The effect of foot orthoses on muscle activity and morphology, foot biomechanics and skin sensitivity

Reeves, JE

Abstract

Foot orthoses with a medial wedge or medial arch support are commonly used to treat musculoskeletal pathologies by altering external forces applied to the foot, which could consequently alter internal forces generated by muscles. However, little is known about whether systematic changes in foot orthosis geometry result in systematic changes in activation of lower limb muscles. This PhD investigated the effects of foot orthoses on selected lower limb muscles.
A systematic review was conducted to establish if evidence exists that footwear, foot orthoses and taping alter lower limb muscle activity during walking and running. The review identified some evidence that foot orthoses can decrease activity of tibialis posterior in early stance and possibly increase activity of peroneus longus in mid-late stance, while not altering activity of other lower limb muscles. Findings concerning the peroneus longus were limited by previous reports of the poor reliability of EMG recordings from this muscle. A reliability study was thereafter conducted to demonstrate a reliable protocol for recording EMG from the peroneus longus, using ultrasound guidance and small surface sensors to improve results. This technique was used in the subsequent study on the effect of foot orthoses on lower limb muscle activity.
A study of the immediate effect of foot orthoses was undertaken, with the aim of establishing whether medial heel wedging and increased medial arch height affect EMG of shank muscles and foot and ankle moments/motion. Muscle activity was recorded from 23 healthy participants using surface EMG and fine-wire EMG (tibialis posterior) in combination with kinematic and kinetic data during walking in shoes with four different foot orthoses. Tibialis posterior activity decreased in early stance by 17% (p=0.001) with a Salfordinsole orthosis with an additional 8 mm increase in medial heel wedging and by 14% (p= 0.047) with a Salfordinsole orthosis with both a 6 mm increase in arch height and an 8 mm increase in heel medial wedging. The reduced tibialis posterior activity with medial wedging in combination with reduced external ankle eversion moment provides a possible link between foot orthosis design and biomechanical effect and could be used to inform treatment practice.
Building on the literature review and the results of the immediate effects study, it was hypothesised that altered loading of the foot with long term use of foot orthoses would alter the mechanical work required of internal structures. The purpose of the final study in this PhD was to investigate any effect of using foot orthoses over three months on soft tissue morphology and skin sensitivity. Twenty three healthy participants wore an orthosis that changed peak pressure in the medial arch and the heel by 8%, while nineteen healthy participants continued to wear their convention footwear. There were no changes in skin sensitivity, or the thickness and cross sectional area of intrinsic foot muscles and connective tissue after three months of orthoses use. This finding provides evidence to challenge the view held by some that foot orthoses make muscles smaller (and weaker).

• Thesis Type: Thesis
• Deposit Date: Oct 9, 2019
• Publicly Available Date: Oct 9, 2019