rate monitor (Polar Electro, Finland). Data was subsequently downloaded to a laptop computer (Satellite 1110, Toshiba, J
PRELIMINARY STUDY OF THE PHYSIOLOGICAL DEMANDS OF MARS ANALOGUE EXTRAVEHICULAR ACTIVITY Cardiorespiratory &Vascular Dynamics Lab
Abstract The purpose of this study was to investigate the physiological demands of simulated Mars exploration as a first step in determining the physical fitness requirements of interplanetary explorers. The study took place during a geological training mission to the Mars Desert Research Station (MDRS) in Utah, USA. Six crew members were outfitted with a CosMed portable gas exchange analyzer to determine metabolic cost during two hill runs to exhaustion and during at least two extra-vehicular activities (EVA)s while donning an analogue Mars suit. The average VO2 peak during a hill run was 52.4 ± 0.99 ml/kg/min. The peak VO2 reached during a given EVA was 35.87 ± 0.78 ml/kg/min. There was a correlation between aerobic fitness and distance covered during an EVA (R2=0.34) resulting in a greater demand for oxygen in a given time period for more fit crew members (R2=0.86). Therefore, we recommend that future simulations use distance covered rather than time elapsed as the criteria for termination of EVA in order to better represent life support constraints. Furthermore, this investigation shows that physiological testing is possible within the framework of current Mars analogue missions, and that further study would be useful in determining both the physical fitness requirements of Marsnauts as well as life support decisions for mission planners. It is hoped that a full scale study of this type will be included in future science focused Mars analogue expeditions.
Kenneth S Dyson and Richard L Hughson. University of Waterloo, Waterloo, Ontario, Canada.
Methods Subjects Six (one female) healthy, volunteers with no family history of premature cardiovascular disease were recruited for the experiment from the crew of Mars Society Canada’s Expedition Alpha. Physiological Cost Analysis Expired oxygen and carbon dioxide were measured in a breath by breath manner by a CosMed portable gas analysis system (K4 b2, CosMed, Italy). Heart rate was monitored continuously with a Polar heart rate monitor (Polar Electro, Finland). Data was subsequently downloaded to a laptop computer (Satellite 1110, Toshiba, Japan) and processed with the CosMed software (K4 b2 version 7.6) to be expressed as 10 second mean values. Experimental Protocol Each participant was outfitted for gas analysis during two EVA excursions and two graded hill runs, each performed on a separate day. The EVA excursions were for the purpose of training the crew for geological surveying, were between one and two hours in duration, and were performed while wearing the Mars EVA suit provided for at the Mars Desert Research Station (Mars Society, USA). Pacing was at the discretion of the participant. The hill runs consisted of continually running up and down a 200m hill path (10% grade). Pace was increased every two minutes at the encouragement of an investigator and the participant was instructed to run until exhaustion. The peak 10 second mean value recorded over the two hill sessions was taken to represent VO2 peak.
Results
Discussion
Figures
This investigation showed that a typical Mars analogue EVA does not require a sustained challenging physical effort. The peak VO2 levels reached of ~70% of peak VO2 are comparable to moderate exercise, and these peak efforts were not sustained for more than a few minutes. None the less it is imperative that interplanetary crew members arrive at their destination at least with the capacity to perform this level of work.
A
We were not surprised to find that the greater the distance covered the more oxygen was consumed as is has been established that oxygen consumption is proportional to work performed. An interesting observation was that those crew members who were more fit tended to take longer excursions and thus consumed the most oxygen. This leads us to conclude that distance covered and not time elapsed should be the determining factor for the termination of EVAs on subsequent analogue missions in order to better simulate the actual life support constraints.
B
Figure 1. Heart rate (blue) and VO2 (red) data from one participant during a hill run (A) and an EVA (B).
The fact that Expedition Alpha was a training mission limited the amount of focus on the science aspect of the mission. The EVA Figure 2. Peak oxygen consumption (VO2) protocols were allowed to evolve during the achieved during hill runs and EVA. Values are course of the mission as crew members and command centre discussed the best way to 30 second averages for 6 subjects. perform the geological survey. As such we were unable to compare EVAs of identical duration or distance. Also a lack of resources forced us to employ the hill runs to determine VO2 peak as opposed to the more accurate methods of VO2 max determination by treadmill or cycle ergometer testing protocols. It is safe to assume that the peak VO2 values obtained from the hill runs were an underestimate of true VO2 max and therefore relative EVA peak VO2 was likely overestimated. Regardless of these limitations this investigation was able to observe genuine physiological phenomena in the unique environment of the Mars analogue scenario. To our knowledge this was the first investigation that utilized breath by breath analysis of expired gasses during Mars analogue EVA. Our experience during this experiment revealed that meaningful physiological data can be obtained during Mars analogue EVA excursions working in concert with investigations in different disciplines. It is hoped that a full scale study of this type, which would have access to specialized exercise equipment for determination of VO2 max as well as more standardized EVA procedures, will be included in future science focused Mars analogue expeditions.
Figure 1 shows representative data from one participant during a hill run (panel A) and an EVA (panel B). The average VO2 peak recorded during the hill runs was 52.4 ± 0.99 ml/kg/min (figure 2). As is shown in Figure 1, VO2 was extremely variable over the course of a given EVA. This reflects the varying terrain and level of activity required for the many tasks involved in geological surveying, including hill climbing, flat terrain walking, utilization of rock hammer, and quiet standing (see photos). The peak VO2 reached during a given EVA was 35.87 ± 0.78 ml/kg/min, representing 69% of VO2 peak reached during hill runs (figure 2). Data for heart rate showed the same trend as VO2, with a maximal increase to 81% of peak (figure 1). Figure 3 shows the relationships between the crew members’ fitness level as determined by the hill runs with distance covered in one hour, oxygen consumed in one hour, and the maximum heart rate achieved during EVA. There was a correlation between aerobic fitness and distance covered during an EVA (R2=0.34) resulting in a greater demand for oxygen in a given time period for more fit crew members (R2=0.86). Maximal heart rate was independent of fitness level.
Photos
Figure 3. Relationships between the participants’ fitness level as determined by the hill run with distance covered in one hour (green), oxygen consumed in one hour (blue), and the maximum heart rate (red) achieved during EVA. Each value represents an average for each subject over two tests.
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