Functional asymmetries in inside-outside foot mechanics when curvilinear sprinting in baseball

The purpose of this study was to determine whether inside-outside foot asymmetries were observed when running multiple bases in baseball. Fifty-four trained male high school baseball position players performed two linear 54.7-meter sprints and two home-to-second base sprints. Ground contact time (GCT), stride length (SL), and average push-off and impact were quantified using inertial measurement unit foot pod technology. The sprints were divided into four segments (0–13.7 m; 13.7–27.4 m; 27.4–41.1 m; 41.1–54.7 m) for both curvilinear segments (C):C1–C4, and linear segments (L):L1–L4. The primary findings of this study were that for linear sprinting, GCT was not significantly different between feet across all segments, but SL was significantly shorter (L2–L4) in the outside foot (−0.76% to −1.34%; ES = −0.20 to −0.37) and push-off were significantly greater (L1–L4) in the outside foot (2.95% to 4.39%; ES = 0.27 to 0.40), with significantly greater outside-foot impact only in L1 (5.63%; ES = 0.29). In curvilinear sprinting, the inside foot was found to have significantly longer GCT in Segments 2–4 (−3.13% to −7.79%; ES = −0.38 to −1.29), higher push-off (3.83% to 4.39%; ES = 0.31 to 0.41), and segment-specific SL changes. Inside–outside foot asymmetries are driven by the linear-curvilinear demands of specific segments, peaking in Segment 3 where stabilization demands are greatest. These findings highlight the need for segment-specific training that develops inside-foot stability and outside-foot propulsion to optimize base-running performance in base runners.