An Analysis of Isometric and Isokinetic Spinal Lifting Motions

Low back pain is a condition which, at some time, affects over half of the world's population and is also the number one cause of physical limitation for persons under 45 years of age. The etiology of most low back pain largely is unknown. However, it is known that after injury the biomechanics of the back change drastically. The present study investigates the ability of normal men and women to move and exert force with the back (as is done during lifting). Twenty men and women were monitered as they attempted to exert maximal force with the back under isometric and isokinetic conditions. The back angle and velocity of movement were controlled while torque, intra-abdominal pressure and the electromyographic activity of the ten trunk muscles monitored. The relationship between isometric and isokinetic exertions was determined as well as the interactive contribution of muscle forces and abdominal pressure to spinal loading. These results suggest new manual material handling implications as well as a new method for employee screening.