Dr. Peter R. Cavanagh is leading a project to develop and validate a miniaturized accelerometer-based system that could be worn by astronauts to collect data on how much load stimulus is put on the lower body each day and to interpret the information in relation to bone health. After validation, the final product – the Accelerometric Daily Load Sensor – will consist of a small shoe-mounted sensor that will transmit signals to a BioWATCH, a device that can collect, store and transmit data on many human body systems. Software in the spacecraft or lunar habitat will read the data to determine how much more exercise is needed to maintain bone health.
Monitoring Bone Health by Daily Load Stimulus Measurement During Lunar Missions
Peter R. Cavanagh, Ph.D., D.Sc.
University of Washington
One of the key questions that remains unanswered as we prepare for prolonged lunar sojourns is the degree to which living and exercising on the lunar surface will provide an osteoprotective stimulus to prevent the loss of bone mineral density (BMD) that has been observed in microgravity. The concept of daily load stimulus is useful in this regard since it has the potential to estimate the "dose" of load to the lower extremities that will maintain skeletal integrity even in the setting of concurrent therapeutic drug and exercise countermeasures. Most observers believe that some form of supplementary exercise will be required during lunar activity, but this will need to be optimized to provide the most efficient use of crew time.
Cavanagh et al. (J. Biomech., 2010) have recently published reports that on average, only 43 minutes of the approximately 150 minutes assigned for exercise during a day resulted in loaded, osteoprotective exercise. Given the continued loss of BMD observed in crew members after long-duration spaceflights, this amount of loaded exercise is not enough to preserve an acceptable amount of bone strength.
Original Project Objectives
- Allow quantification of a crew health risk.
- Develop technologies to monitor a health risk.
- To develop hardware based on Micro Electro Mechanical Systems (MEMS) technology that can unobtrusively monitor the accelerations applied to the body and interface with an ambulatory monitor.
- To extend the Daily Load Stimulus Algorithm to account for recent developments in bone mechanobiology, to incorporate accelerometric signals and to write software to perform this analysis in real-time.
- To demonstrate the feasibility and validity of the approach in Earth's gravity and in 1/6 gravity analogs: the enhanced Zero Gravity Locomotion Simulator (eZLS) at NASA Glenn Research Center and the lunar bedrest analog at the University of Texas Medical Branch.
- To integrate the hardware and software into a package suitable for flight development.
1. Foot forces suggest IVA lunar and Martian locomotion (walking, running, loping, hopping) alone may not be osteoprotective, and that a simulated lunar EVA (body weight plus ~200 Earth lbs of suit mass) locomotion may not be osteoprotective.
2. Foot forces suggest that locomotion in a simulated Martian EVA (body weight plus ~200 Earth lbs of suit mass) may provide adequate loading under some locomotion conditions to be osteoprotective depending on the duration of the activities.
3. Lunar and Martian hopping and loping result in higher foot forces than walking, while running provides the highest foot forces in any one environment.
4. The Artificial Neural Network (ANN) developed can precisely recognize lunar locomotor activity, which is useful during remote monitoring scenarios.
5. An ankle mount configuration was tested in a small cohort (n=6). There is a marked decrease in signal magnitude between the ankle and in-shoe mounting. The ANN will need to be retrained with ankle mount data.
The wireless activity tracking device has been designed, manufactured, and tested in a series of studies in 1g, 1/6g, and 3/8g simulated environments. Initial data analysis is starting to reveal potential crew health risks to bone health maintenance in reduced gravity environments. The sensor has been interfaced with a Smartphone to allow data collection in the field. This is an important step in moving towards flight readiness. The transition to the Smartphone interface has allowed a spin-off use of the wireless sensor system in a study aimed to reduce the rate of loading during running and ultimately reduce the rate of injury in female runners. The NASA Human Research Program (HRP) has decided to not utilize the lunar bed rest model, and as such the system has not been tested in that analog as originally proposed. An alternative test environment such as a parabolic flight would be an ideal environment to test the system in, and the feasibility of conducting such a test is under review. The initial parabolic flight has demonstrated the system is ready for a full parabolic flight study. The study would provide the data needed to validate the system and compare to the results of the simulated reduced gravity environments test conducted in the eZLS. These tests would help to bring the activity sensor system to a high Technology Readiness Level (TRL=7). Final data analysis will help determine if additional software updates are necessary and help solidify drawings and design requirements that will be prepared for a CDR during Year 4.
Year 4 Aims
• Further enhance the Activity Recognition library to recognize activities collected in the ankle-mounted configuration and to include automated detection of additional mission critical tasks such as ladder climb, rock translation, platform jump down, squat exercise, and obstacle avoidance.
• Continue to test the interface between our wireless sensors and the BioNet software framework in the laboratory setting, for future automated data management aboard the International Space Station (ISS).
• Utilize the Smartphone platform as a portable data logger that is capable of communicating with the wireless sensors and the BioNet software framework.
• Test the activity monitoring system on a parabolic flight as a validation of system operation in a simulated Martian (1 parabola), lunar (2 parabolas) and microgravity (22 parabolas) environment.
• Review results from a data-sharing arrangement with the Integrated Medical Model team at NASA Glenn who received Jump Down data from this study, and with colleague Joern Rittweger who received static hopping data to assess the loss of energy during a stiff legged hop at 1g, 3/8g, and 1/6g.
• Present data at the annual NASA Human Research Program Investigators’ Workshop and other scientific meetings.
• Prepare manuscripts for publication to peer reviewed journals.