Latest research in football - week 30 - 2022

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 Dynamic Postural Stability Is Decreased During the Single-Leg Drop Landing Task in Male Collegiate Soccer Players With Chronic Ankle Instability

Reference: Orthop J Sports Med. 2022 Jul 25;10(7):23259671221107343. doi: 10.1177/23259671221107343. eCollection 2022 Jul.

Authors: Kohei Kawaguchi, Shuji Taketomi, Yuri Mizutani, Hiroshi Inui, Ryota Yamagami, Kenichi Kono, Tomofumi Kage, Seira Takei, Sayaka Fujiwara, Toru Ogata, Sakae Tanaka

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Summary: Chronic ankle instability (CAI) is commonly encountered in soccer players. The feelings of instability and anxiety caused by CAI can lead to poor performance, such as difficulty in sharp change of direction during soccer play. The single-leg drop landing (SLDL) task is often used to evaluate dynamic postural stability. The purpose of this study was to clarify whether dynamic stability measured during SLDL is altered in male collegiate soccer players with CAI. The hypothesis was that athletes with CAI would show poor dynamic postural stability. A total of 103 male collegiate soccer players were recruited, and their limbs were classified based on the new international CAI criteria. All players performed three 5-second SLDL trials on a force plate. The main outcome measures included time to stabilization of the horizontal ground-reaction force (GRF); peak GRF in the vertical, horizontal, and sagittal directions; and trajectory length of the center of pressure during SLDL. Data from 59 CAI limbs and 147 non-CAI limbs were collected in this study. Time to stabilization of horizontal GRF was significantly longer in the CAI limbs (P < .001), and the peak GRFs in all directions were significantly lower in the CAI limbs (vertical, P < .001; horizontal, P < .001; sagittal, P = .001). Additionally, the trajectory length of the center of pressure was significantly greater in the CAI limbs (P = .004). Soccer players with CAI had decreased dynamic postural stability that led them to land softly when performing the SLDL task. Measurement of dynamic postural stability may be useful in the evaluation of CAI.



#2 Adaptation and Validation of a Test for the Evaluation of Tactical Knowledge in Soccer: Test de Conocimiento Táctico Ofensivo en Fútbol for the Brazilian Context (TCTOF-BRA)

Reference: Front Psychol. 2022 Jul 14;13:849255. doi: 10.3389/fpsyg.2022.849255. eCollection 2022.

Authors: Leandro Rechenchosky, Vanessa Menezes Menegassi, Matheus de Oliveira Jaime, Paulo Henrique Borges, Jaime Serra-Olivares, Wilson Rinaldi

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Summary: Studies and tests to assess the tactical domain of young soccer players are recent, and few instruments meet the majority of quality criteria. The aim was to adapt and validate the Test de Conocimiento Táctico Ofensivo en Fútbol (TCTOF) for the Brazilian context (TCTOF-BRA). The article consists of two studies. Study 1 (n = 111) included the translation, theoretical/semantic analysis, back translation, cross-cultural equivalence, and content and face validity (pre-test). In study 2 (n = 768), a theoretical and empirical item analysis was carried out, followed by construct validity [exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and the known-groups method] and reliability (internal consistency and repeatability). In the cross-cultural evaluation, the Coefficient of content validity total (CCVt) of the instrument was 0.96 and in the content validity, the CCVt of the instrument was 0.87. The face validity was confirmed (>95%). After theoretical and empirical analysis, 15 questions were included in the Teste de Conhecimento Tático Ofensivo no Futebol (TCTOF-BRA). The EFA showed a model with adequate fit (KMO = 0.69; Bartlett p < 0.001), with a factor structure considered very good, composed of four factors (decision making, operational tactical principles, collective tactical-technical elements, and rules). The CFA by the Asymptotically Distribution-Free estimation method demonstrated good and very good goodness of fit indices (X 2/df = 1.54, GFI = 0.99, CFI = 0.94, TLI = 0.92, PGFI = 0.71, PCFI = 0.76, RMSEA = 0.03, and ECVI = 0.26). The known-groups method showed significant differences (p < 0.01) and effect sizes varying from small-to-medium to large. With respect to reliability, coefficients of 0.89 (CR) and 0.74 (KR20) for internal consistency and 0.85 for repeatability were found. The TCTOF-BRA presented satisfactory evidence, demonstrating it to be an instrument with valid and reliable measures for the evaluation of tactical knowledge (declarative and theoretical procedural), based on specific knowledge and decision making (cognitive domain), of Brazilian young soccer players from 12 to 17.9 years old.



#3 Football Research Takes Center Stage

Reference: Int J Sports Physiol Perform. 2022 Aug 3;1. doi: 10.1123/ijspp.2022-0300. Online ahead of print.

Authors: Iñigo Mujika, Karim Chamari

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#4 Classified metabolic power-based measures in professional football players: comparison between playing positions and match period

Reference: BMC Sports Sci Med Rehabil. 2022 Jul 30;14(1):146. doi: 10.1186/s13102-022-00541-y.

Authors: Zeki Akyildiz, Erhan Çene, Coşkun Parim, Onat Çetin, Çağatay Turan, Yılmaz Yüksel, Rui Silva, Ana Filipa Silva, Hadi Nobari

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Summary: The aim of this study was (i) provide reference data of metabolic power-based measures during professional football matches; and to (ii) analyze the between-position and between-halves differences of power-based measures during professional football matches. Forty-six professional male players from two Turkish Super League teams were observed during two seasons, and 58 matches were analyzed. Total distance, equivalent distance, Low Power (LP), Intermediate Power (IP), High Power (HP), Elevated Power (EP), Max Power (MP) and power metabolic measures Pmet at different match moments were considered. Significant between-position differences were observed for IP (p: 0.000; d: 0.284), HP (p ≤ 0.001; d = 0.45), EP (p ≤ 0.001; d = 0.44), and for MP (p ≤ 0.001; d = 0.56), with the central defenders (CD) showing the lower values, and the central midfielders (CM) showing the higher values for the overall measures. Power-based measures are dependent on playing positions. While the CD have lower Pmet values when compared to all positions, the CM have the greatest values. Training and recovery strategies must be ensured for CM players, especially those who have greater match participation.



#5 Coordination variability reduced for soccer players compared to non-athletes during the stance phase of gait

Reference: J Sports Med Phys Fitness. 2022 Aug 1.  doi: 10.23736/S0022-4707.22.13964-2. Online ahead of print.

Authors: Morteza Yaserifar, Ziya Fallah Mohammadi, Sayed E Hosseininejad, Iman Esmaili Paeen Afrakoti, Kenneth Meijer, Tjeerd W Boonstra

Summary: Soccer is a unilateral sports activity that may alter the spatiotemporal characteristics of gait. This may alter motor control of gait in the dominant leg in soccer players and lead to a sport-specific gait pattern, which has not yet been considered. We aimed to determine whether soccer players exhibit differences in the lower extremity coupling variability during gait compared to healthy non-athletes. Hip, knee, and ankle joint angles from fourteen soccer players and sixteen controls were acquired during treadmill walking. Hip-knee coupling, knee-ankle coupling and coupling angle variability (CAV) of the right leg in the sagittal plane were assessed using a vector coding technique. Soccer players showed reduced hip-knee CAV during the mid-stance and terminal-stance phases of gait compared to the control group (Padj = 0.04 and P < 0.001, respectively). In addition, soccer players less often used an ankle coordination pattern, in which only the ankle joint but not the knee joint rotates (Padj = 0.01). In summary, soccer players show altered gait dynamics during normal walking, possibly due to intense soccer training. These changes provide evidence of adaptive strategies of the motor control system to sports activities that can be used for gait rehabilitation. Clinicians should note that some sport, such as soccer, may result in sport-specific gait patterns However, further works are needed to confirm this finding.



#6 Assessing Eccentric Hamstring Strength Using the NordBord: Between-Session Reliability and Interlimb Asymmetries in Professional Soccer Players

Reference: J Strength Cond Res. 2022 Jun 27. doi: 10.1519/JSC.0000000000004303. Online ahead of print.

Authors: Chris Bishop, Jack Manuel, Ben Drury, Marco Beato, Anthony Turner

Summary: The aims of the current study were to (a) determine between-session reliability of peak force during the Nordic hamstring exercise (NHE) in professional soccer players during the preseason and (b) determine the subsequent magnitude and direction of peak force asymmetry from the NHE between all test sessions. The NHE was used as a weekly monitoring tool in 14 professional soccer players, throughout a 6-week pre-season period to record peak force from the NordBord device (in Newtons-N) across an average of 6 repetitions for the dominant and nondominant limbs. The first 2 weeks were used as familiarization sessions, with 4 data collection sessions thereafter. When considering relative reliability, intraclass correlation coefficients (ICCs) showed moderate levels of between-session reliability across the 4 weeks on both limbs (dominant = 0.54-0.73 and nondominant = 0.68-0.73) and for the sum total (0.69-0.73). For absolute reliability, both limbs showed coefficient of variation (CV) values <10% across all 4 weeks, with the exception of the dominant limb between sessions 1-2 (10.06%). When determining systematic bias, no meaningful changes were evident in peak force on either limb (g = -0.59 to 0.40) or for the magnitude of asymmetry (g = -0.24 to 0.35). However, when assessing consistency in the direction of asymmetry, levels of agreement ranged from 43 to 57% across the data collection period, indicating substantial variation in the superior performing limb from session to session. The findings from this study indicate that 2 familiarization sessions is enough to elicit reliable peak force data during the NHE in professional soccer players during preseason, despite a very small learning effect across the testing period.



#7 Platelet polyphosphate and energy metabolism in professional male athletes (soccer players): A cross-sectional pilot study

Reference: Physiol Rep. 2022 Aug;10(15):e15409. doi: 10.14814/phy2.15409.

Authors: Takashi Ushiki, Tomoharu Mochizuki, Katsuya Suzuki, Masami Kamimura, Hajime Ishiguro, Satoshi Watanabe, Go Omori, Noriaki Yamamoto, Tomoyuki Kawase

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Summary: Human platelet polyphosphate (polyP) is a multifunctional molecule; however, its functions are not yet fully understood. A recent study demonstrated that similar to skeletal muscle, polyP is involved in energy metabolism in platelets, which suggests that well-trained athletes may exhibit elevated platelet polyP levels for energy storage. To test this hypothesis, we quantified platelet polyP along with NADH, a component involved in ATP production in non-trained and well-trained male Japanese participants of the same generation. Washed platelets were prepared from the venous blood of young, healthy, non-athletes, and professional soccer players (pro-athletes). NADH and polyP levels were spectrophotometrically determined using tetrazolium reduction and fluorometrically determined using 4',6-diamidino-2-phenylindole at the excitation/emission wavelengths of 425/525 nm. Body weight and impedances were measured simultaneously. Statistical analyses were performed using the Mann-Whitney U test and Spearman correlation coefficient. Although basal metabolic rate levels were significantly higher, platelet polyP levels were significantly lower in pro-athletes than in that in non-athletes. No significant differences were detected in other body compositions or platelet indices between the two groups. The pro-athlete group showed a moderate, nearly significant correlation (R = 0.439; p = 0.0512) between platelet polyP and NADH levels. Taken together with the weak correlation data between polyP and body mass index, it is suggested that platelet polyP levels may be influenced by platelet and body energy metabolic activity. Further biochemical studies are needed to elucidate this mechanism.



#8 Biomechanical Characteristics of the Support Leg During Side-Foot Kicking in Soccer Players With Chronic Ankle Instability

Reference: Orthop J Sports Med. 2022 Jul 28;10(7):23259671221112966. doi: 10.1177/23259671221112966. eCollection 2022 Jul.

Authors: Akihiro Tamura, Keita Shimura, Yuri Inoue

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Summary: Chronic ankle instability (CAI) in soccer players can increase the risk of recurrent ankle varus sprains and damage the articular surface of the ankle joint, thus increasing the risk of osteoarthritis. It is important to understand the biomechanical characteristics of the support leg during kicking in soccer players with CAI. The purpose of this study was to clarify the kinematics of the kicking motion of soccer players with CAI. It was hypothesized that at the point before ball contact when the support leg makes flat-foot contact with the ground, soccer players with CAI will land with ankle inversion in the support leg during a side-foot kick compared with players without CAI. The study cohort included 19 male college soccer players (mean age, 20.5 ± 0.9 years) with greater than 8 years of soccer experience who were recruited from August 2019 to March 2020. Of these athletes, 10 had CAI and 9 had no CAI in the support leg, as diagnosed according to the Cumberland Ankle Instability Tool. Kinematic data for the trunk, hip, knee, and foot of the support leg during a side-foot kick were obtained using a 3-dimensional, motion-analysis system. The Mann-Whitney U test or Student t test was selected to identify differences in variables between the CAI and non-CAI groups. There were no significant differences in physical characteristics between the CAI and non-CAI groups. At the point when the support leg made flat-foot contact with the ground, the players with CAI had more eversion of the hindfoot with respect to the tibia (-28.3° ± 12.1° vs -13.9° ± 14.2°; P = .03), a more varus alignment of the knee (26.0° ± 10.7° vs 13.7° ± 10.5°; P = .03), and a lower arch height index (0.210 ± 0.161 vs 0.233 ± 0.214; P = .046) compared with non-CAI players. Significant differences between players with and without CAI were seen in the support leg kinematics at flat-foot contact with the ground during the kicking cycle. The biomechanical alignment of the support leg during a side-foot kick in players with CAI may reflect a subconscious attempt to avoid inversion of the foot and further ankle sprains.



#9 "What needs to be seen": An exploration into the visual anticipation behaviour of different skill-level football referees while observing long passes on-field

Reference: Hum Mov Sci. 2022 Jul 28;85:102980. doi: 10.1016/j.humov.2022.102980. Online ahead of print.

Authors: T van Biemen, T F van Zanten, G J P Savelsbergh, D L Mann

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Summary: It is well established that elite football referees possess superior anticipatory skills in specific game scenarios such as when assessing foul situations. Referees might also have better anticipatory skills in other important scenarios such as when observing a long pass. In these often-occurring situations, a referee has to use visual information to anticipate the outcome of the pass, in particular to foresee any potential infringements that might occur when players battle for ball possession. However, little is known about if and how football referees might anticipate outcomes in these scenarios. The aim of the current study was therefore to analyse the visual anticipatory behaviour of football referees when long passes occur during actual football matches. Elite (N = 4) and sub-elite referees (N = 12) officiated an actual football match while wearing a mobile eye-tracker to analyse their gaze behaviour when long passes occurred (N = 196). The results revealed differences in the way that the elite and sub-elite referees tracked the ball and anticipated the outcome of the ball trajectories. The elite referees used a lower search rate (1.3 vs 1.8 fix/s; p < .05) and were more likely to direct their gaze towards the ball during the moment of kick (77 vs 52%; p < .05) and the early flight-phase of the pass (68 vs 45%; p < .05), and subsequently produced earlier anticipatory eye movements to the player(s) receiving the ball (at 50% vs 60% of the ball flight; p < .05). This earlier anticipation may help the elite referees to better pick-up relevant information about the receivers that could be vital in making adjudications about any potential infringement when the ball does arrive. Referee education programs can use the current study to highlight the importance of visual search behaviour and help referees to adapt a strategy that is beneficial for long-pass situations.



#10 Recreational Football and Bone Health: A Systematic Review and Meta-analysis

Reference: Sports Med. 2022 Jul 19. doi: 10.1007/s40279-022-01726-8. Online ahead of print.

Authors: Zoran Milanović, Nedim Čović, Eva Wulff Helge, Peter Krustrup, Magni Mohr

Summary: Recreational football is an intense, versatile form of exercise with multiple high- and odd-impact actions. Recreational football is therefore hypothesized to be suitable for bone modeling and bone health. The aim of the present systematic review and meta-analysis was to evaluate the effects of recreational football on bone mineral density (BMD), bone mineral content (BMC) and bone turnover markers (BTM). MEDLINE, PubMed, SPORTDiscus, Web of Science, Cumulative Index to Nursing and Allied Health Literature (CINAHL) and Google Scholar were searched prior to September 2021. A manual database search was also performed using the following key terms, either singly or in combination: recreational football/soccer, street football/soccer, recreational small-sided games, effect, influence, impact, bone turnover markers, bone mineral density, bone turnover marker, bone health, osteogenesis, CTX, osteocalcin, P1NP. Randomised and matched controlled trials with participants allocated to a recreational football group or any other type of training intervention or passive control group were included. The primary outcome measures were total BMD, lower limb BMD, total BMC, lower limb BMC, osteocalcin, procollagen type 1N-terminal propeptide (P1NP) and collagen type 1 cross-linked C-telopeptide (CTX). A total of 17 papers met the inclusion criteria and were included. Comprehensive Meta-analysis V.2 software (Biostat, Englewood, New Jersey, USA) was used for the meta-analyses. Agreement between the two reviewers was assessed using RoB2 tool and k statistics for full-text screening and rating of relevance and risk of bias. The k agreement rate between reviewers was k = 0.92. The football interventions included were based on studies having a duration of 12-64 weeks with one 5-year follow-up study and with a training frequency of 1-3 sessions/wk. Training sessions were 45-60 min sessions of 3v3 - 7v7 small-sided games. The subjects covered an age span from 9 to 73 years. Five studies examined recreational football effects in females, nine studies in males and three studies included both sexes. Recreational football training produced a statistically significant effect (mean difference = 0.02 g/cm2, 95% confidence interval: 0.00-0.03, P = 0.02) on lower limb BMD and negligible effects for total BMD compared to no-exercise controls. The recreational football effects on total and lower limb BMC, when compared to both no-exercise controls and exercise controls, were negligible. A moderate to large significant increase in osteocalcin, P1NP and CTX was observed for recreational football compared to both no-exercise controls and exercise controls. In conclusion, recreational football training regimes lasting 12-64 weeks have a large osteogenic impact on bone turnover markers in comparison with no-exercise controls as well as exercise controls, and beneficial effects on lower limb BMD compared to no-exercise controls. Short and medium duration recreational football interventions have negligible effects on whole-body BMD and BMC (total and lower limb), with magnitudes similar to those of other exercise modes.



#11 Fluid Balance and Carbohydrate Intake of Elite Female Soccer Players during Training and Competition

Reference: Nutrients. 2022 Aug 3;14(15):3188. doi: 10.3390/nu14153188.

Authors: Caroline A Tarnowski, Ian Rollo, James M Carter, Maria Antonia Lizarraga-Dallo, Mireia Porta Oliva, Tom Clifford, Lewis J James, Rebecca K Randell

Summary: This study examined sweat rate, sweat sodium concentration [Na+], and ad-libitum carbohydrate and fluid intakes in elite female soccer players during training (n = 19) and a match (n = 8); eight completed both for comparisons. Body mass (kg) was obtained before and after exercise to calculate sweat rate. The sweat [Na+] was determined from absorbent patches on the thigh or back. Sweat rate, percentage body mass change, and sweat [Na+] for 19 players during training were 0.47 ± 0.19 L·h-1, +0.19 ± 0.65%, and 28 ± 10 mmol·L-1, respectively. Sweat rate was higher during a match (0.98 ± 0.34 L·h-1) versus training (0.49 ± 0.26 L·h-1, p = 0.007). Body mass losses were greater post-match (-1.12 ± 0.86%) than training (+0.29 ± 0.34%, p = 0.003). Sweat [Na+] was similar for training (29 ± 9 mmol·L-1) and a match (35 ± 9 mmol·L-1) (p = 0.215). There were no differences in match versus training carbohydrate intakes (2.0 ± 2.3 g·h-1, 0.9 ± 1.5 g·h-1, respectively, p = 0.219) or fluid intakes (0.71 ± 0.30 L·h-1, 0.53 ± 0.21 L·h-1, respectively, p = 0.114). In conclusion, female soccer players' sweat rates were higher during a match than during training, and carbohydrate intakes were below recommendations for matches and training.



#12 Practices of strength and conditioning coaches in Brazilian elite soccer

Reference: Biol Sport. 2021 Sep;39(3):779-791. doi: 10.5114/biolsport.2022.108703. Epub 2021 Oct 6.

Authors: Irineu Loturco, Tomás T Freitas, Pedro E Alcaraz, Ronaldo Kobal, Renan F Hartmann Nunes, Anthony Weldon, Lucas A Pereira

Summary: Brazil is the leading global exporter of soccer players, with approximately 2,000 international transfers to different clubs per year. Although Brazilian players compete in the most prestigious soccer leagues worldwide, the habitual training methods, strategies, and routines of Brazilian soccer strength and conditioning coaches (SCCs) are undocumented. This study used a standard online survey to collect and characterize the strength and conditioning practices of Brazilian soccer SCCs. Forty-nine SCCs (age: 40.4 ± 7.5 years; professional experience: 15.3 ± 7.5 years) working in Brazilian professional soccer teams participated in this study. The survey consisted of eight sections: 1) background information; 2) muscular strength-power development; 3) speed training; 4) plyometrics; 5) flexibility training; 6) physical testing; 7) technology use; and 8) programing. Results indicated that training and testing practices of Brazilian SCCs are strongly affected by the congested fixture schedules, extensive traveling distances, and socio-economic disparities between different regions of the country. We describe all these different strategies and methods in detail, providing a comprehensive view and a critical examination of Brazilian soccer strength and conditioning practices. Brazilian SCCs and professional soccer organizations can use the findings from this study to develop training strategies and customize education programs. Practitioners from other countries can use this information to design training programs closely tailored to the background of Brazilian athletes, which may support their adaptation to different competitive scenarios and game demands, such as those found in the most important soccer leagues worldwide.



#13 Relationship between aerobic fitness and metabolic power metrics in elite male soccer players

Reference: Biol Sport. 2021 Sep;39(3):599-606. doi: 10.5114/biolsport.2022.106389. Epub 2021 Jul 28.

Authors: Vincenzo Manzi, Giuseppe Annino, Cristian Savoia, Giuseppe Caminiti, Elvira Padua, Matteo Masucci, Rosario D'Onofrio, Ferdinando Iellamo

Summary: The aim was to assess the relationship between aerobic fitness and metabolic power metrics in elite male soccer players, and the possible differences that playing positions might impose during match play over new metabolic power metrics. Sixty-two elite professional male soccer players (13 central backs, 13 side backs, 22 midfielders, and 14 forwards) took part in the study. Players were monitored during eleven months of full training (including pre-season and in-season) and over all official matches (Serie A matches, Italy Cup matches). Aerobic fitness tests were conducted one week after the start of the preseason, and 8, 24 and 36 weeks after the beginning of the Championship. Players' aerobic fitness and metabolic power metrics were considered as the mean of all seasonal testing and of pooling data of 38 championship matches and 3 or 6 Italy Cup matches for all the calculations respectively. The velocity at 4 mmol·L-1 (VL4) was significantly related to metabolic power metrics match variables with correlation ranging from trivial to very large (r = 0.32 to r = 0.89). Receiver-operating-characteristic (ROC) analysis showed that speed at VL4 was sensitive in detecting high metabolic power distance (HMPD) changes in all but central back players as revealed by area under the curve (central back .78, 95%CI .47 to .95; full back .93, 95%CI .64 to 0.99; midfielder .88, 95%CI .67 to 0.98; forward .90, 95%CI .62 to 0.99). This study's findings provide further evidence for the ecological validity of aerobic fitness in elite male soccer players. Players having a HMPD cut-off equal to or higher than > 1450 m for central backs, > 1990 m for full backs, > 2170 m for midfielders and > 1670 m for forwards may be considered as possessing superior aerobic fitness status. In light of this study's findings, the VL4 test may be considered a valid test to evaluate meaningful information for direct generic aerobic training in soccer players.



#14 Effects of a resistance training intervention on the strength-deficit of elite young soccer players

Reference: Biol Sport. 2021 Sep;39(3):615-619.  doi: 10.5114/biolsport.2022.106157. Epub 2021 Jul 28.

Authors: Irineu Loturco, Lucas A Pereira, Chris Bishop, Vinicius Zanetti, Tomás T Freitas, Fernando Pareja-Blanco

Summary: The aim of this study was to examine the effects of a traditional resistance training scheme on the relative strength (RS), relative peak-force (RPF), strength deficit (SDef), and vertical jump and sprint abilities in elite young soccer players. Thirty-five under-20 soccer players from two professional clubs were assessed before and after a 4-week competitive period. One team performed 12 sessions of a structured resistance training program and the other maintained their regular soccer-specific training and competitive routines. Resistance training sessions consisted of half-squat and jump-squat exercises at intensities of 30-80% of the one-repetition maximum. Both teams performed pre- and post-measurements in the following order: (1) countermovement jump (CMJ), (2) 20-m sprint, and (3) half-squat one-repetition maximum to determine the RS, RPF, and SDef. A two-way analysis of variance was used to test for group x time interaction among variables. Effect sizes (ES) and 95% confidence intervals (CI) were also calculated. Group x time interactions were demonstrated for RS ([ES [95%CI] = 1.21 [0.57; 1.85], P = 0.001), RPF (ES [95%CI] = 1.18 [0.52; 1.80], P = 0.001), SDef (ES [95%CI] = 0.86 [0.01; 1.71], P = 0.04), and CMJ (ES [95%CI] = 0.64 [0.28; 0.99], P = 0.001); whereas a non-significant interaction was observed for 20-m sprint performance (ES [95%CI] = 0.02 [-0.32; 0.36], P = 0.85). Traditional strength-power oriented training resulted in improved maximum strength performance and CMJ ability but, paradoxically, increased the SDef. As a consequence, stronger athletes are not necessarily able to use greater percentages of their peak-force against relatively lighter loads.



#15 Effects of plyometric jump training on soccer player's balance: a systematic review and meta-analysis of randomized-controlled trials

Reference: Biol Sport. 2021 Sep;39(3):765-778. doi: 10.5114/biolsport.2022.107484. Epub 2021 Oct 6.

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Daniel Castillo, Javier Raya-González, Markel Rico-González, Rafael Oliveira, Thomas Rosemann, Beat Knechtle

Summary: Plyometric jump training (PJT) can be used for improving balance through bilateral and unilateral jump-landing drills. Since the increased number of articles testing the effects of PJT on dynamic and static balance, it is relevant to summarize the evidence and determine the effects across different original articles. This systematic review with meta-analysis was conducted to assess the effects of PJT programs on dynamic and static balance in soccer players. The data sources utilized were Cochrane, Medline (PubMed), SPORTDiscus, and Web of Science. (i) Soccer players of any age or sex without injury, illness, or other clinical conditions; (ii) PJT-based programs restricted to a minimum of three weeks (duration); (iii) passive or active control groups; (iv) pre-post interventions values of dynamic and/or static balance; (v) randomized-controlled trials; and (vi) peerreviewed original full-text studies written in English, Portuguese, and/or Spanish. The database search initially identified 803 titles. From those, eight articles were eligible for the systematic review and meta-analysis. The results showed no significant differences between PJT and active controls in dynamic anterior, postero-medial, or postero-lateral balance for both left and right legs (p > 0.05). Additionally, no significant differences were found between PJT and active controls in terms of static balance (p = 0.495). The current evidence suggests that PJT has no significant advantage over active control groups in terms of dynamic or static balance.



#16 Variability of internal and external loads and technical/tactical outcomes during small-sided soccer games: a systematic review

Reference: Biol Sport. 2021 Sep;39(3):647-672. doi: 10.5114/biolsport.2022.107016. Epub 2021 Aug 27.

Authors: Filipe Manuel Clemente, Rodrigo Aquino, Gibson Moreira Praça, Markel Rico-González, Rafael Oliveira, Ana Filipa Silva, Hugo Sarmento, José Afonso

Summary: Small-sided games (SSGs) are widely used in soccer training. However, some of the typical outcomes related to human responses during these games (namely internal and external load) may vary between sessions for similar practice conditions. Thus, the study of intra- and inter-bout variability in response to SSGs is progressively growing. This systematic review aimed to (1) identify studies that have examined the intra- and inter-session bouts' variability levels regarding the internal and external load and technical/tactical outcomes during SSGs and (2) summarize the main evidence. A systematic review of PubMed, SPORTDiscus, Cochrane, and Web of Science databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. From the 486 studies initially identified, 24 were fully reviewed, and their outcome measures were extracted and analyzed. Sixteen studies analyzed internal load, 13 studies analyzed external load variables, six studies analyzed technical execution, and two studies analyzed tactical behavior. All studies included SSGs with a range number of players between 2 to 14 (1 vs. 1 to 7 vs. 7 SSGs). Internal load and low-speed external load variables presented a low variability, while high variations were reported regarding the technical execution and high-speed external loads.



#17 Monitoring Psychometric States of Recovery to Improve Performance in Soccer Players: A Brief Review

Reference: Int J Environ Res Public Health. 2022 Jul 31;19(15):9385.  doi: 10.3390/ijerph19159385.

Authors: Okba Selmi, Ibrahim Ouergui, Antonella Muscella, Giulia My, Santo Marsigliante, Hadi Nobari, Katsuhiko Suzuki, Anissa Bouassida

Summary: In order to maximize adaptations and to avoid nonfunctional overreaching syndrome or noncontact injury, coaches in high-performance sports must regularly monitor recovery before and after competitions/important training sessions and maintain well-being status. Therefore, quantifying and evaluating psychometric states of recovery during the season in sports teams such as soccer is important. Over the last years, there has been substantial growth in research related to psychometric states of recovery in soccer. The increase in research on this topic is coincident with the increase in popularity obtained by subjective monitoring of the pre-fatigue state of the players before each training sessions or match with a strong emphasis on the effects of well-being or recovery state. Among the subjective methods for players' control, the Hooper index (HI) assesses the quality of sleep during the previous night, overall stress, fatigue, and delayed-onset muscle soreness. Additionally, the total quality of recovery (TQR) scale measures recovery status. The HI and TQR recorded before each training session or match were affected by the variability of training load (TL) and influenced the physical and technical performances, and the affective aspects of soccer players. Researchers have recommended wellness monitoring soccer players' psychometric state of recovery before each training session or match in order to detect early signs of fatigue and optimize high-level training performance. This method allows for better detecting signs of individual fatigue and allows coaches to adapt and readjust the TL, and avoid physical and technical gaps in order to improve the performance of soccer players.



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