Mechanical work, efficiency and energy redistribution mechanisms in baseball pitching

Though baseball pitching is assumed to achieve proper technique in which a great deal of energy is imparted from the trunk to the throwing arm, through a kinetic chain of the entire body, few studies have answered the question of how segmental energy is generated/transferred by muscles and intersegmental joint forces. The purpose of this study was to calculate the mechanical energy produced by the individual joint moments or joint forces in throwing, and further breaking down the joint moments into their muscular and non-muscular interactive moments, assessing their contribution to the generation of mechanical energy. The pitching motion of eight collegiate baseball pitchers was measured using a three-dimensional motion capture system. A model including multiple segments and joints of the throwing arm, non-throwing arm and trunk was developed to establish the relationships between causal muscle work and distributed segmental energy. Using the model, the mechanical energy of each segment was decomposed into the muscular and non-muscular interactive components. The results showed that the kinetic energy of the throwing hand and ball at the ball release were primarily produced by the trunk backward/forward tilt and counterclockwise/clockwise rotation, while the contribution of the throwing shoulder external/internal rotation to the hand kinetic energy was relatively small. The centrifugal force was identified as a more important factor in energy transfer than other interactive components (Coriolis force and gyroscopic moment). In conclusion, the trunk flexor and rotator muscle power generated in an earlier phase provides the primary source to the consequent arm acceleration, and the energy redistribution mechanism due to the centrifugal-effect that transfers energy from the proximal segment to the distal one plays a more critical role in enhancing the distal arm kinetic energy than additional muscle work produced in a later phase.