The objective of our research is to investigate and characterize cardiovascular, pulmonary; and musculoskeletal responses (i.e., foot forces) to ergometer exercise in hypogravity conditions (between 0 and 1 g) to fill the gap between those gravitational levels. Astronauts on space missions experience various detrimental physiological effects including (but not limited to) muscular atrophy; diminished cardiopulmonary function, and redistribution of internal fluids .

These changes can lead to orthostatic intolerance and diminished exercise capacity; upon return to a gravitational environment. Artificial gravity (AG) combine with exercise has been propose as a multi-system countermeasure; that can provide benefits to multiple physiological systems at once. However, the specific parameters and conditions (i.e., gravitational level, intensity, duration); under which this exercise should be ideally performed to be most effective are still unknown.

Simulate hypogravity conditions on Earth

We conducted a ground-based study on healthy human subjects; using a HDT/HUT paradigm to simulate hypogravity conditions on Earth. Specifically, we investigated the effects of multiple gravity levels (including Microgravity, Moon, Mars, and Earth) by varying posture and exercise intensities to generate gravitational dose-response curves between simulated 0 and 1 g.

The Altered-gravity Exercise Platform Simulator (AEPS) is a custom-built platform design; to perform cycling ergometer exercise in multiple, simulated gravitational environments. Using HDT and HUT positions, the AEPS can replicate known gravity-induced fluid shifts based on appropriate tilt angles. Thus, the platform is capable of providing a -6° HDT, a +9.5° HUT, a +22.3° HUT, and a +90° upright orientation, corresponding to Microgravity, Moon, Mars, and Earth gravitational conditions, respectively.

All subjects tested were able to successfully complete the exercise protocol except for one subject; who exceeded the maximum blood pressure criteria and thus, the testing session was terminated immediately. The subject was completely excluded from the study (i.e., subject not included in the cohort of 14 subjects analyzed); and therefore any related data have not been included in the results reported in this manuscript.

Cardiopulmonary responses at rest

Cardiopulmonary responses at rest due to postural changes are consistent with previous studies. Pisk et al. measured resting pulmonary gas exchange in eight subjects in standing upright; supine, and microgravity conditions (Spacelab flights SLS-1 and SLS-2). Their results showed that VT decreased in the supine position with respect to standing upright; and it decreased even more in real microgravity conditions.

Subjective data in simulated microgravity conditions showed the lowest comfort punctuation. Major complaints reported were lower back pain and discomfort in the arms due to the handlebars. Future suggestions that could improve these issues include a better platform lining, intermediate cycle ergometer positions; and different handlebar configurations to enable a more ergonomic positioning of the subject on the platform.

The results showed that there are not significant differences in human cardiopulmonary and musculoskeletal responses; between Mars and Earth experimental conditions. This indicates some degree of similarity in human performance during ergometer exercise under Martian and terrestrial gravitational environments; suggesting that this type of exercise conducted under a gravitational stress of ∼3/8 g could provide similar physiological stimuli than cycling under 1 g on Earth.