The Immediate Effect of Foot Orthoses on Subtalar Joint Mechanics and Energetics

ABSTRACTPurposeFoot orthoses maybe used in the management of musculoskeletal disorders related to abnormal subtalar joint (STJ) pronation. However, the precise mechanical benefits of foot orthoses for preventing injuries associated with the STJ are not well understood. The aim of this study was to investigate the immediate effect of foot orthoses on the energy absorption requirements of the STJ and subsequently tibialis posterior (TP) muscle function.MethodsEighteen asymptomatic subjects with a pes planus foot posture were prescribed custom-made foot orthoses made from a plaster cast impression. Participants walked at preferred and fast velocities barefoot, with athletic footwear and with athletic footwear plus orthoses, as three-dimensional motion capture, force data and intramuscular electromyography of the TP muscle were simultaneously collected. Statistical parametric mapping was used to identify time periods across the stride cycle during which footwear with foot orthoses significantly differed to barefoot and footwear only.ResultsDuring early stance, footwear alone and footwear with orthoses significantly reduced TP muscle activation (1 - 12 %), supination moments (3 - 21 %) and energy absorption (5 - 12 %) at the STJ, but had no effect on STJ pronation displacement.ConclusionThe changes in TP muscle activation and STJ energy absorption were primarily attributed to footwear as the addition of foot orthoses provided little additional effect. We speculate that these results are most likely a result of the compliant material properties of footwear. These results suggest that athletic footwear may be sufficient to absorb energy in the frontal plane and potentially reducing any benefit associated with the addition of foot orthoses. Purpose Foot orthoses maybe used in the management of musculoskeletal disorders related to abnormal subtalar joint (STJ) pronation. However, the precise mechanical benefits of foot orthoses for preventing injuries associated with the STJ are not well understood. The aim of this study was to investigate the immediate effect of foot orthoses on the energy absorption requirements of the STJ and subsequently tibialis posterior (TP) muscle function. Methods Eighteen asymptomatic subjects with a pes planus foot posture were prescribed custom-made foot orthoses made from a plaster cast impression. Participants walked at preferred and fast velocities barefoot, with athletic footwear and with athletic footwear plus orthoses, as three-dimensional motion capture, force data and intramuscular electromyography of the TP muscle were simultaneously collected. Statistical parametric mapping was used to identify time periods across the stride cycle during which footwear with foot orthoses significantly differed to barefoot and footwear only. Results During early stance, footwear alone and footwear with orthoses significantly reduced TP muscle activation (1 - 12 %), supination moments (3 - 21 %) and energy absorption (5 - 12 %) at the STJ, but had no effect on STJ pronation displacement. Conclusion The changes in TP muscle activation and STJ energy absorption were primarily attributed to footwear as the addition of foot orthoses provided little additional effect. We speculate that these results are most likely a result of the compliant material properties of footwear. These results suggest that athletic footwear may be sufficient to absorb energy in the frontal plane and potentially reducing any benefit associated with the addition of foot orthoses. Corresponding author: Jayishni Maharaj, School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, 4072, Queensland, Australia. Email address: jayishni.m@uq.edu.au The authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by the ACSM. J.N. Maharaj was supported by a National Health and Medical Research Council postgraduate scholarship, APP1075000. The authors would like to acknowledge Australian Podiatry Education and Research Foundation (APERF) for their financial contribution and ASICS Oceania for providing footwear in kind. The authors declare no conflict of interest. Accepted for Publication: 19 February 2018 © 2018 American College of Sports Medicine

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