Background: Pencil beam dual energy x ray absorptiometry (DXA) has been shown to provide valid estimates of body fat (%BF), but DXA fan beam technology has not been adequately tested to determine its validity. Objective: To compare %BF estimated from fan beam DXA with %BF determined using two and three compartment (2C, 3C) models. Methods: Men (n = 25) and women (n = 31), aged 18-41 years, participated in the study. Body density, from hydrostatic weighing, was used in the 2C estimate of %BF; DXA was used to determine bone mineral content (BMC) for the 3C estimate of %BF calculated using body density and BMC (3C BMC ). DXA was also used to determine %BF. Analysis of variance was used to test for significant differences in %BF between sexes and among methods. Results: Women were significantly shorter, weighed less, had less fat free mass, and a higher %BF than men. No significant differences were found among methods (2C, 3C BMC , DXA) for determination of %BF in either sex. Although not significant, Bland-Altman plots showed that DXA gave higher values for %BF than the 2C and 3C BMC methods. Conclusion: DXA determination of %BF was not different from that of the 2C and 3C BMC models in this group of young adults. However, to validate fan beam DXA fully as a method for body composition assessment in a wide range of individuals and populations, comparisons are needed that use a 4C model with a measure of total body water and BMC.

The objective of this project was to develop a comprehensive methodology to assess the suit fit and performance differences between a nominally sized extravehicular mobility unit (EMU) spacesuit and a nominal +1 (plus) sized EMU. Method: This study considered a multitude of evaluation metrics including 3D clearances and pressure point mapping to quantify potential issues associated with using offnominal suit sizes. Results: There were minimal differences with using a plus suit size. Discussion: Analysis of the results indicates that future suit size evaluations should consider this ergonomic approach to understand and mitigate potential suit fit and performance issues.

Values of ΔP as inputs to the model would be calculated from the Tissue Bubble Dynamics Model based on the effective treatment pressure: ΔP=P2-P1|=P1×V1/V2-P1, where V1 is the computed volume of a bubble at low pressure P1 and V2 is computed volume after a change to a higher pressure P2. If 100% ground-level oxygen was breathed in place of air, then V2 continues to decrease through time at P2 at a faster rate.

Quantifying the preferred transition speed (PTS) from walking to running has provided insight into the underlying mechanics of locomotion. The dynamic similarity hypothesis suggests that the PTS should occur at the same Froude number across gravitational environments. In normal Earth gravity, the PTS occurs at a Froude number of 0.5 in adult humans, but previous reports found the PTS occurred at Froude numbers greater than 0.5 in simulated lunar gravity. Our purpose was to (1) determine the Froude number at the PTS in actual lunar gravity during parabolic flight and (2) compare it with the Froude number at the PTS in simulated lunar gravity during overhead suspension. We observed that Froude numbers at the PTS in actual lunar gravity (1.39±0.45) and simulated lunar gravity (1.11±0.26) were much greater than 0.5. Froude numbers at the PTS above 1.0 suggest that the use of the inverted pendulum model may not necessarily be valid in actual lunar gravity and that earlier findings in simulated reduced gravity are more accurate than previously thought.

Chronic exposure to a PIo2 of 127 mmHg is well-tolerated by healthy humans on Earth. A similar short-duration exposure on the shuttle resulted in no increased reporting of possible hypoxia-related symptoms. However, chronic mild hypoxia interactions with physiological changes due to microgravity adaptations remain unclear.Wessel JH III, Schaefer CM, Thompson MS, Norcross JR, Bekdash OS. Retrospective evaluation of clinical symptoms due to mild hypobaric hypoxia exposure in microgravity. Aerosp Med Hum Perform. 2018; 89(9):792-797.

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Physical effort, compensation, and controllability in a spacesuit can be affected by suit mass and gravity level. Because of limitations in certain reduced-gravity simulators and the finite selection of lunar prototype suits, it is difficult to ascertain how a change in suit mass affects suited human performance. One method of simulating a change in mass is to vary the total gravity-adjusted weight (TGAW), which is defined as the sum of the suit mass and subject mass, multiplied by the gravity level. PURPOSE: To determine if two methods of changing TGAW during parabolic flightchanging suit mass or gravity level-affect subjective ratings of suited human performance equally. METHODS: A custom weight support structure was connected to a lunar prototype spacesuit, allowing the addition of mass to the suit while maintaining a near-constant center of mass. In the variedweight (VW) series, suit mass (120 kg) was constant at 0.1-g, 0.17-g, and 0.3-g, yielding TGAWs of 196, 333, and 588 N, assuming an 80-kg subject. In the varied-mass (VM) series, gravity level was constant at 0.17-g and suit mass was 89, 120, and 181 kg, yielding TGAWs of 282, 333, and 435 N. The 333 N condition was common to both series. Direct comparison was not possible due to limited adjustability of suit mass and limited options for parabolic profiles. Five astronaut subjects (80.3 11.8 kg) completed 4 different tasks (walk, bag pickup, lunge, and shoveling) in all conditions and provided ratings of perceived exertion (RPE) and the gravity compensation and performance scale (GCPS) upon completion of each task. RESULTS:

BACKGROUND: NASA has been making efforts to assess the carbon dioxide (CO2) washout capability of spacesuits using a standard CO2 sampling protocol. This study established the methodology for determining the partial pressure of inspired CO2 (PIco2) in a pressurized spacesuit. We applied the methodology to characterize PIco2 for the extravehicular mobility unit (EMU).METHODS: We suggested an automated and mathematical algorithm to find the end-tidal CO2 and the end of inspiration. We provided objective and standardized guidelines to identify acceptable breath traces, which are essential to accurate and reproducible calculation of the in-suit inhaled and exhaled partial pressure of CO2 (Pco2). The mouth guard-based method for measurement of inhaled and exhaled dry-gas Pco2 was described. We calculated all individual concentrations of PIco2 inhaled by 19 healthy subjects classified into 3 fitness groups. The transcutaneous Pco2 was monitored as a secondary measure to validate washout performance.RESULTS: Mean and standard deviation values for the data collection performance and the CO2 metrics were presented (e.g., minimum time weighted average Pco2 at suited workloads of resting, 1000, 2000, and 3000 (BTU h1) were 4.75 1.03, 8.09 1.39, 11.39 1.26, and 14.36 1.29 (mmHg s1). All CO2 metrics had a statistically significant association and all positive slopes with increasing metabolic rate. No significant differences in CO2 metrics were found between the three fitness groups.DISCUSSION: A standardized and automated methodology to calculate PIco2 exposure level is presented and applied to characterize CO2 washout in the EMU. The EMU has been operated successfully in over 400 extravehicular activities (EVAs) and is considered to provide acceptable CO2 washout performance. Results provide a basis for establishing verifiable Pco2 requirements for current and future EVA spacesuits.Kim KJ, Bekdash OS, Norcross JR, Conkin J, Garbino A, Fricker J, Young M, Abercromby AFJ. The partial pressure of inspired carbon dioxide exposure levels in the extravehicular mobility unit. Aerosp Med Hum Perform. 2020; 91(12):923931.