Motor adaptations during stair ascent and descent in individuals with chronic primary low back pain

Altered neuromuscular strategies, such as lumbar muscle activity spatial redistribution, have been observed in individuals with chronic primary low back pain (CLBP), particularly during intense isometric efforts, but not during low-effort functional tasks. This cross-sectional study aimed to determine whether lumbar muscle activity distribution and trunk kinematics differ between individuals with CLBP and healthy controls during a dynamic, moderate-effort task, namely stair ascent and descent, and to investigate the relationship between muscle activity distribution and psychological factors of CLBP. Forty adults (20 CLBP, 20 controls) completed stair ambulation trials while lumbar high-density surface electromyography and kinematic data were recorded. Spatial redistribution and RMS amplitudes of electromyography were analyzed during ascent and descent, and across swing and stance phases. Participants with CLBP exhibited spatial redistribution of muscle activity on the left side during both phases of ascent, and during the swing phase of descent. Higher RMS amplitudes were observed bilaterally in CLBP participants across all tasks and phases, except during the stance phase of descent. No kinematic differences were found between groups. No relationship was found between muscle redistribution activity and psychological factors. These results suggest that CLBP participants exhibit altered neuromuscular strategies during stair ambulation, a moderately challenging functional task.