It must be emphasized that the separation of adaptive thermogenesis between resting and nonresting is artificial, given the possibilities of their interactions illustrated in Figure 2. For example, energy expenditure during sleep, which is generally nested under resting energy expenditure, also comprises a nonresting component due to spontaneous movement (or SPA) occurring during sleep, the frequency of which seems to be highly variable between individuals. Furthermore, nonresting energy expenditure or NEAT may also include heat production resulting from the impact of physical activity (exercise or SPA) on postabsorptive metabolic rate or postprandial thermogenesis. There is evidence that relatively low-intensity exercise can lead to potentiation of the thermic effect of food, and that the effect of physical activity on energy expenditure can persist well after the period of physical activity (postexercise or post-SPA stimulation of thermogen-esis). Reduction in postexercise stimulation of metabolic rate has also been proposed as a mechanism for energy conservation in individuals who are considered to be chronically energy deficient since childhood. Thus, any changes in metabolic efficiency in the resting or nonresting state that would tend to attenuate energy imbalance or to restore body weight and body composition toward its set or preferred value constitute adaptive changes in thermogenesis
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