BACKGROUND This study aimed to describe changes in thoracic and pelvic movements during the acceleration phase of maximal sprinting, and to clarify which kinematic variable relates to better accelerated sprinting performance. METHODS Twelve male sprinters performed 60-m sprints, during which three-dimensional step-to-step changes in thoracic and pelvic angles, as well as the trunk quasi-joint angle, were obtained throughout a 50-m distance. RESULTS The patterns of thoracic and pelvic movements were maintained throughout the entire acceleration phase, although the phase profiles of the relative movements between the thorax and pelvis in three planes differed. Increase in peak thoracic and pelvic tilt angles terminated (-10.3° and 3.2° from the vertical line) and trunk extension range (≈21.7°) decreased from the 13th-15th steps. Moreover, thoracic and pelvic obliquity angles decreased from 15.3° and 8.8°, and conversely, rotation angles increased to 23.5° and plateaued (≈16°), during the entire acceleration phase. Moreover, smaller inclination of the thorax and deeper inclination of the pelvis, smaller rotations of the pelvis and trunk quasi-joint and greater thoracic obliquity during the initial section (to the 4th step), deeper inclination of the pelvis during the middle section (to the 14th step), and smaller trunk torsion and thoracic obliquity during the final section in the entire acceleration phase of sprinting were associated with increases in running speed. CONCLUSIONS The results suggest that sprint acceleration toward maximal speed is not performed with only proportional increases in magnitudes of trunk movements, and important factors for better sprint acceleration performance alter with increasing running speed.