Comparison of different structural foot types for measures of standing postural control.

STUDY DESIGN Matched group comparison of 3 subject groups with 3 different foot structures for force plate and clinical measures of postural control. OBJECTIVES To determine if subjects with different weight-bearing foot structure would demonstrate differences in static standing postural control, and to determine the reliability of study procedures. BACKGROUND Weight-bearing foot structure may influence postural control either because of a decreased base of support (supinated foot structure) or because of passive instability of the joints of the foot (pronated foot structure). METHODS AND MEASURES Young adults were categorized based on weight-bearing foot structure into neutral, pronated, or supinated groups (15 subjects per group). Postural control in single-limb stance with eyes closed was assessed using force plate measures and by measuring duration of single-limb stance on a firm floor and on a balance pad. Force plate measures were normalized center-of-pressure average speed; and standard deviation and maximum displacement in the anterior-posterior and medial-lateral directions. RESULTS Individuals in the supinated group had significantly greater center-of-pressure average speed, greater maximum displacement in the anterior-posterior direction, and greater SD and maximum displacement in the medial-lateral direction than individuals in the neutral group. The individuals in the pronated group had significantly greater SD and maximum displacement in the anterior-posterior direction, used more trials to complete force plate testing, and had shorter single-limb stance duration than those in the neutral group. CONCLUSION Individuals with pronated feet or supinated feet have poorer postural control than individuals with neutral feet, but perhaps through different mechanisms.