Which of the following adaptations increases the efficiency of oxygen delivery during exercise?

The adaptation that increases the efficiency of oxygen delivery during exercise is efficient pulmonary ventilation. This process refers to the ability of the lungs to take in oxygen and expel carbon dioxide effectively. Improved pulmonary ventilation enhances the exchange of gases in the alveoli, allowing for more oxygen to enter the bloodstream and improve oxygen saturation. This is crucial during physical activity as the body demands more oxygen to sustain increased metabolic activity.

Efficient pulmonary ventilation can be influenced by factors such as respiratory rate, tidal volume, and lung capacity, which can all improve with training, leading to a more effective oxygen supply during exercise. This adaptation not only improves endurance performance but also optimizes overall respiratory function.

In contrast, increased blood viscosity, decreased stroke volume, and decreased capillary density would not support the efficient delivery of oxygen. Higher blood viscosity can hinder blood flow, decreased stroke volume can mean less blood pumped per heartbeat, and decreased capillary density can limit the exchange of gases at the tissue level. These factors would not enhance, but rather impede, oxygen delivery efficiency during exercise.