Humanoid robots that mimic human movement have garnered significant attention in recent years. This study focuses on mimicking the efficient pitching motion of humans by incorporating two main approaches into a humanoid robot: (1) the use of elastic elements to assist joint torque, and (2) the optimization of motor torque to minimize energy consumption. This robot is intended to emulate human physical characteristics, such as mass, link length, and center of gravity, with a particular focus on utilizing the elastic energy generated during shoulder internal and external rotation. A leaf spring is attached in parallel with the motor at the shoulder pitch joint to release the elastic energy stored during shoulder external rotation, thereby assisting internal rotation in a manner similar to human biomechanics. Additionally, motor torque optimization is addressed by formulating the torque minimization problem as a combinatorial optimization challenge and solving it using Fujitsu's quantum-inspired Digital Annealer. Experiments conducted through simulations and with an actual pitching robot assessed the effectiveness of these technologies in mimicking human-like pitching motion. The results suggest that combining elastic elements with motion optimization techniques enable robots to achieve more efficient human-like movements.