Strength Tests Add Useful Information for Patients with Low Back Pain
Muscles in the back that extend or straighten the spine are often weak in patients with chronic low back dysfunction (CLBD). CLBD is not a single disease or disorder. It's a group of disorders that occurs with back pain. Patients with CLBD report a wide range of history, symptoms, and disability.

Scientists around the world are trying to find a valid way to measure muscle performance. They'd like to tell if a patient is giving his or her best effort during testing. Sometimes, and for different reasons, people pretend to contract the muscles fully. This is called feigned effort.

In this study, physical therapists in Israel and Australia measured trunk extension strength (TES). They used a special piece of equipment for testing muscles called a dynamometer. The dynamometer has computer software to make calculations. DEC is the math term used when measuring strength at different speeds during muscle contractions. Previous studies have measured maximal muscular capacity in normal adults. This group measured TES in patients with CLBD.

They found that the strength scores in patients with CLBD followed the same patterns as for normal adults. However, the scores were greatly reduced from normal. The DEC scores in 89 percent of the patients showed full effort was given during testing.

It is nearly impossible to know if a patient is giving his or her best effort during muscle strength testing. Physical therapists can use a dynamometer and DEC scores to look for less than full effort. A DEC score greater than 1.02 in women and 0.95 in men strongly suggests feigned effort. The score shouldn't be used to support or discount a person's symptoms, however. Instead it offers another useful bit of information in a thorough evaluation.
Zeevir Dvir, PhD, and Jennifer L. Keating. Trunk Extension Effort in Patients with Chronic Low Back Dysfunction. In Spine. April 1, 2003. Vol. 28. No. 7. Pp. 685-692.