Which scenario would likely involve active expiration?

Active expiration refers to the process in which muscles are engaged to force air out of the lungs, typically in response to increased demands for oxygen, such as during physical exertion. In the context of running a marathon, the body's demand for oxygen rises significantly as energy expenditure increases, leading to the need for more efficient expulsion of carbon dioxide.

During rigorous exercise like running, the body employs the internal intercostal muscles and abdominal muscles to actively push air out of the lungs to facilitate quicker and deeper breaths. This helps maintain peak performance and adequate oxygen supply to muscles in use. In contrast, situations such as sitting quietly, reading a book, or sleeping usually involve passive expiration, where air is expelled from the lungs primarily through the natural recoil of the lung tissue and thoracic cavity following inhalation. Active expiration is not necessary during these activities as the body's oxygen demands are much lower.