Which factor can contribute to increased respiratory rates during physical activity?

Increased metabolic demand is a key factor that influences respiratory rates during physical activity. When a person engages in exercise or physical exertion, the body's muscles require more oxygen to produce energy. This increase in energy production results in a higher metabolic rate, which, in turn, necessitates more oxygen intake and carbon dioxide removal. To meet this heightened demand, the respiratory system increases the rate and depth of breathing, allowing for enhanced gas exchange to support the body’s needs during exercise.

The other factors listed may have effects on respiration under different contexts, but they do not directly relate to the acute responses during physical activity in the same way. Reduced lung capacity can impair breathing efficiency but is not a factor that inherently increases respiratory rates. Environmental pollution can negatively impact lung function and respiratory health over time but does not directly lead to an increased respiratory rate during activity. Cold air temperatures may cause constriction of the airways or discomfort, which might affect breathing but typically do not increase the respiratory rate as a direct physiological response to increased activity. Therefore, the increase in metabolic demand during physical activity is the primary driver of elevated respiratory rates.