Comparison of clinical and objective methods of assessing trunk muscle strength--an experimental approach.

An objective method was used to evaluate the validity of the sit-up, prone trunk extension, and double leg lowering clinical tests. Normal men and women and patients with a history of backache served as subjects. The vast majority of the subjects were able to perform the Grade 1 level, which was the highest resistance imposed by the sit-up and prone extension tests. The double leg lower was superior to the other two clinical tests but was able to identify only broad differences in strength capability. In the main, the subjective clinical tests were poor discriminators and seemed to lack the range of resistance necessary to be definitively useful as methods of assessing trunk muscle strength and may not provide appropriate resistance for improving trunk muscle strength in most patients.