THE EFFECT OF CHRONIC PAIN INTENSITY ON THE STABILITY LIMITS IN PATIENTS WITH LOW BACK PAIN

Objective: The purpose of this study was to evaluate if the intensity of recurrent chronic pain would modify postural performance in reaching the functional limits of stability (LOS) in chronic low back pain (CLBP) patients. Methods: Three groups of subjects were investigated. Healthy persons comprised the asymptomatic group (n = 32) while CLBP patients (n = 36) were divided into 2 subgroups, according to the reported intensity of resting pain on a numerical rating scale: patients with low (LP) and high pain (HP) levels. The maximal displacement of the center of pressure (COP) indexing the LOS magnitude and the COP mean velocity indexing the performance in reaching LOS were calculated on a Kistler force plate during forward and backward voluntary body lean with eyes open (EO) or closed (EC). Results: The forward LOS was lower in both the LP (P < .01) and HP (P < .01) subgroups than in the asymptomatic under EO and EC conditions, while no differences between the LP and HP groups were found. The backward LOS was lower in the HP group than in asymptomatic but only with EC (P = .01). Eye closure caused an increase in forward (P = .02) and backward (P = .001) COP velocity in the LP group and forward COP velocity in the asymptomatic (P = .04) only. With EC, the only intergroup difference was lower forward COP velocity in the HP than LP group (P = .04). Conclusion: Subjects with CLBP had reduced forward LOS regardless the pain level. However, the higher level of pain was associated with slower execution of voluntary leaning tasks, with EC only.