Towards the investigation of the tensor fascia lata muscle and iliotibial band function in runners: the relevance of the why and the how

Abstract

From a clinical perspective, it is commonly assumed that weakness/underactivity of the gluteal muscles and overactivity of the tensor fascia lata (TFL) muscle increase the tension or strain in the iliotibial band (ITB), contributing to ITB pain/syndrome. Although differences in structure and activation of the gluteal muscles have been widely studied in several musculoskeletal conditions during running, the TFL muscle has received little attention and is poorly understood. The function of the ITB is directly related to the function of the TFL and gluteal muscles. The mechanical properties of the ITB have been investigated for its application in surgical procedures, but the relevance of its function and potential implications for clinical populations are only beginning to be investigated. This thesis encompasses two overall aims. The first aim (Part A) was to explore the activation and structure of the TFL muscle in the context of common musculoskeletal conditions of the lower limb by systematically reviewing the literature, and to address methodological issues of electromyography (EMG) applied to the investigation of the TFL muscle. The second aim (Part B) was to explore the mechanical properties of the ITB in individuals with and without musculoskeletal conditions of the lower limb by systematically reviewing the available literature and by application of ultrasound-based measures to estimate the in-vivo mechanical properties of the ITB in pain-free runners. In Part A, Study 1 systematically reviewed the literature on TFL muscle activation and structure in individuals with musculoskeletal conditions of the lower limb. Results of this review highlight that the TFL muscle has been poorly investigated in common musculoskeletal injuries. There are a limited number of studies concerning the potential role of the TFL, with small sample sizes and a range of musculoskeletal conditions, limiting the ability to draw robust conclusions for a particular condition. Two main issues were identified in EMG studies that precluded interpretation of the findings - the type of electrode and the methods used for amplitude normalisation. Previous studies have used surface recordings, which because of the small size of TFL and its close proximity to synergist muscles, are likely affected by crosstalk. Methods to normalise EMG amplitude are necessary when the purpose of the study is to compare the EMG amplitude between groups. The identification of consistent methodological problems regarding EMG raised in this review, and the lack of recommendations in this area led to the initiation of an international initiative, which aims to guide decision-making in recording, analysis, and interpretation of EMG across all applications. The Consensus for Experimental Design in Electromyography (CEDE) project aims to develop decision-making tools (e.g., a series of decision matrices) for this purpose. Two CEDE projects were undertaken as part of this thesis – “electrode selection” (Study 2) and “amplitude normalisation” (Study 3). The decision matrices in these studies were developed through an expert consensus approach and present general considerations and pros/cons of the methods, definitions, and experimental contexts or research questions with specific recommendations, including an explanation for those recommendations. Study 4 was an empirical evaluation of the application of the CEDE design recommendations to EMG recordings for the TFL muscle. This study compared surface and intramuscular EMG recordings of TFL, and different normalisation methods to highlight some key aspects when investigating amplitude features of the EMG signal and activation patterns of this muscle. Part B explored the mechanical properties of the ITB. Study 5 systematically reviewed the literature regarding the mechanical properties of the ITB for ex-vivo, in-situ, and in-vivo methods. Comparisons were made on the basis of age, sex, and anatomical regions. Differences in cadaveric and in-vivo measures were considered, as well as differences in longitudinal and transverse measurements. Although there was substantial variation in measurements between studies, even when the same methods were used, there was some evidence that individuals with musculoskeletal conditions exhibit higher strain and strain rate, and greater thickness compared to asymptomatic controls. Some methodological issues in the use of shear wave elastography were identified. Study 6 investigated the influence of transducer orientation on estimates of shear wave velocity (SWV). This study highlighted that transducer orientation requires control and that measures change predictably with orientation relative to fibre direction. Study 7 used the same method to estimate changes in SWV (as an index of stiffness) during different static and dynamic tasks, at different ITB regions. Between-session reliability was also investigated during these tasks. ITB stiffness was higher under passive or active tension, but reliability measures were acceptable only for the middle region during standing tasks. Study 8 further explored the function of the ITB in terms of the displacement of its fascial layers during a weight shift task. Findings show that the displacement of ITB fascial layers varies between individuals and that this variation could be explained by individual variation in joint movement, muscle activity, and morphological features.