The term physical activity is used loosely when compared to the terms exercise and physical fitness. It refers to a lifestyle of casual activities that result in the expenditure of energy. The term moderate refers to an intensity of activities that utilizes 3 to 6 metabolic equivalents (METs). One MET is defined as the amount of oxygen utilized while the body is at rest, which is 3.5 ml/kg of body weight/minute. Intermittent activities performed throughout the day are also beneficial to one's health. Individuals who are currently physically active will reap additional benefits by increasing the duration or intensity of their current activities.
To assess the activity level within the LSAH population, information from the LSAH Health Lifestyle Questionnaire (LSQ) was compiled and compared with data from the 1990 National Health Interview Survey (NHIS). Information from the NHIS was gathered from 22,760 noninstitutionalized U.S. civilians at least 18 years of age. NHIS participants were divided into four basic categories based on the intensity, frequency, and duration of physical activity: Sedentary, Irregular, Moderate, and Vigorous. Sedentary indicates no leisure activity, Irregular indicates leisure activity that does not meet the current public health recommendation. Moderate refers to activities with an intensity of 3 to 6 METs performed a minimum of 30 minutes at least five days per week. Vigorous refers to activities with an intensity of greater than 6 METs performed a minimum of 20 minutes at least 3 days per week. The LSQ was developed in 1993 to collect essential data on NASA astronauts and LSAH comparisons. Two hundred twenty out of 272 astronauts and 780 out of 889 comparisons have completed this questionnaire. The physical activities of LSAH participants were categorized according to the NHIS definitions; however, their data were gathered using different time intervals, so both Moderate and Vigorous categories refer to activities performed a minimum of 20 minutes. Walking was categorized as a Moderate activity. Since the number of METs of an activity refers to the intensity with which it is performed, the assumption is made that the remaining activities listed on the LSQ were performed in a vigorous, energetic manner. These activities are running, swimming, bicycling, weight lifting, skating, aerobics/ dancing, racquet sports, rowing, and other organized sports.
About one third of the NHIS participants reported a level of physical activity that meets the current public health recommendation. This is compared with nearly half of the comparisons and two-thirds of the astronauts. The higher degree of physical activity of LSAH comparisons, as compared to the NHIS population, may be a manifestation of the healthy worker effect. The latter simply describes the phenomenon in which an employed population exhibits healthier characteristics than the general population. This effect is even more pronounced in the astronaut corps because it is in their interest to remain physically active in order to perform their duties effectively.
A higher percentage of male NHIS respondents reported participation in the recommended level of physical activity as compared to female respondents; this trend is also observed to a lesser extent in the LSAH comparisons. However, female astronauts reported a greater percentage of participation in physical activity than male astronauts. This increase may be due to the younger average age of female astronauts as compared with the older average age of male astronauts. The results may also be affected by the smaller number of female astronauts. When the results are broken down by age, older NHIS respondents reported less physical activity than younger respondents, while LSAH comparisons reported about the same level of physical activity across the age groups. The decrease in physical activity with age was also seen in the astronauts, though in the 25-44 years age group this cohort reported more than double the participation in physical activity as compared to the corresponding age group of NHIS respondents. The higher relative participation of astronauts in moderate and vigorous physical activity was further displayed as more than half of the astronauts in the oldest age group reported participating in such activity. However, one must keep in mind that the number of astronauts in the oldest age group is much smaller than that of the NHIS respondents.
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