Trunk Stability in Dynamic Movement

Spinal stability has been characterized in static but not in dynamic movements. The goal of this study was to determine whether movement pace and direction of dynamic trunk flexion influence the control of spinal stability. Twenty healthy subjects performed dynamic lifting movements at 20 and 40 cycles per minute. Lyapunov exponents were calculated from the measured trunk kinematics to estimate stability. Complexity of torso dynamics required at least five embedded dimensions thereby indicating that torso dynamics requires more than the 3-dimensions of movement for sufficient characterization. Dynamic stability is was greater in slow lifting movement than in fast movements. Asymmetric movements demonstrated greater multi-dimensional kinematic divergence than asymmetric movements. This indicates that the sagittal plane of movement may not be a principle dynamic axis of torso movement. Results provide biomechanical insight regarding the role of workplace design and risk of musculoskeletal instability in dynamic lifting tasks