Latest research in football - week 21 - 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 Hamstring Injury Prevention in Soccer: Before or After Training?
Reference: Scand J Med Sci Sports. 2017 May 24. doi: 10.1111/sms.12925. [Epub ahead of print]
Authors: Lovell R, Knox M, Weston M, Siegler JC, Brennan S, Marshall PWM
Summary: We examined the effects of a 12-week program of Nordic hamstring exercises (NHE), administered before or after football training, upon eccentric hamstring strength, muscle activity, and architectural adaptations. Amateur soccer players were randomized into 3 groups. The control group (CON; n=11) undertook core stability exercises, whereas a periodized NHE program was delivered either before (NHEBEF ; n=10) or after (NHEAFT ; n=14) bi-weekly training sessions. Outcome measures included peak torque and concomitant normalized peak surface electromyography signals (sEMG) of the biceps femoris (BF) and medial hamstring (MH) muscles during knee flexor maximal eccentric contractions, performed at 30°·s-1 . Ultrasonography was used to determine BF muscle thickness, muscle fiber pennation angle, and fascicle length. Performing the NHE derived likely moderate peak torque increases in both NHEBEF (+11.9%; 90% confidence interval: 3.6% to 20.9%) and NHEAFT (+11.6%; 2.6% to 21.5%) versus CON. Maximum sEMG increases were moderately greater in the BF of both NHE training groups versus CON. There were likely moderate increases in BF muscle thickness (+0.17 cm; 0.05 cm to 0.29 cm) and likely small pennation angle increases (+1.03°; -0.08° to 2.14°) in NHEAFT versus CON and NHEBEF . BF fascicle length increases were likely greater in NHEBEF (+1.58 cm; 0.48 cm to 2.68 cm; small effect) versus CON and NHEAFT . A 12-week eccentric hamstring-strengthening program increased strength and sEMG to a similar magnitude irrespective of its scheduling relative to the football training session. However, architectural adaptations to support the strength gains differed according to the timing of the injury prevention program.

#2 Heart Rate Variability Discriminates Competitive Levels in Professional Soccer Players
Reference: J Strength Cond Res. 2017 Jun;31(6):1719-1725. doi: 10.1519/JSC.0000000000001795.
Authors: Proietti R, di Fronso S, Pereira LA, Bortoli L, Robazza C, Nakamura FY, 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 SD of successive RR intervals [SDNN] and the root mean square difference of successive normal RR intervals [RMSSD]), recently the use of the stress score (SS), which is an inverse function of the SD2 index derived from the Poincaré plot, and the sympathetic/parasympathetic ratio (S/PS) to monitor soccer players has been proposed. 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 3 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 3 different teams of 2 European countries (Italy and Germany) participated in the study. The intraclass correlation coefficient 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%, although the CV for SS was 6.13% and for S/PS, it was 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 is able to differentiate between international- and national-level players.

#3 Maximal Sprinting Speed of Elite Soccer Players During Training and Matches
Reference: J Strength Cond Res. 2017 Jun;31(6):1509-1517. doi: 10.1519/JSC.0000000000001642.
Authors: Djaoui L, Chamari K, Owen AL, Dellal A
Summary: The aim of the present study was to compare (a) the maximal sprinting speed (MSS) attained by soccer players during matches (MSSmatch) according to their level of play (professional first French division vs. elite amateur fourth French division) and the playing positions and (b) the MSS attained by professional soccer players during 14 different types of small-sided games (SSG, MSSSSG) and match-play. All players monitored through the study performed a 40-m sprint test to assess individual MSS (MSStest) and compare it to the training and match activity, with the calculation of the percentage of MSStest (%MSStest) reached. No differences were found according to the level of play; however, positional wide players achieved a higher MSSmatch, %MSStest, and MSSSSG than central players (both defenders and midfielders) during matches and SSG. MSSmatch were higher than all MSSSSG, and MSSSSG were positively correlated with the area of the pitch (0.45, p < 0.001), its length (0.53, p < 0.001), and the number of players involved (0.38, p < 0.001). The closer SSG was to match situation in terms of rules, the higher the MSSSSG. Wide players reached higher MSS in match and SSG than central players, confirming the relevance of using SSG close to match situation to specifically prepare elite players to the maximal running speed demand of the match.

#4 Quantifying the High-Speed Running and Sprinting Profiles of Elite Female Soccer Players During Competitive Matches Using an Optical Player Tracking System
Reference: J Strength Cond Res. 2017 Jun;31(6):1500-1508. doi: 10.1519/JSC.0000000000001629.
Authors: Mara JK, Thompson KG, Pumpa KL, Morgan S.
Summary: Quantifying the high-speed running and sprinting profiles of elite female soccer players during competitive matches using an optical player tracking system. J Strength Cond Res 31(6): 1500-1508, 2017-The aim of this study was to determine the high-speed running and sprinting profiles of elite female soccer players during competitive matches using a new Optical Player Tracking system. Eight stationary video cameras were positioned at vantage points surrounding the soccer field so that when each camera view was combined, the entire field could be viewed simultaneously. After each match, an optical player tracking system detected the coordinates (x, y) of each player for every video frame. Algorithms applied to the x and y coordinates were used to determine activity variables for 12 elite female players across 7 competitive matches. Players covered 9,220-10,581 m of total distance, 1,772-2,917 m of high-speed running (3.4-5.3 m·s) distance, and 417-850 m of sprinting (>5.4 m·s) distance, with variations between positional groups (p < 0.001; partial η = 0.444-0.488). Similarly, the number of high-speed runs differed between positional groups (p = 0.002; partial η = 0.342), and a large proportion of high-speed runs (81-84%) and sprints (71-78%) were performed over distances less than 10 m. Mean time between high-speed runs (13.9 ± 4.4 seconds) and sprints (86.5 ± 38.0 seconds) varied according to playing position (p < 0.001; partial η = 0.409) and time of the match (p < 0.001; partial η = 0.113-0.310). The results of this study can be used to design match-specific conditioning drills and shows that coaches should take an individualized approach to training load monitoring according to position.

#5 Exercise Intensity and Technical Demands of Small-Sided Soccer Games for Under-12 and Under-14 Players: Effect of Area per Player
Reference: J Strength Cond Res. 2017 Jun;31(6):1486-1492. doi: 10.1519/JSC.0000000000001615.
Authors: Martone D, Giacobbe M, Capobianco A, Imperlini E, Mancini A, Capasso M, Buono P, Orru S
Summary: The aim of this study was to evaluate the effects of 6 different areas per player (AP) on exercise intensity (EI) measured during small-sided games (SSGs) and expressed as percentage of maximal heart rate (%MHR) and technical actions (TAs) involvement with the ball, crosses, headers, tackles, shots on goal, dribbling, passing, and target passing-in U-12 and U-14 soccer players during SSGs. Seventeen male U-12 soccer players (age 10.0 ± 0.5 years, body mass 39.3 ± 5.3 kg, and height 143.8 ± 4.6 cm) and 16 male U-14 soccer players (age 13.2 ± 0.3 years, body mass 46.6 ± 11.9 kg, and height 154.8 ± 8.5 cm) performed SSGs with different AP: 40, 50, 66.7, 90, 112.5, and 150 m. Our results indicate that at larger AP, the U-12 group's mean EI values were significantly higher than those at smaller AP (p ≤ 0.05); in addition, intergroup comparison showed that EI was higher in U-12 than that in U-14 players when AP of 112.5 and 150 m were considered (p ≤ 0.05). Technical action analysis evidenced that moving from smaller to larger AP, U-14 players adapted better to AP changes. In conclusion, these results suggest that AP influences differently EI and TAs in U-12 and U-14 players. Our results could be taken into account by conditioning coaches to better tailor the physiological and technical training in young players through the modulation of AP.

#6 Relationship Between Internal Load Indicators and Changes on Intermittent Performance After the Preseason in Professional Soccer Players
Reference: J Strength Cond Res. 2017 Jun;31(6):1477-1485. doi: 10.1519/JSC.0000000000001613.
Authors: Campos-Vazquez MA, Toscano-Bendala FJ, Mora-Ferrera JC, Suarez-Arrones LJ
Summary: The aim of this study was to examine the effects of accumulated internal training load (ITL) during the preseason (4 weeks) on changes in the intermittent performance, in a professional soccer team. Twelve professionals soccer players (Mean ± SD age: 27.7 ± 4.3 years; height: 177.1 ± 6.2 cm; body mass: 73.1 ± 5.2 kg; % body fat [Faulkner]: 10.2 ± 1.2) belonging to a Spanish second division team (2013-2014) participated in this study. The 30-15 intermittent fitness test was performed before and after the preseason, and the speed for the last period completed by each player was recorded (VIFT). During the preseason, the team alternated practice of training sessions (TRNs) with friendly matches (FMs). Session rating of perceived exertion (sRPE), heart rate (HR), and HR reserve were analyzed every TRN and FM to calculate ITL (ITL: sRPE-TL, Edward's-TL and Edward's-TLres). The players' VIFT substantially increased after the preseason period (20.1 ± 0.8 vs. 21.1 ± 0.8 km·h; effect size [ES] = 1.15 ± 0.25; almost certainly). The average value of sRPE throughout FMs was substantially greater than the value of the TRNs (7.4 ± 0.9 vs. 5.25 ± 0.2; ES = 2.31 ± 2.45; almost certainly). sRPE-TL, practice volume, and sum of RPE during the preseason were positively and largely correlated (r = 0.70-0.75) with changes on intermittent performance. No relationships were found between HR-derived measures of exercise load and changes on intermittent fitness. The present results suggest that practice volume and subjective measures of TL, related better than HR-based TL methods to changes on intermittent performance after the preseason, in professional soccer players.

#7 Effects of Different Combinations of Strength, Power, and Plyometric Training on the Physical Performance of Elite Young Soccer Players
Reference: J Strength Cond Res. 2017 Jun;31(6):1468-1476. doi: 10.1519/JSC.0000000000001609.
Authors: Kobal R, Loturco I, Barroso R, Gil S, Cuniyochi R, Ugrinowitsch C, Roschel H, Tricoli V
Summary: Effects of different combinations of strength, power, and plyometric training on the physical performance of elite young soccer players. J Strength Cond Res 31(6): 1468-1476, 2017-The combination of strength (ST) and plyometric training (PT) has been shown to be effective for improving sport-specific performance. However, there is no consensus about the most effective way to combine these methods in the same training session to produce greater improvements in neuromuscular performance of soccer players. Thus, the purpose of this study was to compare the effects of different combinations of ST and PT sequences on strength, jump, speed, and agility capacities of elite young soccer players. Twenty-seven soccer players (age: 18.9 ± 0.6 years) participated in an 8-week resistance training program and were divided into 3 groups: complex training (CP) (ST before PT), traditional training (TD) (PT before ST), and contrast training (CT) (ST and PT performed alternately, set by set). The experimental design took place during the competitive period of the season. The ST composed of half-squat exercises performed at 60-80% of 1 repetition maximum (1RM); the PT composed of drop jump exercises executed in a range from 30 to 45 cm. After the experimental period, the maximum dynamic strength (half-squat 1RM) and vertical jump ability (countermovement jump height) increased similarly and significantly in the CP, TD, and CT (48.6, 46.3, and 53% and 13, 14.2, and 14.7%, respectively). Importantly, whereas the TD group presented a significant decrease in sprinting speed in 10 (7%) and 20 m (6%), the other groups did not show this response. Furthermore, no significant alterations were observed in agility performance in any experimental group. In conclusion, in young soccer players, different combinations and sequences of ST and PT sets result in similar performance improvements in muscle strength and jump ability. However, it is suggested that the use of the CP and CT methods is more indicated to maintain/maximize the sprint performance of these athletes.

#8 Immediate effect of ankle balance taping on dynamic and static balance of soccer players with acute ankle sprain
Reference: J Phys Ther Sci. 2017 Apr;29(4):622-624. doi: 10.1589/jpts.29.622. Epub 2017 Apr 20.
Authors: Shin YJ, Kim MK
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Summary: This study aimed to evaluate the immediate effect of ankle balance taping on balance ability of soccer players with acute ankle sprain. This study was conducted with 16 subjects who were diagnosed with ankle sprain. A cross-over randomized design was used. Each subject performed three interventions in a random order. Subjects were randomly assigned to an ankle balance taping, placebo taping, and no taping. For dynamic and static balance, ability was measured using BIORescue (RM Ingenierie, Rodes, France). Limit of stability, sway length and sway speed for one minute were measured. The Limit of Stability, Sway length and Sway speed differed significantly among the three different taping methods. In this study, we found that ankle balance taping was effective in terms of improving balance ability of soccer players with an ankle sprain.

#9 A cross-sectional study on the relationship between nutritional knowledge and physical fitness in soccer players
Reference: Clin Nutr ESPEN. 2016 Jun;13:e70. doi: 10.1016/j.clnesp.2016.03.063. Epub 2016 May 20.
Authors: Nikolaidis PT, Theodoropoulou E

American Football
#1 Relationship between proxies for Type II fiber type and resting blood pressure in Division I American Football Athletes
Reference: Int J Health Sci (Qassim). 2017 Apr-Jun;11(2):16-20.
Authors: DiCesare CA, Adams JR, Claytor RP, Ward RM, Cox RH
Summary: The risk for cardiovascular disease is well-documented. Perhaps surprisingly, specific athletic populations, including American football players, exhibit increased risk for cardiovascular disease as presented by elevated blood pressure. There is evidence suggesting a link between muscle fiber type distribution and resting blood pressure. Acknowledging this association, it becomes important to clarify an individual's risk for developing cardiovascular disease later in adulthood. The purpose of this study was to assess football performance measures-in particular proxies for muscular power-and their effect on resting blood pressure in football athletes. A total of 80 collegiate-level football players participated in this study. Each participant's body fat %, body mass index, waist circumference, and mean arterial pressure (MAP) were measured. Participants performed one-repetition maximums of bench press, back squat, 40-yard dash, and vertical leap, and a power index (PI) defined as the product of vertical leap and mass. Linear regressions were run between body composition variables and performance measures for all players and a subset of skill players only. The PI was found to be positively, significantly correlated with MAP in all players (r = 0.269; P = 0.035) and the skill players subset (r = 0.425; P = 0.004). The results of the present study indicate an association between muscle fiber type distribution, as indicated by muscular power capacity, and resting blood pressure.

#2 Nutrition practices and knowledge among NCAA Division III football players
Reference: J Int Soc Sports Nutr. 2017 May 19;14:13. doi: 10.1186/s12970-017-0170-2. eCollection 2017.
Authors: Abbey EL, Wright CJ, Kirkpatrick CM
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Summary: Participation in collegiate American football is physically demanding and may have long-term health implications, particularly in relation to cardiovascular and neurological health. National Collegiate Athletic Association (NCAA) Division III (DIII) football players are a relatively unstudied population, particularly in terms of their dietary habits and knowledge. The aim of the present study was to descriptively evaluate the dietary intake of DIII football players including a subset of linemen and assess the nutritional knowledge and sources of information of these athletes. The study sample was 88 DIII football players including a subset of nine linemen. All participants completed a food frequency questionnaire, and a nutritional knowledge questionnaire that included a quiz and questions about their main sources of nutrition information. Heights and body masses were also recorded. The linemen submitted written 3-day diet records for assessment of their dietary intake. Of the 88 participants, >50% reported consuming starches/grains, meat and dairy daily, but <50% reported consuming fruits and vegetables daily. Protein powders were the most commonly used supplements (33% reported daily use). Compared to dietary recommendations, linemen consumed high amounts of total fat, saturated fat, dietary cholesterol, sodium, and potassium, but were low in carbohydrates, fiber, and essential fats. The mean nutrition knowledge quiz score for the 88 participants was 55.2%. Those who had taken a nutrition or health course in college scored significantly higher on the quiz than those who had not. Participants reported relying primarily on coaches, websites, and athletic trainers (ATs) for nutritional guidance; ATs were the most trusted source. DIII football players had dietary habits that may both mitigate and increase their risk of chronic diseases. These athletes have room to improve their nutrition knowledge. Their reliance on athletic team staff for nutrition guidance highlights the importance of nutrition education for both athletes and staff and the potential role of a registered dietitian nutritionist.

Australian Football
#1 Australian football players experiencing groin pain exhibit reduced subscale scores of Activities of Daily Living and Sport and Recreation on the HAGOS questionnaire: A case-control study
Reference: Phys Ther Sport. 2017 Apr 20;26:7-12. doi: 10.1016/j.ptsp.2017.04.004. [Epub ahead of print]
Authors: Drew MK, Lovell G, Palsson TS, Chiarelli PE, Osmotherly PG
Summary: The objective was to report normative responses to the HAGOS questionnaire for Australian football players and to determine whether any of the HAGOS questionnaire sub scales can differentiate players with and without groin pain. Professional (n = 66) and semi-professional (n = 9) Australian football (AF) players with current groin pain (n = 16) and controls (n = 57) without current groin pain. The HAGOS subscales were compared between players with and without groin pain using the Wilcoxon rank-sum test with effect sizes (ES) calculated. Floor and ceiling effects were examined. A post-hoc factor analysis was undertaken. Participants with current groin pain showed lower Physical Function of Daily Living (PFDL) and Physical Function in Sport and Recreation (PFSR) subscale scores (p < 0.05, ES: 0.77 and 0.90 respectively). Any groin pain (current and/or historical) lowered the Pain and Quality of Life (QOL) subscale scores (p < 0.05, ES: 0.38 and 0.72 respectively). Factor analysis showed 8 significant factors with one main factor identified representing items describing forceful activities (Eigenvalue = 18.02, Proportion = 0.49). The HAGOS can distinguish AF players with current groin pain in the PFDL and PFSR subscales but not in the other four subscales. Any current or historical groin pain lowers scores on the QOL and Pain sub scales.

#2 Optimising Pre-Season Training Loads in Australian Football
Reference: Int J Sports Physiol Perform. 2017 May 22:1-19. doi: 10.1123/ijspp.2016-0695. [Epub ahead of print]
Authors: Carey DL, Crow J, Ong KL, Blanch P, Morris ME, Dascombe BJ, Crossley KM
Summary: The purpose was to investigate whether pre-season training plans for Australian football can be computer generated using current training load guidelines to optimise injury risk reduction and performance improvement. A constrained optimisation problem was defined for daily total and sprint distance, using the pre-season schedule of an elite Australian football team as a template. Maximising total training volume and maximising Banister model projected performance were both considered as optimisation objectives. Cumulative workload and acute:chronic workload ratio constraints were placed on training programs to reflect current guidelines on relative and absolute training loads for injury risk reduction. Optimisation software was then used to generate pre-season training plans. The optimisation framework was able to generate training plans that satisfied relative and absolute workload constraints. Increasing the off-season chronic training loads enabled the optimisation algorithm to prescribe higher amounts of 'safe' training and attain higher projected performance levels. Simulations showed that using a Banister model objective led to plans that included a taper in training load prior to competition in order to minimise fatigue and maximise projected performance. In contrast, when the objective was to maximise total training volume, more frequent training were prescribed in order to accumulate as much load as possible. Feasible training plans that maximise projected performance and satisfy injury risk constraints can be automatically generated by an optimisation problem for Australian football. The optimisation methods allow for individualised training plan design and the ability to adapt to changing training objectives and different training load metrics.

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