THE STRENGTH OF THE LIFTING ACTION IN MAN

Abstract

The maximum isometric force exertable on a horizontal bar situated in a frontal plane was found to vary, for eight young male subjects and for the different lifting conditions observed, from 15 to 120 kg. Increase of foot placement distance from 30 cm to 50 cm effected the largest reduction in lifting force. The reduction produced by increase of grasp height from 12½ cm to 50 cm was very much less, and the effect of type of grasp (overhand or underhand) and type of lifting action (using or not using knee extension) was generally small. It appeared that the magnitude of the lifting force was largely determined by the magnitude of the force moment which the body mass could exert to counterbalance the reaction of the lifting force upon the body. The nature of the muscular activity associated with this stabilization of the body during lifting operations is discussed.