The composition of energy flow in the upper extremity under different lower extremity mechanics in baseball pitching

Generating high ball speed is crucial for achieving competitive baseball pitching performance. The lower extremity mechanics play a key role in generating high ball speed during a baseball pitch. However, some previous studies have reported no significant difference in ball speeds despite differences in lower extremity mechanics, highlighting the need to examine how energy is transferred through the upper extremity to the ball under these conditions. This study examined how upper extremity energy flow differed across stride-length conditions in relation to the observed differences in ball speed. Twenty college baseball pitchers pitched with under-stride length (US) and over-stride length (OS) in addition to normal-stride length (NS). We analyzed the mechanical energy of the upper extremity segments at key events during pitching, and the energy flow through each joint between events. The mechanical energy in the proximal segments at the stride foot contact increased as the stride length extended. In contrast, the mechanical energy in the distal segments at maximum external rotation in the shoulder joint was greater in the NS than in the US and OS, consistent with ball speed differences. During this phase, the energy flow to the upper arm through the shoulder joint was greater in the NS than in the US and OS, and the same condition pattern was observed for energy transfer through the elbow and wrist joints and for ball speed. Additionally, although no statistically significant difference in ball speed was observed between the US and OS, the JFP and STP components of shoulder energy flow showed different condition patterns, suggesting that shoulder energy flow composition may differ even when no statistically significant difference is observed in total energy flow into the upper arm.