This study aims to explore comprehensive kinematic patterns of all body joints utilizing a nonlinear functional data analysis (FDA) approach during a step-up task in patients with nonspecific chronic low back pain (NSCLBP). The kinematics of the trunk, pelvis, and upper- and lower-extremities during step-up exercises were assessed in NSCLBP (N = 23) and control (N = 22) groups using a Motion Analysis System. FDA was employed to compare movement-patterns of 15 segments between two groups. In the NSCLBP group, there was a significant decrease in flexion in specific spine regions (upper-thoracic and upper-lumbar segments) and increased flexion in the lower-thoracic-segment and most lower limb joints (except the dominant-knee) during the first phase (swing phase of leading-leg). Throughout the movement-cycle, in frontal-plane, increased adduction and inversion, along with decreased abduction and eversion were found in most lower limb joints (except the non-dominant hip and knee). Furthermore, during the movement-cycle, in transverse-plane, were observed, increased internal-rotation and decreased external-rotation in both hips and dominant knee, increased contralateral-rotation and decreased ipsilateral-rotation (relative to leading-limb) in all spine-segments, and increased forward-rotation in the pelvis. Notably, the upper-limbs showed decreased dominant-shoulder flexion, increased abduction of both shoulders, and increased upward-rotation of the non-dominant scapula throughout the movement-cycle in LBP group. This study revealed compensatory-mechanisms in NSCLBP-patients to counterbalance reduced sagittal-plane movement in specific spine regions, leading to increased motion across various joints in all three-planes, particularly frontal- and transverse-planes. Overall, FDA showed a prevalent pattern of flexion, adduction, and internal-rotation in most segments during step-up task in NSCLBP-patients.