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The aim of this study was to look into the alleged impact of the physical fitness performance of elite junior soccer players on the professional career according to playing position. The physical tests (sprint test, countermovement jump [CMJ], and maximal aerobic speed [MAS]) performed by 165 players enrolled in the junior team of a Spanish 1st Division club (1998-2010) were evaluated. Players were classified as those who were promoted to the reserve team (Reserve Team) and those who were not (non-Reserve Team), and as those who were promoted to the Spanish 1st/2nd Divisions (PFL) and those who were not (NPFL) until the 2020-2021 season. Overall, no significant differences (p>.05) were found between the Reserve Team and non-Reserve Team or between the PFL and NPFL players in neuromuscular performance. Aerobic fitness was greater (p<.05; ES = .79 ± .60, moderate; mean difference = 3.0%) for the Reserve Team lateral midfielders in comparison to that for the non-Reserve Team. The results suggest that the impact of physical fitness on the promotion of elite junior soccer players is limited.

The aim of this study was to assess the changes in jump and sprint performances after the preseason period across 14 seasons depending on the initial performance level and the playing position in young professional soccer players. In total, 162 soccer players (age = 20.6 ± 1.8 years) belonging to the same reserve team of a Spanish La Liga club participated in this study. Countermovement jump (CMJ) and 5 and 15 m sprints were assessed in each season at the start of the preseason (July), Test 1 (T1), and the start of the competitive period (September), Test 2 (T2), from the 1998 to 2013 seasons. Considering all seasons, a trivial change was found in the sprint (5 m, Effect Size [ES] = −0.01; ±0.11, most-likely; and 15 m, ES = 0.05; ±0.09, most-likely) and countermovement jump (CMJ) performances (ES = −0.03; ±0.07; most-likely) after the preseason, but this varied across the seasons. While the fastest players in 5 m and 15 m tests and the most powerful worsened their performances in sprinting capacity (ES = 0.53–0.65, small very-likely) and in jump ability (ES = −0.54; ±0.25, small very-likely), respectively, the slowest players and the less powerful improved their performance likely/most-likely (ES = −0.33 and −0.68, small and moderate) and very-likely (ES = 0.40; ±0.20, small) after the precompetitive period. The changes in CMJ and sprinting were trivial and trivial/small for all tactical positions. The changes in neuromuscular performance after the preseason were not stable across the seasons and varied depending on the initial performance level. Individualization strategies should be considered in the design of strength and conditioning programs in order to optimize the training process.

The aims were to assess differentiated perceived match exertion and its variability according to playing position for professional soccer players. Nineteen Spanish players declared their respiratory and muscular perceived exertions (PEs) after official matches during an entire season. Players were classified according to their playing position. In order to assess differentiated perceived match exertion, soccer players were asked to assess their perceived level of exertion following each official match. Considerable differences (p<.05; ES=.41 to 2.49) were found between some playing positions but not always in both dimensions of PE (respiratory and muscular). Advanced midfielders (AvMs), wide midfielders (WMs) and wing backs (WnBs) reported the highest match respiratory PE and muscular PE scores. Furthermore, match-to-match differentiated perceived match exertion variability ranged from 12.8 to 27.7% for respiratory perceived exertion and from 11.5 to 25.2% for muscular perceived exertion according to playing position. Match respiratory-muscular PE differences varied among the playing positions, showing higher muscular PE than respiratory PE in central backs (CBs), WMs and central midfielders (CMs) (p<.05; ES=-.35 to .68), but higher respiratory PE than muscular PE in wing backs (p<.05; ES=-.35). Soccer differentiated perceived match exertion is different inter and intra some playing positions, showing large swings for match-to-match variability between playing positions. These facts confirm that the deconstruction of the overall PE provides a more accurate evaluation of the subjective match internal load in some playing positions.

The aim of this study was to examine the association of perceived respiratory and muscular exertions and associated training load (TL) for monitoring changes in several aerobic fitness and neuromuscular performance parameters during 32 weeks of soccer training in young professional players. Twenty male soccer players (age=20.6±1.8 years, body height=1.80±.06 m, body mass=73.6±6.7 kg) belonging to the same reserve team of a Spanish La Liga Club participated in this study. Countermovement jump (CMJ), CMJ with arm swing, linear sprint running (over 5 m and 15 m) and an aerobic fitness running test were performed at the start of the pre-season (Test 1) and 32 weeks later (Test 2). During these eight months, after each training session and match, players rated their perceived exertion (sRPE) separately for respiratory (sRPEres) and leg musculature (sRPEmus) effort. Training load was calculated by multiplying the sRPE value by the duration of each training session or match. Accumulated training and match volume (i.e., time) and associated respiratory and muscular training loads were negatively correlated with the changes in aerobic fitness performance after 32 weeks of training (r=-.53/-.62). In addition, accumulated perceived respiratory load was negatively correlated with the changes in 15 m sprint performance (r=-.51/-.53). A high practice volume (time) and associated respiratory and leg muscular TL can impair the long-term improvement of aerobic fitness and sprint performance in professional soccer players.

The purpose of this study was to determine the underlying structure of stretch-shortening cycle (SSC) jumping, acceleration and change-of-direction (COD) abilities in soccer players using principal component factor analysis (PCA). Based on the results of recent studies on male college athletes, we hypothesized that slow SSC jumping, acceleration and COD represent independent motor abilities in soccer players. Forty two soccer players (23.2±2.36 yr) performed three tests for each group of rapid lower-body movements: a) three vertical slow SSC jumping tests - squat jump (SJ), countermovement jump (CMJ) and arm swing countermovement jump (CMJAS), b) three acceleration tests - 5, 10 and 15 meter sprint times (ACC5, ACC10 and ACC15), and c) three COD tests - modified agility test free (MATF), the 505 agility test (505) and 20 yard agility test (Y20). PCA was applied to establish the relationships among the factors (i.e. the motor abilities) underlying the included manifest variables (i.e. the performance tests). This procedure reduced all variables to a smaller number of independent latent dimensions. The results indicated three separate factors that may correspond to slow SSC jumping, acceleration and COD abilities. The magnitude of the correlation coefficients among the three motor abilities extracted was r<.56. Therefore, it is suggested that slow SSC jumping, acceleration and COD abilities represent independent motor abilities and consequently these should be trained and evaluated separately to assess soccer players’ physical profiles.

The aim of the study was to determine which agility training program (low, moderate or high contextual interference) was more effective in fi rst-grade primary school students to provide reliable information to physical education teachers for designing more effective agility programs. A total of 57 fi rst-grade elementary school students participated in the present study. They were randomized into three groups to compare the effects of three different agility training programs based on contextual interference: low contextual interference (N=19), moderate contextual interference (N=19), and high contextual interference (N=19). Contextual interference refers to the relative amount of interference created when integrating two or more tasks into a particular aspect of a training session. Signifi cant improvements in agility were found in the low (p<0.01, ES=1.79) and moderate (p<0.05, ES=0.61) contextual interference groups after a 4-week training period. These improvements were higher in the low contextual interference group. The high contextual interference group showed no improvements (p>0.05, ES=0.28) after the intervention program. Our results suggested that the low contextual interference program is still more effective than the moderate contextual interference program in this group of primary school students.

The aim of this study was to profile physical characteristics of soccer players measured by acceleration, vertical jump (VJ), horizontal jump (HJ) and change of direction ability (CODA) tests, and to quantify the relationships between these characteristics. Additionally, leg asymmetries between the dominant and nondominant legs during unilateral VJ and HJ were assessed. Thirty-nine male soccer players (22.9±2.8 years, 179.9±6.01 cm, 77.0±8.3 kg), competing in the third division of the Spanish Soccer League, participated in this study. Soccer experience of these players amounted to 15.19±3.15 years. Significant moderate correlations (p<.05) were found between all HJ tests and the modified agility (MAT) or the 505 test, and between all VJ tests and the Y20 or the 505 test. The significant differences between the dominant and non-dominant legs were found for the horizontal drop jump test (p=.001, d=.66) and horizontal three jump test (p=.017, d=.33). No significant differences between the dominant and non-dominant legs were found for VJ tests. The correlation between jumping and CODA varied depending on the characteristics of test types. The significant leg asymmetry in horizontal jumps with bounds found in the present study suggests that soccer players have greater leg asymmetries in the horizontal jump than in the vertical jump.

The purposes of the study were to assess sprinting and agility performance characteristics and to determine the relationship between these two motor skills in elementary education students. Sprinting and agility performance were assessed in 176 children (88 boys and 88 girls) divided into three groups: Group 1 (G1, n = 98; 48 boys and 50 girls), from the first year of elementary education; Group 2 (G2, n = 38; 15 boys and 23 girls), from the second year of elementary education; Group 3 (G3, n = 40; 25 boys and 15 girls), from the third year of elementary education. Significant differences (P < 0.001) were found in agility ability among the groups and between G1- G3 and G2- G3 in the 5 and 15 m sprint. Regarding gender of the students of the same age, significant differences (P < 0.001) between boys and girls in group G1 and G2 were obtained in the 5 and 15 m sprint. The correlation between agility and acceleration was significant but moderate (0.3 < r ≤ 0.7) in all groups (G1, G2, and G3), in most cases. When the gender factor was included, the results were heterogeneous. Assessing this correlation according to age and gender produced heterogeneous results. For this reason, we think that both are independent qualities and that age and gender are two factors that influence the correlation results.