Date of Award

2013

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Exercise and Health Sciences

Faculty

Computing, Health and Science

First Advisor

Professor Robert Newton

Second Advisor

Associate Professor Anthony Blazevich

Third Advisor

Dr Prue Cormie

Abstract

In this thesis great emphasis has been placed on vastus lateralis (VL) muscle-tendon unit (MTU) structure, behaviour/movement and adaptation. Of particular interest was how external loading and movement speed influence these variables. In the first study (Chapter 3) we developed a new methodology by which electromyography (EMG) could be normalised during large range of motion knee extensions. This methodology was then used as part of a larger study, which investigated how external loading influenced the interaction of muscle and tendon (MTU behaviour) during stretch shortening cycle isoinertial knee extensions, and how muscle activity and intrinsic tendon force (Ft) influenced MTU behaviour (Chapter 4). In this study it was observed that as external loading increased the tendon strain decreased despite muscle activity and Ft increasing. It was concluded that the rapid rate of Ft development (RFDt) and speed of movement resulted in an increase in tendon stiffness that was neglected additional strain that is normally associated with increased load/force.

We then investigated how external loading influenced MTU behaviour during parallel depth jump squats (JS-P), which is a more complex but also more commonly performed movement (Chapter 5). Our findings in this study contrasted those of our previous study in that we observed tendon strain increased as external loading increased. Further investigation revealed that while peak Ft increased and movement velocity decreased with increased loading intensity, the RFDt through the tendon did not significantly increase with external loading. In addition, when comparing the results from this study to those of the previous study it was found that the peak RFDt observed during heavy squat jumps was a fraction of the value observed during heavy leg extensions. These results led us to the conclusion that the RFDt that is the primary determinate of MTU behaviour and the influence of loading on MTU behaviour varies between tasks.

In our next study we investigated how speed of movement influences MTU behaviour during parallel depth squatting-type movements (Chapter 6). In this study it was observed that the influence of speed of movement had on MTU behaviour differed between the eccentric and concentric phases. Specifically, it was observed that during initial tendon loading the tendon went through less strain when the movement was performed at faster speeds, however, late in the movement tendon strain increased with increased movement speed. Further investigation revealed that during initial tendon loading RFDt significantly increased with increasing movement speeds, which resulted in the viscoelastic properties of the tendon to predominate the movement. However, late in the movement when relative differences in RFDt were small the tendon behaved as a predominately elastic structure. The results from this study along with the studies prior highlighted that changing either the external load or the speed at which the load it lifted can vastly influence of the VL-MTU behaviour.

In the final study of this thesis we compared the training specific structural and mechanical adaptations to slow-speed, high-load (SHL) squat training to determine how this might differ to relatively fast-speed, light-load (FLL) jump squat training (Chapter 7). In this study we observed that both groups significantly increased their strength, the cross sectional area of their quadriceps muscles, and the fascicle length of their VL. However, only subjects in the SHL group were able to increase the stiffness of their quadriceps tendon and only subjects in the FLL group increased their VL fascicle angle. It is believed that the observed training specific adaptations resulted from previously observed differences in MTU behaviour, intrinsic forces, and muscle activity observed in the previous studies. Because of this it is concluded that intentional manipulation of external load and speed of movement are viable ways to target specific muscular and tendinous adaptations. The results of this thesis has potential practical applications for designing training programs for athletes and sets the stage for further investigation into how these variables can be manipulated for prevention and rehabilitation of musculotendinous injuries.

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