Marras et al (1999) studied back motion in 335 patients with chronic low back pain and 374 healthy, asymptomatic subjects. They considered symmetric and asymmetric motion in flexion-extension, lateral bending, and rotation. They not only measured range of motion, but also velocity and acceleration. The emphasis was on the performance of tasks.
Using complex equations that reflect patterns of movement, they were able to discriminate patients from healthy subjects with up to 94% accuracy. They found greater differences in velocity and acceleration than in range of motion. Performance was reduced more in asymmetric tasks. Most interesting for the present discussion, they found that motion profiles were very different in low back pain of muscular vs structural origin. They then used these measures to track patients over time and against response to treatment. As pain improved, so did velocity and acceleration (but not range of motion). Patients with persistent pain did not show any such improvement.
Many other studies emphasize the importance of dynamic patterns of movement (Esola et al 1996, Steffen et al 1997). There may be change in the balance of lumbar and pelvic movements, or between flexion and extension. There may be different mobility in the upper and lower lumbar spine. Spinal movement occurs in three dimensions and there may be complex changes in coupled movements. Perhaps most important of all is what happens during movement and how the various musculoskeletal components work and interact, even if that is more difficult to measure.
Davis et al (2002) studied how mental processes can affect spinal movement and loading. They measured spinal loads in 60 subjects, and the impact of simple or complex mental decisions before or during lifting. They found that simultaneous, more complex, and faster decisions led to poorer muscle coordination and greater loads on the spine. They suggested this might be a mechanism by which greater psychosocial stress could increase biomechanical load and the risk of injury or dysfunction.
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