Latest research in football - week 3 - 2018

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 Mixed Training Methods: Effects of Combining Resisted Sprints or Plyometrics with Optimum Power Loads on Sprint and Agility Performance in Professional Soccer Players
Reference: Front Physiol. 2017 Dec 12;8:1034. doi: 10.3389/fphys.2017.01034. eCollection 2017.
Authors: Loturco I, Kobal R, Kitamura K, Cal Abad CC, Faust B, Almeida L, Pereira LA
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Summary: The aim of this study was to compare the effects of two different mixed training programs (optimum power load [OPL] + resisted sprints [RS] and OPL + vertical/horizontal plyometrics [PL]) on neuromuscular performance of elite soccer players during a short-term training preseason. Eighteen male professional soccer players took part in this study. The athletes were pair-matched in two training groups: OPL + RS and OPL + PL. Unloaded and resisted sprinting speeds at 5-, 10-, 20-, and 30-m, change of direction (COD) speed, and performance in the squat jump (SJ), countermovement jump (CMJ), and horizontal jump (HJ) were assessed pre- and post- a 5-week training period. Magnitude based inference with the effect sizes were used for data analysis. A possible increase in the SJ and CMJ heights and a likely increase in the HJ distance were observed in the OPL + PL group. Meaningful improvements were observed in the COD speed test for both training groups comparing pre- and post-measures. In both unloaded and resisted sprints, meaningful decreases were observed in the sprinting times for all distances tested. This study shows that a mixed training approach which comprises exercises and workloads able to produce positive adaptations in different phases of sprinting can be a very effective strategy in professional soccer players. Moreover, the possibility of combining optimum power loads with resisted sprints and plyometrics emerges as a novel and suitable option for coaches and sport scientists, due to the applicability and efficiency of this strength-power training approach.

#2 Time course of oxidative stress, inflammation and muscle damage markers for five days after a soccer match: effects of sex and playing position
Reference: J Strength Cond Res. 2018 Jan 3. doi: 10.1519/JSC.0000000000002436. [Epub ahead of print]
Authors: Souglis A, Bogdanis GC, Chryssanthopoulos C, Apostolidis N, Geladas ND
Summary: This study examined the influence of sex and playing position on the time-course of selected oxidative stress, inflammation and muscle damage markers following an official soccer match. Sixty professional soccer players (30 male and 30 female) were divided into three groups, according to their playing position: defenders, midfielders and attackers. Each group consisted of 10 male and 10 female players. Sixty healthy volunteers (30 males and 30 females) served as control. Blood samples were taken before and after the match and daily for five days after the match. Analysis of variance revealed different responses over time between sex and playing positions, as shown by the 3-way interaction, for creatine kinase (CK), protein carbonyls (PC), catalase, fibrinogen (FIB), uric acid (UA), lactate dehydrogenase (LDH), reduced glutathione, C-reactive protein and interleukin-6 (IL-6) (p < 0.01).Male players had higher values compared with females of the same playing position, for all oxidative, inflammatory and muscle damage indices (p<0.01). Also, in both sexes, midfielders had higher peaks in all indices compared with defenders (p < 0.05). Five days after the game CK and UA concentrations had not returned to pre-game levels in any exercise group, whereas PC were still elevated in male midfielders and attackers (p < 0.05).These results show that sex and playing position influence the time-course of selected oxidative stress, inflammation and muscle damage markers following an official soccer game. This information should be taken into account by practitioners for the design of training programs following match play.

#3 Comparison between traditional strength training and complex contrast training on soccer players
Reference: J Sports Med Phys Fitness. 2018 Jan 4. doi: 10.23736/S0022-4707.18.07934-3. [Epub ahead of print]
Authors: Spineti J, Figueiredo T, Willardson JM, Bastos de Oliveira V, Assis M, Fernandes DE Oliveira L, Miranda H, Machado de Ribeiro Reis V, Simao R
Summary: The purpose of this study was to compare traditional strength training (TST) versus and contrast training (CCT) on sprint, change of direction speed (COD) and squat jump (SJ) in young male soccer players. Twenty-two soccer players (age: 18.4 ± 0.4 years, body mass: 70.2 ± 9.1 kg, height: 179.9 ± 7.5 cm), were randomly assigned to one of two groups: TST (n=12) and CCT (n = 10). The study was conducted using a randomized experimental design over an eight- week period. The participants assigned to the CCT group performed high-power exercises paired with high-velocity exercises. The participants assigned to the TST group performed resistance exercises in a straight-set forma. During the study period, sprint tests for 5, 10, 20 and 30 m split times, COD and SJ were applied. A two-way ANOVA was applied, and the alpha level was p <0.05. The results demonstrated that the CCT regimen elicited significant within-group differences in 5 m sprint time (1.032 s to 0.997 s, pre- and post-intervention, respectively, effect size (ES) = -0.5, medium; p = 0.04), COD (5.963 s to 5.639 s, pre- and post-intervention, respectively, ES = -2.7, large; p<0.001) and SJ (30.9 cm to 34.4 cm, pre- and post-intervention, respectively, ES = 0.8, large; p<0.001). Conversely, the TST did not elicit significant within-group differences for any of the dependent variables. No differences were found between post-test time point. In conclusion, the CCT protocol could be used to improve sprint, in male soccer players.

#4 Differential Learning as a Key Training Approach to Improve Creative and Tactical Behavior in Soccer
Reference: Res Q Exerc Sport. 2018 Jan 19:1-14. doi: 10.1080/02701367.2017.1412063. [Epub ahead of print]
Authors: Santos S, Coutinho D, Goncalves B, Schollhorn W, Sampaio J, Leite N
Summary: The aim of this study was to identify the effects of a differential-learning program, embedded in small-sided games, on the creative and tactical behavior of youth soccer players. Forty players from under-13 (U13) and under-15 (U15) were allocated into control and experimental groups and were tested using a randomized pretest to posttest design using small-sided games situations. The experimental group participated in a 5-month differential-learning program embodied in small-sided games situations, while the control group participated in a typical small-sided games training program. In-game creativity was assessed through notational analyses of the creative components, and the players' positional data were used to compute tactical-derived variables. The findings suggested that differential learning facilitated the development of creative components, mainly concerning attempts (U13, small; U15, small), versatility (U13, moderate; U15, small), and originality (U13, unclear; U15, small) of players' actions. Likewise, the differential-learning approach provided a decrease in fails during the game in both experimental groups (moderate). Moreover, differential learning seemed to favor regularity in pitch-positioning behavior for the distance between players' dyads (U13, small; U15, small), the distance to the team target (U13, moderate; U15, small), and the distance to the opponent target (U13, moderate; U15, small). The differential-learning program stressed creative and positional behavior in both age groups with a distinct magnitude of effects, with the U13 players demonstrating higher improvements over the U15 players. Overall, these findings confirmed that the technical variability promoted by differential learning nurtures regularity of positioning behavior.

#5 The neuromuscular, biochemical, endocrine and mood responses to small-sided games training in professional soccer
Reference: J Strength Cond Res. 2018 Jan 17. doi: 10.1519/JSC.0000000000002424. [Epub ahead of print]
Authors: W S, An T, M W, M R, Mj J, Lp K
Summary: The 24h responses to small-sided games (SSG) soccer training were characterized. Professional soccer players (n=16) performed SSG's (4vs4 + goalkeepers; 6x7-min, 2-min inter-set recovery) with performance (peak-power output, PPO; jump height, JH), physiological (blood creatine kinase: CK, lactate; salivary testosterone, cortisol), and mood measures collected before (baseline), and after (immediately; 0h, +2h, +24h). For PPO and JH, possibly small-moderate reductions occurred at 0h (-1.1W·kg; ±0.9W·kg, -3.2cm; ±1.9cm, respectively), before returning to baseline at +2h (trivial) and declining thereafter (small-moderate effect) at +24h (-0.9W·kg; ±0.8W·kg, -2.5cm; ±1.2cm, respectively). Lactate increased at 0h (likely-large; +1.3mmol·L; ±0.5mmol·L), reduced at +2h (likely-small; -0.5mmol·L; ±0.2mmol·L), and returned to baseline at 24h (trivial). A very-likely small increase in CK occurred at 0h (+97u·L; ±28u·L), persisting for +24h (very-likely small; +94u·L; ±49u·L). Possibly-small increases in testosterone (+20pg·ml; ±29pg·ml) occurred at 0h, before likely-moderate declines at +2h (-61pg·ml; ±21pg·ml) returning to baseline at +24h (trivial). For cortisol, possibly-small decreases occurred at 0h (-0.09ug·dl; -±0.16ug·dl), before likely-large decreases at +2h (-0.39ug·dl; ±0.12ug·dl), which persisted for 24h (likely-small; -0.12ug·dl; ±0.11ug·dl). Mood was disturbed by SSG's at 0h (likely-moderate; +13.6AU, ±5.6AU) and +2h (likely-small; +7.9AU; ±5.0AU), before returning to baseline at +24h (trivial). The movement demands of SSG's result in a bimodal recovery pattern of neuromuscular function and perturbations in physiological responses and mood for up to 24h. Accordingly, when programming soccer training, SSG's should be periodized throughout the competitive week with submaximal technical/tactical activities.

#6 Effects of Contrast Strength vs. Plyometric Training on Lower Limb Explosive Performance, Ability to Change Direction and Neuromuscular Adaptation in Soccer Players
Reference: J Strength Cond Res. 2018 Jan 17. doi: 10.1519/JSC.0000000000002425. [Epub ahead of print]
Authors: Hammami M, Gaamouri N, Shephard RJ, Chelly MS
Summary: The aim was to compare the effects of two differing 8-week in-season strength training programs (contrast strength training [CST] vs. plyometric training [PT]) on selected performance tests (5 and 40m sprints, S 4 X 5 m change of direction test, squat (SJ) and countermovement (CMJ) jumps , leg peak power on a cycle ergometer force-velocity test, 1-repetition maximal (1-RM) half squat, and electromyographic [EMG] activity of the vastus lateralis, vastus medialis and rectus femoris muscles during vertical jump tests). Forty male soccer players (age = 15.8 ± 0.4 years; body mass = 58.8 ± 6.3 kg; body height = 1.74 ± 0.06 m; body fat = 10.5 ± 1.9 %) were divided between a contrast strength (CSG, n = 14), plyometric (PG, n = 14) and control groups (CG, n = 12). Both training programs enhanced sprint performance (p<0.001 in 5m; p≤0.05 in 40m) and change of direction test scores (p<0.001) relative to controls. PG and CSG increased SJ height relative to the CG, with a slightly greater response in CSG compared to PG (p≤0.05). The majority of CMJ scores increased significantly in both CSG and PG relative to the CG, with no inter-group differences in training response. The majority of force-velocity scores increased significantly in the CSG relative to PG and CG. The EMG parameters also increased in the CSG relative to both PG and CG. In summary, most measures of athletic performance in male soccer players were enhanced after CST and PT. However, the improvement of physical performance was better with eight weeks of CST than with PT. Thus, coaches should be encouraged to include CST as an element of in-season conditioning.

#7 Preseason Adductor Squeeze Strength in 303 Spanish Male Soccer Athletes: A Cross-sectional Study
Reference: Orthop J Sports Med. 2018 Jan 11;6(1):2325967117747275. doi: 10.1177/2325967117747275. eCollection 2018 Jan.
Authors: Esteve E, Rathleff MS, Vicens-Bordas J, Clausen MB, Holmich P, Sala L, Thorborg K
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Summary: Hip adductor muscle weakness and a history of groin injury both have been identified as strong risk factors for sustaining a new groin injury. Current groin pain and age have been associated with hip adductor strength. These factors could be related, but this has never been investigated. The purpose was to investigate whether soccer athletes with past-season groin pain and with different durations of past-season groin pain had lower preseason hip adductor squeeze strength compared with those without past-season groin pain. We also investigated whether differences in preseason hip adductor squeeze strength in relation to past-season groin pain and duration were influenced by current groin pain and age. In total, 303 male soccer athletes (mean age, 23 ± 4 years; mean weight, 74.0 ± 7.9 kg; mean height, 178.1 ± 6.3 cm) were included in this study. Self-reported data regarding current groin pain, past-season groin pain, and duration were collected. Hip adductor squeeze strength was obtained using 2 different reliable testing procedures: (1) the short-lever (resistance placed between the knees, feet at the examination bed, and 45° of hip flexion) and (2) the long-lever (resistance placed between the ankles and 0° of hip flexion) squeeze tests. There was no difference between those with (n = 123) and without (n = 180) past-season groin pain for hip adductor squeeze strength when adjusting for current groin pain and age. However, athletes with past-season groin pain lasting longer than 6 weeks (n = 27) showed 11.5% and 15.3% lower values on the short-lever (P = .006) and long-lever (P < .001) hip adductor squeeze strength tests, respectively, compared with those without past-season groin pain. Male soccer athletes with past-season groin pain lasting longer than 6 weeks are likely to begin the next season with a high-risk groin injury profile, including a history of groin pain and hip adduction weakness.

#8 Are Current Physical Match Performance Metrics in Elite Soccer Fit for Purpose or is the Adoption of an Integrated Approach Needed?
Reference: Int J Sports Physiol Perform. 2018 Jan 18:1-23. doi: 10.1123/ijspp.2017-0433. [Epub ahead of print]
Authors: Bradley PS, Ade JD
Summary: Time-motion analysis is a valuable data-collection technique used to quantify the physical match performance of elite soccer players. For over 40 years researchers have adopted a 'traditional' approach when evaluating match demands by simply reporting the distance covered or time spent along a motion continuum of walking through to sprinting. This methodology quantifies physical metrics in isolation without integrating other factors and this ultimately leads to a one-dimensional insight into match performance. Thus, this commentary proposes a novel 'integrated' approach that focuses on a sensitive physical metric such as high-intensity running but contextualizes this in relation to key tactical activities for each position and collectively for the team. In the example presented, the 'integrated' model clearly unveils the unique high-intensity profile that exists due to distinct tactical roles, rather than one-dimensional 'blind' distances produced by 'traditional' models. Intuitively this innovative concept may aid the coaches understanding of the physical performance in relation to the tactical roles and instructions given to the players. Additionally, it will enable practitioners to more effectively translate match metrics into training and testing protocols. This innovative model may well aid advances in other team sports that incorporate similar intermittent movements with tactical purpose. Evidence of the merits and application of this new concept are needed before the scientific community accepts this model as it may well add complexity to an area that conceivably needs simplicity.

#9 Effects of Late-Night Training on "Slow-Wave Sleep Episode" and Hour-by-Hour Derived Nocturnal Cardiac Autonomic Activity in Female Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Jan 18:1-26. doi: 10.1123/ijspp.2017-0681. [Epub ahead of print]
Authors: Costa JA, Brito J, Nakamura FY, Oliveira EM, Rebelo AN
Summary: The purpose was to assess the sensitivity of nocturnal heart rate variability (HRV) monitoring methods to the effects of late-night soccer training sessions in female athletes. Eleven female soccer players competing in the 1st division of the Portuguese soccer league wore HR monitors during night-sleep throughout a one-week competitive in-season microcycle, after late-night training sessions (n = 3) and rest days (n = 3). HRV was analyzed through "slow-wave sleep episode" (SWSE; 10 min duration) and "hour-by-hour" (all the RR intervals recorded throughout the hours of sleep). Training load was quantified by session rating of perceived exertion (sRPE: 281.8 ± 117.9 to 369.0 ± 111.7 a.u.) and training impulse (TRIMP: 77.5 ± 36.5 to 110.8 ± 31.6 a.u.), added to subjective well-being ratings (Hopper index: 11.6 ± 4.4 to 12.8 ± 3.2 a.u.). These variables were compared between training and rest days using repeated measures ANOVA. The ln-transformed SWSE cardiac autonomic activity (lnRMSSD varying between 3.92 ± 0.57 and 4.20 ± 0.60 ms; ηp2 = 0.16 [0.01-0.26]), lnHF, lnLF, lnSD1 and lnSD2 and the non-transformed LF/HF were not different among night-training session days and resting days (P > 0.05). Considering the hour-by-hour method (lnRMSSD varying between 4.05 ± 0.35 and 4.33 ± 0.32 ms; ηp2 = 0.46 [0.26-0.52]), lnHF, lnLF, lnSD1 and lnSD2 and the non-transformed LF/HF were not different among night-training session days and resting days (P > 0.05). Late-night soccer training does not seem to affect nocturnal SWSE and "hour-by-hour" HRV indices in highly-trained athletes.

#10 Post-match Perceived Exertion, Feeling and Wellness in Professional Soccer Players
Reference: Int J Sports Physiol Perform. 2018 Jan 18:1-22. doi: 10.1123/ijspp.2017-0725. [Epub ahead of print]
Authors: Fessi MS, Moalla W
Summary: The aim of this study was to assess post-match perceived exertion, feeling and wellness according to the match outcome (winning, drawing or losing) in professional soccer players. Twelve outfield players were followed during 52 official matches where the outcomes (win, draw or lose) were noted. Following each match players completed both a 10-point scale rating of perceived exertion (RPE) and an 11-point scale rating of perceived feeling. Rating of perceived sleep quality, stress, fatigue and muscle soreness were collected separately on a 7-point scale the day following each match. Player RPE was higher by a very largely magnitude following a loss compared to a draw or a win and higher by a small magnitude after a draw compared to a win. Players felt more pleasure after a win compared to a draw or loss and more displeasure after a loss compared to draw. The players reported a largely and moderately better-perceived sleep quality, less stress and fatigue following a win compared to draw or a loss, and a moderately bad-perceived sleep quality, higher stress and fatigue following a draw compared to a loss. In contrast, only a trivial-small change was observed in perceived muscle soreness between all outcomes. Matches outcomes moderately to largely affect RPE, perceived feeling, sleep quality, stress and fatigue whereas perceived muscle soreness remains high regardless of the match outcome. However, winning a match decreases the strain and improves both pleasure and wellness in professional soccer players.

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