Controlling the Ground Reaction Force during Lifting

Abstract

The control of the ground reaction force vector (F_g ) relative to the center of gravity (CoG) was examined while subjects performed a back-lifting task. Six male subjects (aged 24.0 ± 2.5 years) repeatedly lifted a barbell. A biomechanical analysis that used a linked segment model revealed that the summed rotations of body segments during lifting yielded a specific rate of change of the angular momentum of the entire body. This equaled the external moment provided by F_g relative to CoG. This implies that multisegment movements involve control of the angular momentum of the entire body through an appropriately directed F_g . Thus, in dynamic tasks F_g is pointed away from rather than lined up with the CoG, as is the case in static tasks.

Key Words:

• angular momentum
• center of pressure
• coordination
• ground reaction force
• lifting
• linear momentum
• linked segment model
• multijoint movement