Immediate effect of exercise on mechanical and morphological properties of the human Achilles ...

213 Pages·2016·3.98 MB·English

by  Steven Obst

Immediate effect of exercise on mechanical and morphological
properties of the human Achilles tendon in vivo

Mr Steven John Obst
BHMS, BExSc, BPhty

School of Allied Health Sciences
Griffith Health
Griffith University

Submitted in fulfilment of the requirements of the degree of Doctor of
Philosophy

August 2015

Abstract
The Achilles tendon is the strongest, yet most commonly injured tendon in the human
body. Repeated or sustained loading of the Achilles tendon during exercise could induce
transient changes in gross mechanical and morphological properties that impact on
muscle-tendon performance and tissue homeostasis, and may therefore be important in
the context of tendon injury and adaptation. Characterising the immediate effect of
commonly performed exercise routines on these properties would broaden our
understanding of exercise-induced tendon adaptation and lead to more targeted exercise
interventions. The aim of this thesis was to use freehand three-dimensional ultrasound to
investigate the mechanical and morphological properties of the human Achilles tendon
complex in healthy young adults and characterise the change in these properties
immediately after eccentric exercise. Chapter 3 established that freehand three-
dimensional ultrasound can be used to provide accurate and reliable estimates of free
Achilles tendon morphology in vivo at rest and during a submaximal isometric
contraction. In Chapter 4, three-dimensional ultrasound was used to provide the first in
vivo data that describe the regional three-dimensional morphology and deformation of
the human free Achilles tendon during an isometric plantar flexion muscle contraction.
The results of this study suggest that when lengthened the free Achilles tendon
experiences a complex change in three-dimensional shape that is characterised by an
inverse and proportional biaxial transverse strain and ‘twisting’ of the tendon that peaks
within the mid-portion. Findings from the systematic review in Chapter 5 concluded that
the mechanical and morphological properties of the human Achilles tendon complex are
responsive to acute exercise; however the effects are confined to high intensity and long
duration interventions and appear consistent with cycle and/or time dependent tendon
fatigue. Consistent with these conclusions, Chapter 6 showed that isolated eccentric
exercise induced an immediate increase in length and longitudinal strain of the free
Achilles tendon, with no change in relative stiffness, and no change mechanical
properties of the proximal Achilles tendon or whole Achilles tendon. The changes were
consistent with mechanical creep and indicate that the free Achilles tendon experienced
low level mechanical fatigue in response to the exercise intervention. Chapter 7 revealed
that the changes in free Achilles tendon mechanical behaviour after eccentric exercise
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were coupled to changes in transverse morphology, and characterised by reduced cross-
sectional area strain in the mid-proximal region that was primarily driven by a reduced
anteroposterior strain, with no change in mediolateral strain. The findings of this thesis
highlight the complexity of exercise-induced changes in Achilles tendon mechanical and
morphological properties, the potential vulnerability of the free Achilles tendon to
mechanical fatigue, and the value of freehand three-dimensional ultrasound for
examining regional Achilles tendon properties in vivo.

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Acknowledgements
First and foremost I would like to thank my wife and best friend Sally for her unwavering
support and encouragement throughout my long and almost never-ending university
career. You have been with me every step of the way, and without your support, both
emotionally and particularly financially, this thesis would not have happened. I just hope
now that I can begin to repay my many debts back to you….

To my supervisors, Professor Rod Barrett and Dr Richard Newsham-West, thank you for
allowing me the freedom and confidence to pursue research directions that may not have
always seemed clear at the time, but I hope in the end have been worth the effort. You
have both taught me a tremendous amount about what it takes to conduct and present
research that was both pragmatic by design, but also innovative in its interpretation.
Such a compromise would not have been possible without the freedom you afforded me
during my candidature, as well as an almost unfettered access to your time and brains! I
look forward to working with you both well into the future.

Finally, a hefty thank you must go out to the founding members of the ‘man cave’- David
Graham (aka ‘Gramsy’), David Saxby (aka ‘the great Saxby’) and Hans Kainz (aka ‘the pool
cleaner’). The many, many coffees, and sometimes beers, that were enjoyed over the
years and often coupled to deep and profound discussions about life, research and the
Simpsons, made this journey possible, and more often than not enjoyable. I look forward
to remaining friends and colleagues with you for many years to come.

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Statement of Originality
This work has not been submitted either whole or in part for a degree or diploma at this
or any other institution. This thesis, to the best of my knowledge, does not contain
material previously published or written by another person, unless explicitly
acknowledged in the thesis.

Steven J. Obst (BHMS, BExSc, BPhty)
August 2015

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List of Original Articles
Chapters 3-7 of this thesis are based upon the following published papers, which are co-
authored by other researchers. My contribution to each of co-authored paper is outlined
at the front of each relevant chapter. The bibliographic details for these papers, including
all authors, are:

Chapter 3
OBST, S. J., NEWSHAM-WEST, R. & BARRETT, R. S. 2014. In vivo measurement of human
Achilles tendon morphology using freehand 3-D ultrasound. Ultrasound in Medicine and
Biology, 40, 62-70.

Chapter 4
OBST, S. J., RENAULT, J. B., NEWSHAM-WEST, R. & BARRETT, R. S. 2014. Three-
dimensional deformation and transverse rotation of the human free Achilles tendon in
vivo during isometric plantar flexion contraction. Journal of Applied Physiology 116, 376-
84.

Chapter 5
OBST, S. J., BARRETT, R. S. & NEWSHAM-WEST, R. 2013. The immediate effect of exercise
on Achilles tendon properties: a systematic review. Medicine and Science in Sports and
Exercise, 45, 1534-1544.

Chapter 6
OBST, S. J., NEWSHAM-WEST, R. J. & BARRETT, R. 2015. Changes in Achilles tendon
mechanical properties following eccentric heel drop exercise are specific to the free
tendon. Scandinavian Journal of Medicine and Science in Sports, doi: 10/1111/sms.12466.

Chapter 7
OBST, S. J., NEWSHAM-WEST, R. & BARRETT, R. S. 2015. Three-dimensional morphology
and strain of the human Achilles free tendon immediately following eccentric heel drop
exercise. Journal of Experimental Biology, 218, 3894-3900.
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