Early sprint acceleration in field sport athletes : analysis of technique and training methods

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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- Running speed is an essential component of a range of different sports, such as the different football codes. The ability to accelerate to a high velocity over a short distance is an important skill for these athletic activities, and is a key determinant for success. A number of technique variables contribute to acceleration performance. However, the parameters of technique that contribute most to successful field sport acceleration have not been clearly established. Furthermore, a range of training techniques are used for acceleration development in field sport athletes. Despite their widespread use, the mechanisms by which many of these protocols improve acceleration in field sport athletes are largely unknown. In Study 1, we determined the biomechanical and performance factors that differentiate acceleration ability in field sport athletes. Twenty male, field sport athletes completed sprint tests for biomechanical analysis, and tests of strength, power and leg stiffness over two days. Day 1 consisted of the kinematic analysis of acceleration, with subjects completing 10-metre (m) sprints that were timed and filmed to assess velocity, step length and frequency, and contact and flight time. The analysed intervals were 0-5, 5-10, and 0-10 m. Subjects then completed tests of horizontal (five-bound test: 5BT), vertical (countermovement jump: CMJ), and reactive (reactive strength index: RSI) power. On Day 2, subjects completed a hopping leg stiffness assessment, and 5-m sprints over a force plate for the kinetic analysis. The first and second contacts were recorded to analyse vertical and horizontal force. Absolute and relative strength were assessed by a three-repetition maximum (3RM) squat. Following data collection, subjects were split into faster and slower groups based on 0-10 m velocity. A one-way ANOV A determined variables that significantly (p = .05) distinguished between faster and slower acceleration. All subject data were then pooled for a correlation analysis to determine what factors contributed most to acceleration performance. The results showed that average contact times for the faster group were significantly lower within the 0-5 m interval, where the difference was ~16%, and the 0-10 m interval, where the difference was ~11 %. The faster group had a greater CMJ (14%), and RSI (48%). The relative strength difference approached significance (p = .07). For the 5-10 m interval, correlations between mean CMJ and velocity equalled 0.71. Correlations between mean RSI and 0-5 m velocity equated to 0.65. There were no significant differences in peak force between the groups. However, times to peak vertical and horizontal force during ground contact were lower for the faster group. This was associated with the reduced ground contact times achieved by quicker accelerators, and their ability to generate force in shorter time periods. The ground support force profiles appear to be a useful discriminator of sprint performance in field sport athletes. From these results, it was suggested that acceleration training programs should focus on reducing contact time and increasing ground contact force production. In Study 2, we determined the effects that four common training protocols (free sprint [FST] , weight [WT], plyometrics [PT], and resisted sprint [RST] training) had upon velocity, technique (step length and frequency, contact and flight time, ground contact kinetics), leg stiffness, power, and strength. This study was designed to ascertain the effects of these different protocols on the afore-mentioned variables, as opposed to directly comparing the effectiveness of each training modality. As such, the results from this study would determine the specific adaptations caused by each of these protocols. Furthermore, Study 2 would also determine whether these protocols targeted those variables that Study 1 established as being important for acceleration. Thirty-five male, field sport athletes were divided into four training groups (FST = 9; WT= 8; PT= 9; RST = 9) matched for 10-m velocity. The testing battery used in Study 1 was also used here pre- and post-training. 10-m sprints were added to the kinetic analysis to determine the force characteristics of the last contact in a 10-m sprint. Training involved two one-hour sessions a week for six weeks. Paired samples t-tests found significant (p ~ .01 and .05) within-group changes following the training period. After training, each group increased 0-5 and 0-10 m velocity by 9-10%. The WT and PT groups increased 5-10 m velocity by 10%. The FST group increased step length and contact time, and decreased step frequency. The great increases in step length across all intervals for the FST group made them more susceptible to changes in step frequency. The other groups also increased step length, but step frequency and contact time generally did not significantly change. Protocols that provide a greater overload on the athlete (e.g. weights, plyometrics, and resisted sprinting) may allow a greater maintenance of contact time and step frequency. All groups exhibited similar ground kinetics adaptations. This included reduced time to peak braking and propulsive force for the first contact of the 5-m sprint, and the last contact of the 10-m sprint. This is indicative of an improvement in ground contact efficiency. The FST group improved horizontal and reactive power, while the PT and RST groups improved reactive power. All groups increased absolute and relative strength, although the WT group had the greatest nominal percentage increase (~15%) for both strength measures. With correct administration, all protocols can improve field sport acceleration. This occurs primarily through step length development and support efficiency. Step length development occurs principally through improved horizontal and reactive power after free sprint training, improved reactive power after plyometrics and resisted sprint training, and improved strength after weight training. To summarise, faster acceleration for field sport athletes involves higher step frequency and lower contact times, and greater efficiency of force production during ground support. Faster field sport athletes also have greater vertical and reactive power, and relative strength. Regarding training for acceleration in field sport athletes, free sprint, weights, plyometrics, and resisted sprint training can all improve acceleration velocity, primarily through step length development. This increase in step length occurs predominantly through improved horizontal and reactive power after free sprint training; reactive power after plyometrics and resisted sprint training; and strength after weight training. Future research should dete1mine the effects of combinations of these training protocols on field sport athletes, as well as evaluation of training protocols designed to improve step frequency during acceleration.
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