Leg muscle structure and function in long-distance runners: Implications for medial tibial stress syndrome

Background: Current strategies used to prevent and manage medial tibial stress syndrome (MTSS) for long-distance runners are ineffective. To improve these strategies, we need to identify modifiable risk factors upon which future prospective treatment intervention studies and clinical management recommendations can be based. Research question: The overall aim of this thesis was to systematically ascertain whether leg muscle structure and function are risk factors associated with the development of MTSS in long-distance runners. Methods: To achieve the aim of this thesis, a systematic literature review was initially conducted to clarify whether the structure and function of the leg muscles were associated with MTSS (Chapter 2). The findings of this systematic literature review then helped to guide the development of the experimental research protocol (Chapter 3), which was used in the retrospective and prospective studies (Chapters 4, 5 and 6) to address a major gap in knowledge related to possible modifiable risk factors associated with developing MTSS. Sixty three long-distance runners (MTSS symptomatic = 11, asymptomatic = 52) were included in the retrospective and prospective studies of this thesis. Of the 52 asymptomatic long-distance runners assessed at baseline, 2 participants developed bilateral MTSS (incidence rate = 4.4%), 43 participants completed 12 months of running free of MTSS injury and 7 participants were lost to follow up. The retrospective and prospective studies aimed to determine whether the modifiable factors of leg muscle structure (leg girth and in vivo leg muscle size) and function (leg muscle strength and plantar flexor endurance capacity) of long-distance runners differed between MTSS symptomatic and asymptomatic long-distance runners (Chapter 4) or were associated with MTSS development (Chapter 5). Finally, modifiable factors reported to influence tibial bone load during the stance phase of running, including leg alignment and the active peak force, were assessed retrospectively and prospectively to determine whether they were associated with MTSS development (Chapter 6). Major conclusions: Based on the results of this thesis, it is recommended that clinicians assess plantar flexor muscle strength and endurance of asymptomatic and MTSS symptomatic long-distance runners. Asymptomatic long-distance runners with less gastrocnemius than soleus muscle strength could be at an increased risk of developing MTSS, and clinical management should aim to improve gastrocnemius muscle strength for these individuals. Improving the strength of the flexor hallucis longus, soleus, tibialis anterior and peroneal muscles is also recommended for individuals suffering from MTSS. Incorporating these recommendations into clinical management could improve the outcomes for long-distance runners at risk and currently suffering from MTSS.