Year

2010

Degree Name

Doctor of Philosophy

Department

School of Health Sciences

Abstract

BACKGROUND Ankle flexibility defined by passive dorsiflexion ROM and plantar-flexor stiffness, is associated with injury risk, particularly during landing tasks involving rapid dorsiflexion and elongation of the plantar-flexor MTU. However, the biomechanical mechanisms associated with poor ankle flexibility that may be inferred as potentially injurious during landing movements are not thoroughly understood. Furthermore, although dorsiflexion ROM and plantar-flexor stiffness may be affected by training, adaptations reported in the literature have been conflicting and the possible effects of training on landing biomechanics have not been investigated.

THESIS AIM The primary purpose of this thesis was to determine whether variations in ankle dorsiflexion ROM affect ankle biomechanics during a drop landing task and whether these effects were moderated by training that was designed to alter dorsiflexion ROM.

METHODS Using a randomised controlled trial (RCT) study design, ankle flexibility and landing biomechanics were assessed in 48 male volunteers, each assigned to one of three experimental training interventions (stretch, eccentric strength or landing training) or a control group. Results from this RCT were analysed and presented in three main parts, with each part systematically contributing to the primary thesis aim. Part I explored the baseline RCT data to investigate the relationship between dorsiflexion ROM (in weight-bearing and non-weight-bearing) and plantar-flexor stiffness in order to establish whether these measures of ankle flexibility assessed different characteristics (Chapter 2). Part II again explored the baseline RCT data to determine the effect of dorsiflexion ROM and plantar-flexor stiffness on ankle biomechanics and plantar-flexor loading during drop landings (Chapters 3 and 4). Part III then used the whole RCT data set (baseline and post-intervention) to investigate the effects of different training interventions, designed to increase dorsiflexion ROM or take advantage of the concept of training specificity, on flexibility characteristics and ankle biomechanics during drop landings (Chapters 5 and 6).

Baseline and post-intervention assessments included measurements of passive DROM, passive plantar-flexor stiffness and ankle biomechanics during a single-limb drop landing task. Data collection for the outcome variables characterising landing biomechanics included EMG from four shank muscles and three-dimensional kinematics of the foot and shank as participants landed on a force platform. These biomechanical data provided input for inverse dynamic calculations of ankle kinetics and an estimation of Achilles tendon force generated during landing.

MAJOR CONCLUSIONS Passive DROM or passive plantar-flexor stiffness do not affect ankle biomechanics during drop landings. However, relative to the demands of the task, athletes with a low DROM may be absorbing landing loads with their plantar-flexor MTU in a more extended length, thereby exposing them to an increased risk of both acute and repetitive overuse plantar-flexor MTU strain injuries. Long-term static stretch training is recommended, as more effective than eccentric strength or task-specific landing training, in order to increase DROM. Static stretch training may also provide some biomechanical advantages during drop landings, with respect to injury mechanisms, by potentially reducing plantar-flexor MTU strain. Specificity provided by landing training may also offer protection from injury during drop landings by developing more synchronous plantar-flexor muscle activation to control the landing movement and increase the time over which to absorb the potentially injurious loads generated during high impact landing tasks.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.