Foot placement angle and arch type: effect on rearfoot motion.

The purpose of the study was to describe the relationship between foot placement angle, arch type, and rearfoot motion during running. Twenty women were filmed in the frontal plane at 100 fps. Subjects displaying a variety of foot placement angles were chosen. Before data collection, arch indices were calculated. Each subject ran five trials at a pace of 3.5 m/sec. All subjects wore the same type of shoe. All trials were digitized to determine rearfoot angles throughout foot contact. The following mean values were obtained: total rearfoot was 10.09 degrees, maximum pronation was -9.63 degrees, foot placement angle was 7.58 degrees and arch index (AI) was 0.23 cm2. Non-linear regression was used to predict the relationship between maximum pronation and total rearfoot motion using foot placement angle and AI. Foot placement angle was the best single predictor of total rearfoot motion. When using both foot placement angle and arch type as predictors of total rearfoot motion, r2 was .35. Less abduction was associated with more total rearfoot motion. Arch type exhibited a quadratic relationship with total rearfoot motion. Normal-arched individuals (.21 cm2 less than AI less than .26 cm2) exhibited less total rearfoot motion than high-arched (AI greater than .26 cm2) and flat-arched (AI less than .21 cm2) individuals. For maximum pronation, foot placement angle was the only significant predictor (r2 = .13). Greater foot placement angles (more abduction) were associated with less maximum pronation.