Date of Award


Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)


Physical Therapy

First Advisor

Susan Jeno


Purpose/Hypothesis: Spinal rotation is a very common movement that occurs multiple times each day during normal daily activities or even during certain sport performances. Since this motion is a contributing factor to back injuries, it will be important for physical therapists to consider this concept with rehabilitation programs for current back injuries as well as prevention of future injuries. The LD has attachments to many areas of the body, including the spine, humerus, scapula, and pelvis, which explains why this muscle also contributes to multiple actions at the trunk and upper extremity. Due to the attachment sites and the large size of the LD, this muscle is capable of influencing spinal motions during different activities. However, while there is some research regarding muscles involved with spinal rotation, there is currently limited findings for the LD and its contributing factors to spinal rotation. The purpose of this study was to improve the understanding and determine the muscle activity the LD has during spinal rotation and compare that muscle activity throughout different fixed and non-fixed positions.

Methods: Participants progressed through ten spinal rotation positions (standing non-fixed rotation right/left, quadruped rotation right/left, and standing rotation right and left with arms fixed on the wall at 45°, 90° and 120° of shoulder flexion). While performing pelvis rotation in testing positions, muscle activity was recorded using EMG surface electrodes. Muscle Activity was normalized by using Maximal Voluntary Contraction (MVC) to normalize muscle activity. Findings were analyzed for significance at α=.05.

Results: Significant differences were found in LD EMG activity in fixed and non-fixed movements with the ipsilateral LD being more active in fixed rotation. The ipsilateral LD EMG activity was found to be significantly greater in fixed rotation than right or left MT and ES, as well as the contralateral LD. During non-fixed spinal rotation, the ipsilateral ES EMG activity was found to be significantly greater than the right or left MT and LD, as well as the contralateral ES.

Discussion/Conclusion: The findings propose the LD contributes significantly more than the MT and ES during fixed ipsilateral spinal rotation. This implies that while performing closedchain spinal rotation the LD has better positioning to participate in spinal rotation or spinal stabilization. During non-fixed positions the ipsilateral ES were most active during spinal rotation. This suggests that while performing non-fixed rotation the LD is not in optimal position to rotate or stabilize the spine. Future studies should analyze the impact on gender differences, hand dominance, and larger sample size in muscle activation.

Clinical Relevance: This study is for clinicians to better understand how the LD, MT, and ES contribute to rotation of the spine. Once clinicians understand how different muscle groups affect spinal rotation, they will be able to improve the evaluation and intervention process in a variety of pathologies such as LBP. Physical therapists will be able to determine the source of pain more efficiently and prescribe more effective exercises. Understanding the actions of these muscles and how they affect spinal rotation will allow the rehabilitation process to be more time efficient and cost beneficial.