Task-specific fear influences abnormal trunk motor coordination in workers with chronic low back pain: a relative phase angle analysis of object-lifting

Abstract

Background: Pain-related fear influences impaired trunk movement (e.g., limited movement of range and velocity), but it is unclear how fear relates to trunk motor coordination (e.g., a more "in-phase" upper-lower trunk motion pattern). We conducted the present study to: (1) identify the motor coordination pattern of the in-phase upper-lower lumbar movements during the lifting, and (2) determine how pain-related fear is related to the trunk coordination pattern in workers with chronic low back pain (CLBP).

Methods: We examined 31 male workers with CLBP (CLBP group) and 20 healthy controls with no history of CLBP (HC group). The movement task was lifting a box, the weight of which was 10, 30%, or 50% of the subject's body weight. We used a 3D motion capture system to calculate the mean absolute relative phase angle (MARP) angle as an index of coordination and the mean deviation phase (DP) as an index of variability. We used a numerical rating scale to assess the subjects' task-specific fear.

Results: The MARP angle during trunk extension movement in the 50% condition was significantly decreased in the CLBP group compared to the HCs; i.e., the upper lumbar movement was more in-phase with the lower lumbar movement. The hierarchical multiple regression analysis results demonstrated that a decreased MARP angle was associated with high task-specific fear.

Conclusions: A more 'in-phase' upper-lower lumbar movement pattern was predicted by task-specific fear evoked when performing a work-related activity. Our findings suggest that an intervention for task-specific fear may be necessary to improve an individual's impaired trunk motor coordination.

Keywords: A relative phase angle analysis; Deviation phase; Kinematic; Lifting; Low back pain; Mean absolute relative phase; Work-related activity.

Fig. 1

The subjects were asked to lift a box (520 × 365 × 305 mm) placed on the ground. The attachment positions of the 11 markers (30-mm dia.) are shown: the subject’s thoracic spine (Th12 spinous process), lumbar (L3 spinous process), pelvic (S1 spinous process), and bilaterally on the lilac crest, great trochanter, lateral femoral epicondyle, and lateral malleolus. A marker was also attached to the box

Fig. 2

Time series variation of the trunk movement during lifting. The time series was divided into two phases according to upper trunk movement and box position

Fig. 3

Phase diagram for the upper trunk segment. The phase angle, φ, at any point of flexion and extension can be calculated using the formula tan⁻¹ (Angular velocity/angle). The phase angle was calculated in this study by dividing the flexion phase and extension phase

Fig. 4

Flowchart of inclusion and exclusion criteria for this study