Latest research in football - week 22 - 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 Biomechanical Analysis of a Change of Direction Task in Collegiate Soccer Players
Reference: Int J Sports Physiol Perform. 2015 May 26. [Epub ahead of print]
Authors: Condello G, Kernozek TW, Tessitore A, Foster C.
Summary: This study aimed to investigate biomechanical parameters during a change of direction task in collegiate soccer players. Fourteen male and twelve female players performed a 10-m sprint with a 60° change of direction at 5 m. Vertical and mediolateral ground reaction force (GRF) and contact time were measured by having the subjects run in both directions while contacting a force plate with either their preferred (kicking) or non-preferred leg. Using the midpoint between two pelvic markers, further parameters were evaluated: performance cutting angle and horizontal distance. Relationships between parameters, sex and leg preference were analysed. Significant correlations emerged between vertical and mediolateral GRF (r = 0.660 to 0.909) and between contact time and performance cutting angle (r = -0.598 to -0.793). Sex differences were found for mediolateral GRF (p = 0.005), performance cutting angle (p = 0.043), and horizontal distance (p = 0.020). Leg differences were observed for vertical GRF (p = 0.029), performance cutting angle (p = 0.011), and horizontal distance (p = 0.012). This study showed as a sharper change of direction corresponded to a longer contact time, while no relationships were found with GRF. Moreover the measuring of the angle revealed that the real path traveled was different from the theoretical one highlighting the performance of sharper or more rounded execution. In conclusion, this study showed that specific biomechanical measurements can provide details about the execution of a change of direction highlighting the ability of the non-preferred leg to perform better directional changes.

#2 Effects of an eight-week proprioceptive neuromuscular facilitation stretching program on kicking speed and range of motion in young male soccer players
Reference: J Strength Cond Res. 2015 May 21. [Epub ahead of print]
Authors: Akbulut T, Agopyan A.
Summary: The aim of this study was to determine the effect of the 8-week of Proprioceptive Neuromuscular Facilitation (PNF) exercises which were carried out on lower extremity on kicking speed and range of motion (ROM) performance in young soccer players. Twenty-four soccer players (15.6 ± 0.4 years) were selected from non-professional young soccer team. All players' height, weight, ROM (ankle plantar and dorsal flexions, hip flexions and extensions) and kicking speed tests were evaluated before and after 8-week. The participants were divided into PNF (n=11) and control (n=11) groups. Both groups continued technical and tactical soccer training together three days (120 minutes/day) a week. PNF group attended additionally unassisted PNF-Contract-Relax (CR) stretching through 8-week, 2 days per week, 20 minutes session duration. The control group did not participate in any additional PNF stretching sessions. There were significant differences in kicking speed, right ankle active dorsal flexion, hip active flexion (right and left) (p < 0.05) of the PNF group, whereas there were no significant differences between groups in left ankle active dorsal flexion, hip active extension (right and left), ankle active plantar flexion (right and left) (p > 0.05). We conclude that an 8-week unassisted PNF-CR improved on the ROM of particular lower extremity joints and the kicking speed in the young male soccer players. These results provide strength and conditioning coaches with a practical way to use unassisted PNF-CR in warm up for positive improvements in the ROM of the hip and ankle and the applications of the kicking speed.

#3 Heart rate-based training intensity and its impact on injury incidence among elite-level professional soccer players
Reference: J Strength Cond Res. 2015 Jun;29(6):1705-12. doi: 10.1519/JSC.0000000000000810.
Authors: Owen AL, Forsyth JJ, Wong del P, Dellal A, Connelly SP, Chamari K.
Summary: Elite-level professional soccer players are suggested to have increased physical, technical, tactical, and psychological capabilities when compared with their subelite counterparts. Ensuring these players remain at the elite level generally involves training many different bodily systems to a high intensity or level within a short duration. This study aimed to examine whether an increase in training volume at high-intensity levels was related to injury incidence, or increased the odds of sustaining an injury. Training intensity was monitored through time spent in high-intensity (T-HI) and very high-intensity (T-VHI) zones of 85-<90% and ≥90% of maximal heart rate (HRmax), and all injuries were recorded over 2 consecutive seasons. Twenty-three, elite professional male soccer players (mean ± SD age, 25.6 ± 4.6 years; stature, 181.8 ± 6.8 cm; and body mass, 79.3 ± 8.1 kg) were studied throughout the 2-years span of the investigation. The results showed a mean total injury incidence of 18.8 (95% confidence interval [CI], 14.7-22.9) injuries per 1,000 hours of exposure. Significant correlations were found between training volume at T-HI and injury incidence (r = 0.57, p = 0.005). Further analysis revealed how players achieving more time in the T-VHI zone during training increased the odds of sustaining a match injury (odds ratio = 1.87; 95% CI, 1.12-3.12, p = 0.02) but did not increase the odds of sustaining a training injury. Reducing the number of competitive match injuries among elite-level professional players may be possible if greater focus is placed on the training intensity and volume over a period of time ensuring the potential reduction of fatigue or overuse injuries. In addition, it is important to understand the optimal training load at which adaptation occurs without raising the risk of injury.

#4 Effect of soccer heading ball speed on S100B, sideline concussion assessments and head impact kinematics
Reference: Brain Inj. 2015 May 25:1-7. [Epub ahead of print]
Authors: Dorminy M, Hoogeveen A, Tierney RT, Higgins M, McDevitt JK, Kretzschmar J
Summary: The purpose of the study was to examine the effect of soccer heading ball speed on S-100B serum concentration, concussion sideline assessments and linear head impact acceleration. Sixteen division I soccer players participated in this pre-test post-test design study. Athletes performed five standing headers over a 10 minute period at 30 (n = 5), 40 (n = 5) or 50 (n = 6) miles per hour (mph) (randomized). S-100B serum concentration (ng mL-1) and sideline concussion assessments were measured prior to and post-heading. Peak resultant linear head acceleration (gravitational units; g) was measured during soccer heading. No statistically significant interaction effects were identified between ball velocity groups over time on S100B (effect sizes ranged from 0.03-0.23) or concussion assessments tests. There was a non-significant increase (p = 0.06) in head impact acceleration from the 30 (30.6; SD = 6.2 g) to 50 mph (50.7; SD = 7.7 g) ball speed. In this controlled setting, an acute bout of soccer heading across various ball velocities did not affect S100B or concussion assessment test scores. These findings are preliminary, as the small sample size in each group may have played a role in the lack of significant findings.

#5 The effects of regular supplementary flexibility training on physical fitness performance of young high-level soccer players
Reference: J Sports Med Phys Fitness. 2015 May 25. [Epub ahead of print]
Authors: Hadjicharalambous M1.
Summary: The present study examined the effect of regular static flexibility training on selective physical fitness components in young high-level soccer-players. Twenty three players (mean +/- SD) were randomly assigned into Flexibility (Flex) and Control (Con) groups [(Flex group: n = 12, age 16.1 +/- 0.6 years; height 1.71 +/- .06 m; body mass 62.4 +/- 7.5 kg; peak oxygen uptake (VO2 peak) 55.8 +/- 4.1; (Con group: n = 11, age 15.9 +/- 0.6 years; height 1.73 +/- .07 m; body mass 61.5 +/- 5.6 kg; VO2 peak 54.2 +/- 5.2]. The Flex group performed a specific static stretching training-program before and after each training session, for four weeks (4 days/week). The two groups performed two series of anthropometrics and physical-fitness tests prior to and following the application of the stretching training performed on the Flex group. There were initially no main treatment effects on aerobic capacity ( VO2 peak), on 10m sprint and on Broad-jump. However, sit-and-reach flexibility, 35m sprint and agility (p < .05) performance, and when results corrected with Δ (magnitude of changes), Δ flexibility, Δ 35m-sprint, Δ agility and Δ Broad jump (p < .05) scores were significantly improved in Flex group compared with Con group. The present results suggest that regular specific supplementary application of static stretching training is effective in improving flexibility, 35m speed, explosiveness and agility performance in young high-level soccer-players.

#6 Multilevel lumbar transverse process fractures in a professional association football player: a case report
Reference: Oxf Med Case Reports. 2015 May 15;2015(5):288-91. doi: 10.1093/omcr/omv037. eCollection 2015.
Authors: Gray M, Catterson P
Download link:
Summary: We present a case of multilevel lumbar transverse process fracture in a professional association football player, incurred after a fall from height during competitive play. Traditionally associated with high impact trauma in the general population, this injury is relatively rare in the context of professional football where it is more likely to be associated with lower impact trauma. We outline our experience of mechanism of injury, treatment options and recovery time serving as a guide for fellow clinicians when treating this condition in practice. In this particular case, the return to play time was 68 days.

The Training Manager -