Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science (Sports Science)

School

School of Medical and Health Sciences

First Advisor

Professor Ken Nosaka

Second Advisor

Associate Professor Sophia Nimphius

Third Advisor

Professor G Gregory Haff

Abstract

Previous studies on change of direction (COD) have reported that braking is an important factor for COD performance. However, previous studies have focused on the plant step and the penultimate step (PEN), thus little is known about deceleration before these steps. This study compared ground reaction forces (GRF) of two braking steps, the PEN and the step prior to PEN (PEN-1), the entry and exit velocity of the COD, and muscle function measures (leg press and leg curl one-repetition maximum, isometric and isokinetic strength, and drop jump performance) between faster and slower participants for a 90o sidestep cut. This study also examined the associations between the time taken from 1 m before and 1 m after COD (1-1 m COD time), braking GRF during deceleration and muscle function. Twenty-two male recreational athletes from AFL (n = 2), soccer (n = 8), rugby (n = 2), basketball (n = 5), squash (n = 1) and tennis (n = 4), performed a total of six cuts with their dominant (DL) and non-dominant legs (NDL). The faster group (n =10; DL: 0.19 ± 0.02 s, NDL: 0.22 ± 0.02 s) and the slower group (n = 10; DL: 0.24 ± 0.02 s, NDL: 0.31 ± 0.04 s) as well as pooled (n = 20) DL and NDL (DL: 0.21 ± 0.03 s, NDL: 0.26 ± 0.04 s) were used for analyses. Dependent variables between the groups were compared using independent t-tests with sequential Bonferroni corrections to control for type I error. Pearson’s correlation was used to examine the relationship between the 1-1 m COD time and dependent variables. Faster DL COD participants showed significantly greater change in braking impulse from PEN-1 to PEN (-0.50 ± 0.31 vs -0.20 ± 0.15 m⋅s-1, p = 0.027) whereas faster NDL COD participants showed greater isometric knee flexor torque (1.94 ± 0.25 vs 1.63 ± 0.26 Nm⋅kg-1, p = 0.005), isometric extensor torque (3.37 ± 0.42 vs 3.17 ± 0.71 Nm⋅kg-1, p = 0.017) and concentric isokinetic (90o⋅s-1) knee extensor torque (3.02 ± 0.47 vs 2.47 ± 0.39 Nm⋅kg-1, p = 0.03). Pooled DL and NDL comparison revealed significantly higher plant step braking impulse (0.61 ± 0.23 vs 0.47 ± 0.23 m⋅s-1, p = 0.043) and lower propulsive impulse (2.42 ± 0.47 vs 2.77 ± 0.47 m⋅s-1, p = 0.008) during DL COD. Faster NDL COD was associated with greater NDL eccentric knee flexor at 90o⋅s-1 (r = 0.648, p = 0.003), 60 cm drop jump (r = 0.556, p = 0.010), greater NDL isometric knee flexor torque (r = 0.473, p = 0.024) and greater NDL eccentric knee extensor at 90os-1 (r = 0.470, p = 0.041). These results indicate that mechanical factors influencing DL and NDL COD performance were different. In addition, deceleration steps ranged between three to five steps with braking between PEN-1 and PEN resulting in faster DL COD performance. Further studies are is required to examine the deceleration starting at PEN-1 and should consider multifactorial analyses to capture multiple strategies potentially implemented.

Available for download on Saturday, December 19, 2020

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