Balancing Offloading and Comfort: The Effect of Forefoot Rocker Curvature on In-Shoe Plantar Pressure and Gait Kinematics

Therapeutic footwear with rocker soles is widely used to reduce plantar pressure in individuals at risk of diabetic foot ulceration. Of the various rocker sole characteristics, apex position, rocker angle, and apex angle have been extensively studied; however, the effect of forefoot rocker curvature has been seldom investigated. The aim of this study was to assess the isolated effect of forefoot rocker curvature on plantar pressure distribution, lower limb gait kinematics, and comfort. Ten healthy adults walked in a modular footwear setup with three interchangeable midsoles featuring a straight-line rocker profile (CRi), a rocker radius of 60% (CR60), and 45% (CR45) of the shoe length. In-shoe plantar pressure was measured using 99-sensor capacitive insoles. Kinematics of lower limb joints were measured via inertial measurement units. Comfort-related parameters were assessed using a Visual Analog Scale. Data were analyzed using non- parametric tests. CRi demonstrated significantly lower pressure at the metatarsal heads than CR60 and CR45 (kPa; median[Q1-Q3]; mean pressure=80 [67-81]; peak pressure=151 [139-169]; p=0.002). CR45 showed significantly lower mean pressure and pressure-time integral in the midfoot than CRi (p=0.002). CR60 showed the largest maximum dorsiflexion angle (deg, median [Q1-Q3]: CR60=17.8[13.4-23.5]; p<0.001) and range of motion (deg: CR60=20.3[18.8-23.3]; p=0.007). CRi was perceived as the least comfortable rocker condition (score 0-100; median[Q1-Q3]; overall comfort=44 [35-57]; p=0.008). A straight rocker maximizes offloading at the expense of ankle kinematics and comfort; lower rocker radii enhance comfort, thus making the rocker curvature a key design parameter for therapeutic footwear.