Abstract This study aims to examine if upper torso rotation is caused mainly by pelvis rotation during baseball pitching from the viewpoint of energetics. Twelve right-handed males participated in this study. Five were and seven had been collegiate baseball pitchers, and all used an overarm style. They threw a baseball as fast and precisely as possible, and data from three strikes were used. A motion capture system consisting of 13 cameras and two force platforms was used to collect the data and calculate joint torques of the thoracic and the lumbar joint. The joint torque of the thoracic and the lumbar joint were calculated using a top-down and a bottom-up approach, respectively. Then, the mechanical energy generation and transfer by the torsional torques were quantified. The mechanical energy generation exerted by the torsional torques of the thoracic and lumbar joints were 0.03 ± 0.03 and 0.15 ± 0.04 J kg-1 m-1, respectively. The mechanical energy transfer exerted by the torsional torques of the thoracic and lumbar joints were 0.72 ± 0.19 and 0.88 ± 0.24 J kg-1 m-1, respectively. These results indicated that torsional torques transferred a substantial amount of mechanical energy from the pelvis to the upper torso. Furthermore, the findings indicate that the mechanical energy transfer exerted by the torsional torques was a major contributor to the upper torso rotation.