The load on the lumbar spine during isometric strength testing.

Reports of back discomfort and even back injuries during isometric strength testing in specific lifting positions indicated an analysis of the loads on the lumbar spine during this type of testing. A biomechanical analysis, which has been validated against EMG and intravital disc pressure measurements, was used for the calculations of the loads in four test persons. The calculations indicated compressive loads on L3 ranging from 5000-11,000 N during squat and torso lifting. Such loads in vitro have been found to cause structural failures of the vertebral endplates. Similar loads also may result in damage to the spine in vivo.