Nm ∙ kg-1 (P = 0.024) 24 h post-kicking. This may have implications for the soccer player's ability to maximally activate the hip adductors during kicking and acceleration, and thereby improve performance the day after a kicking drill session.


#3 Modelling Developmental Changes in Yo-Yo IR1 in Elite Pubertal Soccer Players
Authors: Deprez D, Valente-Dos-Santos J, Coelho E Silva M, Lenoir M, Philippaerts RM, Vaeyens R.
Reference: Int J Sports Physiol Perform. 2014 Mar 19. [Epub ahead of print]
Summary: The present study aimed to model the development of soccer-specific aerobic performance, assessed by the Yo-Yo IR1 in 162 elite pubertal soccer players, aged 11 to 14 years at the baseline. Longitudinal multilevel modelling analyses comprised predictors related to growth (chronological age, body size (stature and weight) and composition (fat mass, fat free mass)), motor coordination (three KTK subtests: jumping sideways, moving sideways, backward balancing) and estimated biological maturation groups (APHV, earliest (<percentile 33) and latest maturers (>percentile 66)). The best fitting model on the soccer-specific aerobic performance could be expressed as: -3639.76 + 369.86 x age + 21.38 x age + 9.12 x stature - 29.04 x fat mass + 0.06 x backward balance. Maturity groups had a negligible effect in the soccer-specific aerobic performance (-45.32 ± 66.28; p>0.05). The present study showed that the development of aerobic performance in elite youth soccer is related to growth, muscularity and emphasized the importance of motor coordination in the talent identification and development process. Note that biological maturation was excluded from the model which might endorse the homogeneity in estimated biological maturation status in the present elite pubertal soccer sample.


#4 The relationship between impact force, neck strength, and neurocognitive performance in soccer heading in adolescent females
Authors: Gutierrez GM, Conte C, Lightbourne K.
Reference: Pediatr Exerc Sci. 2014 Feb;26(1):33-40. doi: 10.1123/pes.2013-0102.
Summary: Head impacts are common in contact sports, but only recently has there been a rising awareness of the effects of subconcussive impacts in adolescent athletes. A better understanding of how to attenuate head impacts is needed and therefore, this study investigated the relationship between neck strength, impact, and neurocognitive function in an acute bout of soccer heading in a sample of female high school varsity soccer players. Seventeen participants completed the ImPACT neurocognitive test and had their isometric neck strength tested (flexion, extension, and bilateral flexion) before heading drills. Each participant was outfitted with custom headgear with timing switches and a three-dimensional accelerometer affixed to the back of the head, which allowed for measurement of impact during heading. Participants performed a series of 15 directional headers, including 5 forward, 5 left and 5 right headers in a random order, then completed the ImPACT test again. Neurocognitive tests revealed no significant changes following heading. However, there were statistically significant, moderate, negative correlations (r = -0.500:-0.757, p < .05) between neck strength and resultant header acceleration, indicating that those with weaker necks sustained greater impacts. This suggests neck strengthening may be an important component of any head injury prevention/reduction program.


#5 Magnetic resonance imaging of the iliac crest: age estimation in under-20 soccer players
Authors: Wittschieber D1, Vieth V, Timme M, Dvorak J, Schmeling A.
Reference: Forensic Sci Med Pathol. 2014 Mar 22. [Epub ahead of print]
Summary: Age assessment of living individuals represents a valuable tool in both forensic medicine and sports medicine. In soccer, age-related tournaments play an important role in guaranteeing equal chances to the competitors. However, age estimations in this field should not rely on imaging methods that include exposure to radiation. Therefore, the present study investigates the possibilities of magnetic resonance imaging (MRI) of the iliac crest apophysis for the purpose of evaluating skeletal maturation in under-20 (U-20) soccer players. To this end, gradient echo 3D sequences of the whole pelvis of 152 male tournament soccer players between 18 and 22 years of age were prospectively evaluated. A four stage classification system was applied for the assessment of the apophyseal ossification. Reliable stage determination was possible in all cases. Further sub-classification did not appear feasible due to the limitations of MRI. Analysis of the statistical parameters showed that age medians increased steadily from stage to stage. However, they did not allow for further differentiation of skeletal maturity in the cohort studied. Thus, MRI of the iliac crest appears to be generally suitable in age diagnostics of living individuals, but further investigations, especially in a cohort of individuals aged between 10 and 20 years, are needed in order to establish this method as novel criterion in sports or forensic medicine.


#6 Football for life versus antidoping for the masses: ethical antidoping issues and solutions based on the extenuating experiences of an elite footballer competing while undergoing treatment for metastatic testicular cancer
Authors: Weiler R, Tombides D, Urwin J, Clarke J, Verroken M.
Reference: Br J Sports Med. 2014 Mar 25. doi: 10.1136/bjsports-2014-093550. [Epub ahead of print]
Summary: It is thankfully rare for extenuating circumstances to fully test the processes and procedures enshrined in national and world antidoping authorities' rules and laws. It is also thankfully very rare that a failed drugs test can have some positive implications. Antidoping laws are undoubtedly focused on ensuring fair competition, however, there are occasions when honest athletes discover medical diagnoses through failed antidoping tests. The purpose of this paper is to broadly discuss antidoping considerations encountered, based on the four principles of medical ethics and to propose simple solutions to these problems. Unfortunately, extreme medical circumstances will often test the limits of antidoping and medical processes and with open channels for feedback, these systems can improve. Performance enhancement seems an illogical concept if an athlete's medical treatment and disease are more inherently performance harming than unintended potential doping, but needs to be carefully managed to maintain fair sport.


#7 Adaptive mechanisms and behavioural recommendations: playing football in heat, cold and high altitude conditions
Authors: Born DP, Hoppe MW, Lindner N, Freiwald J, Holmberg HC, Sperlich B.
Reference: Sportverletz Sportschaden. 2014 Mar;28(1):17-23. doi: 10.1055/s-0034-1366055. Epub 2014 Mar 24. [Article in German]
Summary: Football is played worldwide and players often have to cope with hot and cold temperatures as well as high altitude conditions. The upcoming and past world championships in Brazil, Qatar and South Africa illustrate the necessity for behavioural strategies and adaptation to extreme environmental conditions. When playing football in the heat or cold, special clothing, hydration and nutritional and acclimatisation strategies are vital for high-level performance. When playing at high altitude, the reduced oxygen partial pressure impairs endurance performance and alters the technical and tactical requirements. Special high-altitude adaptation and preparation strategies are essential for football teams based at sea-level in order to perform well and compete successfully. Therefore, the aim of the underlying review is: 1) to highlight the difficulties and needs of football teams competing in extreme environmental conditions, 2) to summarise the thermoregulatory, physiological, neuronal and psychological mechanism, and 3) to provide recommendations for coping with extreme environmental conditions in order to perform at a high level when playing football in the heat, cold and at high altitude.


#8 Health improvement for men and hard-to-engage-men delivered in English Premier League football clubs
Authors: Pringle A, Zwolinsky S, McKenna J, Robertson S, Daly-Smith A, White A.
Reference: Health Educ Res. 2014 Mar 21. [Epub ahead of print]
Summary: Unhealthy behaviours represent modifiable causes of non-communicable disease. In men, concern focuses on those (i) demonstrating the poorest health, exacerbated by a lack of awareness of the risks that their lifestyles pose and (ii) who neither consult their doctor nor use health services. Classed as 'hard-to-engage', distinctive strategies are needed to reach these men. Impact and process evaluations assessed the effect of a programme of men's health-delivered in/by English Premier League football clubs. Men attended match-day events and/or weekly classes involving physical activity and health education. Validated self-report measures for demographics and lifestyle behaviours were completed pre- and post-intervention. Intention-to-treat analysis was performed on pre-versus-post-intervention differences in lifestyle profiles, whereas interviews (n = 57) provided men's accounts of programme experience. Participants were predominantly white British (70.4%/n = 2669), 18-44 (80.2%/n = 3032) and employed (60.7%/n = 1907). One-third (n = 860) 'never' visited their doctor. Over 85% (n = 1428) presented with combinations of lifestyle risk factors. Intention-to-treat analysis showed improvements (P < 0.001) in lifestyle profiles. Interviews confirmed recruitment of men who were hard-to-engage and unhealthy. Men were attracted through football and/or the clubs, whereas specific design factors impacted on participation. Limitations include use of self-reports, narrow demographics, small effect sizes, lack of follow-up and the absence of non-completers in interviews.