The acute effects of pre-fabricated insoles on running mechanics and perceived footwear comfort of endurance runners

Abstract

Tibial acceleration is a prominent biomechanical consideration associated with common running-related injuries, such as tibial stress injuries. Cushioning insoles are proposed to be capable of reducing tibial acceleration, though there is conflicting evidence. Perceived comfort, primarily through enhanced cushioning, has shown some association with peak axial tibial acceleration, however the magnitude of this correlation has been found to be low. Changes in footwear cushioning have been associated with adjustments in running mechanics that may mask the effect of the cushioning material or potentially increase the risk of injury by altering the biomechanical variables associated with running-related injuries. The majority of research related to running mechanics has historically occurred in laboratory environments, thus compromising ecological validity. The purpose of this study was to investigate the effects of pre-fabricated insoles on running mechanics and footwear comfort in a field setting.

Twenty-nine recreational runners (age: 31.8 ± 6.5 y) completed four separate laps of an athletics track while wearing running shoes containing either the ordinary sock liner (CON), or pre-fabricated insoles namely Sofsole Athlete (AT), Spenco Arch Cushioned (AC), and Spenco Walker Runner (WR) (Implus LLC, Durham, North Carolina, USA). Participants were fitted with seven inertial measurement units (IMUs) (Noraxon, Scottsdale, Arizona, USA). Each IMU included a tri-axial accelerometer, gyroscope, and magnetometer in order to capture segment and joint kinematics in all three planes of motion. Spatiotemporal data was collected using a 10 m length of an optical measurement system (OptoJump by Microgate, Bolzaho, Italy). Subsequent to each lap, the participant completed the Footwear Comfort Assessment Tool comprising of nine 100 mm visual analogue scales. Biomechanical and perceived comfort variables were compared in R using a linear mixed model with main effect for condition. Pairwise comparison between condition was conducted post-hoc with Tukey adjustments for the p-values.

No significant differences for spatiotemporal parameters, tibial acceleration, shock attenuation, knee flexion, hip flexion, or shin inclination were observed. Foot pitch angle was significantly greater between WR versus AC, AT versus CON, and WR versus CON (p < 0.001), as was ankle dorsiflexion at touchdown between WR versus AC and WR versus CON (p < 0.001). Peak ankle dorsiflexion was significantly greater between WR versus AC and WR versus CON (p = 0.006), while ankle dorsiflexion ROM was significantly reduced between WR versus CON and AC versus CON (p = 0.007). Overall comfort was significantly greater for AT versus AC, AT versus WR, and AC versus CON (p = 0.002), and shoe length comfort was significantly less for WR versus CON (p = 0.33).

The pre-fabricated insoles investigated in this study did not result in any significant acute changes to peak acceleration or shock attenuation, however significant and clinically relevant changes regarding ankle dorsiflexion, foot inclination, and overall footwear comfort did occur. Runners should be aware that enhanced cushioning of pre-fabricated insoles may be negated by adjustments to ankle dorsiflexion and foot strike pattern during touchdown. Runners may therefore be advised to select pre-fabricated insoles based on their perceived comfort.