NASA is committed to maintaining astronaut health during exploration missions. The maintenance of astronaut health and fitness during space missions is important to ensure the accomplishment of critical mission tasks in transit to and from the moon and Mars as well as on the lunar and Martian surfaces. Muscles and bones weaken as an adaptation to reduced gravity environments, and no exercise regimen has been effective in successfully combating these effects.

A new exercise harness for crew members on the International Space Station (ISS) has been developed out of the Center for Space Medicine (CSM), a NASA Glenn/Cleveland Clinic collaboration. The CSM harness will be evaluated during on-orbit exercise in a Station Development Test Objective (SDTO). Treadmill exercise has been used on orbit since early space shuttle flights because it has the potential to simultaneously benefit the neurovestibular, musculoskeletal, and cardiovascular systems. Extensive effort has been put forth toward the development of exercise countermeasures, yet bone continues to be lost on current ISS missions and is a major concern for future exploration missions. A treadmill with vibration isolation (TVIS) has been a major component of the exercise hardware on the ISS. However, it has not proven to be a successful countermeasure. The key to the success of load-bearing exercise in space, such as treadmill running, is the application of loads to the crew member via a subject load device coupled to the body by a harness. ISS crew members frequently report discomfort from the current types of exercise harnesses, which makes the exercise protocols less effective. Experiments on the ISS have shown that this has resulted in low ground reaction forces on orbit (approximately 60 percent of 1-g loads), which is likely to be a major factor in the observed loss of bone mineral density in crew members. This project utilized valuable insights from the backpack industry for harness configuration and distributing loads to develop an improved harness for flight. The harness is designed to better distribute loads at the shoulders and hips and to accommodate for individual differences, including gender. The project resulted in the advancement of a new, more comfortable harness design that has been developed for flight testing on the ISS.

This Station Development Test Objective (SDTO) assesses whether crew members can exercise more comfortably and at higher loads using a new treadmill harness, as compared to the existing ISS treadmill harness. The hypotheses are as follows: (i) the CSM harness will provide greater overall comfort than the current ISS treadmill harness; (ii) crew members will be able to tolerate higher external loads from the subject load device; (iii) load distribution measurements collected with strain gauge instrumentation (buckle transducers) between shoulders and hips will correlate with subjective measures of comfort; and (iv) the CSM harness will provide more effective wear and adjustability (easier adjustments, and adjustments will stay fixed once they are set, breathable biocide outer fabric).

The SDTO research protocol is aimed at improving comfort, plus increasing consistent loading for crew members exercising on the ISS treadmill(s).The CSM harnesses will be instrumented to allow for objective correlation with subjective ratings of comfort. To provide a direct comparison with the ISS treadmill harness, the load distribution and subject load device applied to the ISS treadmill harness will also be measured. The ISS treadmill harnesses will be instrumented by the crew on-orbit during a one-time setup activity. Previously, measurement of inflight load distribution of the harness or the applied external load has not been performed—these objective data sets may be correlated with subjective comfort data for improved designs and for existing and advanced concept exercise countermeasures systems requiring crew member harnessing.

The sensors to measure load distribution were developed during pilot testing of the prototype harness. This load sensing methodology will be used during the flight experiment to obtain comparisons of load and comfort between the new CSM harness and the current U.S. ISS harness.

Development of optimized crew equipment for exercise is highly relevant to the ISS and Human Research Programs. The intended outcome of the SDTO is qualitative and quantitative data to demonstrate that crew members prefer the fit and function of the CSM harness, and are able to tolerate higher subject loading during treadmill exercise aboard the ISS. Loading through the subject load system approaching 1-g-like loads (one bodyweight) is thought to be more effective for maintaining musculoskeletal health on-orbit. A second intended outcome is that the design and/or design elements identified as desirable improvements will be implemented as new operational hardware (harness/bungee) requirements for treadmill exercise. Furthermore, the crew member responses to directed questions relating to comfort, ease of use, wear, and durability will provide insight to improvements that may be made for future flight harness designs.

To meet these objectives, Glenn has developed the enhanced Zero-gravity Locomotion Simulator (eZLS), which is a new ground-based simulator developed to address the detrimental physiological effects of spaceflight on the musculoskeletal system through improved exercise countermeasure systems.  The eZLS has the ability to mimic the vehicle and exercise device interfaces found on the International Space Station (ISS) and other vehicles being developed for future space exploration. It is important to replicate the interface configurations seen on the ISS and future vehicles to understand how the interface may affect the resulting forces on the muscles and bones. The eZLS is also a test bed for future exploration missions and can be used to simulate locomotion in partial gravity environments including the moon and Mars. 

In an effort to develop improved exercise routines and equipment for astronauts, the eZLS allows scientists and engineers to conduct research with human participants in the following areas:

• Understanding the metabolic cost of locomotion in partial gravity
• Improving crew comfort during exercise
• Developing exercise prescriptions
• Optimizing hardware
• Developing and characterizing advanced exercise device concepts for exploration missions

Aside from space applications, experiments conducted using the eZLS may help medical researchers improve their understanding of the role of exercise in the prevention of osteoporosis on Earth. The deterioration of bone and muscle during osteoporosis is similar to what occurs in an astronaut’s body, although the process is greatly accelerated in space.

Glenn’s Exercise Physiology and Countermeasures Project is also performing simulations of locomotion in lunar gravity to assess the physiological demands of performing critical mission tasks such as carrying equipment and recovering from a fall on the moon. Since the critical mission task assessments will require the cooperation of different laboratories in other locations, Glenn is developing a database to store, process, and archive the physiological data collected from these assessments.

The Orion crew exploration vehicle, lunar lander, and/or lunar habitats may also have exercise equipment to keep crewmembers healthy and fit for duty. Glenn’s Exercise Physiology and Countermeasures Project is developing advanced exercise device concepts to meet the requirements for exploration missions. There are special challenges posed by providing equipment with adequate capability while meeting volume, mass and power limitations imposed by the vehicle or habitat.

Apollo astronauts are providing valuable insight regarding the benefits of exercise and the limitations of the equipment they used during the Apollo missions. When this information is combined with the critical mission task assessment data, the results will aid in the development of new advanced concept equipment designs and exercise prescriptions for exploration missions.