environment and activity patterns of the subjects. Among the other changes common to all the studies described by LeBlanc in Chapter 12 were diet, season of the year, emotional factors caused by isolation, and changes in physical activity (Kark et al., 1948; Lewis et al., 1960; Milan and Rodahl, 1961). Changes in diet alone seem unlikely to be the cause of the weight gain since the foods used in some of the studies were reported to be less palatable than foods consumed before the study. It is well known that a reduction in food intake does not simultaneously occur with a reduction in physical activity. However, it is not clear from these studies that changes in physical activity could account for all of the weight gain. Likewise there is no clear evidence that the weight gain observed in cold environment studies is due to season of the year or emotional factors caused by isolation. LeBlanc suggests in Chapter 12 that cold exposure per se is not a likely cause of the energy imbalance which leads to the weight gains, because weight gains were not observed for individuals during the coldest months of the year. In addition, the weight gains recorded in these studies (see LeBlanc's review in Chapter 12 in this volume) could have resulted from the sudden change in exposure to a cold environment, i.e., lack of acclimatization. Perhaps the subjects would have reached a new stable weight if the study had continued for a longer time. Clearly the study results tend to indicate that exposure to a cold environment does not depress appetite.
A variety of physiological and mental responses are initiated by the unique physical and environmental factors which characterize the Earth's high altitudes. As reviewed by Allen Cymerman, Robert B. Schoene, and Inder S. Anand and Y. Chandrashekhar (see Chapters 16, 17, and 18 in this volume, respectively), many of these responses have adverse, mission-threatening impacts on military performance, both in the short-term, as exemplified by acute mountain sickness (AMS)2, and in the long term through diminished physical capacity because of decreased muscle mass and the other effects of the environmental stress on the body. Some of these adverse responses may