does not impair physical performance (Taylor et al., 1957). There is a long history of such Army-sponsored research on performance decrements related to energy-deficient diets that reaches back to laboratory studies from the University of Minnesota in the 1940s and 1950s (for review, see Grande, 1986) and field studies conducted by the U.S. Army Medical Research and Nutrition Laboratory in the 1960s and 1970s (for review, see Consolazio, 1983). In the past decade, the Occupational Physiology Division at the U.S. Army Research Institute of Environmental Medicine has repeatedly performed physical testing during ration studies (e.g., Askew et al., 1987; Moore et al., 1992; Teves et al., 1986). The data from these more recent studies have been largely overlooked because of the general absence of findings of performance decrements. These negative findings could be the result of protocols failing to produce an actual energy deficit or because the tests used were insensitive to real performance decrements. However, after these and other interpretations of the data are considered, the conclusion of this chapter will be that militarily relevant physical performance appears to be well sustained through the range of voluntarily low intakes (underconsumption) of modern military rations.

If underconsumption occurs for sufficient duration it will unquestionably produce deficits in physical performance. Changes in the oxidative capacity of muscle, the oxygen carrying capacity of the blood, and the mass of metabolically active tissue probably account for most of the observed decrease in aerobic capacity, which in turn, explains reduced stamina and physical work capacity (Keys et al., 1950; Spurr, 1986). Loss of skeletal muscle, changes in muscle biochemistry, and changes in the balance of muscle fiber types produce reductions in dynamic strength (Henriksson, 1990; Taylor et al., 1957). Such decrements in physical performance have been established at extreme levels of underconsumption in the 1950 Minnesota Starvation Study and in studies of soldiers in the U.S. Army Ranger course (Johnson et al., 1976; Moore et al., 1992 [Ranger I]; Shippee et al., 1994 [Ranger II]). These levels of underconsumption were voluntary only in the sense that the participants could quit the programs; if offered more food, these men would have readily consumed it. However, these studies are important for this book because they illustrate an extreme of underconsumption, which permits interpolation of the effects of the more pertinent (i.e., modest) energy deficits. A different militarily relevant extreme of underconsumption—very high deficits for a short period of time—will also be addressed.