Spatiotemporal and Ground Reaction Force Determinants of Sprint Acceleration in Adolescent Male Baseball Players

OBJECTIVES This study examined the relationships of changes in running speed with spatiotemporal (e.g., step length and frequency) and ground reaction force (GRF) variables during a 30-m sprint acceleration in adolescent baseball players to identify the determinants of sprint acceleration performance.METHODS Twenty-eight adolescent male baseball players performed maximal 30-m sprints, during which GRFs were recorded using a long force platform system. Spatiotemporal and GRF variables were calculated for each step, and mean values were obtained for five step sections (1st–4th, 5th–8th, 9th–12th, 13th–16th, and 17th–18th steps). Relationships of changes in running speed with changes in spatiotemporal and GRF variables were examined.RESULTS Changes in running speed were positively correlated with changes in step length in the 1st–4th and 9th–12th step sections, and with changes in step frequency from the 9th–12th to 17th–18th sections. Moreover, changes in running speed were positively correlated with propulsive impulse in the 1st–4th section, braking impulse in the 9th–12th and 13th–16th sections, and net anterior–posterior impulse and ratio of force across all sections, and were negatively correlated with vertical impulse in the 9th–12th and 13th–16th sections.CONCLUSIONS These findings suggest that better acceleration performance in adolescent baseball players is likely accomplished by greater increases in step length in the initial acceleration, by greater increases in step length and suppressing decreases in step frequency during the middle acceleration, and by suppressing decreases in step frequency during the later acceleration. Moreover, greater net anterior–posterior impulse and ratio of force could be indicators of better sprint acceleration throughout the acceleration phase. In addition, greater propulsive impulse may contribute to greater initial acceleration, while smaller braking and vertical impulses are likely key factors for better middle and later acceleration performance.