The effect of unsupportive and supportive footwear on children’s multi-segment foot dynamics during gait Brian Angus Chard B.Sc. (Podiatry), FAAPSM A thesis submitted for the fulfilment of the degree of Doctor of Philosophy Discipline of Exercise and Sport Science, Faculty of Health Sciences The University of Sydney 2018 Candidate’s Certificate I, Brian Angus Chard, hereby declare that this thesis is my own work and does not, to the best of my knowledge, contain material from any other source unless due acknowledgement is made. The thesis was completed under the guidelines set out by The University’s Faculty of Health Sciences, for the degree of Doctorate of Philosophy and has not been submitted for a degree or diploma at any other academic institution. I, Brian Angus Chard, hereby declare that I was the principle researcher of all work included in this thesis, including work published with multiple authors. An author contribution statement for published work is detailed at the beginning of each relevant chapter. Supervisor’s Certificate This is to certify that the thesis titled, ‘The effect of unsupportive and supportive footwear on children’s multi-segment foot dynamics’ submitted by Brian Angus Chard in fulfilment of the requirements for the degree of Doctor of Philosophy is in a form ready for examination. Professor Richard Smith Discipline of Exercise and Sport Science, Faculty of Health Sciences The University of Sydney September 2017 Abstract Footwear is considered necessary apparel for children’s foot comfort and protection. In Australia, flip-flops (thongs) are an inexpensive and popular footwear style. Despite their popularity among children, strong clinical opinion endures of the potential deleterious effect of thong footwear on developing feet. This anecdotal clinical opinion persists, despite the absence of scientific investigation of the gait-altering effects thongs have on children’s foot motions. On the contrary, thongs may be beneficial for children’s developing feet due to the footwear’s flexible and unrestrictive nature, as children who mature within habitually barefoot communities are observed to develop stronger and healthier feet. The aim of this thesis is to provide clinicians with a firm evidence base on which they can discuss this topic with concerned parents and guardians, while considering the alternative supportive shoe. The background introduces the reader to the established principle that supports the notion that ‘barefoot is best’, outlining the gait-altering effect of footwear, existing knowledge of the effect of thong wear in the context of the developing nature of human ambulation and the physiological basis for children’s foot maturation (see Chapter 1). The method used to determine and describe the effect of footwear on children’s lower limb dynamics is outlined (see Chapter 2). Thongs resulted in increased ankle dorsiflexion during the contact phase of gait by 10.9° while walking and by 8.1° while jogging; increased midfoot plantarflexion during mid-stance by 5.0° while jogging and during propulsion by 6.7° while walking and by 5.4° while jogging; increased midfoot inversion during contact by 3.8° while jogging and reduced hallux dorsiflexion during walking, 10 per cent prior to heel strike by 6.5° at heel strike by 4.9° and 10 per cent post toe-off by 10.7° (see Chapter 3). Sudden directional change during a simulated sidestep, during the stance phase of gait while wearing thongs, resulted in reduced ankle transverse plane motion by 2.0° (22%), while supportive shoes reduced midfoot sagittal-plane motion by 13.1° (45%) and midfoot frontal plane motion by 3.2° (32%). Both thongs and supportive shoes reduced hallux motion by 5° (21%) and 10.4° (44%), respectively (see Chapter 4). In the sagittal plane, wearing supportive shoes reduced midfoot peak plantarflexing angular velocity by 15ᵒ/sec (60%), plantarflexion moment by 0.087Nm/kg (9%), power generation by 4.6W/kg (25%) and increased ankle plantarflexion moment by 4.1Nm/Kg (364%). In the frontal plane, midfoot peak everting angular velocity was reduced by 5.1ᵒ/sec (67%), as was ankle peak inverting angular velocity by 2.6ᵒ/sec (27%). iv In the transverse plane, midfoot peak abducting velocity was reduced by 2.2ᵒ/sec (31%) and peak ankle abduction moment increased by 0.14Nm/kg (90%) (see Chapter 5). The thesis background presented in Chapter 1 provides a basis of understanding for clinicians and scientists to consider the implications footwear may have on children’s developing feet and gait. The methodological approach outlined in Chapter 2 outlines the approach required to determine the effect of footwear on children’s feet using stereophotogrammetry. The three studies presented in this thesis (see Chapters 3, 4 and 5) provide significant insight into the complex mechanisms children engage to wear thongs and the alternative supportive shoe. Ankle dorsiflexion during the contact phase of walking and jogging, combined with reduced hallux dorsiflexion during walking, suggests a mechanism to retain the thong during weight acceptance. Greater midfoot plantarflexion throughout mid-stance while walking and throughout mid-stance and propulsion while jogging indicate a gripping action to sustain the thong during stance. Contrary to anecdotal reports, thongs carry a greater risk of injury than shoes that are not supported by the kinematic results reported in this study, as barefoot motions were unaffected by thongs during the simulated sidestep. The understanding of the sagittal-plane midfoot splinting effect of supportive shoes was reinforced to include a splinting effect in the frontal and transverse planes while sidestepping. Thongs had a minimal effect on barefoot dynamics, while supportive shoes limited midfoot power generation with a corresponding increase in ankle power generation. Although these compensations exist, the overall findings suggest that foot motion when wearing thongs may be more replicable of barefoot motion than originally thought. In terms of foot arch development, thongs may be more beneficial than supportive shoes, due to the minimal alterations to barefoot motions when they are worn. The reported midfoot plantarflexion required to grip the thong may be beneficial to children’s foot arch strengthening and overall foot development. Conversely, supportive shoes, although they have the necessary protective features, have been shown to inhibit midfoot and hallux motions with a compensatory increase in ankle motions. v Acknowledgements I would like to thank my supervisor, Professor Richard Smith, who saw potential in me and invited me to join Sydney University’s Footwear Research Group. Professor Smith has guided me tirelessly throughout the research process, with an unwavering desire to challenge our understanding. To my associate supervisor, Dr Andrew Greene, thank you for repeatedly picking me up and dusting me off with solid intellectual guidance and ever-positive feedback. To my associate supervisor, Professor Joshua Burns, I have been honoured by your guidance as a colleague, clinician and researcher who has championed modern Australian podiatry. I would like to thank my other associate supervisors, Professor Benedict Vanwanseele and Dr Adrienne Hunt, for their support, encouragement and assistance in producing this robust and valuable contribution to lower limb health. I would like to thank my participants and the parents of the children who participated in the studies presented in my thesis. Without their enthusiasm and unwavering interest during the monotonous hours of testing, this thesis would not have been possible. Thank you to my professional podiatry colleagues, with whom I have practiced in the time it has taken to bring this thesis together and, especially, my past practice manager and friend, Amanda Gurney/Azzopardi, who assisted me in managing the constraints of a busy patient load and podiatry practice. A special thanks to Dr Caleb Wegener, whose guidance in the early days showed a maturity beyond his years with his message to maintain focus and avoid the daily distractions faced as a practicing clinician. I dedicate this thesis to my mother, Elizabeth Chard (podiatrist), whose passion and drive for helping people with foot and leg pain was reinforced at every dinner table conversation and is seemingly endless. To my father, Brian Chard, my personal cheer squad, who has always put his family before himself and unquestionably raced me from one sport training to another and from game to game, often at obscene times, all the while cheering louder than anyone else. Capstone Editing provided copyediting and proofreading services, according to the guidelines laid out in the university-endorsed national ‘Guidelines for Editing Research Theses’. Finally, to my wife, Sarah Murray, I love you and am truly excited with the thought of living the rest of my life with you. vi The boat he was on was running down sea when she took ‘one wicked sea from hell’. The stern lifted, the bow dropped, and they started surfing down the face of the wave. When they got to the bottom there was nowhere to go but down, and the crest of the breaking wave drove them like a piling. Chris looked out the porthole, and all he could see was black. If you look out the porthole and see white-water, you're still near the surface and relatively safe. If you see green water, at least you're in the body of the wave. If you see blackwater, you're a submarine. ‘I felt the boat come to a complete stop,’ says Chris. ‘I thought, “My god we’re going