Latest research in football - week 25 - 2019

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 Correction: Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football
Reference: PLoS One. 2019 Jun 19;14(6):e0218865. doi: 10.1371/journal.pone.0218865. eCollection 2019.
Authors: Thomson A, Whiteley R, Wilson M, Bleakley C.
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#2 Growing Pains: Maturity Associated Variation in Injury Risk in Academy Football
Reference: Eur J Sport Sci. 2019 Jun 19:1-21. doi: 10.1080/17461391.2019.1633416. [Epub ahead of print]
Authors: Johnson DM, Williams S, Bradley B, Sayer S, Murray Fisher J, Cumming S
Summary: Reducing injuries to youth players is of primary importance to academies, as injuries can result in a significant loss in both training and match time, as well as negatively affecting player development. In total, 76 talented young football players were analysed over two full competitive seasons. The injury incidence and burden for all non-contact and overuse injuries were recorded. Exposure was calculated as the total number of competitive matches hours played. Somatic maturation was estimated by expressing the current height of each player as a percentage of their predicted adult height (Roche, Tyleshevski, & Rogers, 1983). The period of circa-peak height velocity (PHV) (24.5 injuries per 1000 h) was associated with a significantly higher injury incidence rate and burden compared to pre-PHV (11.5 injuries per 1000 h; RR:2.15, 95%CI:1.37-3.38, P < .001). No significant differences in injury risk between maturity timing groups were observed. The interaction effect between maturity status and maturity timing confirmed there is a risk period circa-PHV, but this was not dependent on maturity timing. The main practical application of this study is that football academies should regularly assess the maturity status of young footballers to identify those players with increased susceptibility to injury. Moreover, academies should individualise training and injury prevention strategies based on maturation.

#3 Epidemiological Study on Professional Football Injuries During the 2011 Copa America, Argentina
Reference: Rev Bras Ortop. 2013 Jun 20;48(2):131-136. doi: 10.1016/j.rboe.2012.09.003. eCollection 2013 Mar-Apr.
Authors: Pedrinelli A, Filho GARDC, Thiele ES, Kullak OP
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Summary: Develop an epidemiological study of injuries occurred among male professional football players during the Copa America 2011, held in Argentina. We conducted a retrospective study of injuries sustained during the 43rd edition of the Copa America football in Argentina, in 2011. The lesions were evaluated by the medical department of the selections and reported to the CONMEBOL. The data were compiled and reported in accordance with rules established by the FIFA Medical Assessment and Research Centre (F-MARC) in 2005. There was a higher prevalence of lesions in the lower limbs. Thighs and knees were the most affected segments. The most frequent diagnoses were muscle injuries. The injuries were mostly minor degrees of severity and there was little difference in the prevalence of lesions according to the stages of the match, with slight predominance in the final 15 minutes. The incidence of lesions per 1,000 game hours was similar to the average found in the literature. The results obtained allowed us to outline a profile of the prevalence, distribution per body segment, minute in which occurred and severity of injuries in professional football players of participating teams in the Copa America 2011 in Argentina. The extreme rigor of referees may be partly attributed to the highly competitive nature of international tournaments. However, this results cannot be considered definitive because of the need to be compared to other epidemiological studies with same design using similar concepts and criteria.

#4 Every second retired elite female football player has MRI evidence of knee osteoarthritis before age 50 years: a cross-sectional study of clinical and MRI outcomes
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Jun 17. doi: 10.1007/s00167-019-05560-w. [Epub ahead of print]
Authors: Prien A, Boudabous S, Junge A, Verhagen E, Delattre BMA, Tscholl PM
Summary: The purpose was to assess knee health in retired female football players, using magnetic resonance imaging (MRI) and self-report. The focus of analysis were degenerative changes of the tibiofemoral joint, and their relationship to osteoarthritis symptoms and previous knee injury. Forty-nine retired elite, female football players (98 knees) aged 37 years on average participated. Tibiofemoral cartilage and meniscus status of both knees were evaluated using MRI and graded according to modified Outerbridge and Stoller classifications, respectively. Symptoms were assessed through a standardised questionnaire (Knee Osteoarthritis Outcome Score: KOOS). Knee injury history was recorded via a semi-structured interview. To investigate how injury variables relate to outcomes, binary logistic regression models were used and reported with odds ratios (OR). Fifty-one per cent of players (n = 25) fulfilled the MRI criterion for knee osteoarthritis, 69.4% (n = 34) had substantial meniscal loss and 59.6% (n = 28) reported substantial clinical symptoms. Chondral- and meniscal loss were associated with significantly lower scores on three of five KOOS subscales (p < .05). Both chondral and meniscal loss were significantly predicted by previous traumatic knee injury (OR = 4.6, OR = 2.6), the injury affecting the non-striking leg (OR = 8.6, OR = 10.6) and type of injury; participants with combined ACL/meniscus injuries had the highest risk for substantial chondral and meniscal loss (OR = 14.8, OR = 9.5). Chondral loss was significantly predicted by isolated meniscus injury treated with partial meniscectomy (OR = 5.4), but not by isolated reconstructed ACL injury. Clinical symptoms were only significantly predicted by previous traumatic knee injury (OR = 5.1). Serious degenerative changes were found in a high number of retired female football players' knees 10 years after their career. Meniscal integrity is key for knee osteoarthritis outcomes in young adults, and thus, its preservation should be a priority.

#5 Quantifying the physical loading of five weeks of pre-season training in professional soccer teams from Dutch and Portuguese leagues
Reference: Physiol Behav. 2019 Jun 24;209:112588. doi: 10.1016/j.physbeh.2019.112588. [Epub ahead of print]
Authors: Clemente FM, Seerden G, van der Linden CMI
Summary: The purpose of this study was to quantify the physical loads of programmed pre-season training in four different professional Dutch and Portuguese soccer teams. Eighty-nine professional players were monitored daily during a five-week period. We monitored the physical loading of training by measuring the external load measures of total distance covered, walking distance, jogging distance, running distance, sprinting distance, high-intensity sprint distance, player's load and number of sprints using a 10 Hz GPS technology. Weekly external load and intra-week external load variations were tested. Repeated measures did not show significant differences between weeks in terms of weekly loads based on total distance and sprinting distance. Significant differences were found between training days considering the duration (p = .011), walking distance (p = .017), running distance (p = .004), player's load (p = .040) and number of sprints (p = .006). Variations between weeks were small, however intra-week variations were observed namely considering the measures associated with great volume and lower intensity.

#6 Technical and tactical performance indicators discriminating winning and losing team in elite Asian beach soccer tournament
Reference: PLoS One. 2019 Jun 27;14(6):e0219138. doi: 10.1371/journal.pone.0219138. eCollection 2019.
Authors: Muazu Musa R, P P Abdul Majeed A, Abdullah MR, Ab Nasir AF, Arif Hassan MH, Mohd Razman MA
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Summary: The present study aims to identify the essential technical and tactical performance indicators that could differentiate winning and losing performance in the Asian elite beach soccer competition. A set of 20 technical and tactical performance indicators namely; shot back-third, shot mid-third, shot front-third, pass back-third, pass mid-third, pass front-third, shot in box, shot outbox, chances created, interception, turnover, goals scored 1st period, goals scored 2nd period, goals scored 3rd period, goals scored extra time, tackling, fouls committed, complete save, incomplete save and passing error were observed during the beach soccer Asian Football Confederation tournament 2017 held in Malaysia. A total of 23 matches from 12 teams were notated using StatWatch application in real-time. Discriminant analysis (DA) of standard, backward as well stepwise modes were used to develop a model for the winning (WT) and losing team (LT) whilst Mann-Whitney U test was utilized to ascertain the differences between the WT and LT with respect to the performance indicators evaluated. The standard backward, forward and stepwise discriminates the WT and the LT with an excellent accuracy of 95.65%, 91.30% and 89.13%, respectively. The standard DA model discriminated the teams from seven performance indicators whilst both the backward and forward stepwise identified two performance indicators. The Mann-Whitney U test analysis indicated that the WT is statistically significant from the LT based on the performance indicators determined from the standard mode model of the DA. It was demonstrated that seven performance indicators namely; shot front-third, pass front-third, chances created, goals scores at the 1st period, goals scored at the 2nd period, goals scored at 3rd period were directly linked to a successful performance whilst the incomplete save by the keeper attribute towards the poor performance of the team. The present finding could serve useful to the coaches as well as performance analysts as a measure of profiling successful performance and enables team improvement with respect to the associated performance indicators.

#7 Post-activation Potentiation: Effects of Different Conditioning Intensities on Measures of Physical Fitness in Male Young Professional Soccer Players
Reference: Front Psychol. 2019 Jun 6;10:1167. doi: 10.3389/fpsyg.2019.01167. eCollection 2019.
Authors: Petisco C, Ramirez-Campillo R, Hernández D, Gonzalo-Skok O, Nakamura FY, Sanchez-Sanchez J
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Summary: The aim of this study was to compare the effects of different warm-up conditioning intensities on the physical fitness (i.e., post-activation potentiation -PAP), of professional male field soccer players. Athletes (n = 10; age: 21.6 ± 3.2 years) completed a control warm-up and warm-ups aimed to induce PAP, in random and counterbalanced order. After control and experimental warm-up sessions participants completed a triple hop test with the dominant (H3Jd) and a non-dominant (H3Jnd) leg, a squat jump (SJ), a countermovement jump (CMJ), a change of direction ability (COD) test, a repeated sprint with a COD (RSCOD) test and a linear 30-m sprint test (S-30). The control warm-up (WU) protocol was designed according to athlete's regular warm-up practice. The experimental warm-ups included the same exercises as the WU, with addition of one set of half-back squats for 10 repetitions at 60%, 5 repetitions at 80%, and 1 repetition at 100% of 1RM (60%-1RM, 80%-1RM and 100%-1RM, respectively.) Threshold values for Cohen's effect sizes (ES) were calculated and used for group's comparison. Likely to most likely improvements were shown in H3Jd (ES = 0.52), H3Jnd (ES = 0.51), COD (ES = 0.38), fasted sprint (RSCODb) (ES = 0.58) and the total time of all sprints (RSCODt) (ES = 0.99) only after the 80%-1RM protocol in comparison to the WU. Conversely, 100%-1RM and 60%-1RM protocols, compared to WU, induced possibly to most likely poorer performance in all jumps, COD and RSCODb (ES = -0.07 to -1.03 and ES = -0.48 to -0.91, respectively). Possibly to most likely improvements were shown in all jumps, COD, RSCODb and RSCODt after the 80%-1RM warm-up protocol in comparison to the 100%-1RM and 60%-1RM warm-up protocols (ES = 0.35 to 2.15 and ES = 0.61 to 1.46, respectively). A moderate warm-up intensity (i.e., 80%-1RM back squat) may induce greater PAP, including improvements in jumping, repeated and non-repeated change of direction speed in male soccer players.

#8 The Effect of Phase Change Material on Recovery of Neuromuscular Function Following Competitive Soccer Match-Play
Reference: Front Physiol. 2019 Jun 6;10:647. doi: 10.3389/fphys.2019.00647. eCollection 2019.
Authors: Brownstein CG, Ansdell P, Škarabot J, McHugh MP, Howatson G, Goodall S, Thomas K
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Summary: Cryotherapy is commonly implemented following soccer match-play in an attempt to accelerate the natural time-course of recovery, but the effect of this intervention on neuromuscular function is unknown. The aim of the present study was to examine the effect of donning lower-body garments fitted with cooled phase change material (PCM) on recovery of neuromuscular function following competitive soccer match-play. Using a randomized, crossover design, 11 male semi-professional soccer players wore PCM cooled to 15°C (PCMcold) or left at ambient temperature (PCMamb; sham control) for 3 h following soccer match-play. Pre-, and 24, 48, and 72 h post-match, participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation (TMS) during isometric knee-extension and at rest were measured to assess central nervous system (CNS) (voluntary activation, VA) and muscle contractile (quadriceps potentiated twitch force, Qtw,pot) function. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump [countermovement jump (CMJ) height and reactive strength index (RSI)] performance. A belief questionnaire was completed pre- and post-intervention to determine the perceived effectiveness of each garment. Competitive soccer match-play elicited persistent decrements in MVC, VA measured with femoral nerve stimulation, Qtw,pot, as well as reactive strength, fatigue and muscle soreness (P < 0.05). Both MVC and VA were higher at 48 h post-match after wearing PCMcold compared with PCMamb (P < 0.05). However, there was no effect of PCM on the magnitude or time-course of recovery for any other neuromuscular, physical function, or perceptual indices studied (P > 0.05). The belief questionnaire revealed that players perceived that both PCMcold and PCMamb were moderately effective in improving recovery, with no difference between the two interventions (P = 0.56).: Although wearing cooled PCM garments improved MVC and VA 48 h following match-play, the lack of effect on measures of physical function or perceptual responses to match-play suggest that PCM offers a limited benefit to the recovery process. The lack of effect could have been due to the relatively small magnitude of change in most of the outcome measures studied.

#9 What Frequency of Technical Activity Is Needed to Improve Results? New Approach to Analysis of Match Status in Professional Soccer
Reference: Int J Environ Res Public Health. 2019 Jun 25;16(12). pii: E2233. doi: 10.3390/ijerph16122233.
Authors: Konefał M, Chmura P, Rybka K, Chmura J, Huzarski M, Andrzejewski M
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Summary: The aim of the research detailed here has been to assess the frequency with which football players engage in technical activity of various different types, in relation to seven phases of a game associated with changes in match status. To this end, 2016-2017 domestic-season matches in Germany's Bundesliga were analyzed, the relevant data being retrieved using an Opta Sportsdata Company system. Technical activity taken into consideration included shots, passes, ball possession, dribbles, and tackles. It was found that there was a large impact of frequency of shots on target (H = 466.999(6); p = 0.001) in relation to the different match-status phases. Furthermore, moderate effect sizes were then obtained for frequency of shots (H = 187.073(6); p = 0.001), frequency of passes (H = 133.547(6); p = 0.001), and percentage of ball possession (H = 123.401(6); p = 0.001). The implication would be that a team trying to change the match score of a game experienced at a given moment in a more favorable direction will need to raise the frequency and accuracy of passes, the percentage of ball possession, and the percentage of tackles ending in success. The maintenance of a winning match status requires a high frequency of occurrence of shots and shots on target as well as greater frequency and effectiveness of dribbling. The main finding from our work is that consideration of the consequences of a game presented in relation to seven potential phases to match status can point to a novel approach to analysis.

#10 Relationships Among Circuit Training, Small-Sided and Mini Goal Games, and Competition in Professional Soccer Players: A Comparison of On-Field Integrated Training Routines
Reference: J Strength Cond Res. 2019 Jul;33(7):1887-1896. doi: 10.1519/JSC.0000000000002804.
Authors: Giménez JV, Gomez MA
Summary: The aim of this study was to investigate and compare different physical variables and load indicators of 2 small-sided game (SSG) formats and ball circuit training (CT). Fourteen professional players participated in 3 training routines using a similar occupied area per player (90 m). The CT, SSGs, and mini goal games (MGs) consisted of 8 repetitions of 4-minute game play, interspersed by 2 minutes of active recovery, and data were compared with the first 32 minutes of 2 competitive match simulations (MS). All movement patterns from walking to sprinting were recorded using 10-Hz global positioning system devices, whereas player perception of exertion was recorded after trial using a visual analogue scale. Practical differences among the 3 drills and MS were analyzed using magnitude-based inferences. The results suggested that the training routines did not exactly replicate the movement patterns of a competitive match. Furthermore, this study provides evidence that if high-intensity play is preferred, then SSGs should be emphasized (because they provide more total accelerations compared with the other drills; most likely effects). Moreover, the CT showed lower load and distance covered (m) than the MGs and SSGs. In conclusion, these drills may be useful for competition and impact microcycles (i.e., intermittent efforts with accelerations, decelerations, and walking actions) to achieve the specific adaptations of high-intensity efforts.

#11 Are two different speed endurance training protocols able to affect the concentration of serum cortisol in response to a shuttle run test in soccer players?
Reference: Res Sports Med. 2019 Jun 25:1-9. doi: 10.1080/15438627.2019.1635131. [Epub ahead of print]
Authors: Vitale JA, Povìa V, Belli E, Lombardi G, Banfi G, La Torre A
Summary: Soccer involves multiple high-intensity physical, technical and tactical actions; as result of this, soccer training must include high-intensity exercises, which can act as a stimulus to the hypothalamus pituitary-adrenal axis, resulting in a significant increase in circulating cortisol levels. This study examined the effect of 4 weeks of Speed Endurance Maintenance (SEM) and Speed Endurance Production (SEP) on the serum cortisol concentration in response to a 5-meter multiple shuttle run test (5-m MST) in young elite soccer players. Fifteen soccer players were divided to SEM (n = 7) or SEP (n = 8) training group. Blood drawings were performed four times: before and after the 5-m MST at baseline (T1a, T1b) and at follow-up (T2a, T2b). Both training regimes determined a cortisol secretion following the 5-m MST at both baseline and follow-up. Data on delta values highlighted that SEP had greater values than SEM at baseline and registered a significant decrease at the follow-up. This difference is probably due to the lack of specific speed endurance training for players of SEP group prior to the beginning of the protocol. The physiological mechanisms behind the observed biological differences should be deeply investigated.

#12 Design and evaluation of sound-based electronic football soccer training system for visually impaired athletes
Reference: Biomed Eng Online. 2019 Jun 24;18(1):76. doi: 10.1186/s12938-019-0695-5.
Authors: Yandun F, Auat Cheein FA, Lorca D, Acevedo O, Auat Cheein C
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Summary: Several countries encourage the practice of football for rehabilitation and social inclusion purposes. For visually impaired people, football is purely sound-based, where the ball and the players are constantly emitting sounds for localization purposes in the field. However, the task of shooting the ball requires of a non-visually impaired extra person, behind the goal (known as caller), whom is punching the four corner of such goal to help the athletes. The presence of the caller restricts the self-sufficiency of the players. This work addresses such problem, by presenting a goal for visually impaired players with the aim of enhancing their self-sufficiency. The electronic goal is designed with four functionalities for training purposes, by returning sound-based feedback of its position and the places where the ball has impacted. The system is validated with seven volunteers from Chilean Football Soccer National Team. A questionnaire was answered by the players before and after the tests to statically validate the proposed device. The presented system is portable and designed following a modular criterion suitable for visually impaired people self-assembling. From a test of 350 shootings, the electronic goal showed to enhance the shooting assertiveness from 82 to 92%, and the accuracy from 20 to 56% compared to the traditional caller. The electronic goal showed to enhance the self-sufficiency of athletes, by improving their assertiveness in shooting training. Nevertheless, and according to the responses to the questionnaires, the system needs improvements in its portability and handling.


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