What percentage of energy expenditure is used at rest for air flow?

The correct choice, which indicates that 3-5% of energy expenditure is used at rest for air flow, reflects the minimal yet essential metabolic cost required to maintain basic respiratory functions. Even during rest, the body requires a certain amount of energy to sustain vital processes, including ventilation, which is the act of moving air in and out of the lungs.

Breathing is not merely an automatic process; it demands energy, primarily from the muscles involved in respiration. The energy expended in this context is relatively small compared to overall metabolic rates during both rest and activity. Other physiological functions, such as heart rate and thermoregulation, consume much larger portions of daily energy expenditure.

Understanding this percentage can help professionals in exercise physiology appreciate the scope of energy expenditures during various states of activity, indicating how efficient the body's systems are even when at rest and how they prepare the body for higher energy demands during exercise.