The effect of load on the coordination of the trunk for subjects with and without chronic low back pain during flexion–extension and lateral bending tasks

Objective. To evaluate if patients move their trunk sections differently than normal subjects and to determine if these differences increase when lifting a load. Design. Comparative study using a repeated measures design. Background. Many studies demonstrate a modification of the lumbar–pelvic rhythm for chronic low back pain patients but the large variability of the results impair the discrimination power. It was hypothesized that the lifting of a load would magnify the manifestation of lumbar impairments. Methods. Fifteen chronic low back pain patients and 18 normal subjects performed maximal flexion–extension and lateral bending of the trunk with and without a 12 kg load. The pelvic, lumbar and thoracic motions were measured with a motion analysis system. Results. During flexion–extension tasks, a significant decrease in lumbar flexion and increase in thoracic flexion were observed for the patients. The load effect was significant for all trunk sections but did not allow a better discrimination between groups. Conclusions. Lifting a 12 kg load during flexion–extension of the trunk did confirm alteration in trunk section coordination but did not help to better discriminate patients from normal subjects. However, it was demonstrated for the first time that chronic low back pain patients compensate for a loss of lumbar flexion by increasing their thoracic flexion.