The effects of postural difficulty conditions on variability of joint kinematic patterns during sit to stand task in normals and patients with non-specific chronic low back pain

Sit to stand (STS) is one of the most important activities of daily living that is shown to be affected in low back pain (LBP) patients. It requires a fundamental coordination action among all segments (DOFs) of the body in order to control important performance variables such as body's center of mass (CM) within base of support (BOS). In this study, possible differences in joint coordination and variability patterns between chronic LBP and healthy control subjects were investigated during STS task. Eleven adults with nonspecific chronic LBP and 12 healthy controls were recruited in the study. The participants performed the task in 3 exerimental conditions including: rigid surface, open eyes (RO), rigid surface, close eyes (RC) and narrow surface, close eyes (NC). The variability of 7 segment motions and also CM positions were calculated across 15 trials in these conditions. A mixed model analysis of variance showed that both LBP and control groups could coordinate their DOFs in order to stablilize body CM position, although elemental variability (segment motion variability) was totally higher in LBPs than controls, especially trunk and head segment variability. These findings confirm the existence of fundamental coordinatiom strategies in deep lying structures of control systems which help the system maintain its functions despite possible impaiments in elements.