Volume 5, Number 5     September/October 1997

Advanced Technologies

Space Device May Assess Bone Density

PORTABLE DEVICE THAT MEASURES THE relationship between bone density and physical activity in space may someday serve as a way to assess a person's risk of osteoporosis. The device, developed by NASA's Ames Research Center, Moffett Field, California, provides a record of "loading"—the major force people apply to their bodies throughout the day—by measuring and recording the force that occurs on the foot during each step. Loading is important in maintaining muscle and bone strength in the lower limbs.

This force, or "loading," can reach one and one-half times a person's body weight during walking and two to three times the body weight during running, according to Dr. Robert Whalen, head of the Musculoskeletal Biomechanics Laboratory in the Gravitational Research Branch at Ames. If muscles and bones are not used, they become significantly weaker—a problem encountered by astronauts during space flight. "With current in-flight exercise devices, it is difficult to achieve force levels equivalent to levels achieved during normal daily activity on Earth," Whalen said. "We are investigating new ways to counteract these changes with devices capable of imposing Earth-equivalent levels of force on the body in space."

The device is a force sensor, resembling a shoe insole, connected by a cable to a small computer carried in a fanny pack, which is capable of storing about two weeks of activity data. The computer samples the applied force 100 times per second. It stores only the significant maximum and minimum forces occurring during each loading or gait cycle, as well as the peak loading and unloading rate and the time at which each event occurred.

The key, Whalen explained, is determining how individuals can "load" their bodies to maintain muscle and bone strength. Because our muscles generate their own forces, we are limited by how strong our muscles are. "If you don't have the muscle strength, you can't exert high forces on bones to increase bone mass," Whalen said. "As people age, a gradual decline in activity level and intensity contributes to a decline in muscle strength, and therefore our ability to load our bones also decreases," resulting in weaker, less dense bones that are more prone to fractures.

This device will allow for the measurement of an individual's activity to assess his or her risk of low bone density from a low physical activity level. It will allow an individual exercise prescription to improve the health of an older person.

For more information, contact Dr. Robert Whalen at Ames Research Center.
Call 415/604-3280 E-mail: rwhalen@mail.arc.nasa.gov

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