The Effects of Strength and Plyometric Training on Sprinting Kinetics in Young Female Athletes
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Sprinting speed is a fundamental motor skill in many sports. The ability to move over short distances can significantly impact the outcome of a game. The natural development of sprinting is similar in boys and girls during the first decade of life. However, due to changes in hormonal levels during puberty the development of kinetic and kinematic variables associated with sprinting may be affected in young females compared to their male counterparts. It is believed that progressive strength and plyometric training can positively influence sprinting performance in youth. Previously researchers have investigated sprinting kinetics, kinematics and the effects of strength and plyometric training on sprinting performance in young males. However, there is a paucity of research in young females. Therefore, the purpose of this thesis was to investigate the kinetics and kinematics of sprinting speed in mid and post peak height velocity (PHV) females and further investigate the effects of strength and plyometric training on sprinting speed in post PHV female athletes. Chapter 1 serves to provide the background, purpose, originality and the structure of the thesis. Chapter 2 reviewed natural development of sprinting speed in the youth population and informed that there is a paucity of research investigating sprinting kinetics and kinematics across maturation in young females. Chapter 3 reviewed existing research on the effects of strength (ST) and plyometric training (PT) on sprinting speed in the youth population, particularly young females. This chapter reported that there is limited research investigating the effects of ST and PT on sprinting speed in young females and no study to date has compared ST vs. PT on sprinting speed in young females. Chapter 4 measured the intraday (n=29) and inter-day reliability (n=14) of sprinting kinetics in young females using a radar gun since no previous reliability study has been conducted in this population. Sprinting kinetic variables including Force (Fo), theoretical velocity (Vo), maximal velocity (Vmax), maximal power (Pmax), 10, 20, 30 m split times using the radar gun showed acceptable reliability with intraclass correlation coefficient (ICC) ranging 0.74-0.98 and coefficient of variation (CV) ranging from 1.70-12.70% for both intra and inter-day analysis. Chapter 5 investigated the kinetics and kinematics of sprinting speed in mid (n=11) and post (n=21) PHV female athletes and reported that Fo, Vo, Vmax, Pmax and step length were significantly higher in post PHV girls than mid PHV girls (p<0.05). In addition, univariate regression analysis reported that the predictors of Vmax over 15 m were contact time, Pmax, step frequency, and step length. Whereas the predictors of velocity over 30 m were contact time, leg length and Pmax, with contact time being the strongest predictor for both 15 and 30 m. Chapter 6 investigated the effects of ST vs. PT on sprinting speed in post PHV female athletes (ST: n=16, PT: n=21, CON: n=15). It is reported that both the ST and PT groups significantly improved all performance variables (p<0.05). The ST significantly improved 10 m split time (6.76%; Cohen’s d=0.66, Hedge’s g=0.65) and Fo (16.36%; d=0.67, g=0.65) whereas the PT group significantly improved Vmax (4.91%; d=0.51, g=0.50), Fo (11.12%; d=0.40, g=0.40) and Pmax (7.88%; d=0.26, g=0.26). Post hoc analysis showed that both ST and PT groups had significantly higher post scores for Vmax, 30, 20,10 m split times and single-leg horizontal jumps (both sides) compared to the Control (CON) (p<0.05). There were no significant differences in post scores for any variable between the intervention groups. Chapter 7 investigated the effects of horizontal (HT) and vertical plyometric training (VT) on sprinting speed in post PHV female athletes (HT: n=10, VT: n=11, CON: n=9) and reported that following VT, participants showed significant improvements in Vo, Vmax, 10, 20 and 30 m sprint time with effect size (ES) ranging from (d=0.42, g=0.40 to d= 0.52, g= 0.50; p<0.05) but not Fo and Pmax whereas following HT, participants significantly improved all sprinting variables with greater effects (d= 0.49, g=0.47 to d=1.36, g=1.30; p<0.05) than the VT group. Post hoc analysis showed that the VT group had significantly higher post scores compared to the CON group for Vo, Vmax, vertical jump (VJ), and broad jump (BJ) whereas the HT group had significantly higher post scores for 20 m split time and BJ compared to the CON group (p<0.05). There were no significant differences in post scores for any variable between the intervention groups. Chapter 8 provided an overall summary which suggested that ST, HT and VT are effective means of improving sprinting kinetics in post PHV female athletes. Finally, chapter 9 provided practical suggestions in designing ST and PT programmes to develop sprinting speed in young females based on the findings of this thesis (chapter 6 and 7), and the two narrative reviews (chapters 2 and 3) respectively.