Comparisons of lumbar spine loads and kinematics in healthy and non-specific low back pain individuals during unstable lifting activities

Abstract

Evaluation of spinal loads in patients with low back pain (LBP) is essential to prevent further lumbar disorders. Many studies have investigated the relationship between lifting task variables and lumbar spine loads during manual lifting activities. The nature of the external load (stable versus unstable loads) is an important variable that has received less attention. Therefore, the present study aimed to measure trunk kinematics and estimate compressive-shear loads on the lumbar spine under lifting a 120 N stable load and 120 ± 13.63 N sensual unstable load in 16 healthy and 16 non-specific LBP individuals during lifting activities. The maximal lumbar loads were estimated using a quasi-static electromyography (EMG)-driven musculoskeletal model of the spine with 18 degrees of freedom (3 rotational degrees of freedom at 6 lumbar T12-S1 joints), seven rigid bodies (pelvis, thoracic, and five vertebrae), and 76 muscle fascicles. Moreover, the maximum velocity and acceleration of the thorax, lumbar, and pelvis, as well as their timing during the lifting activities were analyzed to investigate trunk kinematics. Results indicated that unstable, as compared to stable, lifting activities caused significantly larger peak L5-S1 (4677 N versus 4446 N, p = 0.021) and L4-L5 (4567 N versus 4366 N, p = 0.024) compressive loads in LBP individuals. Larger co-contraction of trunk muscles were found responsible for the larger compressive loads in LBP patients during unstable load lifting. The hand-load type (stable versus unstable) and group (LBP versus healthy) had no effects on kinematic variables and only the onset of peak kinematic parameters was significantly later in LBP patients. Slower movements with a change in movement strategy were observed in the LBP group. It was concluded that the nature of the external load adversely affected spinal loads in LBP patients thereby increasing the likelihood of further injury or pain.