Mitigation of bone loss as a result of long-duration exposure to microgravity is a serious medical concern for astronauts. With stays on the International Space Station (ISS) spanning from 6 months to a year, crew members are returning to Earth with a skeleton whose structural integrity has been significantly compromised, placing them at risk for bone fracture upon re-exposure to a gravitational environment.

Mechanical stimulus delivered to the lower extremity is beneficial to the development, growth or repair of bone. In order to monitor and quantify the mechanical stimulus delivered to the lower extremity during bouts of physical activity such as exercise an accelerometer-based activity monitoring system was developed and tested in a variety of real and simulated gravity environments.

The activity monitoring system has been demonstrated in an operational and flight-like setting to successfully record accelerations during exercise in microgravity. Acceleration and force data were collected and analyzed in various gravity conditions to reveal a positive and significant relationship between accelerations recorded at the hip and vertical ground reaction forces. This will enable future exercise prescriptions to be developed and evaluated. The small package size, wireless Bluetooth capability and the ability to be unobtrusively worn during exercise or activities of daily living make the activity monitoring system appealing not only for use in space exploration, but also for use on Earth.