Quantification and Evaluation of the Biomechanical Behaviour of the Trunk During Fundamental Tasks: Should the Thoracic Spine be Considered?

Thoracic spine research is sparse relative to the lumbar spine. A better understanding of thoracic spine mechanics may provide insight into pain mechanisms in both spine regions. This dissertation quantified and evaluated the biomechanical behaviour of the thoracic spine during fundamental tasks, to determine if monitoring the thoracic spine is necessary in the investigation of spine mechanics. The number of trials required for repeatable and reliable trunk kinematic and muscle activation measures across maximal ranges-of-motion (ROM) were determined (Study #1). Thirty participants performed 10 trials of upright standing and maximal trunk ROM. Most measures demonstrated high repeatability, with two to five trials required.
The head and arm positions enabling maximal spinal ROM were determined in Study #2 using 24 participants, as relationships have been shown in head, arm, and upper back motion. The greatest angles were produced with the active head–loose arm, active head–crossed arm, and active head–abducted arm positions for maximum flexion, bending, and twisting, respectively. Studies #3 and #4 determined the segments and superficial muscles that were necessary to quantify the motion and muscle activation characteristics of the trunk, specifically the thoracic spine. Thirty participants performed upright standing, maximum trunk ROM, and thoracic ROM. A four-cluster marker set quantified motion for most movement tasks. Of the 16 muscles tested, 10–14 were necessary to evaluate trunk muscle activation. These studies provided insight into thoracic function in relation to the lumbar spine. Lumbar co-contraction was quantified during thoracic movements in Study #5. Thirty participants performed upright standing, maximum trunk ROM, and thoracic ROM. Thoracic flexion, bending, and twisting elicited 67%, 45%, and 55% greater co-contraction in the lumbar region than upright standing, demonstrating that the thoracic spine impacts the muscular response of the lumbar spine. These studies quantified and characterized the biomechanical behaviour of the thoracic spine during fundamental tasks. As the thoracic spine demonstrated differences in motion and muscle activation characteristics along its length and compared to the lumbar spine, knowledge of thoracic spine behaviour and interactions may aid in clarifying the behaviour of and elucidating pain mechanisms within the thoracic and lumbar spine regions.