Latest research in football - week 5 - 2017

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 Relationship among Repeated Sprint Ability, Chronological Age and Puberty in young soccer players
Reference: J Strength Cond Res. 2016 Jan 19. doi: 10.1519/JSC.0000000000001799. [Epub ahead of print]
Authors: Perroni F, Pintus A, Frandino M, Guidetti L, Baldari C
Summary: The aim of this study was to analyzed the relationship of Repeated Sprinting Ability (RSA) with chronological age and puberty in 100 young soccer players (Age: 13 ± 3 yr - 160 ± 33 month-; High: 159 ± 16 cm, Weight: 49.7 ± 14.1 kg; BMI 19.2 ± 2.5 kg/m) grouped on "Pulcini" (9 - 10 yrs), "Esordienti" (11 - 12 yrs), "Giovanissimi" (13 - 14 yrs), "Allievi" (15 - 16 yrs) and "Juniores" (> 17 yrs) categories. Anthropometric (Weight, Height, BMI), RSA (7x30 m sprint with 25s active rest: Total Time -TT, the lowest sprinting time (LST) and the fatigue index percentage -%IF), and Development (Self-Administered Rating Scale for pubertal development - PDS; Puberty) parameters were measured. ANOVA among categories was applied to asses differences (p<0.05) in TT and %IF. When a significant effect was found, Bonferroni's post hoc analysis was used. Pearson correlation among all variables was calculated considering all subjects and also within categories. Among categories, statistical analysis showed a significant differences (p< 0.001) in TT and a considerable trend toward significance (p=0.06) in %IF. Significant correlations among variables was found in all subjects and within categories. In particular, TT showed large significant correlation with PDS (r=-0.66) and Puberty (r=-0.67) only in "Esordienti". This study provides useful information for the coach in order to porpose an appropriate training and to obtain the optimal training effect and to minimise the risk of injury and overtraining during the different phases of growth and maturation.

#2 Heart rate variability discriminates competitive levels in professional soccer players
Reference: J Strength Cond Res. 2017 Jan 20. doi: 10.1519/JSC.0000000000001795. [Epub ahead of print]
Authors: Proietti R, di Fronso S, Lucas AP, Bortoli L, Robazza C, Fabio YN, Bertollo M
Summary: Heart rate variability (HRV) has been increasingly used to monitor team sports athletes. Besides the traditional time domain indices (i.e., the standard deviation of successive RR intervals [SDNN] and the root mean square difference of successive normal RR intervals [RMSSD]), recently it has been proposed the use of the stress score (SS), which is an inverse function of the standard deviation 2 index derived from the Poincaré plot, and the sympathetic/parasympathetic ratio (S/PS) to monitor soccer players. However, the reliability of these new indices and the ability of HRV to differentiate between soccer competitive levels are unknown. The aim of this study was to analyze the reliability of the different HRV-derived indices in professional soccer players during the competitive period and to compare HRV of professional soccer players from three teams of distinct competitive levels (i.e., Italian Second Division [2D], European League [EL] and Champions League [CL]). Fifty-four male professional soccer players from three different teams of two European countries (Italy and Germany) participated in the study. The intraclass correlation coefficient (ICC) values of the HRV indices varied from 0.78 (very large) to 0.90 (near perfect). The coefficient of variation (CV) values for RMSSD and SDNN were all <5.00%, while the CV for SS was 6.13% and for S/PS 21.33%. Both the CL and EL groups, assumed to be internationally qualified, presented higher lnRMSSD and lnSDNN and lower lnSS and S/PS than the 2D. Therefore, the HRV can be considered reliable in professional soccer players and able to differentiate between international and national level players.

#3 Effects of knowing the task duration on players' pacing patterns during soccer small-sided games
Reference: J Sports Sci. 2017 Jan 30:1-7. doi: 10.1080/24733938.2017.1283433. [Epub ahead of print]
Authors: Ferraz R, Gonçalves B, Van Den Tillaar R, Jiménez Saiz S, Sampaio J, Cardoso Marques M
Summary: The aim of this study was to identify the influence of prior knowledge of exercise duration on players' pacing patterns during soccer small-sided games. Twenty semi-professional male soccer players participated in this study. In the first game scenario, players were not informed how long they would be required to play the small-sided game and the activity was terminated after 20 min (Unknown Condition). In the second game scenario, players were told that they would play the small-sided game for 10 min, but immediately after completing the 10-min game, they were asked to complete another 10 min (Partially Condition). In the third game scenario, players were instructed that they would play the small-sided game for 20 min and then they completed the 20-min game (Known Condition). The results presented a tendency of higher values in all performance variables in the [0'-10'] min compared with the [10'-20'] min. As the players' previous knowledge about the tasks duration increased, the performance between two moments tended to be similar. Considering the entire 20-min game duration, the Partially Condition of the exercise was the most demanding condition. In conclusion, the knowledge of shorter durations of the exercise seems to lead to an increase of exercise duration demand, and longer exercise durations possibly tend to decrease differences between full knowledge and not knowing the exercise duration.

#4 Broad-spectrum health improvements with one year of soccer training in inactive mildly hypertensive middle-aged women
Reference: Scand J Med Sci Sports. 2017 Jan 25. doi: 10.1111/sms.12829. [Epub ahead of print]
Authors: Krustrup P, Skoradal MB, Randers MB, Weihe P, Uth J, Mortensen J, Mohr M
Summary: The study tested the hypothesis that long-term soccer training has positive impact on cardiovascular profile, body composition, bone health, and physical capacity in inactive, pre-menopausal women with mild hypertension. The study applied a randomized controlled design in which physically inactive middle-aged women were separated into a soccer training group (n=19; SOC) and a control group (n=12; CON). SOC performed 128±29 (±SD) one-h small-sided soccer training sessions over one year. Blood pressure, body composition, blood lipid profile, and fitness level were determined pre- and post-intervention. Over one year, mean arterial pressure decreased more in SOC than in CON (-5±7 vs +4±5 mmHg; P<.05). Total-body fat mass decreased more (P<.05) in SOC than in CON (-2.5±2.5 vs +0.6±3.2 kg; P<.05), while the change scores for lean body mass were not significantly different in SOC (2.6±2.7 kg) compared to CON (1.1±1.9 kg, P=.09). Over one year, change scores in whole-body bone mineral density (0.004±0.032 vs -0.019±0.026 g·cm2 ) as well as bone mineral content (30±70 vs -39±113 g) were positive in SOC compared to CON (P<.05). Post-intervention plasma triglycerides decreased more (-0.1±0.7 vs +0.2±0.2 mmol·L-1 ) and HDL cholesterol increased more (0.2±0.7 vs -0.2±0.2 mmol·L-1 ) in SOC than in CON (P<.05). Yo-Yo intermittent endurance level 1 (122±105 vs 2±21%) and 20-m sprint performance (6±6 vs -1±2%) increased more (P<.05) in SOC than in CON. In conclusion, long-term soccer training resulted in broad-spectrum improvements in the health profile of untrained, pre-menopausal women with mild hypertension, including cardiovascular, metabolic, and musculo-skeletal benefits.

#5 Osteoarthritis and joint replacements of the lower limb and spine in ex-professional soccer players: A systematic review
Reference: Scand J Med Sci Sports. 2017 Feb 2. doi: 10.1111/sms.12846. [Epub ahead of print]
Authors: Lohkamp M, Kromer TO, Schmitt H
Summary: After a professional career as a soccer player, the risk of developing osteoarthritis (OA) in different joints of the spine and lower limb might be increased. The extent of this problem to date is not clear. Therefore, the aim of this systematic review is to summarise the prevalence of OA and joint replacement of the lower limb and spine in former professional soccer players. Relevant databases were searched with different combinations of key words: e.g. osteoarthritis, hip, knee, ankle, foot, joint replacement, soccer. Studies were included if they were original research, included a sample of former professional male soccer players, had OA in the lower limb and/or spine, OA was diagnosed either through questionnaires or x-rays, article in English, Dutch or German. Sixteen studies with 1576 former players and 2153 control subjects were included in the review. Studies agreed that the prevalence of hip OA and hip replacements is significantly higher in former players compared to the control group. For the ankle and spine there is only limited information and for the prevalence of knee OA and knee replacement the results are contradictory. The quality of the included studies was moderate. Future studies should have a prospective design to control for confounding factors, to identify possible risk factors and consequences for the individuals, and to be able to develop a prevention programme.

#6 Repeated Dribbling Ability in Young Soccer Players: Reproducibility and Variation by the Competitive Level
Reference: J Hum Kinet. 2016 Oct 14;53:155-166. doi: 10.1515/hukin-2016-0019. eCollection 2016.
Authors: Duarte JP, Tavares O, Valente-Dos-Santos J, Severino V, Ahmed A, Rebelo-Gonçalves R, Pereira JR, Vaz V, Povoas S, Seabra A, Cumming SP, Coelho-E-Silva MJ
Summary: The intermittent nature of match performance in youth soccer supports relevance of ability to repeatedly produce high-intensity actions with short recovery periods. This study was aimed to examine the reproducibility of a repeated dribbling ability protocol and, additionally, to estimate the contribution of concurrent tests to explain inter-individual variability in repeated dribbling output. The total sample comprised 98 players who were assessed as two independent samples: 31 players were assessed twice to examine reliability of the protocol; and 67 juveniles aged 16.1 ± 0.6 years were compared by the competitive level (local, n = 34; national, n = 33) to examine construct validity. All single measurements appeared to be reasonably reliable: total (ICC = 0.924; 95%CI: 0.841 to 0.963); ideal (ICC = 0.913; 95%CI: 0.820 to 0.958); worst (ICC = 0.813; 95%CI: 0.611 to 0.910). In addition, the percentage of the coefficient of variation was below the critical value of 5% for total (%CV = 3.84; TEM = 2.51 s); ideal (%CV = 3.90, TEM = 2.48 s). Comparisons between local and national players suggested magnitude effects as follows: moderate (d-value ranged from 0.63 to 0.89) for all repeated sprint ability scores; large for total (d = 1.87), ideal (d = 1.72), worst (d = 1.28) and moderate for composite scores: the fatigue index (d = 0.69) and the decrement score (d = 0.67). In summary, the dribbling protocol presented reasonable reproducibility properties and output extracted from the protocol seemed to be independent from biological maturation.

#7 Role of Vertical Jumps and Anthropometric Variables in Maximal Kicking Ball Velocities in Elite Soccer Players
Reference: J Hum Kinet. 2016 Oct 15;53:143-154. doi: 10.1515/hukin-2016-0018. eCollection 2016.
Authors: Rodriguez-Lorenzo L, Fernandez-Del-Olmo M, Sanchez-Molina JA, Martín-Acero R
Summary: Kicking is one of the most important skills in soccer and the ability to achieve ma ximal kicking velocity with both legs leads to an advantage for the soccer player. This study examined the relationship be tween kicking ball velocity with both legs using anthropometric measurements and vertical jumps (a squat jump (SJ); a countermovement jump without (CMJ) and with the arm swing (CMJA) and a reactive jump (RJ)). Anthropome tric measurements did not correlate with kicking ball velocity. Vertical jumps correlated significantly with kicking ball velocity using the dominant leg only (r = .47, r = .58, r = .44, r = .51, for SJ, CMJ, CMJA and RJ, respectively) . Maximal kicking velocity with the dominant leg was significantly higher than with the non-dominant leg (t = 18.0 4, p < 0.001). Our results suggest that vertical jumps may be an optimal test to assess neuromuscular skills involved in kicking at maximal speed. Lack of the relationship between vertical jumps and kicking velocity with the non-dominant leg may reflect a difficulty to exhibit the neuromuscular skills during dominant leg kicking.

#8 Monitoring Salivary Immunoglobulin A Responses to Official and Simulated Matches In Elite Young Soccer Players
Reference: J Hum Kinet. 2016 Oct 14;53:107-115. doi: 10.1515/hukin-2016-0015. eCollection 2016.
Authors: Freitas CG, Aoki MS, Arruda AF, Franciscon C, Moreira A
Summary: The purpose of the present study was to examine SIgA responses (concentration [SIgAabs] and a secretion rate [SIgArate]) to official and simulated competitive matches in young soccer players. The sample was composed of 26 male soccer players (age 15.6 ± 1.1 yrs, stature 177.0 ± 6.1 cm, body mass 70.5 ± 5.7 kg). Four soccer matches (two simulated matches [SM] and two official matches [OM]) were conducted. The matches consisted of two halves of 35 min with a 10 min rest interval. Each assessed player participated in only one SM and one OM. All matches were performed in the same week, during the competitive season, and at the same time of the day (9:00 am), separated by 48 h. Saliva samples were collected before and after every match. The session rating of perceived exertion was reported 30 min after each match in order to determine the internal training load (ITL). A significant decrease in SIgAabs and SIgArate after OM was observed when compared to the pre-match value. In addition, the SIgArate was higher at pre-OM when compared to pre-SM. A higher ITL for OM was observed compared to SM. The current findings indicate that OM may lead to a decrease in the main mucosal immunity function parameter of young soccer players that could increase the risk of URTI. Coaches should be aware of it in order to plan appropriate training loads and recovery procedures to avoid or minimize the likelihood of upper respiratory tract infection occurrences.

#9 The Importance of Postural Control in Relation to Technical Abilities in Small-Sided Soccer Games
Reference: J Hum Kinet. 2016 Oct 14;53:51-61. doi: 10.1515/hukin-2016-0010. eCollection 2016.
Authors: Edis ÇC, Vural F, Vurgun H
Summary: Making assessments regarding postural control and balance is very important for injury prevention in soccer. However, there has been no study that has associated postural control variables with branch-specific technical properties in a game. The aim of the present study was to determine the relationships between variables designating postural control levels and technical performance variables in different (1:1, 2:2 and 3:3) small-sided games (SSGs). Sixteen trained male amateur soccer players volunteered to take part in the study (age 17.2 ± 1.02 years, body height 176.25 ± 0.07 m, body mass 67.67 ± 13.27 kg). Following familiarization sessions, postural control was evaluated using one-leg and both-leg quiet-stance positions by measuring postural sway with a Tekscan HR Mat™ in anterior-posterior and medial-lateral directions. Later, 1:1, 2:2 and 3:3 SSGs were performed at two-day intervals and the technical variables specified for each game were analyzed. A Spearman's rank-order correlation analysis demonstrated the relationship between postural control and soccer-specific technical variables in 1:1 (r-values ranging from 0.582 to 0.776), 2:2 (rvalues ranging from 0.511 to 0.740) and 3:3 (r-values ranging from 0.502 to 0.834) SSGs. In addition, a Wilcoxon signed rank test revealed differences between SSGs in terms of several variables. The results of the study showed that higher postural control levels are among the important variables that affect success in the performance of technical skills under rival pressure and suddenly changing conditions. Therefore, it is recommended that in addition to its use for injury prevention purposes, balance training should be conducted to improve branch-specific technical skills and to increase the levels of their successful performance in a game.

#10 Determinants of feedback retention in soccer players
Reference: J Hum Kinet. 2016 Jul 2;51:235-241. doi: 10.1515/hukin-2015-0187. eCollection 2016
Authors: Januario N, Rosado A, Mesquita I, Gallego J, Aguilar-Parra JM
Summary: This study analyzed soccer players' retention of coaches' feedback during training sessions. We intended to determine if the retention of information was influenced by the athletes' personal characteristic (age, gender and the sports level), the quantity of information included in coach's feedback (the number of ideas and redundancy), athletes' perception of the relevance of the feedback information and athletes' motivation as well as the attention level. The study that was conducted over the course of 18 sessions of soccer practice, involved 12 coaches (8 males, 4 females) and 342 athletes (246 males, 96 females), aged between 10 and 18 years old. All coach and athlete interventions were transposed to a written protocol and submitted to content analysis. Descriptive statistics and multiple linear regression were calculated. The results showed that a substantial part of the information was not retained by the athletes; in 65.5% of cases, athletes experienced difficulty in completely reproducing the ideas of the coaches and, on average, the value of feedback retention was 57.0%. Six variables with a statistically significant value were found: gender, the athletes' sports level, redundancy, the number of transmitted ideas, athletes' perception of the relevance of the feedback information and the athletes' motivation level.

#11 Comparison between two types of anaerobic speed endurance training in competitive soccer players
Reference: J Hum Kinet. 2016 Jul 2;51:183-192. doi: 10.1515/hukin-2015-0181. eCollection 2016
Authors: Mohr M, Krustrup P
Summary: The purpose of the present study was to examine the effects of additional in-season speed endurance production versus speed endurance maintenance training regimes on performance in competitive male soccer players. In a randomised controlled trial 18 male sub-elite players were exposed to additional speed endurance production (SEP) or speed endurance maintenance (SEM) training (two additional sessions/wk for 4 weeks) during the competitive season. Players performed the Yo-Yo intermittent recovery level 2 test (YYIR2) and a repeated sprint test (RST) pre- and post-intervention. Yo-Yo IR2 performance increased (p<0.001) by 50 ± 8% and 26 ± 5% in SEP and SEM, respectively, with greater (p=0.03) improvement in SEP. RST performance improved by 2.1 ± 0.3% and 1.3 ± 0.4% in SEP and SEM, respectively, while the RST fatigue index decreased (4.4 ± 0.8 to 3.4 ± 0.5%; p<0.04) in SEP only. Peak and average speed during training were higher (p<0.001) in SEP than in SEM (24.5 ± 0.3 vs 19.2 ± 0.3 and 15.5 ± 0.1 km·h-1 vs 9.4 ± 0.1 km·h-1). Additional in-season anaerobic speed endurance production and maintenance training improves high-intensity exercise performance in competitive soccer players with superior effects of speed endurance production training.

#12 Effect of the pitch size and presence of goalkeepers on the work load of players during small-sided soccer games
Reference: J Hum Kinet. 2016 Jul 2;51:175-181. doi: 10.1515/hukin-2015-0180. eCollection 2016
Authors: Hulka K, Weisser R, Belka J
Summary: Small-sided games (SSGs) are spontaneous forms of specific training where exercise intensity can be manipulated by modifying external factors. To ensure suitable usage of small-sided games in practice, we have to know which variables can influence internal responses and external loads. The aim of the present study was to determine the influence of presence of a goalkeeper and the pitch size on internal responses and the external load during five-a-side soccer games. Twenty nine junior soccer players (age: 18.11 ± 1.31 years; body mass index: 21.04 ± 2.58 kg·m-2; peak heart rate: 199.53 ± 7.51 beats·min-1) participated in the study. The heart rate, distance covered and the rate of perceived exertion were monitored. We found significantly higher average heart rates of players in 5v5 SSGs without goalkeepers than with them on a small pitch. Analysis showed significant differences in the time spent in 65-85% of the peak heart rate zone and ˂65% of the peak heart rate zone on the small pitch. Furthermore, we found significantly higher distance covered by players during five-a-side games with goalkeepers than without them played on the small pitch. Our results indicate that the pitch size is a very important variable that influences the work load of players. The inclusion of the goalkeeper decreases the work load of the player on a small pitch (28 × 20 m; 560 m2), but not on a medium or large pitch.

#13 The influence of scoring targets and outer-floaters on attacking and defending team dispersion, shape and creation of space during small-sided soccer games
Reference: J Hum Kinet. 2016 Jul 2;51:153-163. doi: 10.1515/hukin-2015-0178. eCollection 2016
Authors: Castellano J, Silva P, Usabiaga O, Barreira D
Summary: The effect of altered game formats on team performances during soccer practice can be harnessed by coaches to stimulate specific tactical behaviours. The aim of the present study was to analyse the influence of using (i) small goals [SG], (ii) goalkeepers [7G] and (iii) floaters [7GF] on the dispersion, shape and available space of teams during small-sided games (SSGs). Twenty-four male soccer players were distributed into four teams composed of five players, two goalkeepers and two floaters that performed six SSG bouts of 6 min, interspersed with 6 min of passive recovery. Offensive and defensive phases were also analysed separately in order to verify the preservation of basic principles of attacking (teams more stretched to create free space) and defending (teams more compact to tie-up space) during SSGs. The variables used to characterize the collective behaviour were: length [L], width [W], team shape [Sh], and team separateness [TS]. Results revealed that the teams showed different collective behaviours depending on SSG format and a playing phase: a) L and W were higher in attack than in defence in all SSGs; b) team shapes were more elongated in defence in all SSGs except SG; c) the space separating players from their closest opponents (TS) was shorter in 7G; and d) SG and 7GF elicited greater defensive openness due to increased team width. The results suggest that manipulating task constraints, such as goal size, presence or absence of goalkeepers and floaters can be harnessed by coaches to shape distinct team tactical behaviours in SSGs while preserving the basic principles of attacking and defending.

#14 The effect of the MTHFR C677T mutation on athletic performance and the homocysteine level of soccer players and sedentary individuals
Reference: J Hum Kinet. 2016 Jul 2;51:61-69. doi: 10.1515/hukin-2015-0171. eCollection 2016
Authors: Dinc N, Yucel SB, Taneli F, Sayın MV
Summary: This study investigated athletic performance and homocysteine (Hcy) levels in relation to the methylenetetrahydrofolate reductase (MTHFR) C677T mutation and explored the relationship between this mutation and other cardiac risk factors in soccer players and sedentary individuals. The study groups consisted of randomly selected soccer players (n=48) from the Turkish Super and Major League and sedentary male students (n=48) aged 18-27. Anthropometric variables, aerobic and anaerobic thresholds were measured, furthermore, biochemical assays were performed. The level of HDL cholesterol, LDL cholesterol, triglyceride, Hcy, folate, vitamin B12, hemogram and MTHFR C677T was investigated. The results showed that there was a statistical difference between the two groups in terms of body mass, body fat, the BMI, the aerobic threshold heart rate (ATHR), aerobic threshold velocity (ATVL) and anaerobic threshold velocity (ANTVL). The soccer players were found to have lower levels of triglyceride, total cholesterol and LDL cholesterol, and higher levels of folate than the sedentary participants. The analysis of the alleles of the MTHFR C677T polymorphism showed that the participants that carried TT genotypes had a lower level of vitamin B12 and folate, and a higher level of Hcy than the participants carrying CC and CT genotypes. In conclusion, the baseline homocysteine and cardiovascular fitness levels of healthy young males with the TT genotypes of the MTHFR C677T genotype were found to strongly correlate with their levels of Hcy.

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