During long duration space flight, astronauts must exercise to prevent bone demineralization. Exercises are used as countermeasures to the bone mineral loss. The effectiveness of the countermeasures is closely related to the mechanical stress developed during the exercises. A finite element model of the human femur was developed to determine the stress distribution during weight bearing. The model was developed using serial, transverse magnetic resonance images. The finite element analysis performed on the femur model showed an area of high stress in the femoral neck of approximately 1,200 psi. The highest stress seen in the model was approximately 2,000 psi. This information will then be used to evaluate the proposed exercises to be used as countermeasures.
People confined to wheelchairs often find that they cannot reach things that are easily reached by those who can stand. They also have a tendency to have more gastrointestinal problems than other people. In order to alleviate some of these problems, a standing assist device was designed and built, for under $1,000, to add to the frame of a manual wheelchair. The device allows the user the ability to reach things that were out of reach. It also allows the user to stand, alleviating many causes of gastrointestinal problems. The design was evaluated by a person with paraplegia.
Under the conditions of weightlessness, astronauts have a tendency to exhibit bone mineral loss in their spines and lower extremities (Oganov et al., 1992). According to Wolf’s law, bone adapts to functional demands by remodeling to reflect the distribution of stress placed on the bone (Bentzen et al., 1987). To prevent remodeling, NASA has suggested a plan of resistive exercises to produce the appropriate stress distributions to counteract the remodeling process. Prolonged bed rest studies are used by NASA to simulate a zero gravity environment on earth. During these bed rest studies, different exercises are performed on a device called the horizontal exercise machine (HEM). These exercises are the same type as those that are proposed for space flight.
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