Effects of Lumbar Spine Posture on Thoracic Spine Range of Motion and Muscle Activation Patterns While Standing

INTRODUCTION Biomechanical studies of spine range of motion (RoM) and electromyography (EMG) typically focus on the lumbar region. The thoracic spine remains a topic less investigated in the literature, especially in terms of complex/relative motion coupled with EMG patterns. Research on complex motion patterns of the thoracic spine is directed towards kinematic measures only [1, 2] and usually focuses on only one area of the spine. Therefore, the purpose of this study was to quantify the muscle activation and movement patterns of the thoracic spine when the lumbar spine was placed in known postures. METHODS Thirteen male participants from a university population were recruited. A Vicon motion capture system (Oxford, UK) was used with 63 markers to track full body kinematics. Eight rigid plates (24 markers total) were used to partition the spine into upper, mid-, lower thoracic, and the lumbar spine segments (UT, MT, LT, LUMBAR, respectively). EMG was collected using two 8-channel Bortec amplifiers (Calgary, Canada) on 16 muscles bilaterally: upper (UTES), lower (LTES) thoracic, and lumbar (LES) erector spinae, superficial lumbar multifidus (SLM), latissimus dorsi (LD), rectus abdominis (RA), internal (IO) and external (EO) obliques. Seven postures were adopted with three repeats of each. Four postures were determined by lumbar position and corresponding thoracic movement: lumbar neutral with thoracic flexion (Ln_Tf), lumbar neutral with thoracic twist to the right (Ln_Tt), lumbar flexion (to 50% of maximum) with thoracic flexion (Lf_Tf), and lumbar flexion (50%) with thoracic twist to the right (Lf_Tt). The remaining three were maximum flexion (MF), and unilateral (right side) maximum lateral bend (MLB) and maximum axial twist (MAT). RESULTS Kinematic results showed significant interactions for both flexion (F(18, 288)=28.29, p<0.001) and twisting (F(18, 288)=5.18, p<0.001) between postures and spine segments. EMG results also showed a significant interaction between posture and muscle (F(90, 1152)=5.69, p<0.001). The LT segment showed the greatest flexion during the thoracic flexion trials while the UT and MT segments did not show a change in RoM when transitioning from a neutral lumbar to a flexed lumbar, as shown in Figure 1a. Selected muscles during thoracic twist are shown in Figure 1b and illustrate the contribution of the right IO and LD muscles in the generation of axial movement. DISCUSSION & CONCLUSIONS Generally, more flexion was found in the lower region of the spine (lumbar and LT) compared to the UT and MT segments. Also, flexion in the lumbar spine tended to increase flexion in the LT segment. The opposite tended to occur during twisting, where an increase in flexion was associated with a decrease in axial twist, especially in the MT region. Right IO and LD showed the greatest activation during all the twisting trials. This study was the first to show EMG patterns of various regions throughout the spine during thoracic motion trials as well as quantifying the RoM differences. Previous research of thoracic spine motion has been done qualitatively and without EMG [1, 3], thereby limiting the amount of information obtained. Results from the current study will facilitate future work quantifying thoracic and lumbar spine motion resulting from upper-limb movement during tasks such as reaching. REFERENCES [1] Edmondston, SJ et al. (2007). J Manip Physiol Ther, 30(3); 193-199. [2] Preuss, R and Popovic, M (2010). J Electromyogr Kines, 20(5); 823-832. [3] Willems, JM et al. (1996). Clin Biomech, 11(6); 311-316. ACKNOWLEDGEMENTS CRE-MSD for funding and A. Schinkel-Ivy for her assistance.