Differences in plantar loading between flat and normal feet during different athletic tasks.

The purpose of this study was to determine if foot type (flat or normal) resulted in loading differences during four sport-specific tasks (cross-cut, side-cut, shuttle run, and landing from a simulated lay-up). Twenty-two healthy subjects (12 normal feet and 10 flat feet) completed five trials in each condition, while in-shoe pressure data was collected at 50 Hz. Contact area, maximum force, and the force time integral were analyzed under the entire foot and in eight-foot regions. Foot type was determined by examining navicular height, arch angle, rearfoot angle, and a clinical score. A series of independent sample t-tests were used to determine statistical differences (alpha<0.05). During the cross-cut, flat feet demonstrated an increase in medial midfoot contact area. During the side-cut, flat feet demonstrated an increase in contact area, force time integral and maximum force in both the medial and lateral midfoot. During the shuttle run, flat feet demonstrated an increase in force time integral in the lateral midfoot and increases in maximum force in both the medial and lateral midfoot. During the landing task, flat feet demonstrated an increase in maximum force in the medial midfoot. However, flat feet demonstrate a decrease in middle forefoot maximum force. All results were statistically significant (p<0.05). Therefore, individuals with a normal foot could be at a lower risk for medial and lateral midfoot injuries such as metatarsal stress fractures, indicating that foot type should be assessed when determining an individual's risk for metatarsal stress fractures.