NOTE: New end date is 9/2/2014 per NSSC information (Ed., 5/9/2013)

Project 1: The purpose was to evaluate the relationships between tests of fitness and several activities that simulate components of Lunar- and Martian-based extravehicular activities (EVAs). Seventy-one subjects completed four field tests: 1) a physical abilities test which consisted of 6 stations -- stair climbing, forward-backward zigzag, ladder climb and descent, horizontal rock wall, lifting heavy objects, and side step duck/step over; 2) a 10 km Walkback test; 3) material transport field test requiring the loading, transport, and unloading of geological samples; and 4) a device operations field test consisting of tasks associated with equipment set-up and the operations of controls and valves. The relationships between test times for each of these tests and the following parameters were determined: running: O2max, gas exchange threshold (GET), speed at O2max (s- O2max), highest sustainable rate of aerobic metabolism [critical speed (CS)]; arm cranking: O2peak, GET, critical power (CP).

Important Findings:

A) Across the 4 tests, CS, running O2max, s- O2max, and arm cranking O2peak had the highest correlations. CS and to a lesser extent O2max are most strongly associated with tasks that simulate aspects of EVA performance, highlighting CS as a method for evaluating astronaut physical capacity.

B) Arm cranking tests are strongly associated with upper-body dependent tasks, highlighting that the nature of mission tasks needs to be considered when evaluating astronaut physical capacity.

C) When comparing arm to leg responses, as expected arm responses were lower than those seen with leg exercise. There was a significant correlation between arm-cranking and lower body O2max, GET, and the O2 at LCS. Backward stepwise regression analyses revealed that arm-cranking physical fitness could explain 67%, 40%, and 49% of the variance in lower body O2max, GET, and CS, respectively. Discussion: Results suggest arm-cranking exercise can be used to obtain an approximation of lower body aerobic capacity.

Project 2: The purpose of the second project was to determine the physiological parameters associated with the ability to complete simulated exploration type tasks at metabolic rates which might be expected for Lunar and Martian ambulation. Two simulated extravehicular activity field tests were completed in 1-g at two intensities designed to elicit metabolic rates of ~20.0 and ~30.0 ml kg-1 min-1, which are similar to those previously reported for ambulation in simulated Lunar- and Martian-based environments, respectively. Important Findings:

A) All subjects were able to complete the field test at the Lunar intensity, but 28% were unable to complete the field test at the Martian intensity (non-Finishers).

B) During the Martian field test there were no differences in O2 between Finishers and non-Finishers, but the non-Finishers were performing at a greater % O2max compared to Finishers.

C) Logistic regression analysis revealed fitness thresholds for a predicted probability of 0.5, at which Finishing and non-Finishing are equally likely, and 0.75, at which an individual has a 75% chance of Finishing, to be a O2max of 38 ml kg-1 min-1 and 40 ml kg-1 min-1, both significantly greater than the current minimum standard of ~32 ml kg-1 min-1 for the astronaut corps.

D) Logistic regression analysis also revealed that the expected % O2max required to complete a field test could be used to successfully predict performance (X2=19.3).

Project 3: the purpose of the current project was to develop an offload hoist system that is able to simulate the gravitational environments of expected future mission destinations that may be used to determine insightful physiological variables and responses to monitor in an astronaut in order to assess mission readiness and EVA performance.

Important Findings:

A) The offload system was successfully designed, implemented, and tested.

B) Proof-of-concept data were collected for ambulatory activities in Earth (1-g), Martian (3/8-g), and Lunar (1/6-g) simulated gravitational environments. Metabolic and ventilatory measurements were collected during ambulation at constant-speeds in each of the gravitational environments.

C) Metabolic and cardiovascular responses were greatest in 1-g and least in Lunar microgravity. While responses for Martian gravity were lower than for 1-g Earth, they were substantially greater than for Lunar gravity. These data emphasize the need for careful consideration of critical mission tasks and the minimum fitness required for astronaut safety and mission success.

NOTE: New end date is 9/2/2014 per NSSC information (Ed., 5/9/2013)

In addition, the hoist suspension system is operational to the point of being able to conduct pilot experiments. We have acquired preliminary VO2 responses during ambulation at 3 mph under 1-g, Martian (3/8-g), and Lunar (1/6-g) offloading. In addition, during the Lunar offloading, subjects naturally and unconsciously assumed an almost skipping stride pattern, very similar to that adopted by the Apollo astronauts during lunar EVAs.

NOTE: New end date is 9/2/2014 per NSSC information (Ed., 5/9/2013)

With 72 subjects we have begun more sophisticated analyses using multiple regression and CART approaches. These approaches continue to reinforce that the most influential predictors of field test performance are critical speed and critical power, as previously found with a subset of subjects.

We have begun collecting preliminary data from wireless biosensors (EMG, respiration, accelerometer) and , near infrared spectroscopy-NIRS) while subjects are performing the field tests. The goal of this work is to characterize the cardiorespiratory and metabolic responses to the field tests, and to identify how these signals change as the subject fatigues. Very promising, in subjects who have failed the planetary navigation field test to date, EMG and NIRS signals have indicated impending fatigue with patterns of change different from those seen when subjects are able to successfully complete the course, while the VO2 responses exceed those associated with the subject's critical speed CS. Finally, the suspension system continues to develop. We are at the stage of evaluating safety redundancy in the hoist system, and anticipate pilot work with humans this summer 2013. This system will eventually permit the creation of a microgravity setting for the subjects while they perform certain of the field test tasks.

Simple regression analysis of the results to date has produced some exciting insights. There was a modest correlation (r = -0.71) between 10 km walk-back time and VO2max, but the correlation with gas exchange (or ventilatory) threshold (GET) was weaker (r = -0.43). In contrast, there were highly significant relationships between both 10 km time (r = 0.90, p<0.0005) and average pace (r = 0.91, p<0.001) with critical speed or velocity.

The total time to perform the material transport test was inversely, significantly correlated with upper body critical power (r = -0.71) and gas exchange threshold (r = -0.65).

With 45 subjects we have been able to begin more sophisticated analyses using multiple regression and CART approaches. Even with these approaches, the most influential predictor of field test performance are critical speed and critical power.

Significant progress has been made identifying wireless biosensors (EMG, respiration, accelerometer, etc.). We have begun collecting preliminary data from these sensors while subjects are performing the field tests. The goal of this work is to characterize the cardiorespiratory and metabolic responses to the field tests, and to identify how these signals change as the subject fatigues. In addition, we have made significant progress with the suspension system which will eventually permit the creation of a microgravity setting for the subjects while they perform certain of the field test tasks.

Preliminary simple regression analysis of the results for the 10 subjects who have completed all aspects of the testing to date has produced some exciting insights. There was a modest correlation (r = 0.583, p<0.05) between 10 km walk-back time and Vo2max, but there was no significant relation with gas exchange (or ventilatory) threshold (GET). In contrast, there were highly significant relationships between both 10 km time (r = 0.894, p<0.0005) and average pace (r = 0.872, p<0.001) with critical velocity.

The total time to perform the material transport test was inversely, significantly correlated with upper body Vo2max and critical power, and with static hand grip endurance, with the correlation coefficients ranging from 0.63 to 0.792, but was not significantly correlated with upper body GET.

It should be noted that much of the statistical evaluation of the data, including the multiple regression and CART approaches, will require results from a greater number of subjects in order to achieve minimal statistical power. This will be accomplished over the summer and fall of 2011.