What type of metabolic activity occurs when the body is at complete rest?

The correct answer is the basal metabolic rate. This refers to the amount of energy expended while at complete rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about 12 hours of fasting in humans). Basal metabolic rate represents the minimal amount of energy required to maintain essential physiological functions, such as breathing, circulation, cell production, and nutrient processing.

In contrast, dynamic metabolic rate is related to the energy expenditure during physical activity and times of growth or stress but does not pertain to the resting state. The thermic effect of food represents the energy required for digestion, absorption, and metabolism of nutrients following a meal, making it a process linked to eating rather than resting. Lastly, exercise-related metabolic rate refers to the increased energy expenditure during physical activity, which is not applicable at complete rest. Thus, the basal metabolic rate is the most accurate representation of metabolic activity when the body is at total rest.