Ten well-trained male volleyball players performed one-legged and two-legged vertical countermovement jumps. Ground reaction forces, cinematographic data, and electromyographic data were recorded. Jumping height in one-legged jumps was 58.5% of that reached in two-legged jumps. Mean net torques in hip and ankle joints were higher in one-legged jumps. Net power output in the ankle joint was extremely high in one-legged jumps. This high power output was explained by a higher level of activation in both heads of m. gastrocnemius in the one-legged jump. A higher level of activation was also found in m. vastus medialis. These differences between unilateral and bilateral performance of the complex movement jumping were shown to be in agreement with differences reported in literature based on isometric and isokinetic experiments.