The overall aim of this thesis is to elucidate the in vivo function of the iliotibial band (ITB) and its mechanical contributions to locomotion by combining new advances in imaging with neuromuscular techniques (i.e., strain tracking, shear wave elastography, direct muscle stimulation, and musculoskeletal modelling). The thesis focuses on how force is transmitted through active contraction of the in-series muscles attached to the ITB to provide insight about the aetiology and rehabilitation of injuries like ITB syndrome (ITBS).

Chapter one of this thesis first outlines the misconceptions of functional anatomy of the ITB, including the experimental and methodological limitations of current literature surrounding the ITB’s function. This is followed by a discussion of the gaps that our current understanding has left, and the specific questions that this thesis will address.

Chapter two contains a detailed narrative literature review summarizing the existing knowledge and understanding of the ITB’s anatomy, relationship with its in-series musculature, and clinical misconceptions that exist today. Published research often neglects the insertion of gluteus maximus (GMax) into the ITB and thus its capacity to transmit force through the ITB. The literature reports confounding evidence for the function of tensor fascia latae (TFL) and gluteus maximus which both insert entirely or partially into the ITB. This chapter calls for investigation into understanding how the ITB can transmit forces generated by these muscles in both healthy individuals, as well as individuals with pain due to ITBS.

Chapter three details the development of an algorithm to track strain in the ITB using ultrasound imaging through the trials and tribulations of the evolution of a tendon tapping technique proposed to quantify force in soft tissues. This chapter documents in detail the extensive testing of ultrasound image processing algorithms for detection of displacement and deformation using brightness mode ultrasound images, as well as the deformation of a single radio frequency line of data due to induced shear waves. The development and testing of these processing algorithms led to the final software implementation used to track the displacement of the ITB due to contraction of GMax and TFL for chapters four and five of this thesis.

Chapter four presents the validity, reliability, and feasibility of strain tracking in the ITB using ultrasound imaging during isolated muscle contractions. This study demonstrated the utility of this strain tracking technique and provided evidence that data collected within a single data collection session and by a single operator, produces repeatable and reliable strain measures. This chapter also shows that this technique can be used to differentiate between different levels of strain occurring due to different levels of contraction.

Chapter five expands on the technique developed and presented in chapter four to determine the effect of contraction of each ITB-in-series muscles, knee posture, and ITB region on strain development in the distal ITB. From this work it is clear that there are different transmission pathways within the ITB during contraction of each muscle, as indicated by the strain in different regions of the ITB. When TFL is stimulated, more strain is generated in the anterior region of the ITB, irrespective of knee posture. When GMax is stimulated, strain is transmitted via the posterior portion of the ITB (albeit less than for TFL stimulation).

Chapter six models the behaviour of force transmission through different regions of the ITB due to changing gait parameters. A lower body musculoskeletal model was developed to elucidate the effect of changing gait parameters aimed at changing the forces and strain experienced by the ITB during walking and running. Motion capture, ground reaction forces from an instrumented treadmill, and fine-wire electromyography (EMG) data were collected and applied via this musculoskeletal model. Changes in EMG, muscle tendon unit forces, and ITB tendon strain in response to changing gait conditions (narrow and wide step width, incline and decline walking and running) were investigated.

Understanding the function of the in-series musculature and the separate force transmission pathways within the ITB will further inform our understanding of the aetiology and management of painful conditions like ITB syndrome. Though detailed mechanisms of compression and impingement of the ITB have been presented, the development of these loading scenarios is still rather ambiguous. Understanding the capacity for force transmission from TFL and GMax through the ITB across the lateral knee allows us to hypothesize that changes in muscular activation may cause atypical loading patterns as compared to normal, level ground gait. These investigations support the theory that with changes in muscular activation, we see changes in force transmission, and resultant ITB strains experienced in different regions of the ITB. Together, these findings and the development of our methods provide insight and implications to a broad range of disciplines, such as musculoskeletal health, physiotherapy, and functional anatomy