Latest research in football - week 45 Part II - 2014

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 Normative data for hop tests in high school and collegiate basketball and soccer players
Reference: Int J Sports Phys Ther. 2014 Oct;9(5):596-603.
Authors: Myers BA, Jenkins WL, Killian C, Rundquist P
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Summary: Objective, reliable, and valid functional tests may assist with the decision-making process for rehabilitation as well as assist in pre-participation screening for targeted interventions to prevent noncontact lower extremity injuries. The purpose of this study was to determine normative values in high school and college basketball and soccer players for four hop tests: the single hop for distance, the triple hop for distance, the crossover hop for distance, and the 6-m timed hop. A sample of convenience of 372 (185 females, 187 males) healthy high school and collegiate student-athletes were included in the study (mean age 17.37 years, range 14-24): 200 were soccer players and 172 were basketball players. Limb dominance was determined based on which extremity participants would choose to kick a ball for distance. A coin flip was used to determine which limb was tested first. Hop test order was randomized using a Latin square design. Participants performed one practice hop and three measured hops for each hop test on each limb. The average hop score for each limb was used for calculations. Significant differences in test performance were found between sexes and levels of competition, p < 0.0005, with males performing better than females and collegiate athletes performing better than high school athletes for all hop tests. There were no clinically relevant differences between dominant sports. There were also no clinically relevant differences between dominant and non-dominant limbs. Normative values for each hop test were proposed, based on sex and level of competition. These findings indicate that separate hop test standards should be used based on participant sex and level of competition. While some statistically significant differences were found between limbs, these differences did not appear to be functionally relevant. Further studies are needed to determine if sport-specific normative hop test values should be utilized and to examine normal limb symmetry indices in specific populations.

# 2 Effect of tyrosine ingestion on cognitive and physical performance utilising an intermittent soccer performance test (iSPT) in a warm environment
Reference: Eur J Appl Physiol. 2014 Oct 19. [Epub ahead of print]
Authors: Coull NA, Watkins SL, Aldous JW, Warren LK, Chrismas BC, Dascombe B, Mauger AR, Abt G, Taylor L.
Summary: The aim of this study was to investigate the effect of tyrosine (TYR) ingestion on cognitive and physical performance during soccer-specific exercise in a warm environment. Eight male soccer players completed an individualised 90 min soccer-simulation intermittent soccer performance test (iSPT), on a non-motorised treadmill, on two occasions, within an environmental chamber (25 °C, 40 % RH). Participants ingested tyrosine (TYR; 250 mL sugar free drink plus 150 mg kg body mass-1 TYR) at both 5 h and 1 h pre-exercise or a placebo control (PLA; 250 mL sugar free drink only) in a double-blind, randomised, crossover design. Cognitive performance (vigilance and dual-task) and perceived readiness to invest physical effort (RTIPE) and mental effort (RTIME) were assessed: pre-exercise, half-time, end of half-time and immediately post-exercise. Physical performance was assessed using the total distance covered in both halves of iSPT. Positive vigilance responses (HIT) were significantly higher (12.6 ± 1.7 vs 11.5 ± 2.4, p = 0.015) with negative responses (MISS) significantly lower (2.4 ± 1.8 vs 3.5 ± 2.4, p = 0.013) in TYR compared to PLA. RTIME scores were significantly higher in the TYR trial when compared to PLA (6.7 ± 1.2 vs 5.9 ± 1.2, p = 0.039). TYR had no significant (p > 0.05) influence on any other cognitive or physical performance measure. The results show that TYR ingestion is associated with improved vigilance and RTIME when exposed to individualised soccer-specific exercise (iSPT) in a warm environment. This suggests that increasing the availability of TYR may improve cognitive function during exposure to exercise-heat stress.

#3 The acute effects of vibration training on balance and stability amongst soccer players
Reference: Eur J Sport Sci. 2014 Oct 30:1-7. [Epub ahead of print]
Authors: Cloak R, Nevill A, Wyon M.
Summary: Abstract Acute whole body vibration training (WBVT) is a tool used amongst coaches to improve performance prior to activity. Its effects on other fitness components, such as balance and stability, along with how different populations respond are less well understood. The aim of the current research is to determine the effect of acute WBVT on balance and stability amongst elite and amateur soccer players. Forty-four healthy male soccer players (22 elite and 22 amateur) were assigned to a treatment or control group. The intervention group then performed 3 × 60 seconds static squat on vibration platform at 40 Hz (±4 mm) with Y balance test (YBT) scores and dynamic postural stability index (DPSI) measured pre and post. DPSI was significantly lower in the elite players in the acute WBVT compared to amateur players (F1, 40= 6.80; P = 0.013). YBT anterior reach distance showed a significant improvement in both amateur and elite players in the acute WBVT group (F1, 40= 32.36; P < 0.001). The improvement in DPSI amongst the elite players indicates a difference in responses to acute high frequency vibration between elite and amateur players during a landing stability task. The results indicate that acute WBVT improves anterior YBT reach distances through a possible improvement in flexibility amongst both elite and amateur players. In conclusion, acute WBVT training appears to improve stability amongst elite soccer players in comparison to amateur players, the exact reasoning behind this difference requires further investigation.

#4 Mechanical determinants of acceleration and maximal sprinting speed in highly trained young soccer players
Reference: J Sports Sci. 2014 Oct 30:1-8. [Epub ahead of print]
Authors: Buchheit M1, Samozino P, Glynn JA, Michael BS, Al Haddad H, Mendez-Villanueva A, Morin JB.
Summary: The aim of the present study was to examine, in highly trained young soccer players, the mechanical horizontal determinants of acceleration (Acc) and maximal sprinting speed (MSS). Eighty-six players (14.1 ± 2.4 year) performed a 40-m sprint to assess Acc and MSS. Speed was measured with a 100-Hz radar, and theoretical maximal velocity (V0), horizontal force (F0) and horizontal power (Pmax) were calculated. Within each age group, players were classified as high Acc/fast MSS (>2% faster than group mean), medium (between -2% and +2%), and low/slow (>2% slower). Acc and MSS were very largely correlated (-0.79; 90% confidence limit [-0.85; -0.71]). The determinants (multiple regression r2 = 0.84 [0.78; 0.89]) of Acc were V0 (partial r: 0.80 [0.72; 0.86]) and F0 (0.57 [0.44; 0.68]); those of MSS (r2 = 0.96 [0.94; 0.97]) were V0 (0.96 [0.94; 0.97]) and Pmax (0.73 [0.63; -0.80]). High/Med have likely greater F0 (Cohen's d: +0.8 [0.0; 1.5]), V0 (+0.6 [-0.1; 1.3]) and Pmax (+0.9 [0.2; 1.7]) than Low/Med. High/Fast have an almost certainly faster V0 (+2.1 [1.5; 2.7]) and a likely greater Pmax (+0.6 [-0.1; 1.3]) than High/Med, with no clear differences in F0 (-0.0 [-0.7; 0.6]). Speed may be a generic quality, but the mechanical horizontal determinants of Acc and MSS differ. While maximal speed training may improve both Acc and MSS, improving horizontal force production capability may be efficient to enhance sprinting performance over short distances.

#5 Influence of the mechanical properties of third-generation artificial turf systems on soccer players' physiological and physical performance and their perceptions
Reference: PLoS One. 2014 Oct 29;9(10):e111368. doi: 10.1371/journal.pone.0111368. eCollection 2014.
Authors: Sánchez-Sánchez J, García-Unanue J, Jiménez-Reyes P, Gallardo A, Burillo P, Felipe JL, Gallardo L
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Summary: The aim of this research was to evaluate the influence of the mechanical properties of artificial turf systems on soccer players' performance. A battery of perceptive physiological and physical tests were developed on four different structural systems of artificial turf (System 1: Compacted gravel sub-base without elastic layer; System 2: Compacted gravel sub-base with elastic layer; System 3: Asphalt sub-base without elastic layer; System 4: Asphalt sub-base with elastic layer). The sample was composed of 18 soccer players (22.44±1.72 years) who typically train and compete on artificial turf. The artificial turf system with less rotational traction (S3) showed higher total time in the Repeated Sprint Ability test in comparison to the systems with intermediate values (49.46±1.75 s vs 47.55±1.82 s (S1) and 47.85±1.59 s (S2); p<0.001). The performance in jumping tests (countermovement jump and squat jump) and ball kicking to goal decreased after the RSA test in all surfaces assessed (p<0.05), since the artificial turf system did not affect performance deterioration (p>0.05). The physiological load was similar in all four artificial turf systems. However, players felt more comfortable on the harder and more rigid system (S4; visual analogue scale = 70.83±14.28) than on the softer artificial turf system (S2; visual analogue scale = 54.24±19.63). The lineal regression analysis revealed a significant influence of the mechanical properties of the surface of 16.5%, 15.8% and 7.1% on the mean time of the sprint, the best sprint time and the maximum mean speed in the RSA test respectively. Results suggest a mechanical heterogeneity between the systems of artificial turf which generate differences in the physical performance and in the soccer players' perceptions.

#6 Two Cases of Rhabdomyolysis After Training With Electromyostimulation by 2 Young Male Professional Soccer Players
Reference: Clin J Sport Med. 2014 Oct 28. [Epub ahead of print]
Authors: Kästner A, Braun M, Meyer T.
Summary: We report 2 cases of enormously elevated creatine kinase (CK) activity after training with electromyostimulation (EMS) by 2 young male professional soccer players. In one of them, a single training session with EMS caused exercise-induced rhabdomyolysis with a maximal CK activity of 240 000 U/L. These cases illustrate that unaccustomed EMS exercise may be harmful and can cause rhabdomyolysis even in highly trained athletes and even after 1 single session. Thus, EMS has to be conducted carefully especially by individuals who are known to frequently show notable increases in CK activity even after modest training stimuli. We suggest that EMS should not be applied as sole training stimulus and should not be conducted by strength training beginners. Furthermore, we recommend controlling plasma CK activity and urine color for beginners with EMS when they report strong muscle ache. Athletes with signs of rhabdomyolysis after EMS should be brought to hospital for monitoring of renal function and possible further treatment.

#7 An examination of injuries in Spanish Professional Soccer League
Reference: J Sports Med Phys Fitness. 2014 Dec;54(6):765-71.
Authors: Noya Salces J, Gomez-Carmona PM, Moliner-Urdiales D, Gracia-Marco L, Sillero-Quintana M.
Summary: The purpose of the study was to examine the injury incidence in the Spanish Professional Soccer League, and to analyse differences between competition and training. Sport injuries data from 11 out of 22 Spanish second division soccer teams (301 players) were prospectively collected during the season 2008/2009. A total of 891 injuries (111 recurrence injuries) were identified during 161602.7 hours of exposure. Competition injury incidence was higher than training (38.8 vs. 3.8 injuries per 1000h; P<0.05). The higher injury incidence was located at lower extremities (4.82 per 1000 h), and mainly affected muscles and tendons (3.1 per 1000 h). Two out of three injuries were due to overuse (54% during competition and 72% during training), and mainly result in players were unable to full soccer participation for less than 7 days (64%). Training injury incidence was higher during the pre-season and tended to decrease throughout the season (P<0.05), while competition injury incidence increased progressively throughout the season (P<0.05). In our best knowledge, this is the first examination of injuries in Spanish professional soccer players. The main findings of the study suggest that competition is much more injurious than training, revealing a progressive decrease of training injury incidence and a progressive increase of competition injury incidence throughout the season. These data might be considered by clubs, coaches, and medical staff in order to design new strategies that reduce injury risk in Spanish Professional Soccer League.

#8 Hamstrings-to-quadriceps strength and size ratios of male professional soccer players with muscle imbalance
Reference: Clin Physiol Funct Imaging. 2014 Oct 27. doi: 10.1111/cpf.12209. [Epub ahead of print]
Authors: Denadai BS, de Oliveira FB, Camarda SR, Ribeiro L, Greco CC.
Summary: The aim of this study was to determine the correlation between the concentric hamstrings/quadriceps muscle strength (Hcon :Qcon ) and cross-sectional area ratios (Hcsa :Qcsa ) in professional soccer players with Hcon :Qcon imbalance. Nine male professional soccer players (25·3 ± 4·1 years) performed five maximal concentric contractions of the knee extensors (KE) and flexors (KF) at 60 s-1 to assess Hcon :Qcon . The test was performed using the dominant (preferred kicking), and non-dominant limb with a 5-min recovery period was allowed between them. Only players with Hcon :Qcon  < 0·60 (range: 0·45-0·59) in both limbs were included in this study. The muscle cross-sectional area (CSA) of KE and KF was determined by magnetic resonance imaging. The correlations between Hcon :Qcon and Hcsa :Qcsa in the dominant leg (r = -0·33), non-dominant leg (r = 0·19) and in the both legs combined (r = 0·28) were not statistically significant (P>0·05). Thus, the Hcon :Qcon seems not to be determined by Hcsa :Qcsa in professional soccer players with Hcon :Qcon imbalance.

#9 Age Differences in Change of Direction Performance and its Sub-elements in Female Football Players
Reference: Int J Sports Physiol Perform. 2014 Oct 28. [Epub ahead of print]
Authors: Hirose N, Nakahori C.
Summary: The purpose was to describe cross-sectional age differences in change of direction performance in female football players and investigate the relationship between change of direction performance and linear sprint speed, muscular power, and body size. The sample of 135 well-trained female football players was divided into eight age groups. Anthropometry (body height, body mass, and lean body mass) and athletic performance (10-m sprint speed, 10 m × 5 change of direction performance, and 5-step bounding distance) were compared to determine inter-age differences. Then, the participants were divided into three age groups: 12- to 14-year-olds, 15- to 17-year-olds, and ≥18 year-olds. Simple and multiple regression analyses were conducted to determine differences among the age groups. Age-related differences were found for change of direction performance (F=10.41, P < 0.01), sprint speed (F=3.27, P < 0.01), and bounding distance (F=4.20, P < 0.01). Post hoc analysis revealed that the change of direction performance of 17-year-old players was faster than that of 16-year-old players (P < 0.01), with no inter-age differences in sprint speed and bounding distance. Sprint speed and bounding distance were weakly correlated with the change of direction performance in 15- to ≥18 year-olds players, but only sprint speed was correlated with change of direction performance in 12- to 14-year-olds players. Change of direction performance improves from 16 to 17 years of age in female players. Linear sprint speed, muscular power, and body size were weakly correlated with the age differences in change of direction performance.

#10 Injury prevention in male veteran football players - a randomised controlled trial using "FIFA 11+"
Reference: J Sports Sci. 2014 Nov 5:1-9. [Epub ahead of print]
Authors: Hammes D, Aus der Fünten K, Kaiser S, Frisen E, Bizzini M, Meyer T.
Summary:  The warm-up programme "FIFA 11+" has been shown to reduce football injuries in different populations, but so far veteran players have not been investigated. Due to differences in age, skill level and gender, a simple transfer of these results to veteran football is not recommended. The purpose of this study was to investigate the preventive effects of the "FIFA 11+" in veteran football players. Twenty veteran football teams were recruited for a prospective 9-month (1 season) cluster-randomised trial. The intervention group (INT, n = 146; 45 ± 8 years) performed the "FIFA 11+" at the beginning of each training session, while the control group (CON, n = 119; 43 ± 6 years) followed its regular training routine. Player exposure hours and injuries were recorded according to an international consensus statement. No significant difference was found between INT and CON in overall injury incidence (incidence rate ratio [IRR]: 0.91 [0.64-1.48]; P = 0.89). Only severe injuries reached statistical significance with higher incidence in CON (IRR: 0.46 [0.21-0.97], P = 0.04). Regular conduction (i.e. once a week) of the "FIFA 11+" did not prevent injuries in veteran footballers under real training and competition circumstances. The lack of preventive effects is likely due to the too low overall frequency of training sessions.

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