Of the Shuttle astronauts, 174 had available data from annual examinations conducted in the six years prior to their flights. Their gender distribution shows that 86.8% are males. Fifty seven percent of these astronauts were between 38 and 49 years of age, with 62.6% of individuals within this age group younger than 43 years of age. More than 90% of the entire group was younger than 50 years of age.
Variables measured were age (at time of examination),percentage of body fat, VO2max and maximum heart rate. BMI is a surrogate measure for fatness which is more accurate for a group of people than for an individual; it is calculated using the weight in pounds and the height in inches. A BMI between 22-26 is about standard. Percentage of body fat is an estimation of fatness based on the sum of three skin-fold measurements and age at last birthday. Values of 10%-15% for men, and 20%-25% for women, are considered to be the norm for the general population. VO2 max and maximum heart rate are estimations of cardiovascular fitness that are measured during an Exercise ECG test. VO2max is measured by the volume of oxygen, in milliliters per kilogram of body weight, expired per minute, and is an indicator of an individuals maximal aerobic capacity. The normative values of VO2max for men and women in good aerobic condition in the 30-49 years age group are 41 ml/kg/min and 37 ml/kg/min, respectively. Maximum heart rate (MHR), is measured in beats perminute; for individuals in the 38-49 years age group the expected MHR is 179.7 beats per minute.
As expected, the Shuttle astronauts showed better fitness than the general population; the majority of the astronauts, those in the 38-49 year age group, had higher VO2max and lower MHR values than the previously mentioned norms. In analyzing EVA data, each EVA per mission is accounted for, so that an astronaut is included for every EVA mission and the age group he/she has achieved. Fifty one EVA participants had data available from examinations. The majority (51%) of the EVA participants were under the age of 43, and 94.1% of them were male. The small number of female participants precludes data analysis of this group. All of the parameters varied only slightly between EVA participants and Shuttle astronauts. The largest age group representation of EVA participants is in the 44-49 years age group (29.4%), while that of the Shuttle astronauts is the 38-43 years age group(35.6%). In comparing the majority of each groups subjects (38-49 years age group), there is very little difference in the BMI or VO2max between the two 38-49 years age groups, but the average percentage of body fat for the EVA participants was slightly lower than that of the Shuttle astronauts. However, the EVA participants also have a slightly higher mean MHR (172.5 versus 171.0 beats per minute). The trend of decreasing VO2max and MHR seen in the older population of the astronaut corps could not be detected in the EVA participants, possibly due to the small sample size in those age groups. Therefore, EVA participants were slightly older, but might be slightly more fit, than the total group of Shuttle astronauts at the time of their examination. These results are preliminary; further analyses of EVA participants should include all participants and examination data within one year of flight. Through such data availability, a more comprehensive analysis may yield some criteria for EVA participants during the International Space Station implementation.
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