The Role of Latissimus Dorsi in Trunk Movement and Stability

Abstract

The latissimus dorsi is the most expansive muscle in the human body, spanning from the pelvis, lumbar spine, ribs, and scapula before inserting on the humerus. Its broad attachments suggest a role in trunk movement and stability, and it is often targeted in rehabilitation with the gluteus maximus due to their link through the thoracolumbar fascia. However, EMG evidence for its role in trunk tasks is inconsistent, partly due to methodological limitations. This thesis addresses these issues to clarify how the latissimus dorsi contributes to trunk function. Chapter 1 outlines the anatomical and theoretical basis for latissimus dorsi’s role in trunk movement and stability and highlights methodological issues in existing EMG research. Chapter 2 presents a systematic review and metaanalysis showing limited evidence of high activity during ipsilateral rotation and stronger evidence of low activity during contralateral rotation, extension, and trunk stability tasks, along with widespread use of surface electrodes and varied normalisation tasks. Chapter 3 and 4 evaluate key EMG methods. Chapter 3 shows that shoulder extension elicits maximal latissimus dorsi activation and is the most appropriate MVC normalisation task. Chapter 4 shows that surface electrodes are valid for submaximal trunk tasks, while indwelling electrodes are required for maximal loading and stability tasks. Chapters 5 and 6 apply these validated methods to examine latissimus dorsi activity during trunk movement and stability tasks. Chapter 5 shows activity remains below 20% MVC during submaximal trunk tasks and reaches only 31-43% MVC during maximal loading. Chapter 6 demonstrates low activation levels during trunk stability tasks, with no effect of contralateral arm support. Chapter 7 summarises the findings and discusses clinical implications. Overall, this thesis demonstrates that latissimus dorsi has only a limited role in trunk movement and stability, refining its relevance in clinical practice.