Abstract
Morphological and mechanical properties of the plantar fascia have been suggested to play a role in developing plantar fasciitis. Clinically, plantar fasciitis has been characterized by an increase in thickness and a decrease in stiffness of the fascia. However, the true etiology and progression of plantar fasciitis are unknown. A more thorough knowledge of the tissue properties prior to injury is important as there are currently no know preventative strategies. Understanding how healthy plantar fascia tissue reacts and it behaves to imposed mechanical demands and stressors may bridge the literature gap between healthy tissue and plantar fasciitis symptoms. Therefore, there is need to determine the acute effects of imposed running demands on mechanical and morphological properties of the PF, moving the science towards preventing plantar fasciitis, rather than merely treatment. This dissertation was designed to introduce three chapters to explore the effects of running on plantar fascia thickness and stiffness, as well as take a next step and evaluate run and foot mechanics potentially associated with plantar fasciitis.The first chapter introduces the topic and the conundrum that is a gap in the literature concerning the timeline and causations behind plantar fasciitis. Overexposure to imposed mechanical demands, such as running, as well as the biomechanical viscoelastic properties the plantar fascia displays when exposed to these demands, are two of the theoretical foundations upon which this dissertation is built. It is not surprising that plantar fasciitis is often diagnosed in running type sports. Thus, a strategy to observe these tissue changes was to evaluate multiple types of running durations, intensities, and frequencies.
The second chapter details the first of the three studies conducted for the present dissertation. Chapter two focuses on increased intensity of the mechanical loading due to running speed and intensity, combined with acute fatigue. The purpose of the study was to evaluate the effects of repeated 400 m sprints on plantar fascia thickness and stiffness, while a secondary purpose was to explore the predictability of arch height index measurements on tissue changes. Sixteen participants completed five maximal effort 400 m sprints, followed by additional maximal effort trials until fatigue. For the first study, it is reported that plantar fascia stiffness and thickness decreased acutely in response to a single session of high intensity track repeats. Both properties returned to pre-run values after 30 minutes of rest. Plantar fascia properties also appeared to have been related to arch height index, as there was a decrease in foot arch measurements from pre-to post-run.
The third chapter focuses on increased duration and frequency of mechanical loading. While the first study introduced a short bout, high intensity type of running, the second study evaluated multiple efforts of long distance running. The purpose of this study was to investigate the effects of three consecutive day 5 km maximal effort runs on plantar fascia thickness and stiffness in healthy, active individuals. The same 16 participants completed this protocol at least 7 days after they had completed the protocol for study 1. In the third chapter, it can be reported that plantar fascia thickness in a rested state (pre-run) increased across three sessions of maximum effort 5 km running on three consecutive days. To the knowledge of the author, this is a novel finding and was reported in the literature for the first time. Furthermore, within each day, thickness and stiffness decreased post-run and returned to pre-run values after 30 minutes of rest. Mechanical overloading and insufficient rest may induce conformational change of the plantar fascia.
The fourth chapter introduces a new population, new running surface, and motion analysis. Study three evaluated people with resolved plantar fasciitis to understand how previously injured tissue recovers, and whether it recovers. Additionally, the third study aimed to evaluate run and foot mechanics between aforementioned population and individuals without history of plantar fasciitis. Thus, the purpose of that study was to investigate the effects of 30 minutes treadmill running on plantar fascia properties and running mechanics in individuals with resolved plantar fasciitis (RPF) and those with no history of plantar fasciitis (NPF). It can be reported that both groups experienced the same decrease in thickness and stiffness immediately after the run. However, people with RPF had a significantly thicker and stiffer tissue compared to never before injured individuals. Additionally, the stiffness of the tissue appeared to alter foot mechanics as it prevented the RPF group from undergoing vital medial longitudinal arch dorsiflexion during the stance phase. It is unclear whether this findings increases risk of re-injury and whether plantar fasciitis does have long-term effects on both the soft tissue, as well as foot mechanics during running.
Lastly, in chapter five, the dissertation comes to a conclusion. Questions still remain regarding the possibility of utilizing the morphological and mechanical properties of the plantar fascia to determine risk of plantar fasciitis. However, the present series of studies affirms that the plantar fascia is a viscoelastic material in vivo, which can be quantified via ultrasound. Individuals, whether without plantar fasciitis history or those with resolved plantar fasciitis, displayed the same biomechanical response to mechanical loading. This response to the plantar fascia occurred regardless of duration, intensity, or frequency of the imposed mechanical demand. Future explorations should