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ABSTRACT: Altmann, S, Neumann, R, Ringhof, S, Rumpf, MC, and Woll, A. Soccer-specific agility: reliability of a newly developed test and correlates of rerformance. J Strength Cond Res 36(5): 1410-1416, 2022-The purpose of this study was to examine the reliability of a newly developed soccer-specific agility test and to determine the correlation of different performance parameters with overall agility performance as measured by the total time. Twenty-two amateur soccer players (age, 25.1 ± 4.0 years) completed a newly developed agility test on 2 separate occasions. The test required the players to conduct 2 changes of direction, one in a preplanned manner and one in response to a stimulus that was provided by a live tester who performed different soccer-specific passing movements. Regarding reliability, very large Pearson's r and intraclass correlation coefficient values were obtained for the total time and the movement time, with moderate and large-to-very large values being evident for the response time and the decision-making time, respectively. The usefulness to detect moderate performance changes was rated as "good" for the total time, the response time, and the movement time. The decision-making time was rated as "OK." The movement time showed a very large relationship with overall agility performance as measured by the total time, while the response time and the decision-making time showed small to moderate relationships. In conclusion, the newly developed soccer-specific agility test is a reliable tool to assess the agility performance of soccer players and can be used by coaches and researchers to detect moderate performance changes. Because physical aspects, represented by the movement time, showed the greatest influence on total agility performance, they are advised to be included in soccer-specific agility training programs of amateur players.

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Effective directional change in sport is imperative to success in key game situations. Change of direction (COD) ability is underpinned by various athletic qualities which can be developed through specific and non-specific training methods. This review examined the effect of specific and non-specific training methods on pro-agility performance, by analysing the intervention type and resulting magnitude of training effects on pro-agility shuttle performance. A total of 20 studies were included for review. Data from 638 subjects and 29 intervention groups involving seven different training methods were extracted and analysed in relation to training method classification and primary outcome measures. Interventions involving sprint training, plyometric training, resistance training, and combined resistance, plyometric, and sprint training were found to produce statistically significant positive change on pro-agility performance per session (p < 0.05). Sprint training (0.108 ES), plyometric training (0.092 ES), resistance training (0.087 ES), and combined resistance, plyometric, and sprint training (0.078 ES) methods were found to have the highest per session training effect. While total time is the typical unit of measure for this test, different types of training may lead to preferential improvements in either acceleration, deceleration, or COD phases of the pro-agility shuttle. Specifically, resisted or inclined sprinting may develop the linear acceleration phases, unilateral resistance training may promote increased strength to overcome the imposed forces during the deceleration and COD phases, multiplanar plyometrics can help enhance stretch-shortening cycle capabilities across different force vectors, and a combination of two or more of these methods may enable simultaneous development of each of these qualities.

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BACKGROUND: Adding wearable resistance (WR) to training results in superior performance compared with unloaded conditions. However, it is unclear if adding WR during warm-up influences training load (TL) in the subsequent session. The aim of this research was to track TL in soccer players during the transition from late preseason to early in-season and examine whether adding WR to the lower leg during a warm-up influenced TL measures during warm-ups and on-field training sessions after WR was removed. HYPOTHESIS: The addition of WR worn on the lower legs during an on-field warm-up would lead to decreases in relatively high-intensity external TL metrics, such as distance covered >6.11 m∙s-1 and acceleration and deceleration >/<3 m∙s-2 and increases in internal TL during the warm-up, yet would have little effect on the subsequent training session when WR was removed. STUDY DESIGN: Matched-pair randomized design. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 28 soccer players were allocated to either a WR training (WRT = 14) or unloaded (control [CON] = 14) group. Both groups performed the same warm-up and on-field training for 8 weeks, with the WRT group wearing 200 g to 600 g loads on their lower leg during the warm-up. External TL was measured via global positioning system data and internal TL was assessed using session rating of perceived exertion (sRPE × time per session). RESULTS: No statistically significant between-group differences (P ≥ 0.05) were identified for any TL measurement during either warm-ups or training sessions. Lower leg WR resulted in trivial to moderate effects for all external TL metrics (-16.9% to 2.40%; d = -0.61 to 0.14) and sRPE (-0.33%; d = -0.03) during the warm-up and trivial to small effects on all external TL metrics (-8.95% to -0.36%; d = -0.45 to -0.30) and sRPE (3.39%; d = 0.33) during training sessions. CONCLUSION: Warming up with lower leg WR negatively affects neither the quality and quantity of the warm-up nor the subsequent training session once WR is removed. CLINICAL RELEVANCE: Using WR on the lower leg during on-field warm-ups may be a means to "microdose" strength training while not unduly increasing TL. However, further research is needed to determine the influence of WR on strength qualities.

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Hertzog, M, Rumpf, MC, and Hader, K. Resistance training status and effectiveness of low-frequency resistance training on upper-body strength and power in highly trained soccer players. J Strength Cond Res 34(4): 1032-1039, 2020-Soccer is classified as a contact/collision sport with many player-to-player duels. Winning these duels, shielding the ball or fending off an opponent requires upper-body strength and power. Therefore, this study aimed (a) to examine the time-related effect of an upper-body resistance training (RT) on maximal strength and power changes in highly trained soccer players and (b) to investigate if the RT status influences these changes throughout a competitive season. Twenty-eight soccer players participated in this study and were divided into an untrained group (UG) and a trained group (TG), according to their RT status. Both groups performed the same upper-body RT once a week, over 30 weeks. Maximal strength (1 repetition maximum [1RM]) and maximal power (MP) were assessed before, during, and after the competitive season. Both groups significantly improved 1RM and MP over the entire competitive season, with a moderate (TG, 13%) to very large (UG, 21%) magnitude in 1RM and with a small (TG, 8%) to moderate (UG, 13%) magnitude in MP. After the initial 10 weeks of RT, UG presented significant and slightly (1RM) to moderately (MP) greater improvements than TG. For all other time intervals, the between-groups' changes in 1RM were rated as similar. For the last 20 weeks of the RT, the change in MP was significantly lower for UG compared with TG. One upper-body RT session per week will provide sufficient stimulus to enable an almost certain improvement in strength and power throughout a competitive season for all players disregarding their initial RT status.

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BACKGROUND: Monitoring athletes' external load during a soccer match may be useful to predict post-match acute and residual fatigue. This estimation would allow individual adjustments to training programs to minimize injury risk, improve well-being, and restore players' physical performance and inform the recovery process. METHODS: Using a systematic review and meta-analysis of the literature, the aim is to determine which monitoring variables would be the strongest predictors of acute (immediately) and residual (up to 72 h) fatigue states in soccer. PubMed, SPORTDiscus, and Web of Science databases were searched (until September 2018). Studies concurrently examining soccer match-related external load metrics and subjective and/or objective measures were selected to determine pooled correlations ([Formula: see text]) with confidence intervals (CI). The quality and strength of the findings of each study were evaluated to identify overall levels of evidence. RESULTS: Eleven studies were included (n = 165 athletes). Acute ([Formula: see text] = 0.67; 95% CI = [0.40, 0.94]) and residual (24 h post-match, [Formula: see text] = 0.54; 95% CI = [0.35, 0.65]) changes in muscle damage markers and countermovement jump peak power output (CMJPPO) were, with moderate to strong evidence, largely correlated with running distance above 5.5 m s-1. No other external load metric was largely correlated with both biochemical and neuromuscular markers. For every 100-m run above 5.5 m·s-1, CK activity measured 24 h post-match increased by 30% and CMJPPO decreased by 0.5%. Conversely, the total distance covered did not present any evidence of a clear relationship with any fatigue-related marker at any time-point. CONCLUSIONS: Running distance above 5.5 m·s-1 represents the most sensitive monitoring variable characterizing biochemical and neuromuscular responses, at least when assessed during the initial 24 h (not at 48 h/72 h) post-match recovery period. In addition, total distance covered is not sensitive enough to inform decision-making during the fatigue monitoring process.

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INTRODUCTION: Speed is an important prerequisite in soccer. Therefore, a large number of tests have been developed aiming to investigate several speed skills relevant to soccer. This systematic review aimed to examine the validity and reliability of speed tests used in adult soccer players. METHODS: A systematic search was performed according to the PRISMA guidelines. Studies were included if they investigated speed tests in adult soccer players and reported validity (construct and criterion) or reliability (intraday and interday) data. The tests were categorized into linear-sprint, repeated-sprint, change-of-direction sprint, agility, and tests incorporating combinations of these skills. RESULTS: In total, 90 studies covering 167 tests were included. Linear-sprint (n = 67) and change-of-direction sprint (n = 60) were studied most often, followed by combinations of the aforementioned (n = 21) and repeated-sprint tests (n = 15). Agility tests were examined fewest (n = 4). Mainly based on construct validity studies, acceptable validity was reported for the majority of the tests in all categories, except for agility tests, where no validity study was identified. Regarding intraday and interday reliability, ICCs>0.75 and CVs<3.0% were evident for most of the tests in all categories. These results applied for total and average times. In contrast, measures representing fatigue such as percent decrement scores indicated inconsistent validity findings. Regarding reliability, ICCs were 0.11-0.49 and CVs were 16.8-51.0%. CONCLUSION: Except for agility tests, several tests for all categories with acceptable levels of validity and high levels of reliability for adult soccer players are available. Caution should be given when interpreting fatigue measures, e.g., percent decrement scores. Given the lack of accepted gold-standard tests for each category, researchers and practitioners may base their test selection on the broad database provided in this systematic review. Future research should pay attention to the criterion validity examining the relationship between test results and match parameters as well as to the development and evaluation of soccer-specific agility tests.

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Jalilvand, F, Banoocy, NK, Rumpf, MC, and Lockie, RG. Relationship between body mass, peak power, and power-to-body mass ratio on sprint velocity and momentum in high-school football players. J Strength Cond Res 33(7): 1871-1877, 2019-The ability to rapidly shift one's body mass horizontally or vertically is common within American football irrespective of field position, and the capacity to generate power is a favorable physical quality. This requires analysis in high-school football players, especially considering the body mass disparities that exist in this population. Sixteen high-school players (7 backs and 9 linemen) completed the vertical jump (VJ) to determine jump height, peak anaerobic power measured in watts (PAPw), and power-to-body mass ratio (P:BM), and a 36.58-m sprint (0-4.57, 0-9.14, and 0-36.58-m intervals) to determine sprint velocity and momentum. Independent-samples t-tests (p < 0.05) determined differences in these variables between the backs and linemen. Pearson's correlations (r; p < 0.05) computed relationships between body mass, VJ height, PAPw, P:BM, with 36.58-m sprint velocity and momentum on the pooled data. Linemen were heavier, and slower in the 36.58-m sprint, but had greater PAPw and sprint momentum compared with backs. Body mass exhibited negative relationships to velocity across all sprint intervals (r = -0.55 to 0.70), and positive relationships with momentum across all intervals (r = 0.95-0.96). The VJ correlated with sprint velocity across all intervals (r = 0.51-0.83), but not momentum. PAPw was positively correlated with body mass and momentum across all intervals (r = 0.77-0.85), but not velocity. There were significant correlations between P:BM with velocity (r = 0.51-0.85) and momentum (r = -0.53-0.62) across all intervals. Heavier high-school players could focus on improving P:BM to positively influence jumping ability and sprint velocity.

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OBJECTIVES: This study investigated the effects of a previously recommended dose of sprint training (ST) in young male soccer players of differing maturity status. DESIGN: Quasi-experimental design. METHODS: Male soccer players from two professional academies were divided into Pre-PHV (Training: n=12; Control: n=13) and Mid-PHV (Training: n=7; Control=10) groups. The training groups completed 16 sprints of 20m with 90s recovery, once per week for 8weeks. RESULTS: Between-group effect sizes (ES) were substantially larger in Pre-PHV (10m [1.54, CI: 0.74-2.23]; 20m [1.49, CI: 0.75-2.23]; 5-10-5 [0.92, CI: 0.23-1.61]) than in Mid-PHV (10m [-0.00, CI: -0.81 to 0.81]; 20m [-0.12, CI: -0.93 to 0.69]; 5-10-5 [-0.41, CI: -1.22 to 0.41]). Within-group effects demonstrated a similar, though less accentuated, trend which revealed ST to be effective in both Pre-PHV (10m [0.44, CI: -0.24 to 1.12]; 20m [0.45, CI: -0.23 to 1.13]; 5-10-5 [0.69, CI: 0.00-1.38]) and Mid-PHV (10m [0.51, CI: -0.38 to 1.40]; 20m [0.33, CI: -0.56 to 1.21]; 5-10-5 [0.43, CI: -0.46 to 1.32]). CONCLUSIONS: ST, in the amount of 16 sprints over 20m with a 90s rest, may be more effective in Pre-PHV youths than in Mid-PHV youths.

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BACKGROUND: The purpose of the present study was to investigate the technical and physical performance parameters that distinguish between teams winning and losing matches in the 2014 FIFA World Cup Brazil. METHODS: Data were derived from the FIFA website and from live-statistics provided during each game of the world cup. Twelve physical (such as total distance covered in meters (TD), TD in distinct locomotor categories: low-intensity running (LIR; <11 km/h), moderate-intensity running (MIR; 11 to 14 km/h) and high-intensity-running (HIR; >14 km/h)) and 21 technical parameters (total passes, short-, medium- and long-distance passes, total pass completion rate, dangerous attacks, attacking attempts, delivery in penalty area, ball possession, goals, goals from set-pieces, goals per shot on goal, defending saves, shots, shots on goal, shot accuracy, set-pieces, crosses, corners, clearances, yellow cards) were analyzed. Forty-two games in which a winner and consequently a loser were presented after 90 minutes of game time were investigated with independent t-tests. A binary-logistic regression was utilized to investigate whether the significant variables predicted success of the winning teams. RESULTS: The winning teams scored significantly (P<0.05) greater amount of goals, goals per set-pieces, goals per shots on goals, shots on goal and shot accuracy and received significantly lower yellow cards. The binary-logistic regression utilized showed that shot accuracy was the best predictor for success. The physical parameters did not differ between teams winning and losing a match. CONCLUSIONS: Technical performance related to goal scoring parameters play a decisive role in World Cup games. Furthermore, scoring efficacy from open-play as well as from set-pieces are crucial to win matches in a World Cup tournament. At this level, physical performance was not the factor to discriminate between winners and losers.

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The purpose of this study is to identify several responsible parameters for back pain (BP) in youth soccer players to create a risk assessment tool for early prevention. An iPad-based survey was used to screen for parameters in a cross-sectional study. This questionnaire includes items regarding anthropometric data, training habits and sports injuries and was put into practice with 1110 athletes. Sex (odds ratio (OR): 1.84), age group (1.48) and playing surface (1.56) were significantly associated with BP. A history of injuries especially to the spine and hip/groin increased the likelihood for evolving recurrent BP (1.74/1.40). Overall 15 factors seem to influence the appearance of pain and were integrated into a feasible nomogram. The nomogram provides a practical tool to identify the risks of developing BP for youth soccer players. Although most factors we identified are non-modifiable, this method allows to rank the importance of factors and especially their prevention treatments for athletes.

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Linear sprinting speed is an essential physical quality for many athletes. There are a number of different training modalities that can be used to improve sprint performance. Strength and conditioning coaches must select the most appropriate modalities for their athletes, taking into consideration the sprint distances that typically occur during competition. The study purpose was to perform a brief review as to the effect of specific (free sprinting; resisted sprinting by sleds, bands, or incline running; assisted sprinting with a towing device or a downhill slope), nonspecific (resistance and plyometric training), and combined (a combination of specific and nonspecific) training methods on different sprint distances (0-10, 0-20, 0-30, and 31+ m). A total of 48 studies fulfilled the inclusion criteria, resulting in 1,485 subjects from a range of athletic backgrounds. The training effects associated with specific sprint training were classified as moderate (effect size [ES] = -1.00; %change = -3.23). Generally, the effect of specific sprint training tended to decrease with distance, although the largest training effects were observed for the 31+ m distance. The greatest training effects (ES = -0.43; %change = -1.65) of nonspecific training were observed for the 31+ m distance. The combined training revealed greatest effects (ES = -0.59; %change = -2.81) for the 0-10 m distance. After this review, specific sprint training methods seem the most beneficial over the investigated distances. However, the implementation of nonspecific training methods (e.g., strength and power training) could also benefit speed and athletic performance.

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Sprinting is an important physical capacity and the development of sprint ability can take place throughout the athlete's growth. The purpose of this study therefore was to determine if the kinematics and kinetics associated with maximum sprint velocity differs in male youth participants of different maturity status (pre, mid- and postpeak height velocity (PHV)) and if maximum sprint velocity is determined by age, maturity or individual body size measurement. Participants (n = 74) sprinted over 30 meters on a nonmotorized treadmill and the fastest four consecutive steps were analyzed. Pre-PHV participants were found to differ significantly (p < .05) to mid- and post-PHV participants in speed, step length, step frequency, vertical and horizontal force, and horizontal power (~8-78%). However, only relative vertical force and speed differed significantly between mid and post-PHV groups. The greatest average percent change in kinetics and kinematics was observed from pre- to mid-PHV (37.8%) compared with mid- to post- PHV groups (11.6%). When maturity offset was entered as a covariate, there was no significant difference in velocity between the three groups. However, all groups were significantly different from each other when age was chosen as the covariate. The two best predictors of maximal velocity within each maturity group were power and horizontal force (R2 = 97-99%) indicating the importance of horizontal force application while sprinting. Finally, maturity explained 83% of maximal velocity across all groups.

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Resisted sled towing is a popular and efficient training method to improve sprint performance in adults, however, has not been utilised in youth populations. The purpose therefore was to investigate the effect of resisted sled towing training on the kinematics and kinetics of maximal sprint velocity in youth of different maturation status. Pre- and post-intervention 30 metre sprint performance of 32 children, 18 pre-peak height velocity (PHV) and 14 mid-/post-PHV, were tested on a non-motorised treadmill. The 6-week intervention consisted of ∼12 sessions for pre-PHV and 14 for mid-/post-PHV of resisted sled towing training with each sessions comprised of 8-10 sprints covering 15-30 metres with a load of 2.5, 5, 7.5 or 10% body mass. Pre-PHV participants did not improve sprint performance, while the mid-/post-PHV participants had significant (P < 0.05) reductions (percent change, effect size) in sprint time (-5.76, -0.74), relative leg stiffness (-45.0, -2.16) and relative vertical stiffness (-17.4, -0.76) and a significant increase in average velocity (5.99, 0.76), average step rate (5.65, 0.53), average power (6.36, 0.31), peak horizontal force (9.70, 0.72), average relative vertical forces (3.45, 1.70) and vertical displacement (14.6, 1.46). It seems that sled towing may be a more suitable training method in mid-/post-PHV athletes to improve 30 metre sprint performance.

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The purpose of this study was to investigate the effect of 4 different step detection thresholds (10, 15, 20, and 30% body mass [BM]) on the kinetics and kinematics of a youth population sprinting on a Woodway nonmotorized treadmill (NMT). A total of 16 male youth athletes sprinted 30 m from a split start position. Of the 15 variables measured, significant differences (p ≤ 0.05) were found in the measurement of 5 kinematic (step length, vertical displacement, contact time, eccentric, and concentric time) and 2 kinetic (vertical and leg stiffness) variables between the 10 vs. 20 and 30% BM step detection thresholds. Contact time was also significantly different (12%) between 15 vs. 30% BM step detection thresholds. In terms of reliability, the 15 and 30% BM step detection thresholds were found the most stable across all variables (average coefficient of variation ∼6.0%). Given this information, a step detection threshold of 15% BM is recommended for quantifying kinematic and kinetic variables on a NMT, as this threshold seems to account for signal variability appropriately without compromising reliability.

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The purpose of this study was to examine sex-related differences in explosive actions during late childhood, while accounting for body size and maturity, and determine the predictive model responsible for performance. Sixty-eight boys (11.0 ± 1.1 years) and 45 girls (11.3 ± 0.9 years) performed a vertical and horizontal jump, 30-m sprint, and change of direction (COD) time trial. After allometric analysis, a common sex scaling factor of body mass was used for vertical (b = 1.02) and horizontal (b = 0.97) power. No significant sex difference in relative leg power was found before and after controlling for maturity status. Gender differences in 10 m, the Zigzag section, and flying 10 m of the COD task were found significant once adjusted for maturity (p ≤ 0.05). However, boys performed better than girls in 20- and 30-m sprint and the COD time trial regardless of maturity status (p ≤ 0.05). Reduced endomorphy in boys was the best predictor of explosive actions (R = 7-22%), whereas female performance was best explained by mass and maturity status (R = 15-19%). Jump power-specific allometric scaling factors need to be determined to account for body size. A training emphasis on sprinting and COD at a younger age in girls compared with boys is recommended because of their earlier onset of puberty and reduced natural ability in these tasks. Somatotype, age, maturity, and body mass should be monitored during the development of youth athletes to better understand explosive performance.

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OBJECTIVES: A possible injury risk factor is limb asymmetry, which may differ across maturation given the adult growth spurt. The aim of this study is to quantify the magnitude of asymmetry in a number of kinetic variables during a running task in male youth of different maturity status. DESIGN: Quantitative observational laboratory study. SETTING: Sports performance laboratory. PARTICIPANTS: Non-injured youth athletes in pre-, mid-, and post-pubescent status. MAIN OUTCOME MEASURES: Inter-limb leg asymmetries whilst sprinting on a non-motorized treadmill. Percent asymmetry was defined as: (Left leg - right leg)/right leg*100 = %asymmetry. RESULTS: Horizontal force presented limb asymmetries of 15.4, 14.8 and 14.7% for the pre-, mid- and post-PHV group respectively. Values for vertical force were higher (18.1, 20.2 and 20.8% respectively). Power asymmetries were 14.9, 15.8, and 15.5% respectively and work asymmetries were significant higher in pre-PHV participants (26.4%) compared to mid- (14.7%) and post-PHV (17.3%) participants. CONCLUSIONS: As the population in this study was characterized as non-injured, asymmetries of 15-20% appeared typical during a running task in developmental athletes.

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The purpose of this study was to investigate whether vertical and leg stiffness, and stretch-shortening cycle (SSC) ability differed in developing athletes of various maturity status during maximal sprint running. Seventy-four male participants between 8 and 16 years of age were categorized into pre-, mid- or post-peak height velocity (PHV) and sprinted for 30 meters on a non-motorized treadmill. Dimensionless vertical stiffness increased significantly (p<.05) from pre-, to mid- and post-PHV state, while dimensionless leg stiffness was significantly higher in post- compared to mid- (18.4%) and pre-PHV participants (44.5%). Eccentric power was significantly lower in pre- compared to the mid- and post-PHV participants. Concentric power increased from pre- to mid- and post-PHV state. An analysis of covariance revealed no significant differences between all groups in dimensionless vertical and leg stiffness, eccentric and concentric time and power when controlling for years from PHV (maturation). Eccentric or concentric power, were found to be the best predictors of maximum velocity across all maturation groups (r2=.37-.68). It seems that maturation affects the ability to absorb and produce power and furthermore these variables are important predictors of maximal running velocity.

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The primary purpose of this paper was to provide insight into the effect of different training methods on sprinting time in male youth aged 8-18 years. Specific and nonspecific training methods were identified, the participants of the five teen studies categorized into pre, mid- and postpeak height velocity and effect sizes and percent changes calculated for each training method were appropriate. Plyometric training had the most effect on sprint times in pre- and midpeak height velocity participants, while combined training methods were the most efficient in postpeak height velocity participants. However, it is difficult to quantify the effects of different training methods due to the limited knowledge in this area e.g., resisted training on pre-PHV participants. Furthermore, it may be worthwhile to investigate additional variables (i.e., stride length, stride frequency, horizontal force), to better determine effect of training methods in different maturity statuses, the development of sprinting and possible stages where individual development can be optimized by training.

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The primary purpose of this paper was to provide insight into the methodological issues and associated reliability of assessments used to quantify running sprint ability in youth athletes aged 8-18 years. Over-ground sprinting was the most reliable and common used choice of assessment to measure sprint performance of youth. In addition, the performance data of those athletes over distances ranging from 5 to 40 meters was collated from 34 published articles and tabulated with regards to the athlete's chronological age. Torque or nonmotorized treadmills have been used to quantify sprint performance in youth with acceptable reliability, this technology providing deeper insight into sprint kinetics and kinematics; however there is limited performance data on youth using the torque and the nonmotorized treadmill. It is suggested that future research should use this technology in youth to better understand changes associated with growth, maturation and training.

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