Abstract: BACKGROUND: Balance ability is an important factor affecting the posture control of patients with chronic nonspecific low back pain and the main reason for falling, fractures and disabilities. Most of the existing studies only analyze the position of bipedal, and rarely report the static equilibrium characteristics and limits of stability of monopodial and bipedal on the premise of distinguishing the mixed factors brought by dominant and non-dominant legs.  
OBJECTIVE: To analyze the characteristics of static balance and limits of stability in patients with chronic nonspecific low back pain.
METHODS: From April 2020 to December 2021, 20 chronic nonspecific low back pain patients (low back pain group) and 20 healthy subjects (healthy group) were recruited among the interns of Guangzhou Panyu Central Hospital. The Pro-kin balancer was chosen to perform the static balance of single/biped standing and limit of stability test and to record the index values of the corresponding test, such as: plantar pressure center and limit of stability when bipedal standing, as well as such as the vertical and horizontal amplitude, the mean of vertical and horizontal sway velocities, the area of the movement, and the length of the movement when single and bipedal standing.  
RESULTS AND CONCLUSION: (1) Under the eyes open/closed state, the plantar center of pressure of the healthy group was concentrated in the axial center, while the low back pain group showed a larger discrete distribution, and the distribution was mainly on the non-dominant leg. (2) Comparing the static balance of bipedal standing: There was no significant difference between the two groups in the open eye state (P > 0.05), and the low back pain group had higher values of static balance indexes than the healthy group in the closed eye state (P < 0.05). (3) Comparing the static balance of standing on one foot: The values of the static balance indexes of the dominant leg in the low back pain group were greater than those of the non-dominant leg (P < 0.05), and there was no significant difference between the superior and non-dominant legs in the healthy group (P > 0.05). The static balance index value of the dominant leg in the low back pain group was significantly greater than that of the healthy group (P < 0.05), and there was no significant difference between the two groups on the non-dominant leg (P > 0.05). (4) The limit of stability values on the left side (positive left, front left, rear left) and right side (positive right, front right, rear right) of the healthy group were significantly greater than those of the low back pain group (P < 0.05). (5) The results indicated that the static balance of standing on two feet with eyes closed, the static balance of standing on one foot of the dominant leg and the limit of stability balance ability on the left and right sides was significantly decreased, and the maintenance of balance ability was visually dependent, and there was a great risk of falling.

Key words: chronic non-specific low back pain, static balance, limit of stability, center of pressure