Michael C. Rumpf

Injury Incidence, Body Site, and Severity in Soccer Players Aged 6–18 Years: Implications for Injury Prevention

INJURY INCIDENCE DATA FOR YOUTH PARTICIPANTS IN SOCCER HAVE BEEN COLLATED AND SUMMARIZED. SUCH INFORMATION SHOULD FORM A BASIS FOR INJURY PREVENTION PRACTICES. PLAYER CONTACT ACCOUNTS FOR MOST INJURIES (40–66%), WHEREAS THE LOWER EXTREMITIES ARE CONSIDERED THE MOST VULNERABLE INJURY SITE IN THE BODY (70%). STRAINS (24%), SPRAINS (31%), AND CONTUSIONS (20%) ACCOUNT FOR 75% OF ALL INJURIES REPORTED THROUGHOUT THE INCLUDED LITERATURE. THESE SOFT TISSUE INJURIES RESULT IN MINOR (1–3 DAYS, 18%), MILD (3–7 DAYS, 36%), AND MODERATE (>1 WEEK, 30%) RECOVERY DURATIONS. SPECIFIC CONSIDERATIONS FOR INJURY PREVENTION PROGRAMS ARE PRESENTED.

Effect of Different Sprint Training Methods on Sprint Performance Over Various Distances: A Brief Review.

Abstract Rumpf, MC, Lockie, RG, Cronin, JB, and Jalilvand, F. Effect of different sprint training methods on sprint performance over various distances: a brief review. J Strength Cond Res 30(6): 1767–1785, 2016—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.

Vertical and leg stiffness and stretch-shortening cycle changes across maturation during maximal sprint running

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.

The effect of resisted sprint training on maximum sprint kinetics and kinematics in youth

Abstract 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.

Sex-related differences in explosive actions during late childhood

Abstract Meylan, CMP, Cronin, JB, Oliver, JL, and Rumpf, MC. Sex-related differences in explosive actions during late childhood. J Strength Cond Res 28(8): 2097–2104, 2014—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 (R2 = 7–22%), whereas female performance was best explained by mass and maturity status (R2 = 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.

Kinematics and Kinetics of Maximum Running Speed in Youth Across Maturity

Sprinting is an important physical capacity and the development of sprint ability can take place throughout the athletes 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.

Effect of Four Different Step Detection Thresholds on Nonmotorized Treadmill Sprint Measurement

Abstract Cronin, JB and Rumpf, MC. Effect of four different step detection thresholds on nonmotorized treadmill sprint measurement. J Strength Cond Res 28(10): 2996–3000, 2014—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.

Training Profiles and Motivation of Male and Female Youth Soccer Players

The objective of this study was to investigate training profiles and motivation of male and female youth soccer players in different age groups and levels of play. A total of 1075 youth soccer players (U15-U19) from the Bavarian Football Association (BFV) in Germany completed a survey which investigated the total hours of training per week, and hours of training spent in endurance, sprint, technical/tactical, strength and other training and warm-up and cool-down procedures. Significant differences (p<0.05) between male high- and low-level players were seen in the amount of hours in sprint, technical/tactical and strength training. These differences were also found on motivation of the players. The total amount of training increased significantly with age in female players, but the only difference between high- and low-level players was in the amount of endurance training in the U19-group and game-related motivation in the U17-group. This study provides guidelines for training load and content in youth soccer players by gender, age and skill levels.

Risk assessment of back pain in youth soccer players

ABSTRACT 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.

Acute Effects of Sled Towing on Sprint Time in Male Youth of Different Maturity Status

The purpose of this study was to investigate the effect of 2.5, 5, 7.5, and 10% body mass load on resisted sled towing 30 meter sprint times in male youth athletes of different maturity status. A total of 35 athletes (19 prepeak-height-velocity (PHV) and 16 mid/post-PHV) sprinted three times in an unloaded and each of the loaded conditions. The pre-PHV athletes were significantly slower (~33%; p < .05) than the more mature athletes across all loads (unloaded, 2.5, 5, 7.5, 10% body mass). Each incremental load (i.e., 2.5% body mass) was found to reduce 30 m sprint times by 3.70% (± 2.59) and 2.45% (± 1.48) for the pre- and mid/post-PHV respectively. The slopes of the pre- (y = 0.09 x + 5.71) and mid/post (y = 0.04 x + 4.38) regression equations were compared and found to be statistically different (p = .004) suggesting that athletes of different maturity status responded differentially to the same relative resisted sprint load. Ten percent body mass load resulted in a reduced sprint time of ~15.8 and ~9.8% for the pre- and mid/post-PHV group, respectively. These results enable predictive equations to be formulated and appropriate resisted sprint loading, based on the intended focus of a session.