Final answer:
The autonomic nervous system is responsible for controlling involuntary functions such as digestion. This is part of the rest-and-digest functions monitored by the parasympathetic division of the autonomic nervous system.
Step-by-step explanation:
Among the given activities, the action in which the autonomic nervous system is engaged is digestion. While lifting weights, holding your breath, and walking require conscious effort and involve the somatic nervous system, digestion is a process controlled by the autonomic nervous system. Specifically, the parasympathetic division of the autonomic nervous system is active during rest-and-digest states, in which it oversees involuntary actions like the secretion of enzymes and peristalsis that are crucial for digestion.
Peristaltic movements of the digestive system and the production of digestive enzymes are stimulated by neural responses to the presence of food through sight, smell, or even thought, and these responses are involuntary and regulated by the autonomic nervous system. Hence, actions such as sweating and digesting food without conscious control fall under the purview of the autonomic nervous system.