Tibial stress fractures are common in runners. However, it is unclear what factors are associated with tibial stress fractures. This study aimed to investigate 1) magnitudes of bone contact forces occurring while running 2) whether or not repeated application of running loads is sufficient to explain tibial stress fractures and 3) whether or not muscle fatigue alters the potential of tibial stress fractures. Tibial stress fractures were predicted through an estimation of the minimum number of cycles to failure (Nfail) using an integrated experimental and mathematical modeling approach. Short running trials within a speed range of 3.5-4 m/s of ten male runners were evaluated with a coupled force plate and 3 dimensional motion analysis system. The collected data were used to estimate joint reaction forces (JRF) and joint moments. Using these JRF and muscle forces predicted from optimization, 2-D bone contact forces at the distal end of the tibia were determined. Next, tibial stresses were estimated by applying these bone contact forces to a tibial model, which were then used to predict the Nfail. All procedures were repeated after plantarflexors fatigued from prolonged running. This study found that peaks of compressive and posterior shear forces occurred during mid stance, and these peaks equaled 8.91 ± 1.14 BW and -0.53 ± 0.16 BW, respectively. These bone contact forces led to a backward bending of the tibia during most of the stance phase and resulted in the maximum stresses of - 43.4 ± 10.3 MPa on the posterior face of the tibia. These maximum stresses predicted the group mean of Nfail as being 5.28*10⁶ cycles. However, 2.5% to 56% of population of runners have a chance of getting tibial stress fractures within 1 million cycles of a repeated foot impact. Within the context of muscle force and stress estimation procedures used in this study, Nfail appeared to increase after fatigue, not decrease as we hypothesized. / Graduation date: 2005

Thesis PlanB (M.S.)--University of Wisconsin--Stout, 2007. / Includes bibliographical references.

Problem: Track and field athletes, along with cross-country athletes have multiple and back to back seasons, creating overuse injuries. Stress fractures or stress reactions to the bone are the overuse injuries focused on in this study and literature review. There is a lack of information in the literature regarding stress reactions. Purpose: The goal of the study is to understand more information about stress reactions to bone and possibly increase the knowledge of health care professionals. Methods: Three case studies were examined through pre-existing medical chart notes and athletic trainer's notes regarding the stress reactions. A literature review was also performed to provide further information about stress fractures and stress reactions. Conclusions: There are multiple risk factors for stress injuries. All three of the athletes in the case studies are female, which is found to be a risk factor. Many risk factors need more studies to provide support. Magnetic Resonance Imaging (MRI) was obtained in all three case studies where there was found to be a stress reaction. These three females also had a recent increase in activity level and had similar symptoms to each other and what is found in the literature.