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The purpose of this study was to investigate force and power outputs during bar twist exercises using barbell shafts, considering various moment of inertia (MOI), corresponding to changes in the bar length and mass. Twenty-one male college athletes performed the bar twist exercise using five barbell shafts: one normal barbell shaft, two long barbell shafts (with changes only in the length), and two heavy barbell shafts (with changes only in the mass). Kinematic and kinetic data were recorded using the Vicon system (250 Hz) and two force platforms (1,000 Hz). The results obtained in this study revealed that: (1) Peak angular velocity of bar and upper trunk for the long barbell shaft condition was higher than the heavy barbell shaft condition; (2) For higher MOI, the trunk-twist torque was higher; and (3) Even when the barbell shaft had equal MOI, the heavy bar showed higher trunk-twist torque prior to the bar rotation.