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Human Research Program

Digital Astronaut: Bone Remodeling Model

Active Technology Project

Project Introduction

Significant progress has been made with regard to the plan outlined in the 2014 report for building in the effects of exercise induced loading on preserving bone mineral density (BMD) with initial focus on the femoral neck. First, let’s review the previous progress accomplishments. DAP completed work on a mathematical model of bone physiology that was able to predict the amount of bone lost during a period of skeletal unloading in bed rest up to 180 days. While that provided an understanding of bone loss in the absence of any exercise countermeasure in microgravity, further development of the computational model was required to incorporate the effects of skeletal loading via exercise. During the last year, DAP delivered an updated model that both improves the accuracy of the original model and includes a Daily Load Stimulus (DLS) algorithm that predicts the effect of physical activity on BMD. In conjunction with the DLS algorithm, a finite element model (FEM) of the proximal femur was integrated into the computational modeling framework for a higher fidelity prediction of the three-dimensional stress-strain environment in bone due to exercise loading, which in turn drives the bone remodeling process. Since we focused on the femoral neck, a level one approach was used in which the stress values in the femoral neck were averaged to obtain an effective strain. Currently, the DLS algorithm has been verified and validated for predicting the cumulative effect of normal walking and running on the bones of healthy adults in Earth gravity, as well as for astronauts following long-duration spaceflight. Overall, the simulation results instill high confidence in the model’s capability to correctly predict bone maintenance from walking and running both for the normal and post-flight astronaut populations for up to one year. As a result of this work, NASA now has a computational bone physiology simulation framework that can predict bone loss in the absence of skeletal loading for up to 180 days and bone preservation from gait loading with a focus on the femoral neck. This framework sets a firm foundation towards establishing a physiologically based model that can help NASA researchers to design optimal exercise protocols that can preserve the long-term bone health of astronauts. Our recent and future work has now turned to extending and developing the computational model for the total proximal femur. This involves gathering together additional data for the total proximal femur. This will include data from a 90 day bed rest study as well as data from the 70 day and 120 day studies. The post flight data from a group of 16 astronauts who participated in 4 to 6 months flights will also be considered. More »

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