Awareness of the hazards of repetitive lifting has brought about significant changes in the design of industrial jobs. Pushing and pulling tasks have become increasingly common as the result of the introduction of a variety of carts and other materials-handling assistance devices. In order to predict the peak performance of workers in these tasks, and the biomechanical stresses that can result from them, the exertions involved in cart pushing were studied. Four subjects of various strengths pushed carts with loads from 45 to 450 kg at several heights. Peak push forces reached 500 N for male subjects and 200 N for female subjects. Strong subjects moved a 45 kg cart at velocities of 1.1 m s(-1) and a 450 kg cart at velocities of 0.8 m s(-1). Weaker subjects moved the carts at velocities of 0.5 and 0.4 m s(-1) respectively. Calculated static compression forces at the L5/S1 spinal disc were consistently above the NIOSH Action Limit of 3400 N for strong subjects when the cart load reached 225 kg.