Which of the following adaptations is associated with improved oxygen uptake at higher exercise intensities?

The adaptation associated with improved oxygen uptake at higher exercise intensities is increased cardiac output. This is because cardiac output, which is the volume of blood the heart pumps per minute, directly influences how much oxygen can be delivered to working muscles during intense physical activities.

When exercise intensity increases, there is a greater demand for oxygen in the muscles to produce energy, and an increase in cardiac output ensures that more blood—and thus more oxygen—can reach these active tissues. This enhancement allows individuals to sustain higher exercise intensities more effectively.

While increased stroke volume can also contribute to higher cardiac output (since cardiac output is the product of stroke volume and heart rate), cardiac output encompasses both components. Therefore, while improvements in oxygen uptake certainly occur, the key relationship is seen in the collective increase in cardiac output facilitating this adaptation during higher intensity exercise.

The mention of greater muscle glycogen stores is related to energy production for prolonged activity but does not directly influence oxygen uptake. While improved oxygen uptake can contribute to better use of those glycogen stores, they are not a direct adaptation to improve oxygen delivery during intense exercise.