An investigation into the relationship between rocker sole designs and alteration to lower limb kinetics, kinematics and muscle function during adult gait

Abstract

Introduction Intermittent claudication (IC) is a condition which affects people with peripheral arterial disease in the lower limbs and causes calf muscle pain and limping due to the lack of blood supply to the gastrocnemius muscle in particular. This limits the distance people with IC (known as claudicants) can walk before having to stop because of the pain. The accepted best treatment currently is enrolment onto supervised exercise regimes, but these provide limited improvement and do not alter their antalgic gait. This study aims to investigate the effect of specific footwear designs on gait and lower limb muscle function with the intention of identifying which features would be recommended for inclusion in footwear designed to relieve their painful symptoms by offloading the calf muscles. Method Fifteen volunteer healthy subjects, age range 20-29 years (mean 25.3 ± 2.73) undertook a series of gait laboratory trials with shoes adapted with specifically-chosen outsole features. High street shoes were adapted with the test conditions which included shoes with five different heel heights (varying from a 1.5cm to 5.5cm heels), two heel profile conditions (curved and semi curved heels), three traditional (angled) rocker soles with varying apex positions (55%, 62.5% and 70% of shoe length) and three with varying apex angles (10, 15, and 20 deg.), plus three with different forepart sole stiffness (solid, semi-flexible and flexible). The baseline shoe was taken as being one with no heel curve, a heel height of 3.5mm, an apex position of 62.5% of shoe length, and apex angle of 15 deg. and a stiff forepart to the shoe. Measurement and comparisons were taken of lower limb kinetics and kinematics (Qualysis, Sweden) plus electromyographical (EMG) activity (Noraxon USA) of medial gastrocnemius, soleus, tibialis anterior, rectus femoris and biceps femoris during walking trials where the walking speed was controlled using timing gaits. Data were analysed using Visual3D and OpenSim software to enable interpretation of EMG activity to enable calculation of lower limb muscle function during gait. Results Changes from the baseline shoe were taken as being at a level of significance of p<0.05. The most effective footwear test condition in regards to offloading of the calf muscles compared to the control shoe was that with a 4.5cm heel, a 55% of shoe length apex position, and a 20° rocker apex angle; which demonstrated significant offloading to the calf muscles. The 55% apex position had a significant offloading influence on the calf muscles whilst at the same time not significantly altering knee and hip kinematics. Conclusion This study demonstrates that a potentially useful shoe design was identified for treatment of claudicant calf pain which did not adversely affect more proximal joint kinetics and kinematics