The effect of foot type, body length and mass on postural stability.

Background: Poor postural stability is associated with chronic ankle instability. Previous research showed an effect of foot type on postural stability. However, the specific effect of supinated feet remains unclear.

Research Question: Our study aimed to assess the effect of foot type on postural stability, while taking potential confounding effects of body mass and body height into account.

Methods: Forty-three healthy participants between 18 and 40 years old performed barefooted single leg stance tests with eyes open (EO) and closed (EC) on solid ground, and on a balance board (BB). Foot type was determined from pressure recordings during gait, using the arch index. Ground reaction forces were measured using a force plate. Outcome measures were Center of Pressure Velocity (COPV) divided by body height, and the Horizontal Ground Reaction Force (HGRF) divided by body mass. Generalized Estimating Equations models assessed the differences between supinated, normal and pronated feet during EO, EC and on a BB.

Results: During EO an interaction between supinated feet and body mass showed an increase of COPV with 0.03 × 10 1/s per kilogram of mass relative to normal feet (p = .03). During EC this interaction was more pronounced with 0.22 × 10 1/s increase per kilogram mass (p < .01). The HGRF did not differ between foot types in any of the conditions.

Significance: Supinated feet have a larger increase in COPV compared to normal feet with increasing mass when standing on solid ground during EO and EC. This indicates that people with supinated feet and a higher mass are less stable during single leg stance.

Level Of Evidence: Level 3, associative study.